Shaking while braking??!

['97boostinGST]

Just changed the pads on all four wheels (ceramic) thinking it would fix the problem but it didnt. Every time I slowly brake at 30+mph the entire cars starts shaking like crazy. I didnt resurface the rotors since they still feel smooth and i do need new mounts.
Also all my suspension is stock.
Anyone have some ideas?
Thanks.

 

[blkgst97]

ROTORS. You won't feel by hand that they are warped.

 

[constant_proj21]

Rotors are warped, go out and get yourself a new set.

 

[BoostedinSoFla]

Warped rotors my dude...

 

['97boostinGST]

Damn.
Just my luck. Would a good resurface do the job??
I really dont want to buy new rotors.

 

[blkgst97]

Depends on how worn down they are. If the the rotors are close to discard spec you should just get new ones anyway. The thinner they are the easier they are to heat up and warp again. Take them in and they will mic them before turning and let you know if they are good or not.

 

['97boostinGST]

Cool beans.
Thanks blk.

 

[constant_proj21]

A set of economy rotors cost around $20 a piece, just get a new set.

 

[bjones18]

Actually, there is one dimension that causes "brake roughness," or "shudder." Many say it is warped rotors. Rotors do not warp. From the factory rotors have run-out and thickness variation. Run-out can be thought of as a warp or potato-chip shape, however it is the thickness variation that causes roughness.

You need new rotors to fix your issue. The equipment at all shops pails in comparison to OEM equipment for machining rotors... Why? Warranty for brake roughness has been HUGE. OEMs have spent hundreds of millions resolving brake-roughness. Straddle-cut is the only way to machine rotors.

Essentially run-out from bearings, un-even wheel clamping, and rotor machining - combined TIR (total indicated run-out) causes the rotor to spin around like a potato-chip. This results in the rotor kissing the pad every revolution as you drive down the highway. This "kissing" wears a thin spot(s) on the rotor less than a human-hair. During braking, this thickness variation generates less torque than the thick spots as it passes between your pads. Soooo... during braking the thick spots generate brake torque (and heat), whereas the thin spots generate less torque and less heat. The hot spots expand more, and generate even more heat (greater thickness variation).

The other side of the equation is the suspension, body, and steering column. If a combination of these have natural frequencies that are set off by the torque variation the car is a basket-case and a warranty loser for the OEM.

Very soft, squishy pads, flexible calipers, or expanding brake lines tone the issue down, but are bad ideas for a good brake system.

Very tight tolerances on bearings, rotors, and agressive linings (micro-machining on every stop) are the resolution.

Floating calipers take up side-to-side motion, so run-out (or so-called warping) dose not create torque variation, nor roughness... but it does lead to wearing thin spots, or thickness variations (TV).

The other cause of brake roughness is "lot rot" Where the rotor rusts (except under the pads) after sitting in a wet/humid environment. The different coefficient of friction rusted vs shiny causes a torque variation during braking. This is usually resolved with a few good braking events.

 

[Guzman08]

^^^^^ copy and paste??

 

[jeyventura]

^^^^^ copy and paste??

i think soo i was reading half way down and didn't finish

 

[Lavery]

If your steering wheel shakes too then its your front rotors. If it doesn't then its probably your rear rotors. Might as well change all four though. He probably already bought them though.

 

['97boostinGST]

, nah i havent bought em.
The shop quoted me $15 per rotor.