Intermittent juddering from rear, like we have a flat (but we don't) - any ideas?

[AVR2]

Our 2005 Liberty Limited has started occasionally juddering like hell from the rear, as if both rear tyres have blown. It will just happen out of the blue on a straight piece of road; you pull over, get out to have a look, check that both tyres are fine, pull away again - and the juddering has gone. Then, a few miles down the road, it will start again, and the cycle repeats.

I can't see anything obviously wrong at the back (but then I don't really know what I'd be looking for anyway) but one thing I have noticed is a slight smell of burnt rubber. There doesn't seem to be any specific trigger either; it literally happens out of the blue while you're cruising along, so it's not as if it happens on a gear change or when you use the brakes.

Any suggestions, before it goes back to the garage yet again?

 

[offrovering]

have you taken the wheels off and inspected brakes? shouldnt cause the wheels to lock but could be brake related, specially if you are smelling something burnt.

 

[kj924]

Have the u joints checked out, you may have a cap starting to seize.

 

[Greenjeep]

agreed with both the above. I had my axle replaced due to the u-joints with similar symptoms. You can also do a simple check with the brakes by feeling the rotor temperature after you get that vibration. If it's hot (as in feel an excessive amount of heat as compared to the other rotors), you probably have a seized caliper.

 

[AVR2]

Thanks guys. The garage has had the wheels off and says it can't see anything obviously wrong, but I've asked them to check the U-joints.