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Steering wheel shaking at 75+ MPH

Old 12-10-2018, 12:43 PM
  #16  
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Originally Posted by Luca Signore View Post
Hey Mac, thanks for the incredible detail in your answer. Thanks for the info on the tires - I was unaware of the N rating when I bought them, the shop I purchased them from said they were popular with Porsches so I did not inquire much further. I've had the same thought about the rim being bent, but all the people who have put on a road force balancer have been unable to detect this. Also, today, I borrowed a set of wheels from a friend and did not notice any improvement.

However, as I mentioned in another reply on this thread, when I was swapping the wheels back with my friend, I noticed that my driver-side front rotor (the area which I suspect the vibration is coming from as my side mirror seems to vibrate rapidly) was significantly hotter than the other three. I drove home - about 40 miles with little braking, mostly freeway - and checked all rotors against using an infrared thermometer. I saved the suspected one for last to make sure that it was not that the other ones had cooled more, and found that three others were 85-90 F, while the driver left was at 120 F. Could this been warped rotor or a caliper issue?
The difference in temperature might be significant or it might be the result/side effect of what is really going on.

For a suspected warped rotor you can with the car in the air and a holder (magnetic or clamp type) arrange to use a dial indicator to check rotor run out by spinning the front wheel/tire assembly.

I don't have the factory manual to refer to as to what is allowable. The Bentley Boxster book might cover this. But you also have the other side and you can check its rotor run out and use this as a benchmark as to what the other side should be if they are not close to the same.

I have had no experience with a stuck or hanging up brake piston. If the brake fluid has not been flushed/bled on 2 year schedule it is entirely possible at least one piston is not retracting properly and could be dragging. I have experienced this in a mild sort of way with a number of cars the cause is not a bad piston but a heavy accumulation of brake dust on the piston boots that interfere slightly with the pistons' normal slight retraction from the rotor face when the brake pedal is released. (This is from the natural hysteresis of the piston seals.) The result is not a shake but the brakes develop a mild squeal when used rather lightly. It is possible the rotors run a tad warmer because of course the pads can still remain in slightly contact with the rotors at least part of the time.

Since the symptom is present with a wheel/tire swap the source of the problem is almost certainly with something other then the wheels/tires which of course leaves the brake assembly, the wheel bearing(s), and suspension/steering as suspects.

You can try this: With the car in the air apply the brake pedal then release. Check each pad with a feeler gauge to see how much clearance/gap there is from the piston's natural tendency to retract slightly when the pedal is released. Be careful. You don't want to force the pad away with the feeler gauge. Just start out with a very thin gauge strip and establish the pad gap is say 0.010". (0.010" is just a number, I'm not sure what the real number will be.) What you are looking for is the majority are all about the same and the suspect brake the gap is much less or nonexistent.
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Old 12-10-2018, 07:50 PM
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A warped rotor will give you vibration under braking but no vibration when the brake is released. A stuck caliper piston will give you vibration under braking and also vibration at speed, in addition to a hot brake disk, caliper and wheel where the caliper is sticking. As I mentioned on another forum, your symptoms are typical of a sticking caliper piston.
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Old 12-11-2018, 12:39 AM
  #18  
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Interesting write-up on warped rotors here: http://www.stoptech.com/technical-su...nd-other-myths, or the myth about them. I had deposits on my rotors, and they vibrated at 65-70mph, no braking.

In any case I think the issue is likely a piston given the heat, but deposits will lead to vibration under no pedal pressure.
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Old 12-11-2018, 03:03 AM
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Originally Posted by daylorb View Post
Interesting write-up on warped rotors here: http://www.stoptech.com/technical-su...nd-other-myths, or the myth about them. I had deposits on my rotors, and they vibrated at 65-70mph, no braking.

In any case I think the issue is likely a piston given the heat, but deposits will lead to vibration under no pedal pressure.
Should I just go ahead and order new rotors, pads, and the rebuild kit? Or should I have a shop double check that it is the caliper sticking? I don't really want to blindly throw money at it, but it does need new rotors/pads anyway, and the rebuild kit is only about $20. Plus, paying a shop to check would be about the same as just buying the parts.
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Old 12-11-2018, 11:14 AM
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Originally Posted by Luca Signore View Post
Should I just go ahead and order new rotors, pads, and the rebuild kit? Or should I have a shop double check that it is the caliper sticking? I don't really want to blindly throw money at it, but it does need new rotors/pads anyway, and the rebuild kit is only about $20. Plus, paying a shop to check would be about the same as just buying the parts.
If it needs new rotors and pads, then that might be the right solution. I've never done any work on the piston/caliper sticking, but seems like a pretty easy job assuming not too far gone. If you remove the wheel/pop the pads you will be able to pretty quickly determine if you have a stuck piston/caliper so you don't have the fear of just throwing money at it.
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Old 12-11-2018, 05:41 PM
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Originally Posted by daylorb View Post
If it needs new rotors and pads, then that might be the right solution. I've never done any work on the piston/caliper sticking, but seems like a pretty easy job assuming not too far gone. If you remove the wheel/pop the pads you will be able to pretty quickly determine if you have a stuck piston/caliper so you don't have the fear of just throwing money at it.
Parts are ordered and fingers are crossed!
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Old 01-02-2019, 02:33 PM
  #22  
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Didnt read the whole thread but did anyone suggest the motor mount?
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