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Audi B8 - OSF brake sticking at highway speeds


AudiJackAvant
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Good Morning, all

I have an Audi A4 (2009) with a front right sticking brake. 

I have had the car at a garage, and they were not able to find the fault (i've also checked/ changed a few parts myself). I took it to Audi in the end and their mechanic diagnosed water in the servo/ master cylinder and quoted for replacement. They claim debris under the scuttle panel was blocking the drain holes. I've taken the scuttle panel off and cleaned it as best as I can - there was some debris but nothing major. 

However, my understanding was that the brake lines split and go to each wheel from the ABS pump, not the master cylinder and I'm therefore not convinced by their diagnosis. Maybe somebody on here has had a similar issue or knows where to look?

At highway speeds when the car is up to temperature, the front right brake lightly sticks. This causes a vibration through the pedals and steering wheel. This brake is also noticeably hotter than the other side.

The issue is intermittent and sometimes starts as soon as I get on the motorway (without using the brakes), other times it doesn’t start until the car is up to temperature and the brakes are warm (again it can start without using the brakes - it gradually creeps in), finally, it can happen when the car is warm, driving at motorway speeds and I use the brakes. After a short duration of time, it feels like the brake works itself free and the vibration stops but it can come back again later (with or without braking).

The following parts have been changed:

-     Calliper
-     Brake pads and discs (I have since changed the pads again as they are wearing unevenly). Inner right pad looked like a cheese wedge shape. 
-     Flex hose
-     Wheel bearing
-     Abs pump (with a second-hand unit)
-     Brake fluid
-     The calliper carrier bracket

Audi said they had the car on the rolling road (or whatever they use to test the brakes) an they noticed the brake fluctuating. The brakes squeak and when I'm braking lightly as low speeds I can hear the squeak 'pulsing' (for lack of a better word) like i'm dabbing the brakes (only the front right does this).

If anybody has any suggestions, this would be greatly appreciated. 

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On 12/1/2022 at 10:59 AM, AudiJackAvant said:

Good Morning, all

I have an Audi a4 (2009) with a front right sticking brake. 

I have had the car at a garage, and they were not able to find the fault (i've also checked/ changed a few parts myself). I took it to Audi in the end and their mechanic diagnosed water in the servo/ master cylinder and quoted for replacement. They claim debris under the scuttle panel was blocking the drain holes. I've taken the scuttle panel off and cleaned it as best as I can - there was some debris but nothing major. 

However, my understanding was that the brake lines split and go to each wheel from the ABS pump, not the master cylinder and I'm therefore not convinced by their diagnosis. Maybe somebody on here has had a similar issue or knows where to look?

At highway speeds when the car is up to temperature, the front right brake lightly sticks. This causes a vibration through the pedals and steering wheel. This brake is also noticeably hotter than the other side.

The issue is intermittent and sometimes starts as soon as I get on the motorway (without using the brakes), other times it doesn’t start until the car is up to temperature and the brakes are warm (again it can start without using the brakes - it gradually creeps in), finally, it can happen when the car is warm, driving at motorway speeds and I use the brakes. After a short duration of time, it feels like the brake works itself free and the vibration stops but it can come back again later (with or without braking).

The following parts have been changed:

-     Calliper
-     Brake pads and discs (I have since changed the pads again as they are wearing unevenly). Inner right pad looked like a cheese wedge shape. 
-     Flex hose
-     Wheel bearing
-     Abs pump (with a second-hand unit)
-     Brake fluid
-     The calliper carrier bracket

Audi said they had the car on the rolling road (or whatever they use to test the brakes) an they noticed the brake fluctuating. The brakes squeak and when I'm braking lightly as low speeds I can hear the squeak 'pulsing' (for lack of a better word) like i'm dabbing the brakes (only the front right does this).

If anybody has any suggestions, this would be greatly appreciated. 

Hi it could well be that the rear N/S calliper/ handbrake is sticking as the brake system works diagonally I.E. front N/S and rear O/S are one system, front O/S and rear N/S are the other tandem, when the rears stick they don't allow the front partner calliper to release their pressure so they have minimal contact with that disc and cause it to bind and warp the new disc. Audi as usual are talking bullocks about the other stuff

Steve.

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On 12/2/2022 at 7:11 PM, Stevey Y said:

Hi it could well be that the rear N/S calliper/ handbrake is sticking as the brake system works diagonally I.E. front N/S and rear O/S are one system, front O/S and rear N/S are the other tandem, when the rears stick they don't allow the front partner calliper to release their pressure so they have minimal contact with that disc and cause it to bind and warp the new disc. Audi as usual are talking bullocks about the other stuff

Steve.

It had never crossed my mind that this could happen. I'll jack it up over the weekend and take a look. Thank you!

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Hello Jack,

You say your first new set of pads wore the inside pad to a wedge shape - something significantly wrong there then .

When you say the calliper has been ‘changed’ - with a respectable branded new one? 

Kind regards,

Gareth. 
 

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On 12/9/2022 at 2:19 PM, Magnet said:

Hello Jack,

You say your first new set of pads wore the inside pad to a wedge shape - something significantly wrong there then .

When you say the calliper has been ‘changed’ - with a respectable branded new one? 

Kind regards,

Gareth. 
 

Hi Gareth,

Thank you for your reply.

it has been changed with a Pagid, however, I confident the uneven wear was present before the calliper was changed.
 

I’ve not bothered to do any work on the car over the last week with the snow/ I’ve, however, one it’s cleared up I could try another calliper (I have a spare in the shed). 

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