Rebuilt Tranny on Silverado with 12 inch lift

mhowtopat · March 24, 2014

We recently had our transmission rebuilt on our 2001 Chevy Silverado 2500hd. It has a 12 inch lift. The transmission seems to be worst than before. The main problem is that it shifts really hard and the speedometer is way off. It says we are going much slower than we really are. Does this sound like a bad transmission or is it some kind of issue with the truck being lifted? The mechanic said that it was due to the truck being lifted and having big tires. The problem is that the business shut down and we can't get ahold of the owner. Please help....

LongrangeLauber · March 25, 2014

If the speed is off it sounds like your computer isn't calibrated for the bigger tires. This can also throw off shift points cause the RPM's don't match what the computer has calculated. call your local off road shop to get pricing to get the speedo corrected for tire size and gear ratio. Or you can get a full tune either from a handheld programmer or through blackbear performance. I have a BullyDog tuner and it gives me my transmission fluid temp and coolant as well as speed and battery voltage

Sent while drinkin' a cold one...

Silverado4x4 · March 25, 2014

How did it run before your trans rebuild? A lot more info is needed. Trans shifting hard has nothing to do with the lift. Sounds to me the guy is blaming the truck lift and tires on a bad rebuild. I can see the speedo being off if not calibrated for your tire size. Your trans doesn't know you put a lift on or bigger tires the only thing it will do is mess with your ABS due to the vehicle going faster then the drivetrain unless you correct the wheel size difference. Your shift points wont change on the rpm and speedo it will still shift at a stock programed shift point its just the truck will be moving faster then the speedo.

Artey72 · March 26, 2014

Agreed 4x4.if its a 2500hd it likely has a 4l80e. They are very sensitive to the input from the input and output speed sensors. Would check for any diagnostic trouble codes and go from there.

mhowtopat · April 17, 2014

I didn't even know that the truck needed a new transmission, but somehow my husband knew. It actually runs worst now than it did before the rebuild. The funny thing is that the transmission seems to be solid, it just seems off somehow. And there's a vacuum leak somewhere. They also replaced the knock sensors.