I will be looking for a c4 in the next couple months but one of my requirements is a manual trans. I've heard about the overdrive going out on these but was wondering if it effected anything else? Meaning, if the overdrive calls it quits does the car still operate like a regular 4 speed? Is the problem as widespread as a quick internet search seems to bring up? I don't mind the car being a 4 speed if it can run just like that.

I'd like to expand my search years to these older c4's because I haven't seen many 89+ showing up for sale around here lately.

 

I have owned an 88' 4+3 for many years and generally It Is reliable as long as you do routine maintenance being changing the O.D oil and filter regularly. I have raced mine lots and it has stood up just fine. These trans seem to get a bad rep, but its not warranted. Also replacement parts such as flywheels are readily available. Also the 4+3 is pretty easy to remove for service if necessary and all the clutch hydraulics are mounted outside the bellhousing making replacement easy v.s the later ZF6 where you have to pull the trans and bellhousing to replace the clutch slave cylinder. Replacement part for the ZF6 like the flywheel are getting really hard to find also.

I will say the 4+3 aren't for everyone as the 4+3 has a very old school feel. Since your basically driving a super T10 four speed with a push button overdrive. The 4+3 requires you to shift forcefully but you won't ever miss a shift, at least I never have, the linkage is pretty good. Some people don't like the forcefully shifting in the 4+3 compared to the smoother ZF6.

The push button O.D Is actually nice for city driving as you can turn the O.D on or off by pushing a button which is equivalent to shifting up or down one gear. It is also handy for passing on the highway as It will turn the O.D off automatically if you get on the gas while the O.D is on if you are below a certain RPM (equivalent to downshifting to pass).

I will say though that it still does feel a bit odd having a push button O.D on a manual, but it works well.

I tried to give you a through review of my 13+ years of owning a 4+3 trans hopefully it helps you decide If you want one or not.

I agree with you Manual is the way to go, makes driving much more fun.

 

Welcome to the Corvette Forum.

I've owned a 1985 with the 4+3 since it was new and have never hand any issues with it. I primarily attribute this to the fact that I have serviced it regularly in accordance with the service manual.

I believe that many of the problems associated with it are related to incorrect servicing or no servicing at all. It is essentially a 4-speed transmission with a 2-speed automatic attached to the rear of it. Typically problems arise when the two different fluids get co-mingled. I would just look for a vehicle that has good service records and appears to have been well maintained.

If you find a Corvette that otherwise meets your requirements and the 4+3 seems to be operating satisfactorily, I would inspect the manual gearbox oil first to see if there is any evidence of trans fluid in it. If it looks good I would turn my attention to the overdrive unit. Since you will need to drop the pan to inspect the fluid anyway, I would change the fluid and filter in it regardless. If the condition of the manual gearbox fluid is suspect in any way now is a good time to also change it.

Good luck... GUSTO

 

I have an 86 4+3 and love it. No concerns.

 

I agree that they get a bad rap, but to answer your question, if you lose the OD you lose reverse too.

 

I agree with the other posts.

I have a an '84 4+3. It does have that old school feel. Shifting it reminds me of my '66 Chevelle. I like it but some may not.

Can't emphasize enough on the importance of changing the overdrive fluid and filter.

My car has 36k miles. I changed the fluid back in the spring when I got the car. I know it had been changed at least once before.

I could not believe how disgusting the fluid had become. Looked like dirty bilge water and thick as lobster bisque.

GM maintenance schedule I believe calls for 30k between changes. Based on what I saw that was way too long.

 

I have had an '85 and an '87 both with the 4+3 for a total of 28 years.

I never had an OD problem with mine either. I used the OD like a 5th gear on the highway.

However, I have also had the ZF 6 speeds and I prefer them. I like the bigger spread of ratios. It is a 0.5 OD so they get really good mileage on the highway. They shift smoother. They are very strong transmissions. Although it was stated above that the slave cylinder is inside the bell housing, it is not. It can be changed without pulling the transmission or belhousing.

Good luck with your choice.

 

I have 145K miles, on my 85 4+3. Outside of small leak it works great, Everyone that I take for a ride loves the overdrive button, my 7 year old son especially!
I change the fluid and filter yearly. I recently installed a McLeod clutch and it feels great.

 

I'm a "newbee" here and I have been in the process of finding myself a C-4 vette. I have been looking at a ton of cars, and have been on the fence between buying a auto trans or a stick car.
I'm a old school hand grinder guy, JMO that a stick makes driving more fun.
I found this post most helpful as I have had many questions about the 4+3 trans.
The car I would like to buy is suffering only from a problem with the od not working and a very week reverse gear acting like its sliping. After reading this tread it seems that both the rev and od problem could be in the od unit. Are these controlled by the ecm? or is it in need of rebuild. Car has no codes and the check engine light is working properly

 

Shifting into overdrive is controlled by when the ECM allows it to shift based on throttle opening, coolant temp, road speed and gear position.

OD is not allowed in 1st gear; 2nd thru 4th only.


The console button in '85 and the shifter button on '86-'88 allows the driver to disable the shift into overdrive.


My '86 needs rebuilt (OD clutch pack is burned out) as it works as it should up to the actual shift but in won't shift into OD when the light comes on and it freewheels on coast if the light is on. Disable the OD by the button and it drives like a traditional 4-speed.




Jonathan.....

 

my understanding is when they reversed goes, it's a bearing inside.

 

This car acts like it is slipping when in reverse gear. It has been said the the main trans is a t10 borg warner, If so could one make changes to eliminate the OD unit?
Also I herd that one could remove this trans and over drive and install in its place the t5 trans from a firebird or Camaro, Is this a fact and has anyone on here done this????

 

A google search will yield some pretty good write-ups on folks that have done the T5 swap. Apparently a pretty straight forward swap except for a bit of tweaking to the console to accept the T5 shifter.

 

IT would be hard to swap in a "regular" Super T-10 as the tail housing would have to have some way for the C-beam to attach to it. The output shaft would be a different length and it may even require a custom tail shaft. You would have to use a GM shifter or an aftermarket shifter as the C4 shifter bolts to the body, not the trans. The center console would require modifications.

The T5 from the F-bodies were never made to handle high HP and torque. I remember my '83 Trans Am had all of something like 190 HP and about the same torque. An L98 could easily trash that T5. And the T5 bolted in at an angle so the shifter would be a problem in getting it to sit properly in the console. And overall length and attaching the C-beam would be the same problem you would encounter with just a Super T-10.

The OD can be rebuilt (as can the T-10) and you could also use a ZF 6-speed from a later C4.

 

If one were to swap to the t5 or zf 6 speed, would the ecm freek out from not being connected to the OD?

 

Who to contact to have one of the OD unit rebuilt?

 

There is some pretty good info here...
http://www.corvetteactioncenter.com/...-unit-610.html

Even more...
http://www.5speeds.com/dne.htm

Good luck... GUSTO

 

barking, does that mean that the op may infact repair the problem by a soft parts repair kit? clutch packs?

i read in other threads his symptoms were likely due to a toasted bearing. which im finding hard to find!!

 

Thank you everyone. I have lots more research to do and you'll probably see me popping in with more questions in the future. Appreciate the help.

 

The front annular bearing may possibly be replaced with a NAHCHI 6912Z, I also recall the small pinion bearings were a B-88 I forget the manufacturer. Hope this helps in the preservation effort.