I'm wondering about the durability of the '84-'87 4+3 manual transmissions. How good are these transmissions, especially in a stock application? Are they stout, or do they have some weak points? Anything to watch out for when shopping for a used 'Vette with a 4+3? Any input is appreciated.

 

84 through 86 were known for having some issues that were cleared up and fixed in 87 and 88. The very first thing you want to ask the owner of any 4+3 car is when the last time they changed the fluid and filter in the overdrive unit was. If they give you a blank stare just walk away. In fact run way. If they have never changed them then the unit is a ticking timebomb waiting to eventually go off.

But.... if you test drive the car you want to make sure that the 4 speed shifts nice and smoothly. Also you want to make sure the overdrive works. To do this you'll have to get the coolant up to a certain temperature as O/D will not engage unless coolant is at operating temp. It is different for every year.

Year.../Coolant Temp
1984 / 176* (F)
1985 / 140* (F)
1986 / 122* (F)
1987 / 122* (F)
1988 / 122* (F)

Once you have reached those temperatures you should be able to engage overdrive in 2nd, 3rd, or 4th gear. You'll notice an overdrive enabled light come on. In 1984/85 this light was in the center panel of the dash near the gas level gauge. In 86 through 88 it was moved to just over the digits inside the tachometer pane. It looks like a 'D' with a circle around it.

If you don't use the clutch during the overdrive gearchange (which I recommend you do to preserve its life more) you should be able to feel and hear the gear change.

In 1984/85 the switch is an ON/OFF switch. The overdrive program will never be on and O/D will never engage unless the switch is on. The switch is located on the center bezel in 84 and early 85. In late 85 the switch was moved to the shifter **** so that the button is actually the shifter pattern. Most people don't even know it is there.

In 1986-88 it is a momentary ON switch. In 86-88 the overdrive program is ON BY DEFAULT when you start the car so if you depress the button on the shifter **** you can turn it off.

It sounds a hell of a lot more intricate and difficult than it really is. It took me about a month to get used to the entire logic of the program and operation of it.

My 4+3 is the '87 unit with new internal peices that fix the problems 84 through 86 had. Right now my car makes 388hp and 439 ft/lb and the transmission doesn't even sneeze at it.

Good luck. Feel free to ask more. You may find this page very useful.
http://www.gearzone.net/dne.htm

 

The 4+3 is fairly durable if properly maintained. The basic maintnance only involves changing the ATF and filter in the overdrive unit but it tends to be either done very regularly or never done at all :eek:

Mine has been pretty easy to deal with, no major problems. It was rebuilt once before I owned the car. :cheers:

 

I have had no problems with mine in my 87, it was mainted really well by previous owners, I have only had the car about six months or so and I have yet to service the OD unit, but its on my agenda once spring gets here.

 

Scorp, what were some of the weak points with the earlier units?

I've heard about the electronics being designed poorly so the switches go out prematurely.. but what else?

Mine's an '85, and appears to work like its supposed to so far.

BTW, the superT10 takes 4 pints, not 4 quarts, right?

 

I had it in my old vette and loved it. The key to its longevity is only using th OD on the highway. Otherwise just keep it off and forget about it. This is a good transmission that caught a lot of bad rap for people not knowing how to use it properly. This of OD as 5th gear and you will be fine.

 

I'm looking at an 87 4+3 for autocross and occasional track use. While I wouldn't expect to use the OD gears for A-X use, how would it perform on a road course. The courses I use have straights of just over 3/4 mile. What sort of speed can you get in 4th/no OD?

 

Depends on the power level the car has and what RPM you can pull. Right now I can pull 6000 no sweat which is about 151mph in 4th w/o overdrive enabled. If the car is stock you'll be shifting around 4300.

 

My car is stock and 4th without OD takes me to about 104-105mph, with the OD on I have gotten up to 151mph, it was still acclerating, I just backed off