The "Doug Nash 4+3"... [Archive] - Corvette Action Center

Yoda

01-02-01, 10:30 PM

CLABORN1960~~Welcome to the CorvetteActionCenter~~

Back in the dark ages, The Second NEW Corvette I owned was a 1984 with the 4-speed 3-over. It was one of the first 300 made and had the overdrive button (switch) in the console. The car was very quick and worked great until I started autocross racing. By the end of the summer of '84 the trans had been rebuilt once and needed another by winter. From my experience it did not hold up too well being pushed.

The car got great milage on the highway in OverDrive. The OverDrive worked in 2nd, 3rd and 4th, thus the 4-speed 3-over. I haven't heard much good about them if you're a heavy footed gear jamming type driver, but most cars won't hold up to a lot of abuse either :D

I'm sure you'll receive several opinions on this subject ;)

Have you driven one? That might help answer some of your questions or concerns. Be sure to get a maintenance history of they car you think of buying, IMHO and be sure to ask Lots of Questions.

Good Luck
BudD
:w

HwyStar

01-06-01, 10:52 PM

I autocrossed my '84 with 4+3 this season. No problems yet. When I got the car, I was told that I should change the overdrive fluid on a regular bases. I use the kit from Mid America and change the fluid and filter about every six month. So far the trans works as advertised.

CLABORN1960 - 4+3 is a manual 4 speed with an automatic trans mated to it for overdrive. It's not the best transmission. If I was looking for a vette with manual trans, I'd look for an 1989 or newer with a six speed. Much less problems with ZF.

Hib Halverson

01-31-01, 10:38 PM

The 4+3, or as it was known by Corvette engineers back then, the "Doug Nash" was a four-speed manual transmission with an electro-hydraulic overdrive grafted onto the back. Generally the OD worked in the upper three gears, hence the name "4+3.".

When the Borg-Warner got out of the four-speed manual trans business in the late 1970s, it sold the design and tooling for the "Super T10" (used in the Corvette from about 1975 to 1980) to the DNE Corp, which was started by hotrodder Doug Nash.

Nash, sold GM and Dave McLellan on a slightly-strengthened version of the Super T-10 with an electro-hydraulic overdrive unit Nash marketed for RV applications.

Well, the end result was the 4+3 and unfortunately, it was a poor example of quality, reliability and durability. The gearbox section was a pretty good piece, but the overdrive unit was a disaster. The 84-86 OD's are notorious for problems. The 87 and 88s are better, but still a problem child, especially if the car is raced a lot.

Ken

01-31-01, 10:52 PM

Originally posted by Hib Halverson
...The 87 and 88s are better, but still a problem child, especially if the car is raced a lot.

Hib, after talking at some length lately with Dick Guldstrand, I've decided to stay with my 4+3 after all. I was thinking about the Richmond six-speed or the ZF now that it's readily available, but seeing as how I don't have racing in mind for the near future I don't think that I'll do that switch yet.
As for racing, the 4+3 will hold up alright for some road racing and auto-x'ing, correct? At least that's the impression I get from Dick.

"STW"

GusVette

01-31-01, 11:22 PM

Hi, I've got one of those "Doug Nash" Tranny's w/overdrive. I have not had a problem, but I only have 41k miles and I don't beat it up. The overdrive is great for the highway and that is the only time I use it. Otherwise just a normal 4 speed. Hope this helps.
Gusvette

Ken

03-29-01, 05:34 PM

You can find lots more info at www.5speeds.com:

01.06.04: I haven't a clue as to where those attachments came from. I certainly didn't have attachments when I posted this years ago! Curious... Very curious. :L

Ken

03-29-01, 05:36 PM

Hope this will answer some of the questions regarding the Doug Nash 4+3 Overdrive Transmission in '84 thru '88 Vettes.

Ken

01.06.04: I haven't a clue as to where those attachments came from. I certainly didn't have attachments when I posted this years ago! Curious... Very curious. :L

Ken

04-07-01, 03:52 PM

OK, now I'm beginning to run out of both time and patience. And I don't need to hear any bad-mouthing the DN 4+3 anymore! ;)

The following is from some e-mails I've shared with "Paul" from the "Gearzone.com"

At 01:56 PM 3/29/01 -0800, I wrote:
Complete remanufactured Overdrive assembly with 1 year warranty - $1150
Does the rebuilt overdrive unit for the DN 4+3 unit contain the following?
* New design carrier, complete?
* Updated carrier bearing, not available from GM?
* Updated direct clutch thrust washer?
* Updated pump assemblies?

At 03:42 PM 3/29/01 -0800, he responded:
Yes they do, I think that is stated on our website. The bad new is that I am not building them due to the success of out JT5 transmission line.
Thanks,
Paul Cangialosi
www.5speeds.com "Live ! - ShopCam"
www.5speeds.com/guestbook2/
Creators of the JT5 5 Speed and New Rally Clutchless Model RC!

At 08:41 PM 3/29/01 -0800, I wrote:
Paul, sorry to bother you again, but if you are "...not building them due to the success of out JT5 transmission line.", what do you recommend I do?

At 09:46 PM 3/29/01 -0800, he responded:
Call 631-957-9427 ask for Brian. He does a great job
Thanks,
Paul

Well, it turns out that "631-957-9427" is S-K Speed.com, anybody familiar with 'em?
Perhaps you have an alternative? My overdrive is evidently beginning to slip, which is the reason for it not staying engaged. (If it won't stay in overdrive, and it kicks back to direct drive, and the indicator light and button are both ok, that is an indication that the overdrive unit is slipping.)

JUNE IS RAPIDLY APPROACHING, and it is a bit uncomfortable cruising at 3600 rpm, not to mention the reduced gas mileage.

Guldstrand's shop still doesn't have a tranny specialist, and I don't know if I just want to go blindly into the fray and choose my own, although why not?
...WHO SAYS I CAN TRUST YOU GUYS ANYWAY!! :L :L :L

Ken

bruce

04-19-01, 07:38 PM

They are problematic. First things first Nash builds the Overdrive unit not the Tranny. They are found on 84-88 vettes. Most problems are found in the early years 84-86. Many are caused by not putting trans fluid in the OD unit which is similar to an auto transmission stuck onto the rear of the tranny. 87-88 are better but still have their quirk. If u have problems getting it in to reverse have it checked. :w :eek:

Ken

04-19-01, 07:57 PM

I finally broke down and ordered a remanufactured unit from Mid America. It costs $1299.99, plus a $1200.00 core charge, and of course, $35.99 freight charges, and that's not counting the labor for installation at Guldstrand's. (I dunno, in the Solid Axle Lounge last night, Dave said something about taking 1000 hrs. to install! :p )

Actually,after it's all done, it isn't much more costly than most transmission rebuilds. (Hopefully, my 4-speed internals are alright. It feels alright! ;) )

BTW, "Earlene" at Mid America was very helpful in filling the order, and on top of that had an extremely courteous and friendly manner throughout. She actually called back today because she wanted to visit my web site but lost the address! :D

I'll keep y'all updated.

Ken

GS Diva

04-19-01, 08:18 PM

I really haven't been following this post closely though I should as I also have a 4+3. Thanks goodness no problems...yet! Let me know how you make out, Ken!

Ken

04-19-01, 10:00 PM

Well, let's add some more cost to the bill. :D

I figured as long as the transmission will be out of the car, I should replace the clutch while we're at it. It only makes sense to me! :L And besides, I've been thinking about it for awhile anyhow.

I've decided to go with McLeod (http://www.mcleodind.com/) after some "channeling with the spirits, throwing the bones and conversing with the gods."

Now, I've spent hours today shopping around to compare prices and can't find much at all. I couldn't find McLeod at Jeg's (http://www.jegs.com/), Summit (http://www.summitracing.com/), or numerous other known aftermarket distributors.

I did find a McLeod application for my Corvette at RaceSearch.com (http://www.racesearch.com/), but it was lacking in any description whatsoever other than
1985-1988
Size (O.D. & Spline): 10.75 x 1-1/8 x 26
Application: Street
Pressure Plate: Diaphragm
(The price quoted was Retail -$316.00, Our Price - $278.08)

I also found a referrence to one at Internet Racers Supply (http://www.racenet.net):
McLeod Dual Performance Clutch Disc & Pressure Plate Assy 1985-88 L-98 for $229.95, but once again that was all the information to be found.
They also had clutch assemblies for the 1989-1990 L98 and 1992-1996 LT1 at $424.95, and 1990-1995 ZR-1 for $445.95.

There were also several referrences to the Dual Disc Clutch kit, including flywheel, but those were for the LT1 and up Z28 Camaros. Amongst them was this from L.G. Motorsports (http://www.lgmotorsports.com) for $1150.00:
1993-97 LT1
Street Twin Clutch Assembly
1 1/8 X 26 Spline
Aluminum Flywheel
(with a steel flywheel it was $825.00)

I know that McLeod makes the Soft Lok & Soft Lok I for the street (their web site has that info), but I can't tell from any of these sites just what it is they are offering.

Is McLeod's distributorship that limited? :confused:

All of the comparison shopping services like AltaVista or My Simon, etc. only cater to automobile sales or nothing automotive at all. How can I find a fair price with a clear description of the item?

I've gotta come up with a good price; Dave said he'd try to match it. ;)

Ken

lunar

06-07-01, 12:19 PM

Hey,
I have a 1987 vette that's got about 100K on her. a couple months ago, i started to notice that shifting into reverse was pretty tough for her. sometimes it would even grind in. now, i can't shift reverse at all without grinding; i need to kill the engine and start in reverse. all my other gears work fine. any ideas?

Kev

GreyGhost

06-07-01, 01:56 PM

Lunar:

Welcome to the CACC site. You've come to the right place. This is where to get your questions answered and enjoy the company of other Corvette people. Look around this site, Rob has done a wonderful job in setting it up and making it easy to get around.

The Doug Nash 4+3 transmission is a unique combination of a 4-speed manual coupled with an automatic overdrive in 2nd, 3rd and 4th gears. The difficulity and grinding of shifting into reverse is an indicator that your clutch needs replacement. Reverse gear grinding is an early indicator of clutch problems. There is no adjustment on your hydraulic clutch as it finds it's own center. I recommend that you get the entire clutch pac kit which includes the pressure plate, clutch disk, release bearing and alignment tool. Check the surface of the flywheel, it probably needs to be resurfaced. If you resurface the flywheel be sure to shim it upon reinstallation. Also replace the pilot bearing in the flywheel.

Just to complete the process, replace the filter and fluid in the overdrive unit, that service is recommended every 10,000 miles.

Once complete, everything should be as good as new.
__________
:cool
Al

BigRed

06-07-01, 02:00 PM

Wow I just posted clutch probs to (gonna replace her) I grind to bud but 2nd gears my trannys choice LOL
Good Luck~!
:Twist

geeky_bill

06-12-01, 11:02 PM

I seem to have a bad 4th gear switch on my '84. I think it's the 4th gear switch anyway, 4 wire connector on the transmission(only three wires are used). It's either that or the TCC solenoid.

When it's plugged in there is a direct short from the "GAUGES" fuse to ground. Which of course means that pretty much every active sensor on the engine will not work, including MAP and ESC.

What does this switch do besides turn on the "OVERDRIVE" indicator lamp? Has anyone ever replaced one?

Thanks,

...Bill

J.R.

06-16-01, 01:27 PM

After it has warmed up and the OD has kicked in the engine revs
real fast and high almost like something is slipping. Any ideas?

Chick

06-20-01, 08:25 PM

Time for an overdrive unit.:(
I know you can get a rebuilt one from Mid America and I'm sure other places too.

BigRed

06-29-01, 11:06 AM

Sounds like the Clutch isnt grabbing hard enough Id look there first personally( Exact same problem on my 85 I dropped a new clutch in and everythings fine)

vigman

07-01-01, 08:22 AM

Ok when it rev's up do you smell anything? A burnt clutch has a VERY distinctive odor like hot dusty brakes ridden to hard. Where does your pedal engage at near the floor or at the top of travel? can you make it slip without O/D engaged?

It's gonna be about $2-2500 I think the Mid america unit is 1300 and since you will have the tranny out DO THE CLUTCH!
and you will always find OH by the ways.. while things are out

Sorry
Mike

lunar

07-03-01, 06:06 PM

Seems my tranny's always got something going on -

is there anyway to disable the the "automatic" part of the automatic overdrive in an 87 doug nash? i'm tired of my car constantly kicking it on off whenever she sees fit. and while i'm at it, the button on my stick needs to be replaced. actually, i think it's a little more than that (i bought the car used, and right from the beginning i found you really have to kind of "hit" the OD button to engage it; no doubt she's taken abuse somewhere...) The plastic button is gone now, and all that's left is the pin. the pin is really starting to wear down my finger, especially given how hard i need to hit it to engage the OD. and it seems to just be getting less responsive over time. I think just replacing the whole stick will solve this (the leather's worn after 14 years anyway), but i'm not sure. how should i go about doing this, if i should? and where can i get a stick, preferably stock? thanx,

kev

Ken

08-23-01, 06:02 PM

Excerpt from Cars & Parts Corvette Magazine (http://www.carsandparts.com/aboutcorvette.html):
The real trick though is to get rid of all these complicated electronics, and turn this transmission into an eight-speed.

A Major Modification
I discovered this one by accident. Well, not quite by accident. Actually Chris Petris, who used to build transmissions for the Corvette Challenge, helped me with this. There's a switch on the side of the transmission that tells the computer which gear is engaged. This second gear switch is one of the first things to go bad on the 4+3. The switch is engaged every single time you shift the transmission, whether the overdrive is engaged or not. It's no wonder this is usually the first item to wear out.

When my second gear switch went bad the car simply wouldn't engage overdrive properly. I could hit the switch on the console to turn on the OD and it might not actually engage until I drove some 20 miles down the road. You can imagine how aggravating this was. When Chris and I couldn't locate a replacement switch right away, we simply grounded the switch by running a very short shunt from one terminal to the other. This effectively made the OD a completely mechanical unit, operated only by the interior switch, which in my case is on the console.

Eliminating this switch made an the difference in the world. This was like giving me a new Corvette. This same modification was made to the World Challenge Corvettes. While Chevrolet designed all the electronics to pass the EPA fuel mileage cycle, we simply want a useful transmission. The 4+3 actually works better if you take some of the sophistication out of the system.

What we did was fool the computer into thinking that I'm always in second gear or higher. This switch is on the left side of the transmission, and can be seen easily if you have the car on a lift. This switch moved around a little during the years, but it was always the switch toward the rear. Remove the wiring harness from the switch and hook it out of the way with a tie-wrap. You won't be using this harness. Now make a little jumper wire that fits into the two terminals. You can actually remove the switch from the transmission and make the jumper wire on your workbench. It shouldn't take more than 15 minutes.

This explains the difference in the codes also:
http://corvetteobsession3.homestead.com/files/enginecompartment/DN4_3ratiochart.jpg

I keep finding more stuff that previously, for me at least, wasn't to be found. :gap

Paul G

08-27-01, 05:00 PM

My switch was leaking fluid, I got a new one from the local Chevy dealer. I did have it bypassed for a while on my 88. I did not like that. With it bypassed the OD would engage in first gear just like an auto shifting to second. I feel this put to much wear and tear on the OD unit. I like to let it come in while the clutch is engaged. It just feels like it is easier on the OD unit that way.

Ken

08-27-01, 05:06 PM

Originally posted by Paul G
With it bypassed the OD would engage in first gear just like an auto shifting to second.

Do you mean Paul, that you were unable to lock it out? :confused

Paul G

08-28-01, 10:05 AM

I could kept it off by pushing the button. Then it will stay off till the button is pushed again. I normally I let it come in by itself as I shift to second. For normal in town driving I let first wind out a little long then go to second with overdrive. the next shift could be third if traffic is light. Most times in town second with overdrive is the right gear for me.
Otherwise with the overdrive off I could be in fourth gear by 30 MPH. I tend to putz around a lot. Dont really drive it hard that much.

Ken

08-28-01, 04:30 PM

I understand now. I just never use my OD in town. ;)

Ken

afbrat

08-30-01, 11:03 PM

I have just signed on in hopes of receiving some much needed info about my 1987 Z51 Dk Red Conv. It has a rebuilt engine, new transmission with new 6-speed, new compressor and alternator, new leather and carpet and top, refurbished wood trim, etc you get the idea. The mileage is high over 187K.
It runs great, no problems other than a new switch for the passenger window to replace. What is its market value? Thanks to any that can help!

Ken

08-30-01, 11:15 PM

Air Force Brat, eh? Welcome!

I would say the C4s are just about bottomed out as far as depreciation is concerned.

In order to get an accurate idea of the value of yours, checking the auction reports is your best bet. There are plenty of magazines and tabloids out there that carry the weekly or monthly auction reports from around the country; both Corvette Fever and Vette magazines have sections set aside for those reports, and Old Cars Weekly has a ton of aucton information.

Join a club. Many people in your local clubs have a good idea of current marketplace values.

Check out eBay. You can look to see what's selling and for how much.

The resources are limitless, and everybody has different likes and dislikes. Good luck. :upthumbs

Ken

09-06-01, 07:59 PM

I see that Darrell Shepherd (4-Speeds by Darrell) (http://www.pipersauto.com/4speeds.html) is now working with the Doug Nash 4+3.

If ya don't wanna go there, and are unfamiliar with what it looks like:
http://corvetteobsession3.homestead.com/files/enginecompartment/DNOD2.jpg

http://corvetteobsession3.homestead.com/files/enginecompartment/DNOD1.jpg

_Ken

Ken

09-10-01, 09:25 PM

If you already have the button off, you should see the little metal wedge the keeps the knob aligned correctly. Pull that wedge out and unscrew the knob from the shaft.

Oops! Forgot something:
Unscrew the T-bar rod that you'll see towards the front of the knob. Be sure to count the approximate number of turns it takes to unscrew and remove the rod, it will aid in keeping the button surface level with the knob top when you reinstall the button. :o

It's been a while since I replaced mine, but I think it was easier to remove the complete switch assembly from the shifter when replacing the overdrive switch. You'll have to judge for yourself if you can reach the switch (I couldn't).

I don't know if you saw my update on the digital dash repair I just went through (C4 Wiring... (http://www.corvetteactioncenter.com/forums/showthread.php?s=&postid=26217#post26217)), but I think my overdrive is functioning properly since I cleaned the contacts in the dash. Mine does appear to be an electrical problem.

Good luck and I hope this helps you.

_Ken

afbrat

09-10-01, 11:28 PM

[QUOTE]Originally posted by 1987 Z51
[b]Air Force Brat, eh? Welcome!

I would say the C4s are just about bottomed out as far as depreciation is concerned.

In order to get an accurate idea of the value of yours, checking the auction reports is your best bet. There are plenty of magazines and tabloids out there that carry the weekly or monthly auction reports from around the country; both Corvette Fever and Vette magazines have sections set aside for those reports, and Old Cars Weekly has a ton of aucton information.

thank you! yes, raised by a pilot and then married one too!

thanks for the direction, we'll see how I do in the next few months :)
(hope I have submitted the reply properly)

Ken

09-10-01, 11:49 PM

Originally posted by afbrat
(hope I have submitted the reply properly)

You'll get the hang of it. ;)

_Ken

Ken

10-02-01, 06:25 PM

I've got a bunch of information for the DN 4+3, the transmission that was used in the Corvette from 1984 thru 1988, gathered from various sources, and put together on one page at my web site: Doug Nash Info (http://www.corvetteobsession.homestead.com/files/html/garage_projects_dougnash.html) if anybody wants to check it out.

I will be adding more information as I find it, and will keep you all informed. ;)

Ken

10-05-01, 10:55 PM

So many things are inter-connected with this set-up it makes it a pain to diagnose, but from the sound of it, it seems as though the signal is getting through when you punch the button, but not when the throttle goes past, what is it - 60% or 75% depressed in fourth?

That would point towards the throttle position sensor (TPS), or even possibly the electronic control module (ECM).

Are you sure the fluid level is up to where it should be? But a low level there would keep it from staying in overdrive; it would kick back into direct ratio drive in that case.

Keep lookin' and if I think of anything I'll be sure to post it here. ;)

_ken

Ken

10-06-01, 02:25 PM

Len, have you taken a look in My Garage (http://www.corvetteobsession.homestead.com/files/html/garage_projects.html)?

There, can be found, a lot of info on the DN 4+3, including a table showing what SHOULD occur in each gear. ;)

No downshifts over 4100 RPM in fourth gear.

_ken

ROCKO

01-01-02, 02:52 PM

Best info i've seen on this trans. I bought my first 4+3 on my 88 conv and so far it's been running fine. Always like getting more tech info. Keep up the good work.

Rocko:cool

Ken

01-01-02, 05:28 PM

Thank you Rocko.

_ken :w

Edmond

01-27-02, 12:31 AM

Guys,

Please excuse me for asking but what exactly is the 4+3?

Also, what exactly is the automatic overdrive?

racecar

01-27-02, 11:08 PM

I never could tolerate that automatic down shifting. I had an aftermarket computer chip that made the OD totally manual. No guessing about what it was going to do next.

Ken

02-24-02, 05:27 AM

As it turns out, after going through the latest in the ongoing electrical gremlin problems I've had, the overdrive may never have been bad in the first place.

As I was trying to diagnose the electrical problem with my fuel pump, I came across another in the long list of relays on the Corvette. There is a relay for the overdrive unit in a manual transmission (4+3) located right beside and sharing a common bracket with a relay for the fuel pump. As a matter-of-fact, it is the same part number. But do you think that knowledge was readily available in the manual(s)? No! :eyerole

At any rate, when I got the car back the other day and ran around for a while, the overdrive behaved exactly as it was designed. In effect, a twelve dollar part cost me around thirty-five hundred dollars! At least now I know the transmission is good and can be re-sold to benefit another C4.

Now I gotta decide to rebuild the L98 to spec, or simply re-sell the engine as-is. :eyerole

_ken :w

David-F

02-24-02, 05:15 PM

The 4+3 was built by Doug Nash they bought the tooling and what not from Borg Warner but when they got it the tooling was worn out so GM had to loan them the money to retool to go into production, this is one of the reasons they went out of busness when GM went with the ZF in 89.
The 84 and early 85 were the problem units, but through out 85 new revised parts went into production starting with the revised direct clutco bearing thrust washer with the apply piston locking tabs, next came the revised carrier bearing and with it most of the problems went away.
If I were to get a low mileage 84 or 85 I would remove and rebuild the unit before anything could fail, it is much better to repair before something failed then wait untill something does happen, many of the parts are out of production and there is no knowing if some will ever be made again.
Also 84 to 86 can be made to operate bypassing the ECM with very little needed only the 86 would require the change of shifter switch from momentary contact to and on off switch like used on later 85, yes it's only in 85 that some had console switches and shifter switches after that they were all on the shifter and all 84 had console switches. The problem with 87 and 88 is that the O/D light was moved from the teltail assembly to the LCD cluster above the tach to were now the ECM comands the light on through the data stream to the LCD but 84 to 86 used a ligh that got powered up from the O/D relay that powered the O/D unit so by by-passing the ECM 84 to 86 can be converted and the O/D light would still work correctly, but 87 and 88 would require a reprogramed PROM.
If there is someone out there that need more info. on a 4+3 just give me an e-mail I have repaire hundreds of them and am able to help people do their own repair or what ever they are not very hard to do if you are able to get the correct tool and unless ther are major part failure can be repaire for under $600.00.

David Fulcher

Ken

02-24-02, 05:19 PM

Thanks for the info David, we get questions all the time on the DN 4+3 so any help that you can provide is much appreciated. :upthumbs

_ken :w

rrubel

02-24-02, 08:43 PM

So, Dave and anyone else... someone mentioned that the 4+3 might not be good for autocrossing. I assume that would be because of the constant shifting? Anyone think that just turning the OD off for every run (ie, leaving it in direct) would put low or no stress on the OD system?
[RICHR]

maxrevs85

02-24-02, 09:44 PM

I have an 85 4+3. How do you bypass the ecm? And, what kind of torque are they rated for?
I drove mine very little after I bought it . It seemed to work fine . But I believe the only time I had OD was when I activated the switch, in any gear.
Does the kit rebuild the 4sp. and the OD unit?
Oh why oh why couldnt they have just put in a nice simple 5th gear od with no wires !! :eyerole

David-F

02-25-02, 09:06 AM

There is no reason why you can't use a 4+3 in an autoX just keep the O/D off and you will not have a problem, if you do fear it coming on and have not converted it over to manual control just unplug the relay while you are racing.

David Fulcher

David-F

02-25-02, 09:10 AM

maxrevs85;
When I get home tonight I'll dig out my 85 wiring diagram and tell you just wires you need to cut and splice to turn your O/D to manual control, it's real easy and then you can use it just like 5th gear.

David Fulcher

maxrevs85

02-25-02, 06:31 PM

David ,thanks a bunch . Thats the way i want to use it. I like to drive it like a hotrod but, the extra gear is a big relief.

David-F

02-25-02, 06:56 PM

It turns out I had the wiring diagram here at work, this is real easy drop the ECM find terminals C7(light blue) and A7(tan with black stripe) cut the wire a few inches from the ECM and take the body harness wires and splice them together and thats it, to check just turn the key on and watch the telltail assembly to see that the O/D light turns on and off if it does so will the O/D and the ECM is unable to do it for you.

David Fulcher

maxrevs85

02-25-02, 07:17 PM

Thanks again David . I have it writen down for future reference. I have the tranny out ,but havent looked it over yet. have no idea if its been worked on before or if it has any upgrades

rockytoptilidie

03-31-03, 08:52 PM

so, while driving, unless I'm on the highway, I should keep it in UD?
Also, sometimes she grinds when I'm going into reverse-does this mean the clutch is going? How much will that cost me?
Thanks in advance!

Edmond

03-31-03, 09:00 PM

Hi Rocky and welcome to the Corvette Action Center.

I just noticed that it's been more than a year since someone last made a reply!

Sorry I can't help with your question.:(

rockytoptilidie

04-01-03, 10:36 AM

I know I know!!! I just found this in another message board, and it had some great insight. Obviously, this is the place for knowledge. I've been lurking around for the last couple of weeks, but I wanted to ask a question that I should probably know, and know that I wouldn't get ripped for it! Actually, I was told that before I go into reverse, put it in first, and then reverse. Didn't grind, worked like a charmp.

95ZR1#418

04-02-03, 04:14 PM

I loved the 4+3 in my '88 Z51 coupe, the only other choice was the automatic and I would never do that. Simple maintenance is the key to longevity. The previous owner and myself religiously changed the overdrive fluid every 15-20 ,ooo miles with new filter(~ $20.00 or less). You don't use the gasket that comes with the filter.

Car has over 100K OD now and still tight tranny.

WhalePirot

04-02-03, 05:33 PM

I have a heavily hopped-up '84 with 105k and am running the 4+3. I love manual shift but also love the kick-down for highway passing. It's the best of both worlds, to me. The '84 logic was complicated and largely misunderstood. I read and understood the logic and used it to my driving advantage. GM simplified the that logic in '85.

I had some 'control' issues with the O/D; none of which were the unit's fault. ALL were external. One was a pinched brown wire (pax side, firewall) courtesy of the 'tech' at the Chevy dealer. Another was bad plug wires which fooled the ECM into thinking an open loop condition existed. Low ATF levels can prevent engagement in steady state, if low enough; or cycling on/off or disengagement during cornering. Low fluid levels prevent the internal pump from picking up enough fluid to pressurize the failsafe-direct-drive design. The dash light indicates that the unit is trying to switch to O/D; has the electrical signal.

Yes, the relays are the same for O/D and fuel pump. They also like to fail, I hear. Mine are still okay. Both are fed =12vdc fulltime and activate by grounding one lug, completing the circuit.

My O/D was rebuilt by perhaps the best; the shop who did the units for Callaway. Paul is busy but was more cooperative than most in patiently anwering my questions and helping me. Check: http://www.5speeds.com/ in Boca Raton, FL. I shipped mine across the country to him after receiving the rebuild kit and tearing the unit apart. I shipped the mess to him and had him beef it up as much as possible. He assured me that the drivetrain weakness was NOT the +3, but the T-10; specifically first gear. Quote: "You will not break this overdirve".

The worse problem is the 'super' T-10 portion, due to cost constraints, specifically, the thin case hardening on the gears. An old pro, (Anaheim, CA) redid my gearbox, which showed hairline cracks on nearly all teeth and wear-thru on 2nd. I am quite good with mechanical things, but could not tear down and rebuild either box, due to lack of a 'press' for 2nd gear and the tricky reassembly of the +3. It has about 13 springs which need to be held inside, each aligned with a corresponding hole on the other sub assembly, but impossible to reach and hold. Some things are worth having done by a pro.

Case hardening applies a hard material to a softer underlay. These gears last a while, but nothing like the old days. They don't have the torque capacity due to the relative thinness of the surface, but who needed much in a stock, early C4? The metal under it is lighter in weight and softer, unlike the 'old days'. Iwas told the stock box would handle 225 ft.-lbs. (1st gear limiting). Going to a new, close ratio gear set added only 100 to that low number. I stayed put, avoiding all the cutting involved with the Richie or the ZF.

The units were reattached by moi and work great!

Highly recommended is GL-6 spec gear oil in the T-10, which means Red Line or Torco brand oil. I believe the 'spin-down spec for reverse is 8 seconds.

Grinding may indicate a failing clutch or incomplete disengagement; possibly due to one hydraulic component of the release parts. I have replaced 3 or 4 clutch masters and slaves, likely due to the higher heating of the fluid, from my headers. I change that fluid when it darkens, indicating water adsorption; which causes corrosion pitting of the internals.

Understand UR car and enjoy it more!

:w
Mike

one-time AirForce pilot

Edmond

04-02-03, 05:40 PM

I think one of the reasons why the 4+3 is shunned is because of it's short life span. If GM had continued to use it, and refining it, I'm sure it would have just as much respect as today's 6 speeds.

rockytoptilidie

04-03-03, 09:22 AM

Great info, guys. I believe a lot of my grinding was not fully engaging the clutch-It is by far the deepest clutch I've ever driven. Thanks a ton-this Air Force Sergeant appreciates it!

djscomp

09-20-03, 05:06 PM

I've had my 1988 4+3 for a few months and today my Overdrive came on and I cant get it to go off. In 1st gear it's fine and as soon as I shift to 2nd it goes into Overdrive. When I push the button nothing happens. While in 2nd thru 4th gear if I punch the gas the overdrive goes off but then comes back on again. Can anyone help? Thanks

88Z51

09-23-03, 12:08 AM

Newbie here. I just bought a 1988 Z51 (my first Corvette), black/black with the 4+3. Unfortunately, after only about 100 miles of relatively easy driving I still found the 1st gear weak link. I gotta say, I've had some manual trans. failures in the past, but nothing has sounded this bad (1st gear REALLY bangs and clangs)! Anyway, my question is when rebuilding the trans, is there anything that can be done to improve it? I do plan on autocrossing it / club track days and the like, but mostly street driving.

Also, the button on the shifter does not disengage the OD. Only hard throttle will kick it out of OD (any gear). Does this sound like the switch under the console or something else?
I've tried adjusting the T rod to no avail.

Any helpful hints or insight on beefing up / improving this transmission would be greatly appreciated.

Thanks much!

Greg.

Ken

09-24-03, 02:33 AM

My original intent for my personalized plates for my Vette was going to be "87 Z51" but in California four digits and a letter are reserved for motorcycles. I had to settle for "1987 Z51". :D

Originally posted by 88Z51
... the button on the shifter does not disengage the OD. Only hard throttle will kick it out of OD (any gear). Does this sound like the switch under the console or something else?
I've tried adjusting the T rod to no avail.

You will get a lot of response on the 4+3 Greg, I'd rather let someone else handle the trans gear part. However, the overdrive operation, and also the rebuilding, is covered in our knowledgebase. You can view the information here at: 1984-1987: Technical Article: Rebuilding the Doug Nash 4+3 Overdrive Unit (http://corvetteactioncenter.com/kb/question.php?qstId=115).

I'm glad to see that you are keeping the 4-4-2 tradition alive. :cool

WhalePirot

09-26-03, 12:55 AM

My 'early, supposedly problematic' 4+3 only lasted over 105,000 miles; then was rebuilt ONLY because I was redoing the entire drivetrain, behind an engine putting our well over 500 lb.ft of torque. I, luckily, had Paul C. redo it, and strengthen it a bit. He assured me I could not break the overdirve with my 406, but might break the 4-speed.

The only issues found in my 'problematic' tranny-O/D were wear-through of the case hardening on second gear and micro cracks on many teeth throughout the 'super' T-10.

There was an issue early in production, which a recall fixed, dealing with a bearing.

I have always really liked the kick-down feature. I learned the logic from my owner's manual. I learned to tap the console mounted switch with my wrist, for on/off. I typically unloaded the Nash clutches by using the clutch under my left foot. We pilots READ about, and understand our machines in much more detail than any, except perhaps mechanics. We practice again and again, learning to make the design to work FOR us.

All other issues I am aware of involve mis-dis-information on the part of owners and mechanics. As Ken implied, most issues with the overdrive are not mechanical, but electrical, as are most of the newer cars. Others stem from inadequate maintenance or abuse.

Sensors, circuits, connections and grounds must be checked, usually before any mechanical work. Connections, being most prone to problems of dirt and corrosion, are a great place to start.

Maybe ECM should mean Easily Confused Mechanics, as the old-schoolers who refuse to learn electronics are quick to blame that which they do not understand.
:w mike

Ken

09-26-03, 01:10 AM

Originally posted by WhalePirot
This is pure BS! _______, your ignorance is showing on this one, pal.

Mike, can you spell P-O-L-I-T-E? ;)

_ken :CAC

tnovot

09-28-03, 10:53 PM

Mike,
I think you owe Edmond an apology. I believe you misread his message. You did say that you always try to understand your vehicle before using it. What about making sure you understand a person's message before jumping on him?
Edmond's reference to short life span was NOT in reference to the fact that 4+3's do not last long. It WAS referring to the number of years that GM used the 4+3. (1984-1988)
Terry

LongTimer

10-08-03, 07:24 PM

FYI:

I bought my '87 Z52, 4+3 new in May of 1987. It is, and always has been my driver. I have logged about 120,000 miles on it (average 7500 / year). I am a very aggressive street driver, but the car has never been on a track, nor in an accident. I am on my third clutch. I lost a main bearing at 95,000 and installed a very good short block. In addition to regular oil changes, I change all of the fluids (except brake) about every 12-18 months. Have flushed the brakes lines twice.

Although I invite catastrophe with this statement, I am compelled to tell you that I have never had a problem with either the "4" or the "3" in 16+ years.

BTW; I have never liked the "clunk" when the OD engages, so when ever I press the button on the shifter to enter the OD gear, I depress the clutch. I don't know if it has added any life of the DNash OD unit, but I bet it has helped keep all the UJoints and the rear end working without problems for 120,000 miles.

johnny80

11-11-03, 10:01 AM

Hey guys,

I have an 88 4+3 and have had no issues with it at all. I do the same and use the clutch to ease the transistion when engaging the OD. Just make sure you keep an eye on her and check fluids. My 88 "Black *****" never gives me any issues. Just keep up good maintenance and you'll be good to go.

SSG Johnny Drummond
US Army
Bagdad, Iraq

Can't wait to get home and drive mine again...just 4 months left.:cool :cool

Ken

11-11-03, 03:43 PM

Just be careful in those last four months - don't let your guard down, and come back home soon. :pat

ddmau

12-21-03, 11:15 PM

What? No vettes in Bagdad? No wonder the masses are clammering in the streets. Pity.:(

longrr

01-06-04, 07:33 PM

I just purchased an 88 roadster with the Nash 4+3 and am having the same problem as several other folks in the forum with the overdrive. It shifts into OD when the transmission is shifted into second gear and will not disengage with the switch on the shifter. Is this a switch problem?

Thanks.

C4ME

01-10-04, 01:29 AM

SSG Drummond, Thanks for what you do to allow us all to enjoy our Americana. God bless you and your family.

Now my question. I am poised to purchase an 1987 with a DN 4+3 and the overdrive is non-ops. Has anyone heard of the problem being "a relay?" I am new to the 4+3 an don't know if the car would be worth it if there was a rebuild/replace in my near future.

Thanks

johnny80

01-10-04, 11:19 AM

check to see if the switch on the trans (underside) has been cut and rewired. That may have gone bad and or that your OD is now a manual operation due to rewiring. Otherwise, you might need to get her looked at. Be careful of dealerships...i got burned once at a chevy dealership over a ECM. Keep asking at this website...there are alot of good experts here....they will take care of you ...I promise!!!!

Johnny

WhalePirot

01-10-04, 01:11 PM

IF it's a relay, it's simple and rather cheap. The relay is identical to that for the fuel pump and located right next to it. Swap plugs on them. If the cars runs, the relay is fine.

Beyond that, it could be very pricey, especially if the fixer does not understand the circuitry, as even some dealers do not.

The weakest part of the 4+3 is the main shaft in the 'super' T-10, I am told, not the O/D.

I say again, I believe the biggest issue with this box is improper maintenance and misunderstanding, on owners and dealers parts, about how it really works. Both, get expensive.

C4ME

01-16-04, 09:15 PM

Alright...next question. The dude with 4+3 is not ready to sell even though the car is for sale. This is for my learning. After driving (for over 10 mins) and seeing the OD indicator illuminate and not feeling the car shift into OD, I went back today to deal and when I offered my deal he laughed. I mentioned the lack of shifting and the response was "Oh the car has to be @ 160 degrees before it will shift." I have consulted an aftermarket repair manual and it mentioned the ZF 6spd with the 122 degree inhibit, but not the 4+3 having an inhibit. I also have look through the Cor-Vette Spec book on C4s and have found no reference to the "thermal inhibiting." Does any one know the answer.

Thankin' you in advance
Joe

Ken

01-16-04, 11:44 PM

... the car has to be @ 160 degrees before it will shift.

Joe, the overdrive function is bypassed until the engine temperature reaches 80°CF/176°F for the '84, 60°C/140°F for the '85, and 50°C/122°F for the '86/'87 Corvettes.

Top

01-17-04, 04:30 PM

My 86 OD comes "on" at 132 degrees.

:beer

WhalePirot

01-20-04, 11:11 PM

The engine must be in closed loop mode for the overdrive to operate. The temperature, in my experience varies, but loosely means, warmed up. BTW, poor tune has affected mine, but that dash light coming on means that the ECM has okayed the O/D operation, but something 'downstream' is not functioning. It may be a low fluid level, the relay (I think) or a mechanical problem in the Nash. I don't have my manual handy but I HAVE fixed an 'overdrive problem' by changing my spark plug wires!

A good learning exercise for you and likely a deal you should pass upon, given the attitude and misinformation from the seller.

C4ME

01-21-04, 12:43 AM

Thanks WhalePirot et al...Very good info and yes the seller still has his car and will remain in this state (little control lingo) for??? I have family in Valley Joe and am a reformed Californian (just kidding). I am original from the Yuba City area so you may know why I am no longer in CA.

Thanks again,
Joe

unleadedbrew

01-22-04, 07:33 PM

I'm sure glad this thread is still strong. It looks like I'm in for a re-build on the T-10. Howls like a banshee in all 4 and neutral. Wifey says she can't hear it while outside the car. (She stood on the side of the road while I cruised by. Yes, I did go back and get her) Nothing seems amiss with the +3, yet, and still goes into all gears ok. Can someone explain why it is so hard to find someone who can rebuild these? If the OD doesn't need anything, wouldn't it be just a regular 4 speed re-work or does the OD unit have to come apart? The only place I've checked with is Corvette Service of Dallas, and the manager alluded to the fact that once he had determined what the problem was, it might have to be shipped. Didn't say where. One thing he did say, and I haven't seen it brought up here, was the fact that there seems to be a problem with the automatic fluid leaking into the T-10 unit and cohabitating with the 90 wt. creating many problems.
Well, back to what I really need to know..........How much dinero am I looking at? Would I be better off changing to a 6 sp.? He said that would be around 3500.00. Is this a good figure in ya'll's book? :eek :cry

Ken

01-22-04, 07:59 PM

... there seems to be a problem with the automatic fluid leaking into the T-10 unit and cohabitating with the 90 wt. creating many problems.

I've brought this subject up before, but the thread is probably long gone. I came across something a while back where it said the guy used ATF in both the overdrive unit as well as the transmission itself, thereby eliminating the concern regarding fluid contamination. The ATF has enough lubricating qualities to work in the gearbox, it'll just be a little noisier is what they say. I have no direct experience with this so...

As for the cost of a transmission swap, the ROD 6-speed goes for around $3200. I have no idea what the Keisler or the Tremac would go for. ;shrug

_ken

maxrevs85

01-22-04, 08:24 PM

Ken, The ROD is $4000 for the made to fit the vette tranny, I'm sure you remember that expenditure. :). The Tremecs are more costly. About $4800. I used the 70w90 mobile one in my trans and the ATF in the OD. I will most likely go to the ATF in the T10 also, we use it in our racing trans.

Ken

01-22-04, 08:39 PM

Four grand now!! It looks like something at least finally went my way; I paid thirty-two hundred in the spring of 2002. :cool

unleadedbrew

01-22-04, 09:05 PM

:eek :eek :eek :cry :cry :cry

Thanks, Ken, maxrevs. Looks like re-build time. Gonna turn the stereo up for now!

Gordon

WhalePirot

01-26-04, 01:40 PM

If the OD doesn't need anything, wouldn't it be just a regular 4 speed re-work
<< yes, it was, for me.
does the OD unit have to come apart? << No, however.... The answer may depend upon other issues, like the epth of your pockets vs. how long you plan to keep the car, what kind of care the O/D has had, etc.

The swap to a 5 or 6 speed is not free either, and while the unit is removed from the car, it may be time to go through it. The O/D is best serviced by someone who really knows it, but the forward section can be done by any decent tranny shop. I removed mine; sent the back unit to Florida and had the T-10 done by John's Four Speeds, in Anaheim. I plugged 'em back together and bolted the sucker in.