W1WLH

The manual transmission on my 85 C4 has a problem in the overdrive that I'd like to see if anyone else has something similar and/or may know of a solution. If I accelerate with the OD switch ON, when it engages, it does so with a fairly significant clunk (bang). Once engaged it runs smoothly and makes no unusual noises. When I decelerate to a stop, or into 1st gear, I get another clunk (bang) when the OD disengages. The only way I can get a fairly smooth operation during acceleration is to leave the OD switch OFF until I shift into 3rd gear then turn ON the OD switch. The engagement is smooth - no clunk or bang. I haven't found a solution to prevent the positive downshift noise when the OD disengages when slowing to a stop or very slow speed in 1st gear.

I have no other transmission problems shifting up during acceleration into 4th gear or decelerating from 4th gear down to 1st gear. Does anyone know of a solution to this annoying problem?

Thanks,
Bill

mazdaverx7

These transmissions can shift hard sometimes. with my current 86, there is no question when the overdrive is engaging or disengaging. How old is the fluid and has the filter been changed recently? Fluid topped off? Any leaks?

With that said, I have always depressed the clutch pedal when shifting in or out of overdrive. I like to drive the car like a 5 speed. I shift through the four gears and then depress the clutch and turn the overdrive on. When the clutch pedal is released, the overdrive unit is engaged and its butter smooth. Now, if the trans downshifts due to throttle input, the shift on my 86 is very firm. You definitely know when the overdrive unit is disengaging or engaging if the clutch pedal is not used when engaging or disengaging the overdrive unit. My 84 was similar and to minimize wear on the overdrive unit, I always use the clutch when engaging or disengaging it whenever possible.

W1WLH

Thanks for the reply, whoever you are. From what you stated above it looks like you have the same operational issues I have. I always engage the OD in 3rd or 4th gear after depressing the clutch unless I have forgotten that the OD switch was left ON in which case there's an abrupt CLUNK/BANG when the system engages - does it every time.

I'm not so much concerned about managing the up-shift into OD as much as I am the down-shift OUT of OD. There's where there's a BIG problem. Even with the clutch depressed when slowing to a stop, I still get the irritating bang when the OD disengages so clutching makes no difference. It's difficult for me to believe that GM would have released this vehicle for sale with this annoying problem! Surely no one would have spent the $26K for this Vette back in 1985 knowing that the OD is trashed.

Yes, I've done everything short of having the OD transmission rebuilt but unless I can be assured that these problems won't occur after a rebuild, I won't spend the $$$$ to go down that path. I've already invested well over $15K in upgrades and rebuilds to the vehicle during the past 4 years and I don't want to invest more capital into an OD rebuild unless I'm sure what I'll have once that process is completed. I suspect that finding a transmission repair shop that has the knowledge to repair/rebuild this OD unit may also be a BIG headache! Perhaps someone else reading this thread will have further guidance/suggestions.

Regards,
Bill

Silverknight5750

Hello,
I have an 88 C4, and I wonder if anyone else suffers from the problem of an Insufficient clutch Release almost always, I helps if I can push the clutch pedal nearly all the way to the floor, but I believe it is not properly proportioned Master to Slave fluid displacement, for lack of a better description.
This vehicle was purchased approx. 3 years ago with a documented 4600. miles from
Corvette Mike in the Anaheim area.
I have had the Master, Slave and the fluid line replaced but this did not improve the Clutch release travel needs, other than that, It's Great to Drive as a 6 speed...
First Gear thru 4th than Downshift to 3rd Overdrive than into 4th Overdrive, 6 Speeds with little RPM drop, AKA Splitting the gears..
If some one has resolved this issue and reduced the clutch travel, I would be happy to hear what combination Master and or Slave that moves more fluid with less effort.
Thank You,
Mark G.