So I don't know crap about cars, but I have a potential problem. Update as promised.

[Hayabusa Rider]

Just bought a 2005 Impala. 91K and seems in good shape.

Last night when I started out I felt a thump. At first I thought I was rear ended at low speed. Nope. It was the car itself. It then continued to do the same after every shift (not as hard though)

Today, I had it happen just once.

Obviously it's something to do with the drive train, but anyone have an idea of that this might be?

It's under warranty so I can get it fixed, but still, I'd like to know what's going on.

Edit-
I wanted to wait a few days to see if the problem recurred. So far it hasn't. My mechanic said he didn't find a bad mount. He changed the transmission fluid and filter and checked the transmission programming to make sure the shift points were set correctly.

So far so good. I confess I don't know what to make of all this.

 

[Ronstang]

Could be an engine/tranny mount. If you have a jack you can lift the engine/transaxle under each mount and see if any are separated.

BTW, I have been meaning to ask you about your avatar. Sure looks like Tom Lehrer, in fact it looks exactly like one of the pictures of him at Allmusic.com.

 

[Hayabusa Rider]

Could be an engine/tranny mount. If you have a jack you can lift the engine/transaxle under each mount and see if any are separated.

BTW, I have been meaning to ask you about your avatar. Sure looks like Tom Lehrer, in fact it looks exactly like one of the pictures of him at Allmusic.com.

Thanks, and you are right about the avatar. He's funny as hell.

 

[Ronstang]

I'm not even old enough to know who Tom Lehrer is but about 25 years ago when I was in my early 20's a friend's parents used to play his records for us and we all thought they were funny as hell. His material is dated of course but he is hilarious. I think I have all his records now.

 

[LTC8K6]

How's the fluid?

 

[Bignate603]

How's the fluid?

This is the place to start. Low fluid can make the tranny shift hard. If the tranny fluid looks brown or black you're probably burning it. If it looks bad give it a sniff, it will smell burnt.

 

[SooperDave]

From your description I'd think engine/trans mount also.

 

[Meghan54]

From your description I'd think engine/trans mount also.

I would, too, esp. considering the thumping is there one day and gone the next. And low fluid symptoms don't exactly come across as a thump that gets you to think that you've just been rear ended.

 

[IcePickFreak]

+1 on a motor/trans mount.

 

[ElFenix]

motor mounts broke in my taurus a couple times. when broken it felt like running over a brick every time it started or if it shifted.

 

[angry hampster]

From your description I'd think engine/trans mount also.

Same here. That'd be a best-case scenario here. Cheap, easy fix.

 

[Hayabusa Rider]

I'll check the fluid just in case. The guy who sold me the car is also my mechanic and he's a keeper. He once spent 9 hours trying to find an electrical problem with no luck (the dealer couldn't find it either), and didn't charge me a cent.

I made him some baby back ribs

 

[Pacfanweb]

Check the fluid.

Then, to check the mount, raise the hood. Put the tranny in drive, and leave your foot on the brake, HARD.

Then give it some gas. If the mount is broken, the engine will really jump up and you'll feel that bump you described. That'll prove it's a mount.

 

[Hayabusa Rider]

Bump for update- see OP

 

[kevman]

my old buick century had a similar thump when going from Reverse to Drive and vice versa and it turned out to be a motor mount. Check the fluid first and then look into the mount.

Good luck.

 

[nathorofmoo]

I am not a mechanic, but I had a similar symptom and it turned out to be the throttle position sensor was out. The transmission was shifting really hard because it was getting bad data from the sensor about the engine speed. Swapped sensors and the problem instantly disappeared. BTW, there was no CEL on.

 

[cardiac]

U - joints....