so recently my car has been acting up as i brake, but it doesnt happen all the time, at times regardless of how much brake pressure i apply my car seems to shake uncontrollably, i quickly let go and reapply pressure and it brakes fine. i've checked my rotors, calibers and pads and they are all fine,

so im thinking it must have to do with the rear drum brakes. it doesnt do it all the time, like last night i was slowly applying pressure and i felt as if was going to act up again if i applied more pressure but i just slighty eased off but still continued to brake and then it felt fine after about a sec. or two,

anyone have an idea of what it could be?

 

Brake lines. They break down internally and act as one-way check valves.

JamesC

 

how so?

 

IIRC, the rubber inside breaks down and blocks the fluid from returning leaving the caliper clamped against the rotor. Pitted calipers and also un-lubricated sliders can do something similar as well.

 

Check your ball joints too. That happened to me a while back and it was a ball joint that was about to break. It was causing the wheel to wobble an shake the car pretty good.

 

If your rotors are too thin (been turned too many times), your thermal capacitance is down. This means your first apply will have significant thermal transfer that a second apply will not see. I have also seen worn out brake pads do similar. I would verify you don't have a blown axle seal in the rear...this will cause chatter on apply and could change character on the second apply. This can be an issue at high speed for some cars....in this case, the driver will "tap" the brakes, then reapply to brake. This will reduce the likelihood of shutter.