Front Brake Thump

On my 00 XJ I've noticed that after about an hour of driving, I'll get this rather loud thump along with a metallic tap coming from the right front end (the metallic tap only heard when the window is down) This only occurs at slow speeds and goes away when the brake pedal is depressed. You can hear it with every tire rotation and even feel it through the floor. This sound also occurs when I hit a bump.

The brake even feels a little different when it's making the thumping noise. It seems like I can feel the pads grab or slip on the rotors or the calipers aren't quite engaging correctly.

The strange thing is that the thumping will eventually go away in a about 5-10 minutes and then the noise is only heard when I hit a bump. I've had two guys look at it and they can't find anything wrong. The sucker is hard to diagnose because the thumping only occurs during such a small window of time. A friend said the anti-rattle clips for the pads were tossed out during the last brake install but another guy said the clips were still there and can't easily be removed. What the...? My friend said he would help me install these clips but he's pretty busy and ....forgetful. When he looked at it, he slapped the "caliper assembly" from the back side and it made that same metallic tap sound. I'd do it myself but I'm not sure what to look for.

It seems to me that the calipers might be getting a little play at just the right temperature and causing the brake pads to grab the rotors at a high spot. When the temp continues to change the grabbing stops because the pads are at a different distance from the rotors. Does this sound like the most logical thing that's going on?

Anyway, I'm just trying to see if anyone has had something like this happen before and whether or not it's something I should worry about. Or could it be something else that's causing the noise other than the brakes?

Greg

pull the wheel off and just do a visual inspection of the pads/rotors. also check the torque on the caliper bolts i think the torque is 8-15 ft/lbs. the bolts on mine are brass and break at a certain torque load so don't overtighten.

I believe we checked the pads, rotors, and torque. Thanks though.

Have you checked your hub assembly? Just jack up the front right tire, grab it at 12 o'clock and 6 o'clock and try to move it around. If the hub is bad, you will definitely have some movement.

The reason I'm suggesting the hub is that you say the noise goes away when you step on the brake.

I think we checked the hub assembly but I'll double check. Will the movement be in an out or side to side?

If I remember right, there was some movement when you slapped the caliper with your hand, maybe a millimeter or so...the brakeshoe tab would hit the top ledge creating that tapping sound I heard from inside the cab. Is that normal to have that much movement?

"brakeshoe tab hitting the top ledge"...the two notches at the end of each brake pad should be riding along the edge of your steering knuckle. There shouldn't be too much play there unless you've worn a significant grove in the knuckle. One mm sounds okay though I'd think.

-Chuck

Took a closer look at it today right when it started making that thumping noise. I immediately pulled over, jacked it up and spinned the tire...nuthin. Sounded totally normal. The hub assembly seems okay, I couldn't find any play. I pulled the tire and the caliper bolts are tight.

I did notice that one of the top brake shoe tabs, the one on the outside, wasn't flush with the top edge of the knuckle (1-2 mm gap). The other three tabs were flush.

After I slapped the tire back on, the thumping was gone. Maybe it cooled off enough or perhaps my messing around the caliper put it back in it's normal place...who knows...very frustrating. Not sure if it's something I should worry about or not.

My '98 XJ does the same thing...from time to time. Nothing loose here and have never identified what the thump is coming from.

viperbaron said:

My '98 XJ does the same thing...from time to time. Nothing loose here and have never identified what the thump is coming from.

Click to expand...

That makes me feel a little better about it. I can almost set my watch to when it starts thumping and when it stops. I'll be driving along thinking to myself, "that thumping noise should be popping up any minute when I slow down" and whaddya know, a couple of minutes later it starts as I'm approaching a stop light or pulling into a parking lot. A few minutes later, it stops for the rest of the trip.