Brake master cylinder Coupe Quattro 7A

[Tom_]

Guys, any ideas, which main brake master cylinder are straight to fit on Coupe Quattro 7A 125kW ? When i try to bleed brakes, it goes again and again a foam (air) from main brake cylinder, so we think, that the brake master cylinder will be brushed after all these years and after the push, air goes through the gaskets., but new cost a lot, so if u used some of Wilwood or something like that, which are "bolt on "

[steve briance]

weirdly i have been doing exactly the same today! a bleed of the system and from master cylinder and proportioning valve i get a flow of what looks like yellow lemonade there are so many tiny bubbles in the fluid. No bubbles at the calipers though.

What i don't get is that if there is air being let in to cause this, why isn't there fluid coming out through the same hole? Fluid gets through tiny holes under pressure and i would bet that if there is somewhere big enough for air to get in, pressurised fluid will get out...

To the O.P - I have no idea what retro fit options there are but part numbers I've found are:

ATE - 03 2125 3210 3
Delphi - LM43210
VAG - 441 611 021 A
Lucas - PML369
Girling - 4008369

25.4mm bore.

[UrS4boy]

441611021A was used in B3 and C3 Audis since around 1985, e.g. 1985 Audi 100 avant turbo. Should increase the possibilities of good used parts and/or rebuild kits.

[Tom_]

So guys, i had a stripped brake master cylinder, change some gaskets/rubbers in it, today put back on car, and i bleed the whole system, any ideas, why when i bleed the front, i push and open bleeder, that comes a lot of clean fluid without bubbles, but when i do the rear part of car, i push, open bleeder and there are very low flow of fluid than in the front. Any ideas? I remove brake regulator and tommorow i look on him... But i have strange feelings about the flow of fluid in the rear... front going good, but rear not so good...Could be problem inside of brake regulator? For example some dirty inside of them?

[Nuvo]

Did you remember to push the lever on the brake pressure regulator when bleeding the rear calipers?

[Tom_]

There are not any lever on brake regulator. This brake regulator, wich i have, is under the brake master cylinder and this is him...

[Nuvo]

Sorry, my mistake. I thought your Coupe was FWD, when clearly it a quattro.

This might be of some help to you:

You can do a pressure test it if you have the appropriate pressure gauges.
Connect gauges to front left and rear left brake calipers.
Apply pressure to brake pedal and measure pressure at both axles.

With 50 bar at the front axle => rear axle should be 30-35 bar.
With 100 bar at the front axle => rear axle should be 45-50 bar.

[Tom_]

I dont have any appropriate pressure gauges , but i try to ask someone, if have it...

[steve briance]

Nice to see a rebuild sorted the cloud of tiny bubbles. This confirms my conclusion on my master cylinder - it seems to have gone the same way as yours.

Where did you get the rebuild kit from? any part numbers? I have a spare which may or may not be any good as I've never used it so don't know - good place to try a rebuild while still running the car.

On the subject of flow from the rear calipers, have you considered that the brake pressure regulator is doing its job correctly limiting the rear circuit? the piston area is at least half that of the front calipers so won't need anywhere near as much fluid going to it. Have you actually driven the car yet on the road - it would be interesting to see how it is with the new m/c and a good bleed through. :-)

[Tom_]

when i will be in garage, i take a photo of the MC rebuild kits, what i have....I know, that the front brake more than rear...but it was quiet less of brake fluid

[mcandmar]

In my experience it is normal to see very low fluid volume when bleeding the rears, i think its partly because both side are supplied at the same time, and feeding small surface areas vs the fronts. The one thing to be careful of is lifting the brake pedal up, if you have it down to the floor when bleeding you need to raise it back up very slowly otherwise it tends to suck air past the seals. Do that by hand half a dozen times and you should get nice clean bubble free fluid out.

I highly recommend buying a pressure bleeder that connects to the reservoir tank, makes the whole process a breeze.

[popdemonic]

When i bled the brake last 2 weeks on the rear axle took much longer time than the front.
I used the pressure bleeder and cracked the nipples until it was almost out.i just noticed
the old fluid was gradually coming off the line.on the front i spent much lesser time until
Got the new fluid off the nipples.