I've rebuilt/modified the shifter, now it's shifting right. My 4+3 is an 85, are there any differences in diferent years with the 4+3? How much hp/tq can the 4+3 take? What are the drawbacks/problems with them? I want to keep manual trans, and also want od. Are there any mods for this trans to help it survive? :seeya

 

Scorp is so much more knowledgable about this trans, but I'll give a try to the basics. As far as maintaining it, change the fluid regularly, especially in the OD unit. You can get the filters from MidAmerica or others. I would recommend not using the cork gasket supplied, as this is a constant source of fluid leakage on my 86. Now having read the GM repair manual, it also states to simply use RTV and no mention of a gasket.
The other comment I can make is comparing it to the ZF or Borg Warner 6speeds, the shifting is much slower mechanically. I autocross my 86 and have had to adjust my driving style to allow for this slower transition from gear to gear. You simply can't force it to go into the next gear faster than it wants to go.
As for differences, I beleive that the OD button moved from the dash area to the shift **** and it is my understanding that the OD got stronger in its later years.

good luck
david

 

I have the same transmission (85) as you. That year had a cable (TV) that ran from the throttle body into the OD unit. This was in basic terms, a kickdown cable to drop you out of OD when mashing the throttle. Later units do not need this cable since they measure line pressure to determine when to shift out of OD. The pre 88 OD units also had a different (weaker) clutch pack in them, as well as some oiling problems to the sun/planterary gear bearings. The later units tried to address this. My OD unit bearings went bad, which was signaled by a pronounced whining when not in OD, quiet in OD (I know it sounds backwards, but it has to do with the bearings around the sun/planetary gears). I bought a blueprinted post 88 unit and swapped it out for the older unit. The OD section of the unit is definitely the weak link, the standard 4 sp gearbox is fairly reliable. Regular fluid and filter change on the OD unit will help, and always look for debris around the pan magnet. If you start getting any large pieces, it is only a matter of time until a failure. If you want to upgrade your OD, I believe that Gear Zone (gearzone.net) and 4 speeds by Darryl? (not 100% sure) can help you, and there are a few other companies out there buliding up OD units. Mid America even offers rebuilt units. Expect to pay $1200-1500. My post 88 OD unit was spec'd at a 400 hp limit. Hope this helps.

 

Thanks for the input guys. I'm going to address this question to scorp and see what he hsa to say. Once again thanks. :cheers:

 

Just noticed this.

This page has a good rundown on the history. http://corvetteobsession.homestead.c..._dougnash.html

 

Who used this OD post '88? Or are they putting something special in the drinks a the Oceana O'Club? :confused:

 

Yup, a little brain-freeze typo there. It is a blueprinted 88 unit, 89 obviously being the dawn of the 6 speed. The drinks at the O'club are fine, so from a fellow LCDR, lighten up, OpsO.

 

Hey Scorp, per usual...good information. Thanks :cheers:

 

The site scorp gave is great, same info can be found at ww.5speeds.com The only "upgrades" are to run the 84-85 clutches, which you have. Otherwise not much you can do.

Had a discussion with a speed shop guy today about the transmission. He said it should be close to bullet proof. Understanding is that the OD unit basically does nothing as far as power transfer when its off, so it has no real limit. And the ST10 I was told will handle over 600 of each (tq/hp) on stock parts, and can be rebuilt for more.

I got a book off of Ebay for the 4+3's. I havent gotten it yet, but when I do I will look it over and see if there is anything extradanary to post on. I may even scan the book depending on its size :)

Matt

 

No disrespect intended. :D Just checking. Ever been to that little club right on the beach at Dam Neck? Is Dam Neck even still there?

 

Yes, DamNeck is still there. I've been to it a few times for comand events. Usually go to Dam Neck for the good, uncrowded beach. Cheers.