Audi A4 - Braking problems

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Mon 23 Jan 2023 20:43
Audi A4 - Braking problems - JJ100
I have a strange but worrying problem with my brakes. It’s happened 3 times now all in different circumstances.

1. Sudden stop on a motorway. Brakes applied took the car from 60 ish down to 10 ish then it seemed to slip, pedal went straight to the floor subsequently revs were on max as I caught the accelerator but clutch was engaged so no dramas there. Released the brake and reapplied and the car stopped. Immediately took it to Kwik Fit for a brake check, explained the issue but they checked it over and suggested everything checked out fine.

2. Was at a junction. thought I could go but a speeding car in a cross road made me think twice. Applied the brakes and again it over shot slightly. Exactly the same phenomenon, but as I was at a snails pace felt more like I was skidding on ice. Road surface was fine. This time I took it to the local garage and they took the brakes apart and basically rebuilt them on my instruction but couldn’t find an obvious fault. No problems since.

3. About 6 months later, again trying to stop the car this time pulling into a car parking space on quite a steep decline. Over shot the space due to the same lapse in braking. Fortunately nothing in front of me. Tried to repeat it in the same car park…safely but couldn’t. Never the less checked brakes myself (fluid, callipers, pads, discs), nothing seemed out of place. No lights on the dash. A complete mystery.

Each time the sensation is like it’s skidding and/or the ABS is trying to avoid wheel locking but doesn’t feel right as the car is virtually coasting into a potential collision. Seems to be when either the car is on a decline or is dipping forward through braking force. Applying logic it seems like the ABS is kicking in and not disengaging. Doesn’t seem to happen at higher speeds, but if it’s not the car correcting itself why would all four brakes slip? Any feedback would be good

Edited by JJ100 on 23/01/2023 at 21:22

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Mon 23 Jan 2023 21:26
Audi A4 - Braking problems - Adampr

Did your garage check for fault codes?

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Mon 23 Jan 2023 21:29
Audi A4 - Braking problems - JJ100
Yes, nothing showing
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Mon 23 Jan 2023 22:09
Audi A4 - Braking problems - elekie&a/c doctor
If the brake pedal is going to the floor, then it looks like hydraulic pressure is being lost. Are the brake flexible hoses in good order ? Another possibility is a failure of the brake master cylinder. Is there any evidence of fluid loss in the reservoir?
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Mon 23 Jan 2023 22:23
Audi A4 - Braking problems - bathtub tom

Have all these events happened after driving some distance, that is not at the start of a journey?

As well as doing the checks suggested by e&a/c, I'm thinking it may be a brake binding slightly, the heat generated causing the fluid to boil.

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Tue 24 Jan 2023 20:19
Audi A4 - Braking problems - JJ100
All at the start of journeys
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Tue 24 Jan 2023 20:19
Audi A4 - Braking problems - JJ100
Hi, no loss of fluid and hoses looked fine to me.
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Tue 24 Jan 2023 20:21
Audi A4 - Braking problems - JJ100
No fluid showing and hoses looked in good order
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Mon 23 Jan 2023 22:59
Audi A4 - Braking problems - Big John

Is the pedal always going to the floor om every fault condition event? If so it has to be a hydraulic issue. I had a friend who had a similar problem (totally different car make - Renault) that turned out to be trapped air in the abs unit as it must be bled in conjunction with a device triggering abs valves via the on board diagnostics.

Which version/year/engine is it? The last two faults could possibly be related to a lack of vacuum to operate the servo. I've seen a couple of faults over the years like this - one was because of a failing tandem fuel/vacuum pump on a VAG 1.9pd another was a collapsing(internally) brake master cylinder rubber vacuum hose on a Volvo 740.

Just a few random thoughts.

Edited by Big John on 23/01/2023 at 23:00

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Mon 23 Jan 2023 23:22
Audi A4 - Braking problems - elekie&a/c doctor

What is the age of this A4 ?

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Tue 24 Jan 2023 10:02
Audi A4 - Braking problems - elekie&a/c doctor
Something I’ve seen on older model A 4 , is the abs reluctor rings on the rear brakes , corrode and crack . This allows them to spin on the stub axle . This confuses the abs system . The rear discs will need to be removed for inspection.
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Tue 24 Jan 2023 20:21
Audi A4 - Braking problems - JJ100
I’ll check this out cheers
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Tue 24 Jan 2023 20:20
Audi A4 - Braking problems - JJ100
It’s a 2012 Audi Quattro
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Tue 24 Jan 2023 20:25
Audi A4 - Braking problems - Big John
It’s a 2012 Audi Quattro

Which engine?

Also - before this happened anything changed / repaired etc? Mention anything even though you think it might not be related.

Edited by Big John on 24/01/2023 at 20:27

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Wed 25 Jan 2023 20:13
Audi A4 - Braking problems - JJ100
2.0 tdi. The oil indicator was replaced as light was on on the dash, as well as the indicator fuse when didn’t resolve the problem.
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