[GV27]

Hi all,

I have a brake issue that seems like pad knock-off to me, but there are no other indications of a warped rotor so I was wondering what else could cause this symptom.

What I'm getting is a low brake pedal when coming to a stop. Brakes are still strong and pedal feel is quite firm. A second "pump" brings the pedal back up high. I don't think it's a master cylinder issue as I can sit there and hold the pedal down hard and it doesn't move towards the floor. Stays nice and solid. Also, when the car is stationary, I can't reproduce the problem. That is, I suppose if I coasted to a stop then applied the brake, it would still be low. But if I come to a stop with the brake, sit there with the brake off and then apply it again it's nice and high.

So it seems like it could be that the pads are getting knocked back by the rotor. But I don't get any sort of shuddering coming to a stop from high speeds (any speed for that matter) and the symptom will show itself even if I drive a short distance at slow speed - when I've experienced knock-off and had it described to me it's always at the end of a long, fast straight that you have an issue.

I suppose I should take a dial indicator to the rotors and check their run-out, but can anyone think of other issues that might cause a similar symptom?

Thanks,

Chris

 

[Alfa Seltzer]

I'd give all the wheels a good shake.

 

[John M]

Perhaps the soft hoses are bulging...or some air in the system.

Best Regards,
John M

 

[ghnl]

Or loose/worn wheel bearings that are allowing the hub/rotor to move and push the pads back.

 

[GV27]

Seltzer - looking for loose wheel bearings and whatnot? Good idea. Yeah, Eric had the same.

Don't think it's that, John. Pedal is nice and firm, just starts out a bit low.

 

[spiderserie4]

servo problem, leaking? - let it tick over then remove the vacuum pipe from the servo to the inlet manifold, see if there is pressure in it.
Air in system would be my second guess, as we are talking about a low pedal which tightens up and stays higher, after you pump it.

 

[papajam]

Classic symptom of piston knock back. Common causes for this; warped or out-of-parallel rotors and, as Eric said, loose wheel bearings. Not so common is excessive caliper piston seal stiction.

 

[GV27]

That's what I was thinking, Jim.

I think if they were warped I'd get vibration. Can't see how they'd get out-of-parallel without being replaced/disassembled but I can see loose wheel bearings being it and haven't checked that.

edit: spiderserie4 - it doesn't tighten up and get higher, just gets higher. It's solid initially - it'll lock 'em up if you jump on them - just low.

C

 

[GV27]

Wheel bearings it is. Thanks guys!