Converter Lockup problem ?

[evariste]

Since last week, I have no more speedometer, because the cruise control regulator is out.

I have noticed that speed changes are smoother at high revolving ranges (while overpassing for instance). Before it, the motor stayed one second at about 5000 t/mn in the second gear, maintaining the speed desperatly constant, and suddenly, the tranny selected the third gear and it was like a booster light on.

I think that the ECM gets its speed information from the speedo, and drives the converter lockup. I intend to put a new regulator when I receive it, but I would like to keep the smooth and efficient speed changes and save gas with the lockup converter...

I believe that something was going wrong, but what ? Throttle position sensor ? Wich way should I search ?
Does anybody know the logic of the ECM for the converter lockup ?

Evariste

[22229stingray81]

I am having problems with my lockup too, it goes on to early and stays on and I cannot get it off without going wide open... If anyone has any information on this, it would be greatly appreciated... I was reading something about the detent switch? Just a thought, thanks again for any help.

-Tatortot

[Nut]

Guys..... I put in a manual override switch that locks in/out the TCC. I tapped into the disconnect circuit at the brake pedal switch. I used a 12V lighted switch that just happened to fit perfeectly into the rear window defogger switch opening (which I don't use). Switch on (light comes on) TCC is locked on. It will not jump out for any reason. I can downshift to second gear (I have a TH350 tranny) and the TCC stays locked on. Switch off..... TCC is off. It is a sweet set up and took me only a couple hours to set up. I'll have to dig around and see if I can find the schematic diagram that I used to tie it in. I hooked this up years ago and have never had a problem.

........... Nut

[Stingray6974]

Evariste,
The ECM recieves info from the VSS(vehicle speed sensor) on the back of the speedometer. Without the speedo working the ECM is not recieving a signal. You should have a code 24 set.

Tatortot,
The ECM recieves info from the Map sensor and the TCC vac switch to engage the lock-up. It should not engage below 45 mph and should disengage when accelerating, deaccelerating or touching the brake pedal. The TCC soleniod has an internal diode which usually fails causing erratic and early lockup.

Mike

[22229stingray81]

Stingray6974,

So this could all be the cause of the not being able to upshift unless wide open throttle? It wont leave the current gear im in unless I floor it... Thanks for any help you can give me.

-Tatortot

[Stingray6974]

Tatortot,
No, the ecm only controls converter lock-up, not normal shifting. Normal shifts are determined by the vac modulator and the detent(throttle pressure)cable with the govenor acting as a referee between the two. The govenor can override the modulator and detent or can prevent any shifting.
I'm assuming you have a 350C trans. You're saying it won't shift at all unless you floor it. Please explain in a little more detail.
With it in drive, will it 1 - 2 shift normally or do you have to hit hi rpm's? What about 2 -3? If it won't 1 -2 shift what happens when you let off the gas? Does it feel like it's still in gear or feel like it went to neutral?

Mike

[evariste]

Originally posted by Stingray6974
Evariste,
The ECM recieves info from the VSS(vehicle speed sensor) on the back of the speedometer. Without the speedo working the ECM is not recieving a signal. You should have a code 24 set.
Mike
Exact. I checked the codes, and I sure have a 24 code.
Before this speedo cable failure, speeds were'nt passing normally. For instance, at wide open throttle, the 2nd gear could stay engaged although the motor went up to 5000 rpm. After about one second, it passed in 3rd, giving a violent push.
Since there is no more speed information, the transmission behavior is much more friendly. It seems it is because the ECM doesn't know my speed, and doesn't energize the Converter Lockup Relay.
Today, I opened the carburetor. The throttle position sensor itself seems to work perfectly : if I push on it with a screwdriver, it gives a "full throttle information", but if I push the throttle itself, it will tell 3/4 open. It looks like the plunger was too short. It is green and not adjustable.

Evariste

[22229stingray81]

Stingray6974,

Yes I have the th-350. What happens is it seems to prematurely go into gear under any acceleration, it also seems to shift rougher. and when in second gear, accelerating normally, at about 35 mph or 2600 rpm the lockup seems to go on (mechanic verified it) and loses about 300 rpm. It is also very hard to leave the current gear I am in, for example, cruising at 35 mph.. I have to depress the accerlerator pedal to almost wide open to get it to shift back to second, and when in second at very low speeds it will not shift to first at all unless I completely stop or floor the pedal. Ive had to resort to manually shifting gears at times. The lockup doesnt not seem to imediatly come off anymore. At wide open throttle, when it shifts to second gear at around 50mph it seems to sort of stall for a second, then pick up power, it never used to do this. Also, my fuel gauge started reading a quarter of a tank more then it should at this same time all this started happening.. could it all be relatated? (just a thought) Thanks for any help you can give me.

-Tatortot

[Stingray6974]

evariste,
You need to find out what the TPS voltage is. Normal voltage at idle is .5 to 1. volt. At wide open it's 4.3 to 4.5. The TPS is adjustable but not by the green plunger.

tatortot,
It sounds like you have a shorted TCC solenoid inside the trans. On the trans left side just above the pan is a 4 wire connector. Unplug it and test drive the car to see if this solves the problem. As for the gas gauge.....????.

evariste,
Try unplugging yours also after you get the speedo working. It sounds like you may have a bad solenoid also.

Mike

[22229stingray81]

Stingray6974,

Thanks for the help, Ill disconnect it as soon as I can, thanks for bearing with me on my lack of mechanical knowledge. Thanks again.

-Tatortot

[Stingray6974]

Glad to help.

Mike

[evariste]

Originally posted by Stingray6974
evariste,
You need to find out what the TPS voltage is. Normal voltage at idle is .5 to 1. volt. At wide open it's 4.3 to 4.5. The TPS is adjustable but not by the green plunger.


Stingray6974,
I I could'nt measure the voltage, but I measured the impedance.
The TPS is a 20KOhms potentiometer.
When I push the plunger with a screwdriver, the remaining impedance is 3KOhms, that would give a 4,25 V Voltage.
When I open wide the throttle, the remaining impedance is 7KOhms, that would give a 3,25V Voltage... The ECM would think the throttle is only 65% open !

I looked around the pump lever, but I could'nt find any TPS adjusting screw...

Evariste

[Stingray6974]

The TPS adjustment is on the left side of the carb just behind the accelerator pump lever. It has an aluminum plug covering it. The plug must be removed and adjusted with a "double d" tool. This adjustment is for closed throttle only. If you have .5 to 1. volt at idle but won't go above 4. at wide open then you have a bad TPS or a weak spring under the TPS. An open or shorted TPS will set code 21.
Mike

[22229stingray81]

Well I disconnected the tcc solenoid connector today and it didnt help.. still shifted wrong, I just got a check engine light on, thats all.. It seems to be okay for the first 1 or 2 accelerations, but then all of a sudden, its like it has a 3rd and a half gear... and the mechanic says its the lockup.. any other suggestions?

-Tatortot

[Stingray6974]

Tatortot,
The next step will be to replace the TCC solenoid. There is always the possibility that you have a bad torque converter.

Mike

[evariste]

Originally posted by Stingray6974
The TPS adjustment is on the left side of the carb just behind the accelerator pump lever. It has an aluminum plug covering it. The plug must be removed and adjusted with a "double d" tool. This adjustment is for closed throttle only. If you have .5 to 1. volt at idle but won't go above 4. at wide open then you have a bad TPS or a weak spring under the TPS. An open or shorted TPS will set code 21.
Mike

Thank you for your help.
I have no 21 code.
I think my carburetor needs to be opened or replaced.
Is it easy, or should I give this job to a specialist ?
If I can do it, what should I order (rebuild kit, TPS, ...) and where can I find this "double D" tool ?

Evariste

[22229stingray81]

Stingray6974,

When I dissconnected the solenoid nothing changed, was this suppose to happen? Does it still need to be replaced even though it did the same thing when it was connected? Also, is there anyway to test if my torque converter is broken short of just replacing it? Thanks for any help you can give me.

-Tatortot

[Stingray6974]

Tatortot,
The TCC solenoid is just an electric checkvalve to open or close one passage. It uses full-time 12 volts and is ground activated by the ECM. Sometimes it grounds itself and applies the TCC. By unplugging it we have eliminated that possibility. The valve itself can also fail causing lock-up. Only way to confirm this is to replace the TCC solenoid.
Converter diagnosis: when all else fails...replace the converter.

Mike

[Stingray6974]

Evariste,
I don't know what to tell you about rebuilding it yourself. These are not simple carbs(as compared to the pre 80 quadrajets) to work on. If you were in the U.S. I'd say ship it to me and I'll fix it but I think the shipping would be expensive from France.
Basic parts you need are: TPS, carb kit, float, and fuel filter. Additionally you may need:choke pull-off,mixture control solenoid, and/or choke coil.
There are four different double d tools needed to rebuild one of these carbs. You will also need a scanner or analog dwell meter to set the mixture.
Does anyone over there have any experience with these carbs? I know less then a dozen people over here that are capable of rebuilding one. And forget about buying a rebuilt one. Rare81 (Bud) has seen that nightmare not to mention the price.
I don't recommend doing this yourself unless you have had lots of Quadrajet experience. Sorry for the bad news, I just don't have a good solution.

Mike

[22229stingray81]

Thanks for the diagnosis Mike... Do you know of any major corvette parts places I can order a tcc soleniod from? I could not find one on Mid America Corvette parts. Also, I could not find the tcc selonoid in my haynes repair manual, is there anything major I need to know about replacement before I TRY to tackle this job? Any tips or outlines you can give me? If this doesnt work I guess I have to take it into a transmission shop to replace the torque converter, I hope I can find one that will know how to work on my vette and take good care of it. Thanks again for all your help.

-Tatortot

[evariste]

Originally posted by Stingray6974
Evariste,
I don't know what to tell you about rebuilding it yourself. These are not simple carbs(as compared to the pre 80 quadrajets) to work on. If you were in the U.S. I'd say ship it to me and I'll fix it but I think the shipping would be expensive from France.
Sorry for the bad news, I just don't have a good solution.
Mike

Thank you Mike, even these are not so good news...

Originally posted by Nut
Guys..... I put in a manual override switch that locks in/out the TCC. I tapped into the disconnect circuit at the brake pedal switch. Nut

Well, it seems that I am first going to choose Nut's "bypass". I'll make photos to have it documented.

Now, I just wish to know the impact of a TPS malfunction on the motor's performances.
I'll work on 2 scenarios : removing the E4ME, and changing all that is driven by the ECM, or have this E4ME fixed. Not sure that the second is more expensive than the first !

Evariste

[GerryLP]

Tatortot,

If you drop the tranny yourself, then replacing the coverter is as easy as pulling off the old converter and installing your replacement. If so, then ask Stingray6974 if you would be better off with a stock converter or maybe replace it with a higher stall converter. I know that if you plan to mess with the engine in the future (cam replacement for instance), then a higher TQ converter will add choices on cams latter on.

I have lowered the tranny in mine at least 5 times (total), but the last time I used a scissor-type tranny lift available at Harbor Freight Tools. It costs about $50 dollars, and you have to use a ratched to raise it or lower it, but it is alot more stable than using an adapter on the floor jack. One draw back is that you must raise your car on jack stands pretty high, so that you can roll the tranny out from under the car and back in.

I have not researched it yet, but I wonder what would involve in replacing the TCC solenoid. Does the tranny has to come out? Or are we talking tranny oil pan removal and re-installation only to gain access to it? The answer to those questions could help you decide which to do first the TCC or the converter.

GerryLP

[UKPaul]

Changing the Solenoid is easy. Drop the pan & remove the filter & the solenoid is held in place with a couple of 1/2" AF bolts. If it's an MX2 trans then there is a pressure switch wired in series with the solenoid which would be worth changing at the same time.
I've changed my solenoid & pressure switch, the electical system checks out & still it doesn't lock up :( (bypassed the ECU & earthed the solenoid ground lead manually to rule out the ECU).

Evariste: I've got manuals on setting up the E4ME. If you want I can email a copy of the TPS section to you.
Paul

[22229stingray81]

Thanks for the outline of the solenoid replacement, UKPaul. Im thinking about just disconnecting the lockup all together; I really dont get much better gas milage anyways, and this problem of lockup on all the time is very annoying; I dont have all my power all the time and the shifts are very rough. Is there an easy way I can disconnect the lockup (disconnecting wire or fuse) without getting an error code? Thanks for any help.

-Tatortot

[UKPaul]

Hi Tatortot,
A real easy way of removing lockup is to adjust the switch on the brake pedal so that it never sends 12v to the lockup circuit!
There's also the connector on the tranny. This is awkward to get to, but if you follow the wires up the side of the block they join into the main harness at another connector which is just behind the d.side valve cover. When I disconnected that connector I didn't get any error codes. There are 3 pins used on this connector: A, B & C (go to A, D & C on tranny connector). A is a constant 12V feed & B is the ground for the solenoid (goes to the TCC/EGR relay which is switched by the ECU for lockup). If you cut wire B you can then run a wire from it to a manual switch, connected to ground/earth, for a manual lockup ie. bypass the ECU. That is how I've been testing my solenoid & I definately don't get an error code (it doesn't lockup either, but that's a different problem!).
Hope this helps,
Paul

[22229stingray81]

Thanks for the help. I think I'll try the first approach, the second seems a little to "involved" for me.. hehe. I remember reading in the old forum about somehow converting the rear defroster switch to a lockup on/off switch? Since my rear defogger switch has stopped working and I cannot find a replacement anywhere (been looking for 3 years! 81 & 82 model year only switch, no repo part) I think I would like to try this, does anyone have this old forum post bookmarked or can tell me how to do this? Thanks for any help.

-Tatortot

[UKPaul]

Whatever you do, don't pull the switch right out! You won't believe how awkward it is to get back in :)
My defog switch is also dead (try finding one in the UK!!!). Somebody pointed me to a website for one, but the price was out of this world :( I just use a cloth.....
Paul

[22229stingray81]

Thanks for the added advice... I may have resorted to that. Can you by any chance remember the website with the outrageous prices? It just bugs me not having it working. Thanks again for any help you can give me.


-Tatortot

[UKPaul]

Tatortot,
I had a look through my old emails but can't find it. carparts.com may be worth a look. I'll post on another forum & see if I get any replies.
Paul

[22229stingray81]

Thanks again for the help, Ill go check out carparts.com right now.

-Tatortot

[evariste]

Originally posted by UKPaul
Evariste: I've got manuals on setting up the E4ME. If you want I can email a copy of the TPS section to you.
Paul

Thank you UKPaul, I already did all the work to adjust the TPS, but it needs to be replaced. I found a "tech tip" on how to replace it. It seems to be much too risky for me, so I'll let it as is for the moment.

I'm just evaluating two solutions :
1 - Having the carburetor rebuilt, but on this side of the ocean, it seems even more risky than in the US,
2 - Convert my old car to EFI with an Edelbrock Pro-Flo system...

Nothing before next year...

Evariste

[GerryLP]

Evariste,

If you decide to rework your carburator, but you also want to let someone else do it, then consider shipping your unit to an overhaul service; however, I know of one service that did not come through for me, and I wish to warn you about them.

In April of this year, I contacted Superior Carburators (a.k.a Wideworld Carburator Distributors Carburator Distributors Exchange (http://www.carburatorexchange.com) ), and I asked them if they carried the L81 automatic Rochester carburator (P/N 17081218). I explained to them how it was important for me to receive from them that particular P/N carburator. Well, after $304.00 total, I received a carburator with a Buick P/N. I returned the item, I am still contesting the refund (which by the way the Visa people told me I would finally receive my refund/credit in the near future). I got from Superior Carburators a lot of empty promises :mad.

On the other hand, I plan to send my carburator to Specialty Carburator Corporation (a.k.a. Carburator Exchange, El Monte, CA http://info@carb-x.com 1-800-491-2633). I spoke over the phone with them, and they told me that not counting shipping to and fro the sender that they could overhaul the received carburator in about a day. They have other locations, but suggested I send my factory carburator to the main location at El Monte, Ca.

If anyone else in this forum know anything negative about Specialty Carburator Co. please post the information.

I may also purchase another carburator (which type or brand I still not sure) to go with my NEW short block, NEW aluminum heads, NEW cam, and NEW rockers. I paid the core price for my original short block, and I still have my original heads, cam, and anything else that will not be used in or around the new engine. Once I rebuild them (mostly by myself I hope :( ) I'll have my original motor crated ready for a future install in my car.

Fixing one's vehicle is the most satisfying experience one can have. With time one can conquer anything (except perhaps cheat death... :duh) I was trying to drive my own vette to Sharkfest, so that explains hiring someone for my engine, but it did not panned-out. If your car is a daily driver, then time could be limited for you; however, if time is not a problem, then I recommend researching and repairing your own carburator. I can guarantee you that everyone here and in the CAC community will be willing to ;help you along the way. Keep the faith!

Just trying to help...

[22229stingray81]

Hello again all... I am sorry to post yet another problem question, but I'm worried about a few things... recently.. under middle to full throttle I am getting a heavy vibration under the floorboard, but only at low rpm, at about 3,000 it smooths out, and there is no power loss as far as i can tell. I checked transmission fluid, and changed oil and oil filter, no improvement.. is this a problem to worry about? Also I have noticed a rough idle when car is very warm... as soon as I put on gas it smoothes out, but when im at a stop, she seems to shake... related maybe? Thought id post this here cause I didnt want to bother you all with a new thread, thanks for any advice anyone can give.

-Tatortot

[cheeseral]

I had an 87 Cadillac that did that and it turned out to be the converter. I had the trans replaced and it fixed the problem, I hope yours is a different prob. Sounds like your rough idle is unrelated. Good luck

[22229stingray81]

Thanks for the diagnosis... just what I hoped wouldnt happen... Guess I gotta have the mechanic take a close look at it.. thanks again.


-Tatortot

[Tom Bryant]

Originally posted by Stingray6974

The ECM recieves info from the Map sensor and the TCC vac switch to engage the lock-up. It should not engage below 45 mph and should disengage when accelerating, deaccelerating or touching the brake pedal. The TCC soleniod has an internal diode which usually fails causing erratic and early lockup.

Mike

Hey Mike, Are you sure about this? Our '81 has always locked up while driving aroung town at low rpms and light throttle. It will shift 2-3 while locked at light throttle. All other functions are working correctly. A little throttle will unlock it. I have always thought that it shouldn't lock up at slow speeds. Maybe there has always been something wrong since new.

Tom

[22229stingray81]

So it should definatly come off with light acceleration? I have to go almost wide open to get it off, and braking wont disengage it either...

[Tom Bryant]

Yes. But it shouldn't unlock if your cruise control picks up a little to compensate for a slight uphill grade. It should stay locked with a slight increase in throttle but not much more.

Tom

[Stingray6974]

Tom,
The lock-up should never engage below 40 mph. This is a common problem with the 700R4's and the 350C trans. When you let off the gas the converter should disengage. With light throttle it will re-engage but with moderate throttle it won't. I have had them lock up as slow as 15 mph. 99% of the time replacing the solenoid cures it.

Mike

[Tom Bryant]

Ours will probably lock up at 20 too. Something else to check out this winter.

[22229stingray81]

I had my mechanic tell me that the lockup doesnt have a pre-set rpm or speed for when it to go on, but a whole bunch of factors coming together.... so maybe not a problem to have it on at 20mph or so as long as it comes off easy? Just trying to contribute...

-Tatortot

[GerryLP]

Tatortot,

How far have you gotten with the lock up problem? I only ask because I feel that Stingray6974 may be up to something when he assured you that your problem had to be the solenoid.

Last night, I disconnected the tranny harness, and now the tranny does not seem to throw the gears as unpredictable as it was. Someone had described the problem as (and I am paraphrasing!) "it seems that it locks up the converter and then it throws the third gear" or something to that effect. :eek I couldn't believe how accurate that description was.

The car now shifts the gears better with the harness disconnected, and when it shifts I don't see the RPM gauge snap to 2,000 RPM in a flash (almost as if I could feel the converter locking right when the tach snapped). I think that my tranny is suffering from a bad solenoid also. The torque converter could cause this problem, but I feel that it is more unlikely, for in my situation I had replaced mine, and the L81 has good low end torque, but it won't brake a converter. The pin in it for the lock up is not as strong as high torque converters, but it hangs with it well.

I plan to drop the tranny oil pan and replace the solenoid :hb As much as I would hate to do it. I hope I don't forget to put a pan drain before the next time. :lol

[evariste]

I'll try to explain all what I understood of the lockup converter behavior during the last months, and the "bypass" I have installed. As my english is a little bit poor, don't hesitate to ask questions if you don't understand what I mean.

As you may remember, I discovered that there was a problem with the converter lockup when the speedometer cable failed. As the measured speed was always zero, the computer never tried to lock up the converter. And driving the car was really fine...

What I understood is that the computer triggers a converter lockup wire when : 1) The speed is more than 25 mph AND 2) the throttle pedal is not fully depressed. On my car, as the throttle position sensor is out of order, the converter lockup is always triggered on as soon as the speed is over 25 mph. Not so good.

I have two things to do to fix definitely this problem : I can have the minimum lockup speed rise to 40 mph (I think) using the hypertech chip. I also need to have my throttle position sensor fixed to make it work properly. Too much for me now.

Looking at the wiring diagrams, I discovered that when you brake, the converter lockup is automaticaly released by a switch located behind the brake pedal. So I added a manual switch on one of the wires leading to this switch. When this switch is off, the converter never locks up, when it is on, the converter can be locked according to the orders given by the computer.

It's not so handy, but it works. In heavy traffic, or in town, I put the switch "off", and on open road I put it "on".

I hope this will help you !

Evariste

[GerryLP]

Evariste,

That's a very good approach. But now that you mention that -I plan to replace the stock carburator with either an Edelbrock 750 or a Speed Demon 750 (both available with electric choke and vaccum secondaries).

What concerns me is that if I replace the carb for one without the computer hook up, then I may totally loose the converter lock-up feature in my car, unless I install a manual switch or someting.

I will only be concerned if my fuel economy without the lock-up feature drops dramatically (1 less mile per gallon I can live with)

What do you think? ;help Anyones' input requested.

Any L81'ers without the computer hooked-up out there?

[22229stingray81]

GerryLP,

I have not yet done much with my lockup problem. I dissconnected the solenoid harness next to my tranny and nothing changed, just got a check engine light. I feel that there is a major problem and need to take it to a corvette transmission shop which is quite a ways away from me, and I do not trust just anyone. So Im going to deal with it until it gets unbareable. I am thinking about just dissconecting the lockup all together (does anyone know how much mpg it loses without it going on on the highway?); though it seems to have more power with the lockup coming on so early, it is very annoying in traffic. Ill keep you all posted on any changes and repairs, thanks for all your help again.

-Tatortot

[evariste]

Tatortot,

Just try this : look behind the brake pedal. You should see (not so easy) a connector with a purple wire and a pink/black wire. Just disconnect it and try to drive in this configuration. If your car has a smooth behavior, then you can guess something is messing your computer...

Evariste

[22229stingray81]

Evariste-

Thanks for the break down, Ill try it tomarrow as soon as I can, Ill let you know what happens, thanks again.

-Tatortot

[22229stingray81]

Well I looked under above back and all around. I couldnt find that color combination of wires.. There was a connector right above and almost touching the brake pedal itself that had a green wire, a blue wire, and browish purpleish (maybe faded black?) with a white stripe wire.. could this be it? I suppose I could just pull it and find out but I dont want to mess up anything really badly... Any other suggestions? Am I just not looking close enough maybe?


-Tatortot

[evariste]

I know it's not so easy.

If you want to really get access to it, it's better to remove the heater's hose.

If your car has a cruise control, you should have 3 connectors :

- 1 for the brake lights with a white and an orange wire.
- 1 for the cruise control release with a tan and a dark green wire.
- 1 for the TCC realease...

Try to find the orange and white wires. They separate from the main harness juste beside the TCC's one. Notice that it is also the horn relay's place (strapped over the harness).

Have a nice week-end !

Evariste

[22229stingray81]

Thanks for being patient with me, Ill try again tomarrow. You also have a nice weekend!


-Tatortot

[22229stingray81]

Well today I was cruising at about 55mph and I hit the accelerator a little and the lockup actually went off.. then I hit the brake after it came back on again and it went off again.. Seems like the lockup in 3rd gear is starting to work... Still have the same problem in second gear though.. wont come off unless I stop completely. I guess things can fix themselves? Any thoughts would be appreciated.

-Tatortot

[GerryLP]

Tatortot,

Last night I worked my TCC problem. I tried ordering the correct TCC solenoid for the 81 vette (AC Delco 1997591), but this part number is discontinued, and I could not find it even at www.gm-restorationparts.com (http://gm-restorationparts) The dealers kept sending me to a tranny shop and the tranny shops sent me to the dealer...:crazy

Instead, I had to order the TCC Lock-up solenoid (AC Delco P/N 1997592. If you have access to a 81 Corvette Shop Manual, then you can see in page 7A3-15 that the alternate solenoid looks like the solenoid wiring for TH350C model 8VZ, 8VA,8T3...etc at the upper-right corner of the page. The alternate solenoid costs around $50.

Well, page 7A3-14 at the very first paragraph, tell us that the model code is stamped IN the right side of the bell housing. I looked all over, but I could not find the model for my tranny. So I turned it in my mind every which way I could and then it occurred to me that the alternate part number solenoid that I had to settle for and my stock solenoid were only different in that the negative wire (black) and the "D" pin wire (so identified at the tranny plug connection) were crimped together on the alternate P/N solenoid. My stock solenoid had the negative wire and the "D" pin wire separate from each other.

So, after searching for locking wire terminals similar to the stock ones and not finding any at the usual places (Auto Zone and the like), I decided to reuse the terminals on my stock solenoid. I clipped the ones from my old TCC solenoid and I also clipped the alternate solenoid wires to match my stock solenoid. I used No-crimp connectors (by Swenco) to connect them to the alternate solenoid.

I then installed a new 3rd gear switch (AC Delco P/N 8643710) to make sure that I would not have to go back to the tranny pan drop process in a while. I then wired the transmission valve body as it was as stock. For which, by the way, I could not find the exact configuration in the shop manual.

Not trusting my brain power :duh I also installed a B & M tranny oil pan drain kit -in case this repair did not work. It will make my next pan drop less messy. I also had a bit of a scare when my last pan bolt felt like it was stripped. :hb I regained my composure, and used a tap die set to chase the threads with a 5/16 -18 die. (or is it a tap? :confused ). The stock bolt would not work anymore, but a longer one (1" long from Auto Zone) did. Luckily it was at the shifting cable plate hole where it stripped, so the excess lenght was taken up by the plate itself.

I am glad to report that the transmission is shifting fine and my problem is gone. I think that the reason was that the stock solenoid was installed with a gasket, and the gasket was leaking (the solenoid surronds a small hole on the tranny valve body). If the gasket leaks, then you'll experience a delay in the lock up where it seems that the gear changes and then the converter locks up (it sounds very much as if one were to let go the clutch (in a manual tranny) at low RPM for a thrid gear. The alternate solenoid, by the way, has a built-in rubber seal instead of a gasket to seal between the solenoid and the valve body.

Now what remains is for me to follow Evariste's instructions to by-pass the TCC lock-up for whenever a Mustang pulls up next to me :r :_rock. The best of both worlds -TCC lock up for fuel economy and By-pass TCC for fixing Mustangs....:bu :L

[22229stingray81]

Wow.... that is way over my head. I would get confused at dropping the trans pan (haha). I did find it very interesting how you were able to substitute the replacement alternate part, thumbs up on that! And thank you for sharing all the part numbers and websites with me. I have one question though... when the lockup comes on, you loose acceleration? I think my vette feels more powerful with the lockup coming on so early, but I could be wrong. So lockup; good for fuel economy, bad for power?



-Tatortot

[GerryLP]

I have one question though... when the lockup comes on, you loose acceleration? I think my vette feels more powerful with the lockup coming on so early, but I could be wrong. So lockup; good for fuel economy, bad for power?

First let me say that, generally speaking, the converter locks in two ways. Hydraulically and mechanically. With the hydraulic lock-up there is an amount of slippage that varies with the type of converter (the stock converter has minimal slippage). With mechanical lock-up there is a direct connection between the engine and tranny (no slippage).

In my case, I installed a 2,400 stall converter. It is designed to allow my engine (through large amounts of slippage at low RPM's) to reach the best engine speed (while my car is not moving) so that my engine's cam power range can best be utilized.

The mechanical lock-up happens when parts in the converter connect and form a solid link between the engine and transmission through a fluid signal (solenoid operated). Mechanical Lock-up prevents my engine do that unless something else allow the engine reach the target RPM for my cam (such as the rear wheels spinning :bu to allow the engine reach the RPM). This is so because of the mechanical linkage formed through the lockup feature.

On the other hand, without lock-up AND while driving normally around town there is that large percentage slippage happening in the converter because the engine speeds are relatively lower. The result is a large waste of gasoline. To put matters in perspective, I was averaging 18 miles per gallon in everyday driving around town (this is with my new cam too :_rock). When I disconneted the tranny harness to dis-engage the lock-up feature my gas consumption went up to about 12 miles per gallon. So lock-up helps save gas. It also prevents converter shaking which is really bad :blow for the tranny.

In the stock Corvette tranny, the mechanical lock-up helps in that the shifting is crispier, minimizes slippage, and helps corral every bit of engine horse power reach the rear wheels.

The by-pass action that Evariste, Nut, and Mike :BOW are telling us helps us select the lock-up feature at our own convenience :Twist

[22229stingray81]

They say you learn something new everyday... looks like I learned todays "something" and much more! Thanks very much for that explination, I understand how the mechanism works much better now. I thought it was nothing more then a gas saving mechanism, boy now I know! Thanks again for taking time to explain it.

-Tatortot

[GerryLP]

I am glad to report that the By-Pass switch operation was a success. I placed a small duck bill illuminated switch at the air ducting chanel right next to the center console island above and aft of gas pedal. I drilled a 1/2" hole into the channel, but the channel already has other factory-drilled holes. The one on the front of the ducting (facing the gas pedal) worked great to route the wires ot the TCC switch. I found a good grounding point at the brake booster mounting stud inside the cabin.

I can reach the switch easily and it works like a charm. Thanks Evariste, Nut, and Mike for your inputs in this issue and everyone else's inputs to make this a nice little project. ;worship

I used a 3-blade illuminated switch (power, signal, and ground), but the electrical current for the actual signal is not enough to make the switch glow brightly at nite. All I see is a faint glow when I disengage the lock-up circuit (By-Pass).

Maybe I need a 4-blade switch so that the switch light can have its own power source???? Comments?

[22229stingray81]

Well I have new activity on my lockup. I attribute it to the very cool weather I have been having in va (39 for a high yesterday). During the summer, in the heat (90 degrees +), is when I started getting all the problems. Usually as soon as the car accelerated the second time the lockup would come on regarldess of conditions (after a cold start). I now realize it is because of what temperature it is. Now that it is so cold outside it wont come on till the 4th or 5th acceleration, or 3 minutes of straight driving. Yesterday while on the highway whenever I needed power the lockup (in the middle of acceleration) would come off, my rpm would rize a little, then when I stopped the acceleration, the lockup wouldnt come right back on.. it would take about 30 seconds... i think this is because how much cooler the car is running now... so.. could the heat have something to do with all of it? Now that its much colder it is actually starting to work close to normal... any comments would be appreciated.

-Tatortot

[GerryLP]

Tatortot,

You owe yourself to perform this simple check (and maybe you have already done it). Disconnect the harness at the tranny, and while the engine is running at 2,000 RPM and with the tranny in neutral (make sure you have the vehicle wheels blocked so that it won't roll and apply emergency brake) check the voltage at the "A" and "B" wires of the harness. Are you getting 12 volts?

With the diagnostic code display lead grounded AND the ignition in "ON" you should be able to get 12 volts across the "A" and "B" wire at the connector. Remember to keep the brake switch closed (brake pedal pressed). If 12 volts are present on the connector then the problem is internal.

And your cold weather observation makes sense to me. My car's tranny would not act-up until it warmed-up while driving. I think that the seal between the TCC solenoid and the valve body hole withstands the pressure because of the cold temperature of the transmission fluid. While cold, engine oils and tranny fluids have a higher viscosity. While hot, the fluids have a lower viscosity. When the viscosity is higher the fluid pressure increases and this is sufficient for the hydraulic signal to move the converter rotor towards the converter stator and lock-up.

When the transmission fluid reaches warmer temperatures, the viscosity drops, and the fluid pressure also drops. The transmission is having a hard time :hb maintaining a fluid signal strong enough to maintain the converter coupling through a fluid sygnal. It literally "leaks" past the gasket or seal when the fluid is hot.

To complicate matters, your normal driving acceleration, slowing down, brake action, and internal pressure switches are cycling the TCC lock-up solenoid on and off and on again.

I am not sure if you have changed the solenoid already, but if you have not, then I am willing to "bet" that the solenoid is your problem. :CAC

[22229stingray81]

GerryLP,

Thanks for the test outline. I will do it this weekend. Im pretty sure I can handle hooking up a voltmeter to it.. I hope.. haha. Ill let you know what I find. No I have not yet changed the solenoid. I think the job is way to complicated for my mechanical experiance thus far. My mechanic still insists there is nothing wrong, so until I can get it into the corvette transmission shop, Ill just have to live with it. Still a pleasure to drive it even with the lockup going on and off. Thanks very much for bearing with me on my mechanical inclination, or lack there of, ill keep you posted.

-Tatortot

[GerryLP]

Tatortot,

Aren't we all in the same situation on other issues? I am glad to help on this one, but don't feel bad about that -you'll learn something here every day. I also do learn daily...:CAC

[Yoda]

Tatartot,

I remember our firsts "Chats" .. my young Jedi, you are growing in leaps and bounds. Keep coming back, keep asking questions NEVER believe you know it all, and above all be willing to share with others when the time comes.

Proud to have you as a Corvette owner and esp. an L81'er You represent your generation in grand style young Tatartot ;)

Jerry is an excellent person to learn from and a great guy all around, as are many of the people here ;)

[22229stingray81]

Thank you Gerry, and rare, (or mr. rare to me) and everyone else for all your support and help. I really appreciate the patients and detailed descriptions you all give me. Yes I have grown in my corvette knowledge over the years (3 long ones!). I have the L-81 registry to thank for a lot of my "new" knowledge, and im sure there will be more knowledge to come. I hope one day I can contribute also to this wonderful corvette family. And I would much reather represent my generation in a corvette and have people not respect it, then represent it in a honda with people all over it! Thanks again all.

-Tatortot

[22229stingray81]

GerryLP,

I was printing out yoru instructions so I could try to perform the check and I realized I didnt quite understand something. I was a bit confused what you ment by this

"With the diagnostic code display lead grounded AND the ignition in "ON" "

What do you I have to do to ground it?


-Tatortot

[Yoda]

-Tatortot'

I think what Gerry is refering to here is to check computer codes by counting the check engine light flashes you will need to ground or short together terminals "D & E" on the plug under the ashtray.

BudD
:bu :w

[GerryLP]

Tatortot,

I agree with Bud. I think that is what is meant. I can provide you with a manual page number tonight. I had to work today, and I don't have my manual with me (I don't take out the car when it rains anymore...:L).

[GerryLP]

Tatortot,

I paraphrased for you the isolation check to determine if the electronic control module (ECM) is at fault if you're having problems with the TCC.

In the L81 shop manual you'll find this information in page 6E1-37 on the Transmission Converter Control paragraph. This will help you isolate the ECM side.

"Jedi Master, hummm, very kind with words he is" (use the Yoda voice -it is more fun...:L).