4+3 trans

[roger longman]

Hi all, For what years did they use the 4+3 automatic transmission and what are the pros and cons ? Thanks. Roger.

 

[Hib Halverson]

84-88

 

[KANE]

... what are the pros and cons ?

Mostly what I've heard in terms of cons comes down to maintenance. They are really neat transmissions if they've been properly maintained.

 

[GS Diva]

It's not considered an automatic transmission, but rather a 4-speed with overdrive.

Elaine

 

[vetteoz]

what are the pros and cons ?.

Everybody who has never owned one will tell you they are crap and to swap in a ZF6 ;squint:

 

[KANE]

Everybody who has never owned one will tell you they are crap and to swap in a ZF6 ;squint:

:L

I can attest to that!

I've heard many arguments for and against ZF6 swaps on the CAC over the years.



I'd recommend driving one (with a maintained OD) and see what you think. I'd personally pass on any 4+3 that was burnt out... but then again that is good advice for any car- walk away when it is riddled with problems!

Perhaps a search of the CAC forums would help shed more light on what experiences CAC members have had.

 

[G Winter]

A question on the same subject. How difficult is it to rebuild the overdrive and how costly is it. I have rebuilt the old automatic trans so have some knowledge of transmissions.
The reason I ask is that the earlier C4s can be had quite cheap but they may have problems such as the overdrive.
One of those would make a nice work car for my wife.

Glenn

 

[Hib Halverson]

The 4+3 is a combination of a strengthened Super T10 four-speed manual and a two-speed electro-hydraulic overdrive unit. The trans was originally built by Borg-Warner but the 4+3 verison was developed by Doug Nash Enterprises after it purchased Warner's four-speed transmission business because the OEs were moving away from four-speed manuals. The O.D. was a derivation of an overdrive unit Nash had originally designed for RV use and it continued to evolve from the first derivation used in the 84 Vette.

For GM the Nash 4+3 was quality control and warranty nightmare. In fact, one significant driver behing the project that resulted in the ZF S6-40 six-speed for 1989 was the troubles GM had with the 4+3 which some inside GM called simply "the Doug Nash".

My understanding is that the 4+3 underwent significant changes during its production and that the version that worked the best and had the least problems were in cars built in the 4+3's final model year, 1988.

My guess is that, if you could find parts, rebuilding the gearbox section would be easybut rebuilding the O.D. would be difficult and perhaps costly.

My advice is, unless your "restoring" an early C4 and the 4+3 is a requirement, that you convert the car to a Richmond six-speed using Richmonds "bolt-in" kit which is designed just for this purpose.

 

[vetteoz]

if you could find parts, rebuilding the gearbox section would be easy .

Due to the widespread use of the BW SuperT10 the parts are available all most anywhere including on line.
Richmond Gear have part # listed for most parts
http://www.richmondgear.com/07pdfs/RG25.pdf
T10 Parts transmission
org-Warner T10 Manual transmission parts, rebuild and overhaul kits B - Drivetrain.com

 

[vetteoz]

but rebuilding the O.D. would be difficult and perhaps costly.

There are specialist tools listed as needed for the rebuild O/d but several have rebuilt at home using common garage equipment

There are several specialist shops that rebuild or can supply rebuild parts for the O/d unit
Contact
DARRELL
SK Speed - Peformance Auto Parts and Racing Accessories

 

[roger longman]

It's not considered an automatic transmission, but rather a 4-speed with overdrive.

Elaine

Hi, I would have thought that any transmission that shifts itself was an automatic, even if it does have an overdrive on 3 gears. How is it not so in this case ? Roger. :confused

 

[Rogue]

The overdrive was electronically controlled and it engaged in any of the 3 top gears depending on throttle and speed. That was the only "automatic" part to it. The actual shifting of the 4-speed was still manual and so was the clutch.

 

[roger longman]

The overdrive was electronically controlled and it engaged in any of the 3 top gears depending on throttle and speed. That was the only "automatic" part to it. The actual shifting of the 4-speed was still manual and so was the clutch.

Hi al, It seems I have it wrong. What is the transmission in a 1988 automatic ? Sorry to be so obtuse. Roger.

 

[dknight]

Hi, my 87 has the 4+3...the overdrive was rebuilt a few years ago for around $1500. I was told to service, service and service to keep it alive. Apparently you can not change the fluid frequently enought. Currently my problem is with the on and switch for the OD in shifter. Not working. Any tips to a DIY repair is appreciated.

 

[vetteoz]

Currently my problem is with the on and switch for the OD in shifter. Not working. Any tips to a DIY repair is appreciated.

Can you afford $4 and an hours time? A new switch and a soldering iron
Remove shifter boot to access switch at base of shifter. You will need to count the number of turns of the rod that pushes down on the switch to get button back in same height . Remove old switch and replace with this one.You will need to remove the button that comes with the new switch
MUST be this one; Momentary ,not an ON/OFF type
From Radioshack or similar
Mini SPDT 3-Amp Momentary Pushbutton Switch
Model: 275-1549 | Catalog #: 275-1549

When last available from GM this switch was like $80

 

[dknight]

Great, thanks. Sounds like you have done this before. I look forward to driving around town without "lugging down". Thanks Vetteoz! I will let you know how it goes.

 

[tdf]

My Driver has the 4+3

Not a Complaint nor a Recommendation - Just Information from a User of 4+3

I've been driving my 86 with the 4+3 as a daily driver for 3 years now (it has 86k miles). I actually think having 2 sets of 4 gears (1 set for performance and set 2 for better economy(OD)) is kinda nice. OD engages automatically when using light throttle pressures in 2nd, 3rd and 4th, as long as the engine temp is 120 degrees or greater. You can also force shifting in and out of OD with the button. I generally use the clutch when I shift intentionally in or out of OD. It is just a whole lot smoother that way and easier on the OD unit I think. I like to shift, so I don't mind this.

I cannot complain about the automatic shifting of the OD except when it drops out of OD in 2nd gear when too much throttle is applied (intensionally or not) the car launches pretty briskly and my wife gets pissed at me....LOL. She hates speed! I try not to do that when she is in the car. It can also happen in 3rd or 4th gears when you apply a little too much throttle (say on a hill and you want to accelerate a little).

I have no apparent mechanical issues with my OD unit, but I think my 4 speed gear box needs some work. It will pop out of 2nd when compression breaking in 2nd gear. If I avoid down shifting to brake in 2nd I have no big issues with it. It also seems there is drive line play in my unit when you go off the throttle at low speeds (say idling through the neighborhood at 10-15 mph). I have no way of knowing if the play is in the OD or in the gear box.

Don't be fooled into thinking you are going to have 7 gears. It's not like driving a truck with a gear splitter at all. The reason I say this is the ratios the designers have chosen. The ratio of 2nd gear with OD engaged is very close to 3rd gear W/O OD. The same is true for 3rd with OD and 4th W/O OD. Those ratios are very close also.

If all the 4+3 shifters feel the same as mine, then this is an area where GM does not score well with this design. You won't be speed shifting this guy. It is less than smooth in transition between gears. It does not grind or anything. It just feels rough as you slide it from gear to gear (both directions).

Maybe this will help somewhat in understanding how the DNE 4+3 feels/drives for those who have not driven it. Hopefully so!

 

[vetteoz]

The same is true for 3rd with OD and 4th W/O OD. Those ratios are very close also.

Great in traffic ; cruise in 3rd O/d , when you want to accel to merge, punch it and it drops back to 3rd direct

If all the 4+3 shifters feel the same as mine, then this is an area where GM does not score well with this design. You won't be speed shifting this guy. It is less than smooth in transition between gears. It does not grind or anything. It just feels rough as you slide it from gear to gear (both directions).

The gearbox itself is a '50's design.All the external linkage trans ( think '60/'70's muscle cars ) are clunky in the shift ; not helped by wear in the linkage / bushes / selectors with age.It was only the advent of internal rail trans that made muscle cars shift like a Toyota

 

[tdf]

Others of same Era shift better

Great in traffic ; cruise in 3rd O/d , when you want to accel to merge, punch it and it drops back to 3rd direct


The gearbox itself is a '50's design.All the external linkage trans ( think '60/'70's muscle cars ) are clunky in the shift ; not helped by wear in the linkage / bushes / selectors with age.It was only the advent of internal rail trans that made muscle cars shift like a Toyota

My Ford F250 of the same production year (86) with the BW T-19 shifts better than the Vette. Think truck.

 

[vetteoz]

My Ford F250 of the same production year (86) with the BW T-19 shifts better than the Vette. Think truck.

Exactly.
It is a top loading trans with internal linkage; no rods or bushes to wear out