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  1. #1
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    Default 4+3 Doug Nash Trans w Overdrive

    Hello,

    Any comments on the rarity of the MK2 (4+3 Doug Nash) and the Overdrive unit on a 84' Vet.

    Looking at the 84' Vet option list, I can not seem to locate the overdrive option for the MK2?

    Any and all comments are appreciated!


  2. #2
    4+3 Doug Nash Trans w Overdrive rrubel's Avatar
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    You couldn't get a manual transmission WITHOUT the overdrive. That's what makes the +3 part...

    Visit this link http://corvetteobsession.homestead.c...formation.html
    to one of Ken's pages for a nice overview of the DN 4+3.

    [RICHR]

  3. #3
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    Default Reply to RichR

    RichR - "THX"!

    I guess I am showing my ignorance . . .

  4. #4
    4+3 Doug Nash Trans w Overdrive rrubel's Avatar
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    I'll add a little of my ignorance to the pot - looking at the first chart on Ken's page, it shows two different versions of the transmission (diff. gear ratios). One, called the MK2, was only supposed to be used in 85-88 while the MH5 was used from 84-88. But there's no known rhyme or reason why a particular car got a specific model. The 4+3 manual, btw, was RPO #MM4.

    [RICHR]

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    Default Reply to RichR

    Rich,

    THX for your reply, I went to the URL you provided and noticed that the MK2 was for 1985+, but on my build sheet I have the MM4 as well as the MK2, maybe my 84' was built in late 84'.

    What is interesting is Ken's comment regarding how to turn a 4+3 into a 8 speed, any comments on this regarding advantages?

    I was hoping to find am e-mail to send Ken at "My Garage" but I could not find one.

    BTW, this forum is one of the best, thanks to all for your replies and insight . . .

  6. #6
    4+3 Doug Nash Trans w Overdrive rrubel's Avatar
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    Note that most of the items on that page have just been 'collected' by Ken and not written by him. He's one of the moderators of this forum, so you can ask/leave messages here and he'll get them. A couple people here have done the full-manual modification to remove the computer control of the OD. I haven't, because apparently 86 was the only year without the plug to remove...
    [RICHR]

  7. #7
    LarryBible
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    I enjoyed the site about the 4+3. The 4+3 is one of those things that has really gotten an unfair bad rap.

    If you keep it filled with fluids and don't drive too crazy it is bullet proof. Once you learn how to drive it with a little throttle application when shifting with the button, it works great.

    I think it is something that you love or hate and there is no in between. I personally am a lover of these neat gearbox.

    My $0.02,

  8. #8
    Gone but not forgotten Ken's Avatar
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    Originally posted by rrubel
    Note that most of the items on that page have just been 'collected' by Ken and not written by him.
    You got that right Rich.

    Mike, listen to Doc. He sounds like he knows what he's talking about.

    _ken

  9. #9
    4+3 Doug Nash Trans w Overdrive GusVette's Avatar
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    Default 4+3

    Well, I guess I'd have to be in the hate catagory.
    After $2500. to rebuild it and the transmision I now hate it. Of course the major problem is getting parts! I guess if the previous owner had taken care of it and the screen and pick-up tube were not left out at one of those service joints it may have been in better condition. I sold it with 50k miles for a new 2002 SS Camaro and could not be happier. Opps am I not welcome now? No more Corvette's for me. I invested as much as I paid for the car just to keep it driveable.
    ADVICE:
    NEVER BUY FROM A FRIEND!!!!!!
    Gus
    Previous Corvettes: 1982 & 1985 4+3

    P.S. I will admit that after the rebuild, The OD and trans. ran and shifted O.K.

    More stories, but I didn't want to bore you with all the details.



  10. #10
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    Quote Originally Posted by muskiemike View Post
    Hello,

    Any comments on the rarity of the MK2 (4+3 Doug Nash) and the Overdrive unit on a 84' Vet.

    Looking at the 84' Vet option list, I can not seem to locate the overdrive option for the MK2?

    Any and all comments are appreciated!

    The MK2 is a O.D. ratio of 0.68 and the MH5 and it is .060 and i can't find the difference in or any info on the MM4 which is what i have and not listed in my owners manual ?any help is appreciated .

  11. #11
    Technical Writer for Internet & Print Media
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    The 84-88 4+3's gear box section, essentially a beefed-up Warner Super T10 was an ok transmission, but the electro-hydraulic overdrive was a complete POS. Doug Nash sold GM a bill of goods on that deal. As a result, GM's warranty costs for 84-88 manuals was obscene. The overdrive was under continuous developmental change and it wasn't until the final year, 1988, that the OD approached acceptable reliability/durability, and by then Nash was bankrupt.

    There were two reasons the ZF S6-40 six-speed was developed 1) because the 4+3 was a piece of crap and 2) the coming ZR-1 needed a transmission with a much higher input torque rating.

    Even when the Nash overdrives were properly maintained, they still were a reliability/durability nightmare. Granted some had reasonably good luck with them, but Nash's quality control was so freakin' inconsistent that for every good 4+3 out there there was one bad one. But, then, there was some Karma. Trying to support that crappy overdrive combined with mis-management put Doug Nash out of business. Richmond gear bought some of Nash's aftermarket transmission designs, finished the development on them and sells the products today.

    As for the RPOs, the merchandising RPO for 84-88 manuals was MM4. Apparently, there were two different OD ratios, so there would have been engineering RPOs, MK2 and MH5 for each transmission.

    85-88 Service manuals say the OD ratios are either 0.68 or 0.59. GM parts info from back then is conflicted. In the ID section, it says only the MK2 was available for MY84-86 with both MK2 and MH5 available from MY87-88. In the parts listings it says MK2 was stand-alone only in MY84 with either one available in MY85-88.

    So far, I can't find info on what cars had which OD, but my wild-assed guess is that one OD is the early design and the other is at the later, improved design. For some reason the ratios differ by 0.09:1. Interestingly the speedometer gear numbers for both are the same.
    Last edited by Hib Halverson; 01-12-20 at 08:58 PM.

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