Doug Nash 4+3 rebuild....what parts?

[1985 Corvette]

Rather than seeing it sit and take up space, I would rather use it, as I have never really had an issue with the trans, just never got around to understanding how it worked. One of the torque lock sliders is chipped and it can't hurt to go through the box. It's a 1985 model transmission with the kickdown cable OD. An issue I run into is I see rebuild kits from Ecklers for the T10 section, but they specify "84- Early to 1985" or "Late 1985-1988" kits. What are the differences and how can I identify if mine is an early or late 1985 model? Trans did not come with car originally.

The 4 speed section is basically a super T10 correct? If so, best T10 kit available? I've seen some for half what Ecklers wants. Are OD's interchangeable on the back of the 4 speed box? I wouldn't mind rebuilding this OD as well but it uses a kickdown cable and the car will not be set up to run a kick down cable style (1986 and up electronics). Any help is great.

 

[DPC Racing]

All the 4-speeds on those 4+3 are the same,thats not a kick down cable it was there for more pressure on the o/d clutches with speed.There are 2 od unit ratios.Go to Medatonics Corporation 5 speed for parts and a lot of info,hope this helps. Dan

 

[Hib Halverson]

To find the breakpoint for the OD rebuid kit, I'd contact Ecklers and ask. They'll probably give you a serial number span and you'll have to get the SN off your overdrive and match it up to their information.

The Super T10 is still made by Richmond Gear. If you need parts, that'd be the best place to go for them.

 

[1985 Corvette]

To find the breakpoint for the OD rebuid kit, I'd contact Ecklers and ask. They'll probably give you a serial number span and you'll have to get the SN off your overdrive and match it up to their information.

The Super T10 is still made by Richmond Gear. If you need parts, that'd be the best place to go for them.

Thanks! A good place to start.

 

[1985 Corvette]

All the 4-speeds on those 4+3 are the same,thats not a kick down cable it was there for more pressure on the o/d clutches with speed.There are 2 od unit ratios.Go to Medatonics Corporation 5 speed for parts and a lot of info,hope this helps. Dan

Thanks, DPC. That hole will get plugged if it is not needed. Looks like someone has been in the 4 speed section before and the OD portion as well. I'll try to get pics.

 

[WhalePirot]

I didn't find that rebuild an easy chore, at all. After getting the parts sent to me, I opened the case to that sick, bwoing sound then heard the falling springs; then sent it for a professional redo by a shop experienced with the O/D.

Your experience may vary.

 

[1985 Corvette]

I didn't find that rebuild an easy chore, at all. After getting the parts sent to me, I opened the case to that sick, bwoing sound then heard the falling springs; then sent it for a professional redo by a shop experienced with the O/D.

Your experience may vary.

After some hard staring at the OD flipped upside down with the pan off, I think I will leave the OD as is, bolt it back to the T10 and see what happens. If this were a stock restoration, I would have fun rebuilding the whole box. It bothers a lot of Corvette guys but I really like the transmission and if there was a way worth the headache to build up a spunky/bullet proof 4+3, I wouldn't mind. A video tutorial of installing straight cut gears in a powerglide got me daydreaming on that one.

My dilemma is I have someone building a miniram 383 for me, and the 4+3 route lets me get the car back on the road quicker. The 4 speed section, if my research is worth anything, will be fine for a temporary stand in. I don't think I will ever engage the OD but wouldn't mind it around just in case..... I stumbled on a graph of the 4+3 gears (101 projects for your Corvette) mph x rpm and it shows roughly 2800 rpm for non OD 4th gear at 70 mph through a 3.07 rear. My swapped rear is a 3.45, not sure how much more that will make the rpms climb.

I will use the 4+3 until I feel like coughing up the money for a TKO trans or a ZF. Some quick questions following this decision, however:

I got this trans from someone, had to take them on their word about the 50K mile accumulation. I cracked open the case.....there's an ever-so-small chip in the first to second torque lock slider. I didn't consider it a deal breaker for a temp trans in the least. I ingeniously mixed my shift forks but both look identical in terms of wear. Given the state of the torque lock sliders, I didn't think this would be an issue for engaging the gears but if there is one, I'm all ears.

The lines coming off the OD. I can't find a pic anywhere of where they go to. I don't have the manual in front of me at the moment but I'm assuming they go to a separate auto trans fluid cooler? Not a big deal as Summit sales tons of these, I just can't find a pic of where they mate up to on a stock 4+3 car. Car originally was an auto. I USED to think they mated to the radiator but then I drop the OD pan and the valve bodies dripping trans fluid seem to lead to one of the fittings leaving the OD.....

I plan to wire up the OD on demand trick and plug the kickdown cable hole.

EDIT: Also, Eckler's "kit" with the OD filter and pan gasket gave me a chuckle. Everyone I ever talk to says toss the gasket and just use rtv sealant and save money using the same Ford filter. I forget the model but if someone has that info it is greatly appreciated.

 

[WhalePirot]

I like the O/D and know, from years here, that many decry the unit. I was told, way back when, that: 1) there is little one can do to toughen it, and 2) it is a good unit and can handle plenty of power. It has, in my case. Also, it does require maintenance, including the filter the the AT fluid. Many other misconceptions, IMO, are rooted in not understanding the shift logic of the O/D control.

My car had a little over 100k on it when I pulled took it apart. I was shown a great deal of erosion of the case hardening and a number of micro-cracks in the T-10 portion's gear faces, worst on 2nd gear. I typically accelerated harder in 2nd, so you may wish to inspect it carefully for similar pending issues.

I think another posted and I will echo: that is not simply a kickdown cable but determines how firmly the clutches in the O/D are applied; harder accel > firmer shift. I suspect it aids power transfer while improving clutch pack life.

I like the Nash unit a great deal and considered only the (noisy?) Richie 6-speed, back then.