I have a thumping feel in what feels like it is.

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I have a thumping feel in what feels like it is up front but cant really pin point it. It happens only under acceleration and starts around 35 and is the worst the faster I go. I believe is is a speed related issue and not rpm because it doesn't matter what gear I am in. Its only when it is under load, if I stay on the gas but press the clutch, it stops. If I let off the gas to coast, it stops. So it is only under load accelerating and starts around 35. There is no vibration in the steering and no noise when turning. Just a thump feel in the front end and slight thump sound. I have just replaced the motor mounts with no success. I have double checked and torqued down the subframe. I checked all the CV joints and the boots are in great shape. Tires spin nicely with no feel of binding and no noise spinning or when i'm turning. I am lost, not sure if its the tires, wheel bearings or cv joint with no signs they are bad except a thumping feel that almost seems like the tires are flat or something.
Monday, January 7th, 2013 AT 11:50 PM

1 Reply

Given that you've already checked the most likely causes, I'd have the tires checked for a broken belt. Normally you'll feel that in the steering wheel as you eluded to, but there is more to the story and I was tricked a few times. The bulge in the tread can be so slight and occur over such a long period of time that it wears down. Most mechanics perform a quick inspection where they spin each tire and look for irregularities in the tread surface. You need to look at the carcass, meaning the bottoms of the grooves in the tread. As you spin the tire you will see little bumps in those grooves. Those are the wear bars that will show up when the tread is worn out, and they can be ignored during this inspection. If a belt is broken you'll see a more significant bump as you spin the tire.

Inner cv joints can also cause a wobble under acceleration but you'll feel that in the steering wheel. AND, that usually goes away by around 30 to 40 mph.

If you can't see anything with the tires, switch the two right ones, then drive it to see if the symptoms change. If they do, inspect the right rear one. If they don't, switch the two left tires and try it again.
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Tuesday, January 8th, 2013 AT 1:15 AM

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