Thump when I hit the gas from a stop?

pallison74 · May 13, 2003

Hey Everyone. I just bought a 1999 silverado 1500 4X4 with auto with 80k miles. I didn't notice this when I test drove it, but I know notice a problem. When I come to a complete stop, and then hit the gas there seems to be a thump from underneath me or towards the front of the truck right when I hit the gas. Sometimes the thump occurs as soon as I let off the brake, before I even hit the gas. This does not happen if I only slow down and then hit the gas without stopping. I have never owned a car with this many miles, so I have very little experience with problems. I was thinking it might be the tranny, but it shifts very smooth while I am driving.

Has anyone experienced this before?

Thanks

Paul

I also posted this in the Silverado 1500 forum. I hope that doesn't offend.

Fishhunter911 · May 13, 2003

sounds like it might be the transmission mount. It connects the trans to the crossmember. Mine is doing the same thing. If you climb under the truck you will see the mount. Push up on the tranny near the driveshaft. if the rubber comes apart then you know its bad.... hope this helps

TarheelZ · May 13, 2003

There are several potential causes for this, one of which is a broken motor mount. When the engine rpms climb, the torque makes the engine lift somewhat on the driver's side which can crack or break the mount.

There may also be related issues covered by TSBs for your vehicle. Mine had a couple or three outstanding when I first bought it. You might want to look into that.

Good luck!

pallison74 · May 13, 2003

Do you guys kNow where I can get pictures of the undercariage of the Silverado. I am not sure about where this transmission mount would be.

Thanks

Paul

pallison74 · May 13, 2003

OK

I just checked it out under the vehicle and this is what I noticed. Off of the engine is a shaft that runs from the engine to the Transmission. I assume this is called a drive shaft. There is the interlocking connection between the shaft and engine, is this called a U-joint? There is also one at the other end that conects the drive shaft to the Transmission. What i noticed it that the front conection (U-Joint) to the engine is solid, there is no play whatsoever. However for the connection of the shaft to the front of the trnasmission there is a little bit of play, in that I can wiggle the two parts of the joint a little. Would this be causing the above problem?

Thanks All

Bogie · May 17, 2003

that was gonna be my suggestion: U-joints...first thing I woulda checked, even before the transmission mount.

blacksab2 · May 17, 2003

I had the same kinda the same noise on my 2002....It would "chirp" a little also....The dealership replaced the slip yoke, and no more problems......

HillHound · May 24, 2003

<font color='#000000'>I had the same kinda the same noise on my 2002....It would "chirp" a little also....The dealership replaced the slip yoke, and no more problems......</font>

My '01 Silverado did this too and I'm almost certain that's what pallison's noise/thump is. You can try to get the dealer to replace the slip yoke or just remove the rear propeller shaft and lube the slip yoke yourself with some synthetic grease.

I fixed mine by doing this and at the same time changing the transfer case fluid. I did it at about 9000 miles and the noise hand't returned when sold it at 24000 miles. If you need detailed instructions on how to do it send me a "PM".