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4+3 or 6spd?



Well, it seems my 4+3 on my 87 has finally gone to that big scrap pile in the recycle factory. My guy says it'd be better and cheaper to just replace the tranny; half the gears are worn down, the synchros need replacing, etc. He says I should replace it with a 6spd because it's newer and will give me better performance. My question is, 4+3 or 6? I suppose the 6 is technically superior, but the 4+3 is part of an 87, isn't it? and i'm not too sure about performance really being an issue; I;ve seen a 4+3 beat a 96 6spd in the 1/4 mi. so what do u guys think?

If both are going to be around the same $$ I would have to vote on the 6-speed. I'm biased though:) I'm not to familiar with the 4+3.....

Decision time


If it were me, the deciding factor would be the cost involved. Neither choice is cheap. If at all possible, I would try to stay with the 4+3. I just had my 4+3 OD rebuilt by Corvette Doctor in St Pete, Florida. He told me there are only 3 or 4 places in the country that have parts anymore. That's the price of having a drivetrain that GM used in the Corvette for only 5 years, and that was 15 years ago.

Re: Decision time

GreyGhost said:
...He told me there are only 3 or 4 places in the country that have parts anymore.

That's the same thing Charlie Smith in Urbana told me when he did (re-did) mine on my road trip. The internals he used were the ones he used for his classroom seminars. :eyerole

I have a 4+3 in my 88 and, quite frankly, don't like it at all!! I would much prefer a 6-speed but won't spring for the $$ to replace it when there's no need! If it's not a matter of money (and I have no idea what each would cost), I'd go for the 6-speed. It's a proven transmission...

Lemon Peel aka Elaine
Re: 6-speed....

LemonPeel said:
...quite frankly, don't like it at all!!

As for me Elaine, I like it alright, it's just the problems I've been having with mine that I don't like. Mine is now appearing to me to be a relative (spawn?) of the original electrical "gremlins" that have been in residence for awhile. :L

;) Ken :w
Although I still have the 4+3 in my 86, I have read that the change to a 6 speed is a major undertaking. The tranny tunnel must be modified, and there are other issues as well. If you decide to go that route, I would be sure, if you giong to hire it out, that the mechanic has done it before. My .02
See now I heard a ZF 6 out of a Stock Vette will go into the Tunnel of a Earlier C4 No problem But the Richmond 6 Speed (Claiming better than the ZF 6 From Ecklers) Needs Major work done Like tunnel bell housing so forth.

I like the 4+3 I got if you want to race you only have to shift 4 times Vs a 6 speed and if you want MPG on the highway that "7" gear or Overdrive makes my vette out to be 27-29 MPG

Only thing about them is those darn Overdrive units I guess overall they are unpredictable when they are going to malfunction and they DO malfunction like mine at the moment is

NOT A 4+3 its a 4+4!!!

When I shift into 2nd turn the OD on everythings fine BUT when I down shift into 1st again (Now the overdrive supposed to turn off automaticly) the OD stays on!! and I can turn it off in 1st as well!!
(And I cannot shift into OD From 1st only on the down shift)

But WHEN I do the Tires kick and squeel a bit so Im curious


According to the shop manual the ECM controls the unit and will not allow it to run OD in 1st. Guess that ain't entirely true ;-)

It says if OD gets stuck in all gears check the following:
1. Solenoid Plunger Stuck
2. Solenoid Exhaust Hole Plugged
3. Shift Valve Stuck

The remedy is replace Solenoid if 1. Clear exhaust passage if 2.
Free up shift valve or replace valve body if 3.

BigRed said:

BigRed, check out The Gear Zone for DN 4+3 info. This link should take you directly to the page that has the information as to how the overdrive is supposed to work for each year of production. Click this: 5Speeds.com.

Of course, I can't verify the data given. For instance, it says that for first gear -
"Overdrive after downshifting while OD is engaged"
is possible in first gear for all years except '84; the service manual claims otherwise I believe. I've only experienced it once, and that was by accident. ;)
With all the fuss with the ECM, is it possible to just complete turn off the program, and be in complete control of when the OD enages or not?
Believe me Lunar you dont want OD in first gear Like a said the Tire and car jerks quite a bit and it definitly does not sound healthy

I'll try cleaning/check out the solenoid and get back to you guys thanks!
BigRed said:
Believe me Lunar you dont want OD in first gear Like a said the Tire and car jerks quite a bit and it definitly does not sound healthy.

I agree Red. :eek
BigRed, the info i posted is out of the 84 shop manual. maybe they changed it on the 85 but my impression was that the 4+3 was the same in all of them.
To get at any of the solenoids or valves to check it out you will have to pull the trans pan and filter.
I swore the 4+3 on the 84 i had did what it pleased most of the time. I decided in town it was a 4 speed and on the highway i would flip the OD button and get the better mileage cruising.
rebuit 4+3 or spring for 6 speed

I had the misfortune of having my 4+3 break several teeth off the main cluster shaft. I opted to have it rebuilt rather than the costly Richmond upgrade. I was informed the richmond was the only available bolt in without transmisson tunnel modifications. The ZF does not offer as steep of gears and recommends a differential gear change (3.54 or so) to gain back acceleration similar to the 4+3. At that time there was not a replacement cluster shaft available from GM. I waited over six months for them to produce on. The repair proved costly but fortunately the overdrive was not damaged. The 6 speed would probably be more user friendly but the 4+3 is part of the personality of my Corvette so I felt obligated to keep it. Periodically it does like to keep the overdrive engaged when downshifting into first. Watch for the "D" light to stay on when shifting down.

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