Noticed this when i still had my brembos, works perfectly fine under normal circumstances, but while at the track braking after a long straight usually around 100+mph down to 20-40mph, the brake and steering wheel vibrate. Recently installed a front bbk, and its still doing the same thing. Is that the abs or is one of my bushings going out? I have already replaced the lower arm bushings with urethane, but still on the stock compression rod bushing. Ive had warped rotors before and usually it will shake under any braking, so im pretty sure its not that. Still using street pads so i dont think its over braking yet. But hoping someone experienced the same problem and can help me pin point me in the right direction, thanks.

 

prob lca... bushings... and/or wheel bearings.

bbk really exacerbates the exact symptoms you describe.

how many miles w/o lca replaced? any play whatsoever in front
wheel when you're on a lift?

 

I was going to say warped rotors but ... might be bad bearings or bushings. A faulty wheel speed sensor may also cause your ABS to malfunction.

 

replacing the lca made my front end feel like the hand of god.

 

Was going to say warped rotors as well but i'm assumin you got some nice rotors on there with the BBK. Prolly kinda hard for those things to warp....
Did you buy the setup used or new?

 

what kind did you get?

 

just oem...

 

only about 1-2k miles since lca bushings were replaced with whitelines, bbk was brand new before my last track event, about 500 miles on them now. was thinking it might be the wheel bearing but no play on the wheels when in the air.

never thought about the speed sensor, will look into those thanks

also going to try alignment again, did put a wheel off and bent the wheel at my second to last track event

 

just like everyone else I would have gone with warped brake rotors too but with a new bbk doesn't seem likely.

how many miles on the car total (and consequently suspension). when was the last time the alignment was checked?

 

compression rod bushings could very well be torn (and/or bad compression arm ball joint), as well as bad wheel bearings, torn outer ball joints

 

everyone gave the answers needed, lca,bearings,compression rod/ball joints, warped rotors.

 

I would say "uneven pad deposit" rather than warped rotors though. Especially if the brakes werent bedded in after the installation. I've tracked my rotors real hard and never did they warp. IMO it's a very rare case esp. when we use the premium brands

Good luck solving the issue man.

 

Check the run-out on the rotors.......

 

2 separate brake kits doing the exact same thing on the same car, with one brake kit being brand new, sorta rules this out as a possibility

 

Correct, but he still makes a valid point about pad deposit vs rotor warping. This is VERY unlikely to be the problem in this case, as Z1 pointed out, but the fact still stands that rotors rarely warp. It's generally uneven deposits on the rotor.

Anyway, back to the OP...

I'd start by inspecting the LCA bushings as everyone else mentioned. It's not uncommon for them to go out on the Z, and they'll do exactly what you're describing. If they look good, move on to the rest of the suggestions here. Heck, even if they're good, at least inspect all other bushings. 1 bad bushing will strain the remaining bushings. If the budget allows, look into an Energy Suspension HyperFlex Kit since you track the car.

 

Also remove the rotor and check run-out on the hub surface itself.

When i bought my car with 42k miles on it i didn't hit the brakes at high enough speed to find the hard braking shudder.

Long story short i had runout on the hub that caused outer rotor surface runout. I replaced the hub, got zero runout on the rotor outer surface but still had the shutter. Flipped the rotor around backwards and found 30X the max allowable runout on the in board surface of the rotor.

 

but his brake kit is brand new - there shouldn't be runout on a brand new BBK unless it's got a major defect

 

so obv what i stated. brakes are fine.