VW TDI forum, Audi, Porsche, and Chevy Cruze Diesel forum banner

1 - 8 of 8 Posts

·
Registered
2000 Golf TDI ALH
Joined
·
36 Posts
Discussion Starter #1
I have a thumping mystery that is annoying, and so far has no explanation.

When driving on smooth roads, at 35 mph and up, I hear a random thumping sound. It sounds as if someone was banging the underside of the body with a piece of wood. It is vehicle speed related, regardless of which gear is used or if coasting down in neutral. This noise has been going on for 8 years or more. I think it is getting worse, however it's a very slow progression.

Frustrated, I took it to a dealership, where they drained and replaced the transmission oil. No metal particles present. They have also replaced the right drive axle, thinking it was an inner CV joint. They next point to the transmission internals. They say to just drive it.

The car has been driven gently all these years (I'm the original owner), and it seems incredible that the trans would be shot at 220k miles. I've spent a lot of time confirming that it's not the belly cover, and looked for other loose items.

Suggestions much appreciated!
 

·
Premium Member
Joined
·
284 Posts
You say its random but speed related? So how often? Does it do it on smooth roads or bumpy or both? It could be anything from your dogbone mount (or other engine/transmission mounts) to a loose exhaust from the sound of it. With that age and miles, if its never had the suspension rebushed it really should although that wouldn't be dependent on speed unless something is really out of balance. Manual trans or auto?
 

·
Registered
2000 Golf TDI ALH
Joined
·
36 Posts
Discussion Starter #3
The thumping sound begins around 35 mph, and is easier to hear on smooth roads. I presume that smooth roads make it less likely to be a suspension noise. Because of the wind noise, it is harder to hear at higher speeds, however it is still there. It may be less-prominent at high speeds due to the driveline velocity making things balance better. The thumping just seems to begin randomly, and has nothing to do with engine speed. It doesn't seem to get more frequent with vehicle speed increasing.

The car is original with respect to the engine mounts, suspension bushings and struts. The front half of the exhaust has been replaced. I have other experience with swing arm bushings that makes me discount that as a cause.

From what you've said, how do you check a dog-bone mount? Just check torque on the bolts? The sound is similar to a piece of lumber or perhaps a rubber hammer used against the underside of the car. A dog-bone problem is plausible, based on the noise.

I ponder getting a GoPro camera and seeing if that shows anything. I've also pondered mounting the body on jack stands, and driving the wheels to see what can be observed. I wish I had a lift!

This issue is annoying, and a real puzzlement.

Thank you for your thoughts and suggestions.

KarlC
 

·
Registered
Joined
·
7 Posts
I have a thumping mystery that is annoying, and so far has no explanation.

When driving on smooth roads, at 35 mph and up, I hear a random thumping sound. It sounds as if someone was banging the underside of the body with a piece of wood. It is vehicle speed related, regardless of which gear is used or if coasting down in neutral. This noise has been going on for 8 years or more. I think it is getting worse, however it's a very slow progression.

Frustrated, I took it to a dealership, where they drained and replaced the transmission oil. No metal particles present. They have also replaced the right drive axle, thinking it was an inner CV joint. They next point to the transmission internals. They say to just drive it.

The car has been driven gently all these years (I'm the original owner), and it seems incredible that the trans would be shot at 220k miles. I've spent a lot of time confirming that it's not the belly cover, and looked for other loose items.

Suggestions much appreciated!
It started after what? Try to remember. For example, I had thumping noise because the car battery was of smaller dimensions than its housing, so it would eventually move left and right at sharp turns. It took almost two months before I realized that. Then I remembered that it started after I replaced the battery.
 

·
Registered
2000 Golf TDI ALH
Joined
·
36 Posts
Discussion Starter #6
Thanks for the comments and shared learnings.

My latest theory is a rotted dog-bone bushing (or whatever it is). I have one on order, and will install it and see if it changes anything. After all these years and with oil working its way along the dog-bone to the bushing, that seems to be reasonable path to pursue.

To expand on an earlier comment, I've taken the car to the dealership, and had them give it a good lookover (underside, exhaust, suspension/wheels are all secure and in remarkable condition for a 20-year old car). After the trans oil replacement (clear, no filings) and axle replacement didn't resolve the issue, we are all frustrated.

The sound could be likened to someone with a rubber mallet banging against the floor, which steers me to a rotted dog-bone bushing.

Another thing I tried to explore was if a hard accel would affect the sound, figuring this would apply torque to the dog-bone and strike the other side of the bushing. I think it helps, however there are limitations to my ability to do a thorough test on city streets.

Thanks to all for their thoughts and suggestions!
KarlC
 

·
Premium Member
Joined
·
546 Posts
I believe one can visually see if the dogbone is bad. I think that if you shift in reverse you should be able to see significant engine movement. Doesn't sound like this could be the source of your sound if the sound occurs if in neutral (no torque being applied).

Check drive axles. Basically have to get the car up and start pulling and pushing on stuff.

Might be the down pipe, bad brackets.
 

·
Registered
2000 Golf TDI ALH
Joined
·
36 Posts
Discussion Starter #8
An update on the dog-bone... One of the bolt heads snapped off, and after 2 weeks of penetrating oil, it came loose with heat from a propane torch. Unfortunately, replacing the dog-bone did not help the thumping sound. At $50 for parts, it wasn't as expensive as some snipe hunts.

I will have to get the car up on the ramps again, and as UhOh suggests, start pushing on things. My next theory is the exhaust system. I do know that the back half of the exhaust is sagging at the muffler. I also believe I have an exhaust leak somewhere. Exhaust system issues can transmit from the rear to the front, due to the rigidity of a long tube.

I appreciate the comments and suggestions. KarlC
 
1 - 8 of 8 Posts
Top