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Vibration from rear under braking... FIXED.

simon_house

Monza
Joined
10 Apr 2012
Messages
219
I have a vibration/noise from the rear under braking at anything above 50mph, not noticeable-that I can tell-whilst not on the brakes at most speeds:

-The rear brakes are new having only done circa 1000mi-Pagid discs and pads including new shims.

-Can't feel any movement in the wheel bearings when I try to rock the wheels.

However,

- The N/S/R inner bush for the control/coffin bush looks to be showing slight delamination. Can't imagine this causing vibration under braking though?

- I'm ready for some new tyres. Nearly down to the markers on the very inner edges, 2 to 3mm across the rest of the tyre. It was geo'd last year/10000mi ago so I was expecting the tyres to wear evenly but if I've some tired bushes this could be the causing the wear on the inside. I've also just had them rebalanced today with no improvement.

Any thoughts? I shall be ordering tyres this week anyway, but can anyone share any similar experiences and how they got rid of the not-so-good vibrations?

Ta.
 
Did you bed the new brakes in? It sounds like deposits on the discs.

Your tyres might be wearing quite evenly now, but they could have worn significantly on the insides prior to your geo. Plus, due to the camber the tyres tend to wear on the insides more than the outside unless driven very hard.

To see how worn the bushes are, jack the car so the wheel is just off the floor and then put a bar under the tyre and try to rock the wheel. You'll be able to see and feel any movement in the bushes (there should hardly be any movement). This should be done on an MOT.
 
eca02apc said:
Did you bed the new brakes in? It sounds like deposits on the discs.

Your tyres might be wearing quite evenly now, but they could have worn significantly on the insides prior to your geo. Plus, due to the camber the tyres tend to wear on the insides more than the outside unless driven very hard.

To see how worn the bushes are, jack the car so the wheel is just off the floor and then put a bar under the tyre and try to rock the wheel. You'll be able to see and feel any movement in the bushes (there should hardly be any movement). This should be done on an MOT.

Regarding bedding in, I followed the instructions on the Brembo Pdf file online and they've been fine. I'm going to borrow a DTI from work to measure the runout on the discs but they've not really had any abuse to warrant them warping but I'm led to believe this can't happen anyway?

I have however noticed a tiny ridge appearing already on one of the discs so I removed the pads this afternoon but found nothing alien stuck in the pads. I swapped the pads round and went for a drive. Still a noise/vibration under braking coming from the rear.


:?:
 
eca02apc said:
Did you bed the new brakes in? It sounds like deposits on the discs.

Plus, due to the camber the tyres tend to wear on the insides more than the outside unless driven very hard.

+1 on both above points.
 
Forgot to add, the car was geo'd with a brand new set of tyres. Mileage wise they've not done bad, just worn a bit more on the shoulders than the rest of the tyre.
 
Red993C4 said:
eca02apc said:
Did you bed the new brakes in? It sounds like deposits on the discs.

Plus, due to the camber the tyres tend to wear on the insides more than the outside unless driven very hard.

+1 on both above points.

Thanks for the help guys :thumb: If it is to do with the brakes as you suggest how do I lose the deposits and get them back to how they are supposed to be?
 
simon_house said:
Forgot to add, the car was geo'd with a brand new set of tyres. Mileage wise they've not done bad, just worn a bit more on the shoulders than the rest of the tyre.

That's not abnormal, particularly for cars driven extensively on motorways or not otherwise called upon to corner hard regularly. The factory camber settings were chosen such that the full width of the treads are only evenly loaded when the car is being cornered hard. Tracked cars have even more camber for this reason.
 
^^^^ I did not know that. Always learning!

Anyone had any success with removing the deposits? I've just read that scotch-brite on the end of a drill has worked, more abrasive brake pads for a short spell, multi-purpose cleaner left on over night...

It does feel and sound brake related more than anything else.
 
simon_house said:
Red993C4 said:
eca02apc said:
Did you bed the new brakes in? It sounds like deposits on the discs.

Plus, due to the camber the tyres tend to wear on the insides more than the outside unless driven very hard.

+1 on both above points.

Thanks for the help guys :thumb: If it is to do with the brakes as you suggest how do I lose the deposits and get them back to how they are supposed to be?

The deposits are glazed brake pad material adhering to the disc faces, arising when brakes are used relatively lightly. Can usually be removed by doing a series of hard stops from as high a speed as you can get up to wipe off the glazed layer.
The vibration is due this glazing being laid down in patches, resulting in friction variations between pad and disc surfaces.
 
Please check if all of your pistons moving freely. As those are rear they are getting sticky from 30k on the clock.
Once you have your pads out push the pistons in. They should move in with a pressure by fingers not by using of any tools.
If one side is sticky than the brakes will apply pressure on one side of the discs where you will get the vibrations as the discs will fight back.
 
Porsche Calipers said:
Please check if all of your pistons moving freely. As those are rear they are getting sticky from 30k on the clock.
Once you have your pads out push the pistons in. They should move in with a pressure by fingers not by using of any tools.
If one side is sticky than the brakes will apply pressure on one side of the discs where you will get the vibrations as the discs will fight back.

Thanks, I'll be trying this at the weekend :thumb:
 
-----
 
So, last weekend I removed the pads and cleaned the braking surfaces with brake cleaner and scotch-brite pad

Whilst the pads were out I checked operation of the pistons, as advised, by carefully pressing the pedal down 1 or 2 pumps to see if they all moved out and pushed back by hand. Some came out more readily than others but after going through the motions several times I was happy that all the individual pistons were doing their bit.

I replaced all the shims for new and carefully replaced the pads. I went through the bedding in proceedure again and I'm pleased to report so far so good.

The new tyres are still in the porch waiting to be fitted.
 

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