J30 intermittent "thunk" noise under compression (hard breaking)?

[kmotonishi]

My mom's 93 J30 has such a noise under hard breaking. Under normal breaking no such sound is heard. My first thought is warped rotors. Then I noticed it would make the sound occasionally while going over a speed bump. I have not turned the rotors but I did inspect the entire caliper, front suspension for any loose bolts, etc. The noise is inconsistent enough that I started thinking of other things such as bad bushings, etc. The sound and feel is almost as if the subframe feels like it moves a little. Does anyone with any J30 (or not) have any recommendations? While I had the tires off I should have just gotten the rotors turned. I pulled off the caliper and couldn't get the rotor off. I didn't notice any screws holding it on and I tapped it lightly with a hammer to see if it'd loosen up but it did not. Is there a screw or bolt that I've missed or should the caliper be able to be tapped off? I also noticed that the diaganol front link bushings ( connects the front lower A-arms to the subframe) appeared to be old, fatigued and noticed some slight liquid around it. Are these bushings prone to wear and are they filled with liquid? I had a local mechanic look at this part and he told me he didn't think this bushing as the root of the problem. What about upper strut bushings? Are these prone to go?

Any recommendations??

Ken

[NISTECH]

those front strut bushing your talking about are liquid filled. have some one watch your front wheel while you drive the car forward at less then 5 mph. hit the brake hard to bring the car to an abrupt stop imediately when the car comes to a stop release the brake. ask that person if the seen the wheel move back then forward as soon as you released the brake. if it does it will also make a harsh knock when you hit the brakes then another more faint knock upon release of the brake. is this your noise?

[kmotonishi]

NISTECH

Unfortunately I'm not home right now to be able to observe what you recommended about the tire moving after letting off the brakes; however, as far as I can remember there is only one sound it makes. And that is when stabbing the brakes hard. It almost feels as if the subframe is making the clunking noise. About the removal of the brake disc. Should it just come off after removing the caliper? It seemed like it was really glued on there. Should I just tap it with a rubber mallet until it jars itself loose?

Ken

[NISTECH]

yeah they are floating rotors , sorry didnt cover that on my previous post. once you have the caliper and pad carrier off you can either knock it of with a plastic head hammer or a large rubber mallet. it should also have 2 threaded holes on it for useing screws to push it off as well. either way works. just dont use a steel hammer to beat it off it will screw up the rotors.

like i said about the noise the secondary knock is very faint. and is heard upon imediate release once the car comes to a complete stop. if you dont release the pedal imediately the car will settle gently and not even make the secondary knock.

[kmotonishi]

Thanks for the tips. I'll try and figure out the problem.

Ken