I have a '74 with a 454 engine and 3.73 posi rear. I don't know what tranny is in it. The problem is if I'm crusing at 65 mph and take my foot off the gas, the car slows down immediately, as if I hit the Jake Brake (engine compression brake) on a tractor-trailer, instead of just gently slowing down. Any clues? Please speak English, as I just drive 'em, I don't fix 'em. I think the thingamajig maybe fell off the whachamacallit. Oh yeah, also the speedo will say I'm doing 90 while I'm probably doing only 60. Thanks! kingkong2006-12-12 21:21:26

Sounds like a transmission problem to me, but you better talk to our resident guru of xmissions, Joel.  He may not get to ya soon, but he'll get to ya eventually.  He's got a lot on his plate right now.

Is it whinin' in the rearend at steady rpms?  Is it shiftin' into 3rd gear (I'm assuming automatic here)? 

I have an '80 that wasn't shifting up due to a stuck valve inside the transmission body.  Joel talked me thru the fix with pictures and saved me well over $300 on the deal.  My speedo is off the other way by about 10 miles but not 30 like yours.  I think that might just be a vette thing.  Most of the guys I know with C-3's have that problem to one extent or another.

I know this isn't a lot of help but I didn't want ya to think we are just ignoring you.

Dennis

If you have an automatic, it is a 400 trans. Are you sure you still have the 3.73 ratio in the rear end? If the ratio has been changed to a lower ratio, that would answer both of your issues.
The car should slow down dramatically when you let off the gas, but it shouldn't feel like the brakes coming on. If, however, you have a lower ratio rear, it will seem like the brakes are dragging when you let off. Have you had this car long? If so, did this just start happening?
What are the RPMs at 60mph?


btw...if the thingamajig falls off of the whachamacallit, it make a very loud clankity clank-clank sound. This would require the replacement of the gweesh-gweesh valve do-hicky in the flux capacitor reactinator.Adams' Apple2006-12-12 22:19:27

Practically nothing in the car is original, including the motor (I believe it originally had a 350). Bought the car in March, and know it has a 3.73 rear because I had it rebuilt. Had the problem since I bought it. Tach doesn't work, but feels like high rpm's. It shifts very softly, but I know it's hitting 3rd because I can downshift into 2nd and feel the difference. Where can I get one of those flux capacitor thingies? I think I need one. Or a new dilithium crystal. Thanks Joel. kingkong2006-12-13 08:32:34

Dennis, the only whining I'm hearing is coming from me.

Wayne, I think your car is fine. It is operating the way it should, as far as the deccelleration, imo. The trans will create a lot of "drag" when you're trying to spin it with the driveshaft, due to the design of the planetary(gears) system in it. What does it do if you stick it in neutral when you let off the gas? I'll bet it will free-wheel a bit better. You most likely do not have any trans/diff problems...just normal stuff. Check the trans fluid for nasty smells. If it doesn't smell burnt, it's probably otay.

The speed-o being off is easy enough to fix. You need to determine what gears(speed-o) you have now, and compare them to what it should have. I have a chart posted here somewhere...I'll look for it.