couple brake issues

[hahmeta]

alright guys number of different (i think) brake issues has crossed the threshold to solicit your opinions.

i'll go in chronological order with the first problem being the first i noticed.

Problem 1: with constant pressure on the brake, say slowing down from highway speeds to 10-20 mph, at some point i can clearly start feeling the car rocking (shaking back and forth periodically and correlated with speed). basically when i'm braking, 50% of the time it's not stopping as hard as it should. this is irrespective of how hard i press the pedal.
Possible root cause: pretty sure it's warped rotors. any other ideas?

Problem 2: If I'm going very slow, < 10mph, next to a wall or a car (basically something to reflect my car's noise back to me), occasionally I can hear periodic squeaking from rear brakes. it's again correlated with my speed and once I'm above 10 mph I can't hear it anymore.
Possible root cause: warped rotors again??? i think this is related to #1.

Problem 3: i noticed this very recently. after the car has been sitting for a while (long enough for it to cool down), i start moving and for the first three times (i countd several times) i hit the brake pedal, i hear a clanking sound which feels like it's coming from the rear or underside of the car on driver side. it sounds like something gets stuck once parts cool down and it releases as i apply the brakes.
Possible root cause: no clue...

Problem 4: ABS light on all the time. after replacing all bulbs in my cluster yesterday i saw this for the first time. i read it may be the relay. if the relay is open, does it disable ABS? i dont think abs is working. on several hard braking incidents it didn't engage. but i really didnt test it and braking wasn't hard enough to lock wheels.
Possible root cause: relay?

thanks for the help...
Ahmet

[jlevie]

Neither (1) nor (2) sound like warped rotors to me. (1) sounds like uneven pad deposits on the rotors that cause a variation in friction as the wheels turn. (2) could be a binding caliper.

Hard to say what (3) might be. A through inspection of the rear suspension and brakes seems indicated.

If the ABS light is on, the ABS system is disabled.The cause could be a wheel sensor, the ABS relay, or the ABS pump. Figuring out which is a process of elimination.

[hahmeta]

why would there be uneven pad deposits on the rotors? poor quality parts?

[jlevie]

The only way to get uneven pad deposits on the rotors is by exceeding the Maximum Operating Temperature (MOT) of the pads and then bringing the car to a stop before the pads and rotors have cooled off. One might think that this would only happen in a track/racing situation, but depending on what type of pads are in use it is entirely possible for this to happen in street driving. Low dust pads are notorious for this on the street and in the right conditions it can happen with OE or equivalent pads.

[hahmeta]

thanks for the info Jim. i'm honestly more concerned about problem 3 above. but all of these combined will force me to inspect the brakes sooner than anticipated.

i dont know what kind of pads are on right now. PO didn't really take care of this car. but it's slowly coming together. i hope i dont have to rebuild or anything major like that.