Weird sound only when off throttle, driveline, brakes?

I have no clue what this is, any help is appreciated!

Since a little while, my jeep makes a weird sound that is perhaps best described as rubbing sound with a frequency that depends on the speed (wheel rotation), not the revving of the engine. It is only there when I take my foot off the throttle and the car is rolling without power on the driveline. It will do it at every speed (frequency depends on wheel rotation), and will do it worse when car is heavily loaded. But only if my foot is off the throttle. When under power, everything is fine. Also, I noticed (but I am not 100% positive), if I break hard, the sound is gone.

To isolate the sound I jacked up the rear end put in D, made the wheels spin and took foot of throttle. There was no sound whatsoever. Everything was nice and smooth.

I felt for play on wheels, driveshaft etc, but could find nothing obvious.

About two weeks before I started hearing this noise I had done a rear break job (new shoes, springs, and resurfacing drums). Normally if something develops so recently after work on the jeep, I am suspect of my work. However, in this case I cannot understand how this could have anything to do with the breaks (what would the breaks care if the throttle is on or off? why would it get worse if the car is heavily loaded?).

Like I said, I am pretty clueless what this might be. Any suggestion very welcome!

Tim

could be something inthe driveline, but my money is on the BRAKES.

have you taken the drums off and checked to be sure nothing has come loose?

I can picture a shoe shifted over towards the rear that centers itself when you accelerate, drags when you let off gas.

My first thought was also the brakes but I just could not imagine anything in the brakes responding to throttle on/off like that. If you think it certainly can (shoe centering itself under acceleration, something I had not considered), then the brakes do seem a logical place (and easy too). I'll pull them off tomorrow to see if that's where it is. Fingers crossed!

Thanks for the input!

Tim

I am certain it is something in the driveline,... the coast side of the diff perhaps.

Check and or renew the fluid in the diff and the TC. Inspect for unusaul wear.

More info on your XJ will be good.

While the brakes are open, check for play in the rear wheel bearings.

Give us specs on your XJ....I see it's a 92, but is it lifted? How much? SYE? TC drop?

Sometimes we don't always best describe noises we hear....could it be vibrations in your rear driveshaft? Before I had my SYE, it only made the noise while NOT accelerating...just in coasting until I was above 60-65 and then it would have a constant noise from vibes. Just a thought...

Oh Oh, this will get embarrassing...

Ok, so after all my contemplations (which had lead me nowhere), I decided take your advice and just first check the brakes. Guess what...I had not tighten the lug nuts!! I had tightened them while on the jack, but had not pulled them tight with the wheels on the floor. Normally I always double check, but since I have never forgot this before, I had somehow even stopped checking on it.

Tightened nuts, testdrive, all is well!

Now it all makes sense.

1) it didn't start right after the break job --> lug nuts needed to loosen up because of vibrations

2) More noise when heavily loaded.

3) Noise depending on wheel rotation.

4) No sound when on jack

etc..

Lesson learned:

If something starts making noise after you worked on the car, it is most likely that what you worked on...even if it doesn't make any sense.

Guys, sorry to expose myself like this. Thanks for your input and thinking along. Will do better next time!

Hey man we all have :doh: moments...just make sure to learn from them!

I once had a WHEEL fall off while driving down the road. Yup...a wheel. There was some miscommunication between my friend and I and the rear drivers side lugnuts were not tightened so when we set the vehicle down and test drove it we got about 1/4 down the road and it started to wobble in the back and then all the sudden the bottom drops out and I look to my left and see my tire go flying by me. Being passed by your own tire = no bueno. Luckily no damage was done. I now triple check my lugnuts!