When I brake from about 15 mph or above, I get a repetitive thunk that is proportional to speed (slows down, seems to be one thunk per wheel rotation). I had recently done a full brake job. I replaced rotors, caliper hardware, and pads front and back and bled the brakes. I reinspected the brake system after the sound started happening. My brakes are fine. I have ruled them out at this point. Calipers seem to move smoothly and the Jeep stops on a dime.

I tested the wheel bearing on both front wheels by trying to rock the wheel (pulling and pushing with hands at 12 and 6 on the wheel with it jacked up). No movement whatsoever. The sound is not really indicative of a bad wheel bearing (as it only happens during high torque when braking) and I don't have any extra noise when driving.

I am thinking now that it might be the CV axle on the left side. It seems to me that it would have to be related to the rotation of the wheel for it to slow down and match the rotation of the wheel in regularity.

I did notice my upper ball joint rubber was looking ratty. But if that ball joint had gone bad, the Jeep would handle poorly and pull or otherwise have alignment problems. Also, a ball joint is not going to make a thunk thunk noise when braking proportional to the rotational speed.

I had even suspected my brake master cylinder was defective, and it indeed does need to be replaced eventually, as if I really push hard down on the pedal it will eventually go to the floor (takes a while). My brake pedal is pretty firm, but not hard (like a brake booster issue would indicate). So I will eventually replace the brake master cylinder, as the inner o rings are indeed leaking slightly, but given the symptom, I cannot imagine a way that the master cylinder issue would relate to a thunk sound that matches wheel rotation.

I have combed the web looking into this issue. I have not seen a consensus. The sound does appear to be left side biased, and does seem to come from the front, does not seem to be getting worse, and if I brake gradually I cannot hear it at all. It only seems to occur when braking hard, like when decelerating to a stop light from moderate speeds.

2003 Jeep Liberty Limited, 4x4, v6.

Sounds crazy but I had the same type of noise seemed like it is was in the front.Turned out it was the rear drive shaft u joint.Easy to check.

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2003 KJ Renegade, 5 speed, frankenlifted,Al's a Arms 4.5,Moabs 245/75/16 BFG KM2's, custom rock rails, full Mopar skids, Hella ff220 lights,Hd cooling,Front DTT,Riddler diff cover,Rola safari rack,Cobra 29 peaked & tuned.

Pastafari Alum, Pink shovel recipient

disasemble the ft brakes check the pad clips, lube movement surfaces and remove rust from rotors , reassemble and see if sound persists

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03 Renegade (Black)
177k miles 3.7L gas - 45RFE
Command Trac / 4.10s
Lift: ft. 790+ rr. JBA4+
The last of the TrailReady Front&Rear Bumpers and TR Rock Rails
Jarhead Offroad light covers
31x10.5R15 RedLetter Grabbers on Blackrock Dunes
L.O.S.T #KD098632

I reassembled the brake system. No issue there. It is unrelated to the brakes, which are perfect.

Update: The jeep is indeed in the shop now. I noticed that after shifting it from 2wd to 4x4 and back the sound changed. It went from being as sharp to being more smooth and muffled. I figured it was related to the use-it-or-loose-it issue with 4x4's. But upon shifting the lever a few more times, the darn connector snapped, and the vehicle is now stuck in neutral. The shifter was originally very stiff and hard to move. Now it moves freely with no resistance whatsoever. The main drive selector grinds in park, and the vehicle drifts backwards (downhill) in park, indicating it is stuck in neutral.

I will know for sure what the issue is later today, as I dropped it off at the shop last night. Perhaps the thunking was related to the front transfer case. I had pretty much decided it was an issue with the left front CV driveshaft prior to the vehicle completely breaking down yesterday.