Brake fault

Woodwind

Member
Our 1.4 Tdi went to the local garage with a poor handbrake. They replaced both rear wheel cylinders and shoes and both rear cables.
All seemed fine then a few days after, the brake pedal went to the floor.
No warning lights at all. The car was collected by the garage and driven back there, brake pedal returned to normal during their journey of approx 2 miles.They checked their work, found nothing, no fluid loss or outward signs of a leak. They re-bled the brakes and said no air came out. They have since driven it for several miles and the problem did not recur. They have no explanation and cannot say the fault will not recur.
I am concerned as the car is used by my wife.
I have read several threads describing similar issues but wonder if anyone could help put their finger on the problem please?
 

dj_efk

A2OC Donor
I would suspect the master cylinder is failing. When they bled the brakes they may have pushed the pedal (and therefore the cylinder within its bore) past the normal point of travel - not their fault really I don't think - but if the car's high mileage (or moderate mileage but has been driven a lot on urban roads), then master cylinder bore may have worn and caused the seal to behave abnormally as it encounters a wear lip.

Just my theory.
 
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simufly

A2OC Donor
As David above has said, it is possible that the seals on the master cylinder have reversed which could give the symptoms you describe. It would be unusual for the seals to right themselves however.
I do hope the garage was using a pressure bleeder rather than pumping the pedal as we used to do! Pumping is not a good idea.
either a pressure or suction method is infinitely preferable
 

Woodwind

Member
Thank you for your replies and information I'll check with the garage and see if I can determine how they bled.
Mileage on the car is 110k. and gently used but mostly urban driving.
Is the fact that the pedal has returned to normal consistent with the master cylinder fault and is it likely to fail again.
I'm very reluctant to drive the car now.
The garage have agreed to keep the car and drive it over the next few days to see what happens. They are a general garage with no specialist knowledge of the Audi. We had no previous braking problems until the new rear brake kits were fitted. It seems too much of a coincidence that the issue only appeared within days of the repairs.
What would the best way forward be please?
 

audifan

A2OC Donor
If you can access VCDS then you can perform various checks on the braking system and read and clear any stored fault codes. This may shed light onto the matter. I would very carefully check all flexible brake pipes because if they are ballooning the brakes won't work properly with a chance of the pedal falling to the floor.

I can still bleed by the manual pumping method but I place a block of wood under the brake pedal to prevent it travelling down further than normal. This in turn prevents seal damage.
 
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Howey

Member
Manually pumping the brake pedal fully down as been a known risk in the motor trade on any used car, especially renowned as a big no no with 90's vauxhall's
 

Woodwind

Member
Thank you all for your help. It's great to have such support.
I'm tempted to get a new master cylinder. Any advice of where to source?
 

dj_efk

A2OC Donor
It could be the seals have righted themselves and have emerged from the experience unscathed - I would try heavy constant brake pressure with the engine running for a good minute and see if the pedal sinks, then stamp on the brakes multiple times.

Be aware that this is only a theory as to what caused the failure in the first place. If any doubt remains then get the brakes properly inspected and / or change the cylinder.
 

Woodwind

Member
It could be the seals have righted themselves and have emerged from the experience unscathed - I would try heavy constant brake pressure with the engine running for a good minute and see if the pedal sinks, then stamp on the brakes multiple times.

Be aware that this is only a theory as to what caused the failure in the first place. If any doubt remains then get the brakes properly inspected and / or change the cylinder.
Thanks for that. The car is at the garage at the moment and they are closed until Monday. I'll go down and try what you suggest, I think they want to get to the bottom as much as I do.
All of the feedback makes good sense and I am grateful for the help received.
 

A2Z

A2OC Donor
I can still bleed by the manual pumping method but I place a block of wood under the brake pedal to prevent it travelling down further than normal. This in turn prevents seal dadamage.
I was going to say the same thing regarding using a block of wood or similar.

There is absolutely nothing wrong with bleeding the brakes by pumping the brake pedal as long as the travel of the pedal is limited whilst doing so šŸ‘
 

Woodwind

Member
I was going to say the same thing regarding using a block of wood or similar.

There is absolutely nothing wrong with bleeding the brakes by pumping the brake pedal as long as the travel of the pedal is limited whilst doing so šŸ‘
Thank you for expanding my understanding. What a great place the forum is.
 

Howey

Member
I was going to say the same thing regarding using a block of wood or similar.

There is absolutely nothing wrong with bleeding the brakes by pumping the brake pedal as long as the travel of the pedal is limited whilst doing so šŸ‘
You do have to make sure you don't drag air back in which would be prevented totally by pushing and holding the pedal fully down. For this reason you may struggle to find any official half pressed pedal routine. However if you have a good air tight fit on the waste pipe connector to the bleed nipple no air should be able to get in, you may simply see the fluid come out and back in slightly
 

Woodwind

Member
You do have to make sure you don't drag air back in which would be prevented totally by pushing and holding the pedal fully down. For this reason you may struggle to find any official half pressed pedal routine. However if you have a good air tight fit on the waste pipe connector to the bleed nipple no air should be able to get in, you may simply see the fluid come out and back in slightly
Sorry for my ignorance, am I reading this correctly?
"You do have to make sure you don't drag air back in which would be prevented totally by pushing and holding the pedal fully down"
I thought the pedal should not be pushed fully down to avoid damage to the seals. Could you clarify please?
 

A2Z

A2OC Donor
Sorry for my ignorance, am I reading this correctly?

I thought the pedal should not be pushed fully down to avoid damage to the seals. Could you clarify please?
Ideally it's a two man job and the bleed nipple at each caliper should be locked off whilst the brake pedal is pressed and the air expelled and whilst it is held down (hence the block of wood to prevent over pressing) by someone else sitting in the car.

It just needs to be pushing air out rather than allowing air to enter back in, rather like blowing out of your mouth, exhaling not inhaling šŸ˜

It's really not rocket science šŸ˜‚šŸ‘
 

Howey

Member
Ideally pressure bleeding is the answer, tbh any garage not doing this especially on a euro car where connection to the reservoir is easy, needs to not open their shutters!
 

Woodwind

Member
OK Thanks all. I've got a complete grasp now. Let's hope the garage have! At least I now know what they should be doing.
It's something I've done many times in years gone by on older cars without ABS but with advancing years and limited facilities, I have to rely on the local garage.
I just hope they haven't damaged the master cylinder seals.
PS
My first car had rod operated drum brakes all round - There's progress for you.
 
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dj_efk

A2OC Donor
OK Thanks all. I've got a complete grasp now. Let's hope the garage have! At least I now know what they should be doing.
It's something I've done many times in years gone by on older cars without ABS but with advancing years and limited facilities, I have to rely on the local garage.
I just hope they haven't damaged the master cylinder seals.
PS
My first car had rod operated drum brakes all round - There's progress for you.
Iā€™m going to guess Ford Pop?
 

Kyojitsu

Member
Our 1.4 Tdi went to the local garage with a poor handbrake. They replaced both rear wheel cylinders and shoes and both rear cables.
All seemed fine then a few days after, the brake pedal went to the floor.
No warning lights at all. The car was collected by the garage and driven back there, brake pedal returned to normal during their journey of approx 2 miles.They checked their work, found nothing, no fluid loss or outward signs of a leak. They re-bled the brakes and said no air came out. They have since driven it for several miles and the problem did not recur. They have no explanation and cannot say the fault will not recur.
I am concerned as the car is used by my wife.
I have read several threads describing similar issues but wonder if anyone could help put their finger on the problem please?
I'm confused (and apologies if I'm being ignorant) but why would anyone bleed the brakes when replacing the rear drums?? I thought our A2s only had front discs...?
 

audifan

A2OC Donor
Sorry if you are that bad I worry about you driving. Yes all A2 have front discs and all bar the tdi 90 and 1.6 fsi have rear drums. All brakes are operated by the hydraulic brake fluid and as such would need bleeding. So how did you think the car stopped on the rear?
 
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Kyojitsu

Member
Sorry if you are that bad I worry about you driving. Yes all A2 have front discs and all bar the tdi 90 and 1.6 fsi have rear drums. All brakes are operated by the hydraulic brake fluid and as such would need bleeding. So how did you think the car stopped on the rear?
Thanks for the unnecessarily obnoxious reply. The A2 weighs almost nothing. A motorcycle is stopped using the front brakes only, most of the time, ergo, so might the A2. As I said, apologies for ignorance, it was a genuine question.
 
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