Daffy

Looking for some opinions here... I have an original 4+3 car that has had an Automatic in it since I got it.I absolutely hate it..I use the car for Autocross only and have a 4.11 gear in it. Thanks guys

rasrboy

Daffy,
My father has a 88 4+3 car and over the past 15 years of autocrossing and roadracing we have had it rebuilt atleast 10 times.

My 87 had one too and I finally broke down and bought a NEW GM trans 6 speed,used bell housing,new slave,new master and line. Drive shaft yoke is different on an auto too.

I know quite a few people that have had problems as well. The overdrive system is the worst part of the trans btw.

If you can swing it,change to ZF

Aaron Quine

Daffy

Does the overdrive come in to play for autocross???

Carolina C4 Racer

Hey Andy,
I've seen people using the O/D in an autocross. i.e. running at the top of 2nd gear, but the next brake point is fast approaching, bump it into O/D to avoid an up shift & down shift situation.

If I had your unlimited supply of time, knowledge, parts, & cash, I would go with the ZF.

Daffy

I've watched Terry too...While he smokes all of us with his 4+3...All I'm sure of at this point is that I want a manual trans for a change...The blue Z06 has spoiled me...

rasrboy

with Anthony, the O/D can come in handy instead of shifting but life is hard on them.

I can assist you in getting parts rounded up,so let me know.

Aaron

c4cruiser

The OD unit in my 87 has held up to 4 years of track days and 8-10 autocross events in each of those years and it still works fine.

The biggest thing with the OD unit is to be religious about fluid and filter changes. I do them every year (it's cheap to do with 2 quarts of ATF and a $7 filter). Also, I never use the OD unit when racing. Too much shifting in and out will eventually ruin it especially with high RPM or high torque loads.

My 87 has some mild internal engine mods and 127-128 is about all it will do in 4th gear for track days. Most autocross courses I run (50+ second times and speeds sometimes to 65-70) can easily be handled in 2nd.

Daffy

I want to bump this one more time...Sounds like the basic gearbox is pretty durable...

Mojave

The 4.11 rear will not be ideal for auto-x, not without very tall tires or a very high limiter. That said, I love my ZF6 for auto-x with 3.45 rear gear. It will go over 75 in 2nd gear, which makes it ideal for a lot of courses.

Kanmer

As a former owner of a 4+3 I can tell you that the "4" side pf the Doug Nash tranny in almost bullet proof. The OD side is about as durable as toilet paper.

Bob

JaxVette

I ran my '84 C4 for 9 years on the track and autox with my 4+3. I averaged 50 to 60 track days per year plus the autox's. I kept the tranny oil changed often and the OD fluid changed a couple of times a year. In the middle of the 6th track season on it, the 3rd gear syncro went out. But, the tranny had a over a 100K miles on it.

I replaced the tranny with another "newly" rebuilt 4+3 and kept on running. It must be said that I very rarely utilized the OD on the track. Now and then at the end of the back straight at VIR and at Pocono. Other than those two tracks, I never found a place where I needed to get into the OD as the engine redlined at 5800 and that got me to the end of most straights.

You can run the 4+3 for a long time on the track if you take care of it. But, I must say, I like my tranny in my Z06 a lot better than my old 4+3!!!

No Go

How much is a 4+3 nowadays?

The ZF's have been liquidated by GM so snagging one on the market for ~$1300 isn't tough...and it is a far better trans.

I'm pulling my 100,000 mile example out with no defects...just because I found a "New" one to take its place for another 100,000 miles.

Also, the autocrosses I have participated are admittedly small, but 7000 rpm in first is a shade under 60 mph (stock 3.45's)...and I run the whole course in it.