2008 S8 Self Braking Issue - Braking on its own
01-25-2019, 01:04 PM
#11
AudiWorld Senior Member
Thanks everyone for your thoughts.
It it feels comparable to how a sticking caliper would feel. A slow, smooth drag reducing speed. Or how engine braking feels when you downshift manually. If I’m on the gas, obviously I’m fighting it a little bit to increase speed, but hardly noticeable. Off the gas not braking is when I notice it most. If I’m on the brakes they feel normal in every way. There is nothing abrupt and it is consistent at every speed. No lights on the dash.
It it feels comparable to how a sticking caliper would feel. A slow, smooth drag reducing speed. Or how engine braking feels when you downshift manually. If I’m on the gas, obviously I’m fighting it a little bit to increase speed, but hardly noticeable. Off the gas not braking is when I notice it most. If I’m on the brakes they feel normal in every way. There is nothing abrupt and it is consistent at every speed. No lights on the dash.
01-25-2019, 01:10 PM
#12
AudiWorld Super User
This is a great start.....need to figure out if the hydraulic pressure is staying locked or if it is releasing......if it is staying locked or not releasing it's something in the hydraulic system most likely. I can't remember where I read a similiar story....it might of been on the 996 forum....the guy did a lot of what you have done.....but in the end it was something simple.....will have to see if I can find it.
01-25-2019, 01:24 PM
#13
AudiWorld Super User
Here is one thread....interesting that you car had all sorts of light on....have you checked your cowl drains to ensure they are clear? Why did all the lights come on? You sure something didn't get wet along the way?
https://rennlist.com/forums/996-foru...-sticking.html
And I found the other thread that I was referring to:
https://rennlist.com/forums/996-foru...s-problem.html
Here he loosens the brake cap and doesn't know if it works or not:
https://rennlist.com/forums/showpost...4&postcount=30
Then go down a few posts and he figures it out that he didn't have adequate clearance between the master cylinder and brake booster push rod. He got a new vacuum booster and then had proper clearance and all is good.
I would not be surprised if it could be something along these lines.
https://rennlist.com/forums/996-foru...-sticking.html
And I found the other thread that I was referring to:
https://rennlist.com/forums/996-foru...s-problem.html
Here he loosens the brake cap and doesn't know if it works or not:
https://rennlist.com/forums/showpost...4&postcount=30
Then go down a few posts and he figures it out that he didn't have adequate clearance between the master cylinder and brake booster push rod. He got a new vacuum booster and then had proper clearance and all is good.
I would not be surprised if it could be something along these lines.
01-28-2019, 04:50 AM
#14
Audiworld Junior Member
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The tech thinks the low voltage codes previously were to do with the battery not being coded, and likely unrelated to this braking issue.
I just spoke with the service writer at the Audi dealer the car still sits at. He said the LF and RR wheels are the wheels that are dragging. It is a mechanical fault. They do not spin freely on the lift, or while driving. He repeated to me that there are no codes or faults in the system for the EPB or the ABS. He said their master tech certainly as not seen this problem before but it pretty certain it has to do with the brake booster, that's why they are recommending to replace that now.
I'm leaning towards letting them replace the booster/master cylinder. There are lots on ebay used for around $150. New ones seem to be around $650 online for just the booster. Dealer wants $1100 full retail for the parts only and insists doing both the booster AND master cylinder.
I just spoke with the service writer at the Audi dealer the car still sits at. He said the LF and RR wheels are the wheels that are dragging. It is a mechanical fault. They do not spin freely on the lift, or while driving. He repeated to me that there are no codes or faults in the system for the EPB or the ABS. He said their master tech certainly as not seen this problem before but it pretty certain it has to do with the brake booster, that's why they are recommending to replace that now.
I'm leaning towards letting them replace the booster/master cylinder. There are lots on ebay used for around $150. New ones seem to be around $650 online for just the booster. Dealer wants $1100 full retail for the parts only and insists doing both the booster AND master cylinder.
01-28-2019, 05:22 AM
#15
AudiWorld Super User
A booster and master are not the source of your issue- id put $ on it
car in the air, spin the wheels, see if a caliper (or multiple) are hanging up
Were the calipers rebuilt? If so, by whom, and why.
car in the air, spin the wheels, see if a caliper (or multiple) are hanging up
Were the calipers rebuilt? If so, by whom, and why.
01-28-2019, 06:30 AM
#16
AudiWorld Super User
01-28-2019, 06:37 AM
#17
AudiWorld Senior Member
. He said the LF and RR wheels are the wheels that are dragging. It is a mechanical fault. They do not spin freely on the lift, or while driving. He repeated to me that there are no codes or faults in the system for the EPB or the ABS. He said their master tech certainly as not seen this problem before but it pretty certain it has to do with the brake booster, that's why they are recommending to replace that now.
I'm leaning towards letting them replace the booster/master cylinder. .
01-28-2019, 06:38 AM
#18
AudiWorld Super User
I did and it makes zero sense.
Was the car running while they did this test? The master and booster are only functioning while a car is running. The caliper neither knows nor cares if a car is on though - it’s job is simply clamp and release. The booster and master aid this, but does not cause either the clamp or release action.
Was the car running while they did this test? The master and booster are only functioning while a car is running. The caliper neither knows nor cares if a car is on though - it’s job is simply clamp and release. The booster and master aid this, but does not cause either the clamp or release action.
01-28-2019, 06:39 AM
#19
AudiWorld Super User
Did they have the engine running, or if engine was not running, was the ignition on, if no to all, how could the brake booster or ABS have anything to do with the dragging of the wheels as there should be no vacuum to activate or pull on the brake booster, and no electrical to the ABS module, did they have it in neutral as I stated, otherwise with the all wheel drive and trans in park, wheels will have some drag when all are lifted off the ground, like it' fighting the trans if not in neutral...
01-28-2019, 06:39 AM
#20
AudiWorld Senior Member