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The "Doug Nash 4+3"...

My 'early, supposedly problematic' 4+3 only lasted over 105,000 miles; then was rebuilt ONLY because I was redoing the entire drivetrain, behind an engine putting our well over 500 lb.ft of torque. I, luckily, had Paul C. redo it, and strengthen it a bit. He assured me I could not break the overdirve with my 406, but might break the 4-speed.

The only issues found in my 'problematic' tranny-O/D were wear-through of the case hardening on second gear and micro cracks on many teeth throughout the 'super' T-10.

There was an issue early in production, which a recall fixed, dealing with a bearing.

I have always really liked the kick-down feature. I learned the logic from my owner's manual. I learned to tap the console mounted switch with my wrist, for on/off. I typically unloaded the Nash clutches by using the clutch under my left foot. We pilots READ about, and understand our machines in much more detail than any, except perhaps mechanics. We practice again and again, learning to make the design to work FOR us.

All other issues I am aware of involve mis-dis-information on the part of owners and mechanics. As Ken implied, most issues with the overdrive are not mechanical, but electrical, as are most of the newer cars. Others stem from inadequate maintenance or abuse.

Sensors, circuits, connections and grounds must be checked, usually before any mechanical work. Connections, being most prone to problems of dirt and corrosion, are a great place to start.

Maybe ECM should mean Easily Confused Mechanics, as the old-schoolers who refuse to learn electronics are quick to blame that which they do not understand.
:w mike
 
Mike,
I think you owe Edmond an apology. I believe you misread his message. You did say that you always try to understand your vehicle before using it. What about making sure you understand a person's message before jumping on him?
Edmond's reference to short life span was NOT in reference to the fact that 4+3's do not last long. It WAS referring to the number of years that GM used the 4+3. (1984-1988)
Terry
 
FYI:

I bought my '87 Z52, 4+3 new in May of 1987. It is, and always has been my driver. I have logged about 120,000 miles on it (average 7500 / year). I am a very aggressive street driver, but the car has never been on a track, nor in an accident. I am on my third clutch. I lost a main bearing at 95,000 and installed a very good short block. In addition to regular oil changes, I change all of the fluids (except brake) about every 12-18 months. Have flushed the brakes lines twice.

Although I invite catastrophe with this statement, I am compelled to tell you that I have never had a problem with either the "4" or the "3" in 16+ years.

BTW; I have never liked the "clunk" when the OD engages, so when ever I press the button on the shifter to enter the OD gear, I depress the clutch. I don't know if it has added any life of the DNash OD unit, but I bet it has helped keep all the UJoints and the rear end working without problems for 120,000 miles.
 
Hey guys,

I have an 88 4+3 and have had no issues with it at all. I do the same and use the clutch to ease the transistion when engaging the OD. Just make sure you keep an eye on her and check fluids. My 88 "Black *****" never gives me any issues. Just keep up good maintenance and you'll be good to go.

SSG Johnny Drummond
US Army
Bagdad, Iraq

Can't wait to get home and drive mine again...just 4 months left.:cool :cool
 
Just be careful in those last four months - don't let your guard down, and come back home soon. :pat
 
What? No vettes in Bagdad? No wonder the masses are clammering in the streets. Pity.:(
 
I just purchased an 88 roadster with the Nash 4+3 and am having the same problem as several other folks in the forum with the overdrive. It shifts into OD when the transmission is shifted into second gear and will not disengage with the switch on the shifter. Is this a switch problem?

Thanks.
 
Failure of 4+3

SSG Drummond, Thanks for what you do to allow us all to enjoy our Americana. God bless you and your family.

Now my question. I am poised to purchase an 1987 with a DN 4+3 and the overdrive is non-ops. Has anyone heard of the problem being "a relay?" I am new to the 4+3 an don't know if the car would be worth it if there was a rebuild/replace in my near future.

Thanks
 
check to see if the switch on the trans (underside) has been cut and rewired. That may have gone bad and or that your OD is now a manual operation due to rewiring. Otherwise, you might need to get her looked at. Be careful of dealerships...i got burned once at a chevy dealership over a ECM. Keep asking at this website...there are alot of good experts here....they will take care of you ...I promise!!!!

Johnny
 
IF it's a relay, it's simple and rather cheap. The relay is identical to that for the fuel pump and located right next to it. Swap plugs on them. If the cars runs, the relay is fine.

Beyond that, it could be very pricey, especially if the fixer does not understand the circuitry, as even some dealers do not.

The weakest part of the 4+3 is the main shaft in the 'super' T-10, I am told, not the O/D.

I say again, I believe the biggest issue with this box is improper maintenance and misunderstanding, on owners and dealers parts, about how it really works. Both, get expensive.
 
Alright...next question. The dude with 4+3 is not ready to sell even though the car is for sale. This is for my learning. After driving (for over 10 mins) and seeing the OD indicator illuminate and not feeling the car shift into OD, I went back today to deal and when I offered my deal he laughed. I mentioned the lack of shifting and the response was "Oh the car has to be @ 160 degrees before it will shift." I have consulted an aftermarket repair manual and it mentioned the ZF 6spd with the 122 degree inhibit, but not the 4+3 having an inhibit. I also have look through the Cor-Vette Spec book on C4s and have found no reference to the "thermal inhibiting." Does any one know the answer.

Thankin' you in advance
Joe
 
jcrowhurst said:
... the car has to be @ 160 degrees before it will shift.

Joe, the overdrive function is bypassed until the engine temperature reaches 80°CF/176°F for the '84, 60°C/140°F for the '85, and 50°C/122°F for the '86/'87 Corvettes.
 
My 86 OD comes "on" at 132 degrees.

:beer
 
The engine must be in closed loop mode for the overdrive to operate. The temperature, in my experience varies, but loosely means, warmed up. BTW, poor tune has affected mine, but that dash light coming on means that the ECM has okayed the O/D operation, but something 'downstream' is not functioning. It may be a low fluid level, the relay (I think) or a mechanical problem in the Nash. I don't have my manual handy but I HAVE fixed an 'overdrive problem' by changing my spark plug wires!

A good learning exercise for you and likely a deal you should pass upon, given the attitude and misinformation from the seller.
 
Thanks WhalePirot et al...Very good info and yes the seller still has his car and will remain in this state (little control lingo) for??? I have family in Valley Joe and am a reformed Californian (just kidding). I am original from the Yuba City area so you may know why I am no longer in CA.

Thanks again,
Joe
 
I'm sure glad this thread is still strong. It looks like I'm in for a re-build on the T-10. Howls like a banshee in all 4 and neutral. Wifey says she can't hear it while outside the car. (She stood on the side of the road while I cruised by. Yes, I did go back and get her) Nothing seems amiss with the +3, yet, and still goes into all gears ok. Can someone explain why it is so hard to find someone who can rebuild these? If the OD doesn't need anything, wouldn't it be just a regular 4 speed re-work or does the OD unit have to come apart? The only place I've checked with is Corvette Service of Dallas, and the manager alluded to the fact that once he had determined what the problem was, it might have to be shipped. Didn't say where. One thing he did say, and I haven't seen it brought up here, was the fact that there seems to be a problem with the automatic fluid leaking into the T-10 unit and cohabitating with the 90 wt. creating many problems.
Well, back to what I really need to know..........How much dinero am I looking at? Would I be better off changing to a 6 sp.? He said that would be around 3500.00. Is this a good figure in ya'll's book? :eek :cry
 
unleadedbrew said:
... there seems to be a problem with the automatic fluid leaking into the T-10 unit and cohabitating with the 90 wt. creating many problems.

I've brought this subject up before, but the thread is probably long gone. I came across something a while back where it said the guy used ATF in both the overdrive unit as well as the transmission itself, thereby eliminating the concern regarding fluid contamination. The ATF has enough lubricating qualities to work in the gearbox, it'll just be a little noisier is what they say. I have no direct experience with this so...

As for the cost of a transmission swap, the ROD 6-speed goes for around $3200. I have no idea what the Keisler or the Tremac would go for. ;shrug

_ken
 
Ken, The ROD is $4000 for the made to fit the vette tranny, I'm sure you remember that expenditure. :). The Tremecs are more costly. About $4800. I used the 70w90 mobile one in my trans and the ATF in the OD. I will most likely go to the ATF in the T10 also, we use it in our racing trans.
 
Four grand now!! It looks like something at least finally went my way; I paid thirty-two hundred in the spring of 2002. :cool
 

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