Bleeding brake system!

**Crasher** · 19-09-2016,01:39 AM

No, just like everywhere, any way-I don't have any relevant ones to show, all my mechanics do, but not me.

Regulation is coming to the garage service industry but it won't improve anything, just increase costs for everyone.

**jonathanfenton** · 19-09-2016,04:28 PM

Just out of interest how do you bleed the master cylinder?

**FrenchAudi** · 19-09-2016,05:58 PM

Originally Posted by jonathanfenton

Just out of interest how do you bleed the master cylinder?

If you are asking me, when I recently renewed the brake fluid I did not bleed the master cylinder as such, as the reservoir level was correct at the beginning, with no air in the m/cyl, and by bleeding fluid from each wheel cylinder in turn the fluid in the m/cyl was also renewed.

When fitting a new, empty m/cyl on a car without ABS, I fill its reservoir before installing it, then unplug each outlet union on it while pushing the piston gently in by hand with each outlet in turn at the top, to remove as much air as possible. I then install the m/cyl, connect it up, and bleed via each wheel until no more bubbles appear there.

I have not tried this on a vehicle with ABS, but fear that there will be a possibility of getting a small amount of air into the ABS unit. I assume that if this were to happen I would have to get the unit bled by a VAG dealer.

**Crasher** · 19-09-2016,06:01 PM

On the Golf 4 with ESP there are two 8-mm bleed nipples on the MC which you release with a 1/4" drive deep 8mm socket on an extension but you have to let the fluid go everywhere as its impossible to get a pipe on. Then rinse (with the cap on, don't ask!)

**FrenchAudi** · 19-09-2016,06:47 PM

Originally Posted by Crasher

On the Golf 4 with ESP there are two 8-mm bleed nipples on the MC which you release with a 1/4" drive deep 8mm socket on an extension but you have to let the fluid go everywhere as its impossible to get a pipe on. Then rinse (with the cap on, don't ask!)

Nothing that handy on my A4. But I'm getting used to that.

If I have to replace the m/cyl I might try bleeding any air in it by loosening the connections at the top of the ABS unit, applying a small pressure to the m/cyl reservoir, and hoping it's not enough pressure to push air into the unit.

**Crasher** · 19-09-2016,10:10 PM

The A4 uses Bosch ABS not ATE and it needs no fancy procedure.

**jonathanfenton** · 19-09-2016,10:12 PM

Originally Posted by Crasher

The A4 uses Bosch ABS not ATE and it needs no fancy procedure.

Do you know off the top of your head if you can bleed the master on an A3 8p?

**Crasher** · 19-09-2016,11:24 PM

No, not on the PQ35 platform with Mk60 ABS, the bleeding procedure is also significantly less tortuous than PQ34 with Mk20.

**jonathanfenton** · 20-09-2016,08:50 AM

Ah right, changed both rear callipers a while back and had a nightmare of a job to bleed it back up. Ended up taking it in and it took them a week to get a pedal back, few months of driving and it's got slowly better

**FrenchAudi** · 20-09-2016,09:52 AM

[QUOTE=Crasher;1030175]The A4 uses Bosch ABS not ATE and it needs no fancy procedure.[/QUO

Crasher.

My car has Bosch ABS 5.0, and I was simply following the statement, which appears twice, in slightly different forms, in the Haynes manual (A4 - 1995 to Feb 2000).

"If difficulty is experienced in bleeding the braking circuit on models with ABS, this may be due to air being trapped in the ABS hydraulic unit. If this is the case then the vehcle should be taken to a Audi/VAG dealer so that the system can be bled using special electronic test equipment"

Although this is not mentioned at all in the Bentley manual it made me rather cautious about bleeding air from the m/cyl via the ABS hydraulic unit.

Maybe it only applies to the Bosch ABS 5.3? - or is just a received myth? (Plenty of those around)