"Thud" noise coming from underneath the car?

Ok, so I have some weird thud coming from the bottom of my car. I just drove it for the first time since I put it in my garage for winter tonight. It ran fine, but I have a thud coming from the bottom. When I accelerate normally, up to about 30+ or so and let off, I get a thud. I'm thinking it's coming from somewhere near the tranny [automatic] or from the tranny itself.

I don't know if the previous owner installed a shift-kit or not, but I know the tranny is really strong under hard acceleration. I can chirp my tires going into 2nd off the line [but I think it's do to having the stock 245/50/16 Eagle RS-A tires]. I don't think one was installed, because I have all the recipts and paperwork from the previous owner, and nothing suggests any tranny work was done.

Also, sometimes when I'm slowing down to a stop, from say 40mph or so, I sometimes hear a thud coming from the underneath the car from the front. Could it be something suspension, tranny, or motor mount related? Or could the exhaust be hitting something when deaccelerating? The previous owner did have a Borla cat-back installed.

Any help?

Here's a list of stuff that I had installed last year since I took ownership if any of it helps. Prothane transmission mount and a 32mm front swaybar with polyurethane endlinks and durometer bushings.

I'd check the tranny mount/bushing.

Or you could have a big maglight in your bumper cover like I did. I wondered what that thudding was for a long time. :o

I've been having a thud underneath my car for a month I've been trying to chase down... Does it if I'm coming to a stop quickly or sometimes going over bumps... I checked over the brakes, suspension, shocks/struts, everything... Took a look today when the car was on ramps and it turned out to be both bolts on transmission mount that screw into the trans were loose.. Tightened both, no more thud.

Tranny mount :) Don't flog it till ya fix it

When my stock mount ripped it made the most horrendous noise under acceleration.

It shouldn't be my tranny mount since I had a prothane polyurethane one installed last year. But I'll have the bolts checked when I get an oil change later.

I changed my transmission mount just over a year ago... That's why I thought it was something else and didn't even think about it... Turned out to be it.

It may still be in one piece... but it may have loosened up.

I was getting the dreaded thud so I just went out and bought a new mount... I got under the car to fix it and lo and behold, the stocker was just loose(the nuts were about 3/4" down on the threads.... may as well have been broken. LOL).

It was most noticable over bumps, decellerating quickly, and during the 1-2 shift.


About the front end noise, I've heard that poly bushings can bind, I'm not sure if this would cause the noise you're describing though. I'd imagine it would be more of a squeek.

Take me for a ride, I'll diagnose it :thumb:

-Dustin-

I have this thud, its not the trans-mount in my case. I believe someone found out that it was a busted bushing in the torque arm. I am just going off memory here and it's been a long time since i saw that thread. I havent tried to fix it yet.

Or you could have a big maglight in your bumper cover like I did. I wondered what that thudding was for a long time. :o
Now that was funny. :lol:

I'd check the tranny mount/bushing.

Or you could have a big maglight in your bumper cover like I did. I wondered what that thudding was for a long time. :o

I found a flashlight stuck on top of the skid plate on my Silverado 4x4. That rattling drove me nuts for months before I figured it out.

oh its ok all Chevys make funny sounds!

Did you do the motor mount test? Have someone rev the engine and see if the motor jumps excessively? Also have someone shift from park to drive, and see if the motor jumps then.

Good luck

I'll check the motormounts when I get a chance.