Heavy pulsing when brake pedal applied!

[timhypo]

What would cause this? I recently put my 240z back on the road after sitting dormant for 20+ years and stepping on the brakes yields a heavy pulsation from what seems to be the rear end, but it's really hard to say for sure. I've checked the usual brakes and bearings with nothing of note. The pads, calipers, shoes, and pads are all new. The rear tires are new. I'm kinda suspicious of a flat spot on the front tires from sitting, but I'd think I'd feel that all the time, not just when brakes are applied. I wish I had a tow truck so I could test it with the front end in the air and know for sure it's the back...

[Mikes Z car]

I wonder if the bottom of the inside of the drums got rusted from mositure collecting at the bottom from being in one spot and the shoes are grabbing more there than the rest of the drum as the wheel turns?

[Bruce Palmer]

Warpage would be my guess. Rotor or drum. Have a clean up cut done on them and see what you've got then. Back in the old days a lot of parts houses had brake lathes in house and would do this nominally....

[timhypo]

I actually had the rotors turned prior to installing them, but not the drums. I have an extra set of drums, though, so I'll run em up to the auto parts store and see if they can turn em for me...

[Inf]

Warpage would be my guess. Rotor or drum. Have a clean up cut done on them and see what you've got then. Back in the old days a lot of parts houses had brake lathes in house and would do this nominally....

I was told recently at the local AutoZone that almost no parts store in our county (probably pushing 1 million people) still turns rotors/drums. Something about liability, although I haven't looked into it beyond what I was told.

Edited August 17, 2010 by Inf
typo

[timhypo]

I could also just try to swap in my other pair of rotors. If it really comes down to it, I know a guy who runs a motorcycle shop who has a couple a mills and lathes. Hell, I'm might just pull em and check their roundness myself using a micrometer and see if I can sand them round...

[hogie]

Oddly enough most of the Oreilly's Auto parts can turn your rotors for you.

[geezer]

I could also just try to swap in my other pair of rotors. If it really comes down to it, I know a guy who runs a motorcycle shop who has a couple a mills and lathes. Hell, I'm might just pull em and check their roundness myself using a micrometer and see if I can sand them round...

I would do like previously suggested and have them checked for warpage and also cracks. Just use that yellow book, get on the phone and see who can do this for you. Sanding them will likely increase the amount of runout.

[timhypo]

I was thinking more of creating a uniform surface than resurfacing...

[timhypo]

Warpage would be my guess. Rotor or drum. Have a clean up cut done on them and see what you've got then. Back in the old days a lot of parts houses had brake lathes in house and would do this nominally....

BINGO! Today I pulled the driver-side front wheel to retorque the wheel bearing nut and discovered that the rotor will turn about 90% of the way then grinds to a halt, being almost impossible to turn further, and makes the same sound my truck does when it's time to change the pads. I didn't get a chance to remove the caliper today - it was getting dark quickly - but I will tomorrow just to rule out the possibility of it being the wheel-bearing. Thanks, Bruce!

[timhypo]

BTW - a straightedge on the face of the rotor didn't reveal any obvious warpage. Is it possible to have it or the caliper on crooked? I've heard that a rotor being warped even a few thousadths can cause these kind of issues and I certainly wouldn't have detected that with a straightedge and my naked eyeball...