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Loud thud at 55mph and 1500rpm

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Old 12-12-2018, 08:18 AM
Jesseg34's Avatar
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Default Loud thud at 55mph and 1500rpm

Hi all,

I recently bought a 2003 blazer with 103k miles. I’ve been driving it for about the last month and yesterday noticed an interesting issues. When staying at a constant speed of 55mph at 1500 rpms I feel random loud thuds almost like someone rear ended me slightly. The rpms do not change when this occurs and no loss of power felt. It happened 5 times during my 8 mile freeway commute. It’s a similar feeling to when my rear diff would thud upon coming to a stop in my previous car.

The car shifts fine and the only way I have found to replicate the problem is getting up to 55mph at 1500rpm.

Any pointers here would be greatly appreciated!
 
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Old 12-12-2018, 01:48 PM
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Originally Posted by Jesseg34
Hi all,

I recently bought a 2003 blazer with 103k miles. I’ve been driving it for about the last month and yesterday noticed an interesting issues. When staying at a constant speed of 55mph at 1500 rpms I feel random loud thuds almost like someone rear ended me slightly. The rpms do not change when this occurs and no loss of power felt. It happened 5 times during my 8 mile freeway commute. It’s a similar feeling to when my rear diff would thud upon coming to a stop in my previous car.

The car shifts fine and the only way I have found to replicate the problem is getting up to 55mph at 1500rpm.

Any pointers here would be greatly appreciated!
If only you had a loss of power...... then lots of ideas. But if rpms don't change and no loss in power felt, it is a strange one.

I had such an occasional hiccup in my giddy-up like you described for several months a couple of years ago at 55mph steady speed with TCC locked in, but I could see it my tach bounce a bit when it happened. Mine ended up with 3-4 clutches shredded on a 200 mile trip. Had trans fixed - hasn't done it since. Don't know about yours - or even if it could be same problem. Does it get worse the longer that you drive it?
 
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