Over the past year, I have been experiencing a gradual loss of engine braking on my daily driver 1995 Corvette with the original 4L60E. The only modifications to this car are a set of 3.73's gears and a re-flashed computer for speedometer correction (using LT1_Edit). The car has 125K miles on it, has had the transmission fluid and filter changed on 25K intervals, and the fluid level is currently, and has always been, correct. I have owned the car since new. The transmission has never been out of the car and is original GM along with the torque converter. The car is in otherwise well maintained condition.
Basically, about a year ago, I began to notice the car occasionally failing to provide engine braking on downshifts into second gear, but gradually over the course of the year, has deteriorated to the point where the car provides absolutely no engine braking at any speed in 1st-3rd gears. To briefly describe what is happening, if I downshift from any gear to the next lower gear and am not applying any gas, the engine will drop down to idle speed and will basically coast as if in neutral. Similarly, if I am maintaining constant speed in any gear, and for the purpose of example say the RPM is 2500, as long as I keep my foot on the gas enough to maintain speed, the RPM remains 2500. However, once I lift off the gas, the engine RPM again drops to idle and the car coasts. If I want to increase my speed again, I must first bring the RPM's back up from idle to around 2500 before the car will begin to accelerate again. 1st-3rd all behave the exact same way, however, 4th gear overdrive does not exhibit this problem and provides engine braking as it should. Additionally, while it may not be related, the transmission has also recently given up shifting on the 2-3 WOT shift, unless I lift off the gas and let it shift.
I am pretty sure the transmission is gone, but I would like to know what any of you think the problem might be before I take the car in for a rebuild. I have spent a lot of years building and racing cars, but I don't have much knowledge when it comes to the internals of an automatic transmissions as this is my first automatic car.

Thank you for your time.
Paul

 

Well if it were my car, I would probably have somebody who knows the 4L60E well take it out and check it out

I'm no expert with the 4L60E, but I may as well ask a few probing questions so others can help. Aside from the downshifting, is the tranny acting up at all? Does it hold power during more aggressive (anywhere between half throttle and WOT) driving? Are you generally manually shifting it, or do you let it sit in OD all the time?

 

Strahley, I don't generally manual shift the trans. I usually leave it in D for driving around town and OD for the freeway. That is not to say I have not manually shifted the car before. I have done it in the past going down steep grades, passing, and other "normal" driving duties and all downshifts were always to the next lower gear. I don't manually shift every gear from stoplights and such. Otherwise, the car drives fine. It accelerates fine at all percentages of throttle and if it were not for the recent WOT 2-3 hang up, it was shifting the same as it has since the day I bought it.

 

Sounds like it's slowly wearing out to me. Always possible that it's something fairly simple on the inside though. Wish I knew more about the 4L60E so I could help more, but I know very little on that tranny

 

Sounds like the overrunn clutch has failed. This clutch is applied in manual 1st, 2nd and 3rd. Not in the OD range. This could very well be the problem. We at FLT do lots of corvett units and I would suggest checking out our site for info and pricing. www.finishlinetrans.com. or simply give us a call at 1-630-350-7776. Thank You, Vince.