Vibration when braking

[pghjoe]

Car is vibrating (shaking) when braking. Would this be caused by a bad pad or rotor or something?
Thanks

[spmcco]

Usually warped or excessively pitted rotors will cause this. They can be machined. Up to .040" on the front and .010" on the rear. Cheaper than buying new ones. Best to replace the pads at the same time. I can get the exact specs for the rotors if you need them.

[darksky47]

I just replace the pads and rotors on both sides with four new tires and had tie rods /idler arm replaced and it still shaking very bad i dont know what it is sorry.

[frmg0014]

My car's steering wheel and shifter used to shake when braking from 60mph. I replaced all 4 rotors and it is now fine.

[elvin315]

Is the shaking felt through the brake pedal or the steering wheel? Brake pedal.....warped discs. Steering wheel.....worn lower control arm bushings. Specifically the Rear/Verticals. Opel designed these bushings to aid stability during braking. Here is the GM description of the front lower control arm bushings from the Catera Factory Service Manuals.

"Lower Control Arm Bushings: This vehicle utilizes silicone-filled hydro-bushings in the front lower control arms. This specially calibrated bushing improves control while braking by causing a precalibrated level of toe-in to occur at the relevant wheel under heavy braking. This independent toe angle change at each wheel improves control when braking with split-road friction conditions (dry pavement one side and ice on the other). The hydro-bushings also limit the impact of road input and/or tire imbalance."

They're referring to the Rear/Vertical bushing. I've been told that if this bushing splits open and loses its silicone filling the wheel will shudder during braking. It will also cause the car to drift toward the offending side. Alignment will not fix this. Nor will wheel balancing. Only replacing the bushing will. Of course, chances are that all the bushings will be in similar condition so I'd change them all. The Front/Verticals aren't silicone filled but the still tear and split. Want more proof? Read what I found on a BMW site regarding their bushings.

"Front End Shimmy? Check the upper control arm bushings. A common problem on the 5,6, and 7 series cars is front end shake or shimmy. This shake is usually speed sensitive and may be amplified under braking (although the brake pedal itself does not pulse, as with warped rotors). The most common culprit is the upper control arm (or thrust arm) bushings. These rubber bushings have the thankless task of absorbing all of the rearward push or torque loading of the front suspension (and the full weight of the vehicle under braking). Is it any wonder they give up the task after a few years of driving? Replacing these bushings will typically cure the front-end shake."

Read my "Catera Suspension Upgrades" for links to alternatives to GM's standard replacements. These would be for the Front/Horizontal bushings. There are BMW/M5 bushings as well as Polyurethane ones. Poly-bushings are stronger and resist this wear & tear better. Unfortunately there are no alternatives to the GM Rear/Vertical bushings yet. We must still use the GM replacements.

Elvin

[libbysman]

My 97 shook like crazy until my garage told me the pads had been changed by the previous owner without turning the rotors. I had that done and now they are fine. Brian

[darksky47]

Same here beats me to death when i break if you find out what it is please let me know darksky47@cainpro.com
thanks

[AHazzardToAll]

alignment and balancing the tires is always a good idea too. =/

[dkinder]

One other thing to keep in mind is that many people mistake shaking to be a warped rotor when in reality it was caused by the brake pad leaving a "residue" on the rotor itself, causing a raised area that comes through as a shimmy or shake (exactly the same feel as if it were a warped rotor). I see this time and time again at the track, people come in stating that they've warped their rotors when what has actually happened is their street pads have gotten so hot that pad material has literally melted off of the pad and then as soon as it comes in contact with air again and cools it affixes itself to the rotor.

The moral of the story here is DO NOT save money on cheap brake pads, cheap brake pads are just that, CHEAP. If you ever have to make a panic-stop with them (or ever even fancy a spirited drive on a back country road), chances are you'll end up with what seems to be the "warped rotor" syndrome caused by those crappy pads. You still need to turn the rotor or replace it most times to get rid of this because it would take a very, very long time to wear off of the disc. Something like a WearEver Silver pad from Advance Auto Parts might as well be a stick of butter on a brake shim.