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Steering wheels shakes when braking


gregthiara

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Can somebody tell me why on my 996TT 2001 the steering shakes when I apply the brakes?

If im driving over 50mph and brake it feels like the wheels are about to shake off, it can not be the brake disks as if just had them changed.

Please help :(

If you are getting "pulsing" through the brake pedal when you lightly apply the brakes, and your car shudders under heavy braking, there are two main causes: either lateral runout of the rotor or a variation on the thickness of the rotor on the surface that is subjected to friction from the brake pads.

Even if the rotors are relatively new, you can still experience runout if the lugs were improperly torqued (over-torqued or unevenly torqued), or if there is some corrosion build-up between the hub and the rotor.

I am assuming you have checked to make sure that your lug nuts are not loose. eek.gif

Even if the rotors are relatively new, I would check their thickness with a caliper to make sure they are within spec in case the ones that were installed are not up to par.

Checking for lateral runout requires a more expensive tool.

Unless you are getting noise coming from the front wheels under hard cornering, the bearings are not the prime suspect.

Regards, Maurice.

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Maurice, what is "lateral run out" mean?

never heard that term and I am in process of putting new rotors on front of my car and want to know what this is if i have issues.

thanks.

Steve:

Lateral runout is the difference between the maximum and the minimum value that is recorded on a dial indicator gauge. You can measure the difference in those values by mounting the dial indicator gauge on a solid mounting surface with its tip perpendicular to the surface of the rotor, less than one inch from the outside circumference of the rotor. Then you spin the rotor and the gauge will record the maximum and the minimum distance from its tip to the surface because the distance of the surface will vary if the rotor is warped or if the thickness of the rotor is uneven.

Think of it as the rotor being warped. If the lateral runout is too great (i.e., not within spec) that will cause pulsing or heavy shudder, depending on the severity of the runout or warping.

If the rotor is thick enough and the runout is not excessive, the rotor can be turned on a lathe to eliminate the lateral runout or any uneven thickness around the rotor's face, again as long as you don't pass the minimum safe thickness. Turning rotors on a lathe used to be a lot more common in the old days. Nowadays, lots of the rotors, especially some of the aftermarket ones are just disposable.

Also, if there is excessive corrosion on the surface of the wheel hub face, that will not allow the rotor to seat completely flush and square, and that will show up as runout as well.

When you are mounting your wheels on the new rotors, don't use air tools and make sure that you torque the lug bolts by going across from one bolt hole to the bolt hole on the opposite side until you have all of them tightened to the proper torque value, preferably in two stages. Never torque the bolts in a circle.

Regards, Maurice.

Edited by 1schoir
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Im sure my rotors are not the problem as they are brand new from porsche, and when I brake the brake pedal is fine I dont feel anything only the streering shakes. This was happening before I had the brakes changed I thought that this would fix the problem, could it be the wheel is buckled or needs balancing it seems to be coming from front passenger side.

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Im sure my rotors are not the problem as they are brand new from porsche, and when I brake the brake pedal is fine I dont feel anything only the streering shakes. This was happening before I had the brakes changed I thought that this would fix the problem, could it be the wheel is buckled or needs balancing it seems to be coming from front passenger side.

Greg:

Your original post did not mention that the problem was happening before you had the brakes changed.

If it was only a balancing issue or a problem with one of the rims, you would feel the shaking in the steering wheel WITHOUT having applied the brakes, most probably only at a certain speed range.

You could eliminate that as a possibility by swapping the rims left to right for a few miles and then swapping them back.

If you are not feeling any kind of pulsing or shudder from the brake pedal when you apply the brakes at 50 mph, then your problem probably lies elsewhere, perhaps in some component of the suspension such as the lower control arm or its bushings or the upper strut mount bearing.

Regards, Maurice.

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Went through the exact same thing with my Honda Civic! Only showed up on hard braking. As 1Schoir stated, turned out to be the upper strut mount. At first I thought it was the brakes I.E. warped rotor, excessive run out etc. changed rotors and pads and the same thing happened. Pulled struts and found found a bad strut bearing. Replaced and car is back to normal.

Regards, Tom

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