As part of my restore on my 1980 euro spec s I replaced the clutch slave cylinder and the master brake cylinder. I am having a problem with a soft peddal(on brakes). I have all the air out of the lines but cant get the brakes to hold pressure. If I pump the peddal 2-6 times it will build pressure but when I get off the peddal for a few second it looses all pressure.....WTF am I doing wrong.

p.s. the clutch works great I thought that was supposed to be the son of a B!

 

either the pads are not bedded in and the front hubs are loose or the master cylinder is bad

 

new master cylinder from 928 international so....

 

Did you bleed the master?

 

Really sounds like there is still air in it.

 

If it pumps up but then loses pressure, the new master has a bad seal. Even with air in the system, it won't lose pressure.

 

Does the pedal sink when you're holding it?

If not, bleed again and make sure you don't run the reservoir too low.

 

what do you mean by the pads are not bedded in...they only go in 1 way. All the pads and rotors are new....

I had the same problem with the old master....but the new master blows fluid out of the bleeders and the pedal sinks to the floor when the bleeders are opened. I bleed the master cylinder by cracking oll the lines loose off of it....I wonder if I have a bad caliper or???

 

If you are saying that:
- You simply step on the pedal, it goes to the floor.
- You pump the pedal quickly several times and hold it, the pedal will hold pressure.
- You release the pedal, wait a few seconds and step on it, it goes to the floor.

If that is the sequence, you still have air in the system. When you replace a master cylinder, you need to bleed the master cylinder first to get the air out of it, then bleed the brake lines.

Contrary to common lore, you need to bleed the front brakes first (both sides), then the rear brakes (both sides).

You also need to make certain that the pedal is adjusted so that the cups are not pushed into the master cylinder by the pedal at all until you press on the pedal. In other words, if the pedal is pushing on the master cylinder when your foot isn't on it, you will have problems.

"Bedded in" means that the pads need to be run long enough to conform to the rotor, so that there is no angularity involved. Until the pads are bedded in, you will have a slightly soft pedal - but it won't normally go to the floor.

 

thanks wally....I need to get a speed bleeder. I'm not too sure if they can be bleed w/out 1!


I did bleed the master first but what you mentioned is happening exactly! I need a speed/power bleeder!!!!

 

If you don't have a power bleeder, you can also do a gravity bleed. It's not as fast and sometimes not as effective, but does work. Just crack one caliper at a time and let nature take it's course. Maybe 5 minutes per corner. Keep an eye on the reservoir. What you are experiencing is not related to the pads.

 

I rebuilt 4 calipers on an 85 a couple weeks ago. Took longer than expected to get air out. Wondered if it would ever happen, frankly. Finally went to the front left and front right (was working on the back) like Wally suggests and started getting fluid.

Its not necessary to have a pressure bleeder.

Have your helper use slow movements on the pedal. Slow down, hold on floor, release commands.
I don't crack the fitting until the pedal is down or at least showing resistance, then I tighten before I give the call for the helper to slow-release the pedal. Maybe that will help.

Ont he other hand, when Jadz928 did the 87 Perl car, after his brake fluid switching mishap, the master seals were so f'd up that we could never get them bled.

 

I was getting lots of fluid w/no air but I think a speed/power bleeder will do the trick...I just sent Roger a pm.

Thanks again for every1's help!

 

Be my guess, and I could not tell you how many new master cylinders, slave cylinders or any other hydraulic system parts I have put on that were bad, had two of them last week in a VW, both were new master cylinders.