Im looking at an 88coupe, he says it slips in reverse...im totally unfamiliar with the DougNash 4+3...is this possible?

He says it pulls all forward gears fine, but put it in reverse and it feels like it is slipping...

 

likely o/d needs rebuild, friction discs are worn out...sprag clutch in o/d section of trans locks by design and will drive in forward gears, but sprag (again, by design) will 'freewheel' when reverse gear is selected.

 

The OD has left the building....

 

hmm, so it literally is great in the forward gears, but reverse is gone.

So it's driveable like it is, but is in "direct drive" as if the OD unit wasnt even there, and No reverse?

He wants 4K for it, says it runs great, BBK throttle body, lots of new parts...then the OD unit apprently has failed.

 

Is it as simple as installing the 180 dollar kit, or is there more to it?

Anyone got pics of the inside of one of these dumb things?

 

It's toast. It has been awhile since that happened to me, and if I remember correctly, when the 4+3 loses reverse, something that is pressed into the case has spun, turning your Nash into a Mash. I replaced mine with a used 88 unit for 500 bucks. I see them in the parts section occasionally, I got mine on Ebay. There used to be a website that explained all of the Nash problems and the solutions, as well as rebuilt them, but I think it has changed hands and I cannot remember the name.

 

Tell seller it is $1500 to rebuild O/d plus labour for swap
Can contact rebuilders below for rebuild pricing
http://www.pipersauto.com/4speeds.html or
http://www.skspeed.com/
Offer him 2 K and buy this
http://forums.corvetteforum.com/c4-p...-3-tranny.html

 

5speeds.com
The 4+3 info is still on their site
http://www.5speeds.com/nash.htm
but they sold the parts and rebuilding to SK Speed in the link above

 

no, not great...purpose of the sprag (aka, over-running clutch) is to prevent engine over-speed during o/d engage, but design of a sprag begets lock-up in one direction of rotation, unlock in opposite rotate.

in 'proper' trans op, the 'friction discs' in the o/d section 'forward' (aka, 'straight thru', several other terms used) 'clutch pack' are pressed against 'driven plates' by a crowd of small coil springs, transmitting power in forward or reverse...when the friction disc facing material is worn away and the coil springs full extension is insufficient to compensate, slippage occurs.

 

The Front plate for the O/D is $180 by itself......The kit is just seals and stuff.

The 4x3 has a separate reverse shaft out of the Super T10.
if that shaft has wallered out that plate on the O/D, you have to replace that plate just to get back to Zero.

One of the signs that the O/D is gone is that Reverse goes away.

The reason that the Reverse is gone could be a few things.

HOWEVER...that being said......you can find 4x3s for $300-$500 if you look hard enough. People want a 6 speed and pull the old one out.

Pulling this tranny out (leaving the bell housing) was really really simple. It took just a few hours....

So if you get a donor unit, the swap is a few hours of labor.

If you calculate this all into the price of buying the car....you may do very well on the purchase...very well indeed.

The Seller has shopped this around, He is very well aware of the cost to rebuild....why do you think he is trying to sell it "as is"?? No one sells a car with a tranny out...unless they are selling if for "Roller Chassis" price....

He knows this....I'm sure there have been a lot of "lookers" and callers....but no buyers with no reverse.

 

I don't know where you are...but here is one in Michigan

http://forums.corvetteforum.com/c4-p...nz-1984-a.html

$500...........

 

Here is a freshly rebuilt one for $700

http://forums.corvetteforum.com/c4-p...-3-tranny.html

 

So basically what Ive heard is true...the 4+3 was a crappy setup...

How hard is a ZF6 upgrade?

 

The 4+3 is not a "crappy" set-up. The idea behind the trans was to provide sufficient gas economy figures so the early C4's would not get hit with a gas-guzzler tax. The 4-speed portion js a Borg-Warner Super T-10 and that has proven itself over many years behind some pretty strong motors.

At the time the C4 was being designed, there was no 5 or 6 speed trannies that would take the power output from the L83 or L98. The Borg-Warner T-5 used in the 82 and later F-body cars were just too weak.

The 4+3 in 87 was also used behind the Callaway twin-turbo cars and they produced a good 25% more HP and torque than an L98.

Following a good maintenance schedule for the OD is paramount to its long life. Like any other tranny, if you don't take care of it or abuse it, it won't last.

4+3's show up in the C4 Parts For Sale section from time to time. The tranny is not hard to swap out especially if you have access to a hoist. A ZF6 swap can be pricey to do and you need to collect the right parts from a donor car. Keisler has a nice 5-speed that is a direct bolt-in but it runs over $2K.

If you want a manual trans C4, then look for an 89 or later; these will have a ZF trans. There are probably some nice examples out there for the cost it would take to buy this 88 and fix the tranny.

Or just go back to looking at Lincolns, T-Birds, or Caddys.

 

I would say the 84-85 was a fairly crappy set up, but must of the problems were dealt with in the 86-88. Check out the link that Rod posted, it will tell you all about it.

 

The guy sent me a pic of the car, it has brand new C6 black powdercoated rims on it, RED/RED, looks fantastic, but he seems firm on the 4K figure...

So Im passing. I do want a Manual Vette one day though. Probably be a ZR-1 or something..."one day".

 

We have an archived post on our blog for servicing the 4+3. Hope this helps:

http://blog.corvettecentral.com/2007...-transmission/

 

The article was interesting reading especially about the OD unit being originally developed for Jeeps. Doug Nash Engineering had bought the rights to the Borg Warner Super T-10 and Chevrolet Engineering contacted DNE and worked with them to develop the 4+3 for the 1984 Corvette.

There has been a lot of discussion here on the Forum about the 4+3 over the years, and while I'm sure that the Corvette accessory companies want to sell filter kits, it is far easier and cheaper to just buy a filter and use RTV sealant on the pan rails.

The OD unit uses the same filter as a Ford FMX transmission and it's widely available at parts stores for around $8.00. As long as the rubber grommet on the old filter is in good shape it can be pulled off the old filter and re-used. It's interesting to note that the same filter when installed in a FMX tranny, does not use this grommet.

Making sure the pan rail is completely clean of old gasket material and is straight is important for a good seal. Same with the rail on the OD case; it has to be clean. There are some very good RTV sealants like "The Right Stuff" or the MoPar sealant found at any Chrysler dealer. I like to use RTV sealant because you don't have to have all of the pan bolts tightened exactly the same. A cork gasket can split easily if one bolt is too tight. Apply the RTV, immediately install the pan, and bolt it down.

As far as fluid for the OD, Dexron III is the best type to use. Some years ago, some of us here discussed the use of a synthetic ATF fluid and the consensus was that it is not a good idea. Those that tried a synthetic ran into issues with the OD. Maybe it was because of age and high miles on a unit, but standard ATF seemed to work just fine.

There were also some changes in how the OD unit operated between 1984 and 1988. Check out this link to see how they worked.

The cost of a filter replacement for a DIY job should not be much more than $20 and that could include a 6-pack of good beer.

 

The problem with the Corvette OD is people repairing them. The unit does not follow standard conventions.

The sprag is used to drive the car FORWARD.

The direct clutches are loaded statically with springs. They actually only see load or work when the sprag is not working such as when engine braking occurs or REVERSE.

The OD section is a two stage planetary. This is a timed gear set unlike any automatic.

When OD is applied One piston simultaneously releases the static pressure on the direct pack and locks the in and output thru the 2 stage planetary.

The frictions never wear and are well designed. The problem is the front carrier bearing will wear out and effectively create enough clearance that will cause the direct pack to loose its allowed stack height, thus slip ( in reverse).

The late 85 to 88 units have an updated carrier with a better bearing and improved lube to it.