Thumping noise in rear

[tyleemary]

For a year now, I have put up with this 'thumping' in the rear of my 2000 astro. It speeds up and slows with the veh. speed.
I ONLY hear it when I am coasting with my foot OFF the gas.
When I accelerate, the noise is not apparent. It is quite annoying.
I have no clunking when it shifts gears or "slipping" of any kind.
Just the thumping noise.

Any ideas??

[tableman]

Chances are one of your rear tires are out of round or a cord has let go inside the construction of the tire. If you have someone that can put the van up on a jack properly, jack the van up on one side and put the van transmission in neutral and then spin the tire. Watch for two things, watch the tread as it goes around if a cord has let go you will notice the tread pattern is not the same all the way around. Next set something like a block of wood close the spinning tire, if tire is out of round you will notice the tire tread will move close to then away from the block of wood as the tire spins. Also feel for any irregularities in the side wall as the tire goes around. Repeat for the other side. If you find nothing, have a brake shop check you rear brake pads.
Hope this helps, let us know.

[tyleemary]

Originally Posted by tableman

Chances are one of your rear tires are out of round or a cord has let go inside the construction of the tire. If you have someone that can put the van up on a jack properly, jack the van up on one side and put the van transmission in neutral and then spin the tire. Watch for two things, watch the tread as it goes around if a cord has let go you will notice the tread pattern is not the same all the way around. Next set something like a block of wood close the spinning tire, if tire is out of round you will notice the tire tread will move close to then away from the block of wood as the tire spins. Also feel for any irregularities in the side wall as the tire goes around. Repeat for the other side. If you find nothing, have a brake shop check you rear brake pads.
Hope this helps, let us know.

__________________________________________________ _______

I replaced all 4 tires a few months ago. No change in noise. The thumping does not change it's "pitch" or rythym when applying the brakes.
It only goes away when you get on the gas.
I thought it had something to do with the pitching of the driveshaft when I accelerate??

Thanks for reply.

[tableman]

Well I guess you can rule out tires then, Next thing I would try is put the rear of the van up on jack stands, start the van and put it in drive and let the rear wheels spin at idle speed and then walk around and see if you can figure out where the thumping is coming from. You probably don't hear it as you speed up because the frequency of the thump becomes fast then you can hear. If someone is sitting in the back seats, can they feel the thump as you drive?

[tableman]

How about your rear wheel bearings, they could be shot.
Or if you stand on the drive side at the rear of the van and push the van so it starts to rock side to side, do you hear any thumping noises.
I just remembered a friend of mine with a rear drive Olds, when his differential was going, you could shake the rear of the car and produce a thump thump noise.