Thread: Master brake cylinder problems

You may have a cylinder for dual circuit brakes and a car with a single circuit. Some detail on both would assist

Originally Posted by Mathernet

You may have a cylinder for dual circuit brakes and a car with a single circuit. Some detail on both would assist

Please see attached pic - I think it is single circuit.

Compression valve (CV) type the fitting adjacent to the firewall goes to the reserviour the fitting on the top goes to the wheels.

Yes single circuit.

Have you bled it?

I tried to flush the lines as they might contain dirty fluid which I don't want in my new slave cylinders. Do I need air pressure in the reservoir to do this? Also what is the correct bleeding procedure?

We are talking brakes here yes? If so the cyl at the wheels are called wheel cyl. A clutch has a slave cyl.

There are two ways to bleed a master. 1/ On the bench before fitting.

Put it in a vice, fill with fluid and using a phillips head screwdriver push the piston in all the way. Before releasing cover the hole/s where your brake lines connect with your fingers.

Remove fingers and repeat until no more air. Fit to car making sure that you do not lose all the fluid.

2/ On the car. Similar to bleeding the brakes. Fit the cyl completely with all lines connected. Fill with fluid and then get someone to pump the pedal a few times and hold it down.(My SWMBO is an expert at this) Then crack the flare nut on the pipe/s and then close.

Release pedal and repeat process until all air is expelled. After this bleed brakes at wheels.

I have fitted many a master cyl and after doing a bleed on it, have often found that bleeding at the wheels was not needed.

There is no need to worry about dirty crap getting into your wheel cyls as when you bleed the system if you bleed until clean fluid comes out you have basically flushed the system.

Thanks D2dave,


I connected everything up except the flexible lines that connect to the wheel cylinders and had my old Dad pump the brake pedal several times. The result was no flow out of front or rear lines. How would connecting the lines to the wheel cylinders help? Is it an air lock problem in the master cylinder?
I will try the first bleeding method when I get time and get back to you.


MrB.