Brake/driveline noise identification?
Just picked up my '98 TJ a couple months ago. Was in solid shape overall, ended up needing a new clutch (existing master/slave set up proved to be okay) and brakes at all four corners. The brake job involved new rotors and pads up front, new drums and shoes in back.
For about a week after the brake job, all was a-okay. Then I began hearing a noise very similar to one I'd heard prior to the brake replacement: a sort of grinding/clacking noise, the frequency of which is directly proportional to the speed the Jeep's moving when I step on the brakes. In other words the time between instances of the noise is greater the slower the speed. Also, the noise occurs ONLY when I brake--no noise whatsoever when the brakes aren't engaged, regardless of whether I'm coasting in neutral or am in gear. On occasion, the noise disappears entirely for a while. Last time I noticed that was on a 20-mile trip on the highway, and once off the highway driving on secondary streets was surprised not to hear the noise at all. But the next day when I drove the Jeep, the noise had returned.
The guy who did the brake job put the Jeep on his lift and suggested that the noise is actually the result of a front differential that needs a rebuild. As evidence, he twisted the transaxle leading to the front diff and rotated it back and forth, pointing out that it had a slight amount of "play" and that that was the source of the noise. He also removed the filler plug and pointed out that there are some fine metal shavings stuck to it.
I'm fairly mechanically inclined but no pro, and I've only used this mechanic for the clutch- and brake jobs. He seems trustworthy, but one can never be sure. I know with certainty that the new brake components were installed, as I bought them at a Pep Boys with the mechanic right there, and saw all the old parts when the job was completed.
So I paid a visit to another mechanic who does a lot of work on Jeeps and he suggested that perhaps the guy who did the brake job didn't properly install the brake pads. Possibly not installing some type of retaining clip properly, which could result in the pad in question moving around a bit when braking, as opposed to being locked firmly into place. The second mechanic is happy to put the Jeep on a lift and check it out, for $75.
Now $75 isn't bad, but I don't know this second mechanic either, and it's possible he could suggest a repair that really isn't needed.
One other piece of info: thinking that if the problem actually is with the front differential, it might go away or sound different when in 4H, so just yesterday I drove a bit in 4H but the sound was exactly the same as when in 2WD (again, only when braking).
I think I've included all the relevant backstory. Pardon the length of the post, but I'd be grateful for some feedback.