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Sun Jun 29, 2008 10:23 pm

I replaced the Master cylinder on my 78 beetle, but did not bench bleed(a big mistake). Also replaced all lines and wheel cylinders. I bled brakes multiple times but still pedal goes to floor but does pump up if I push again. If I push on brake the pedal it will go to the floor with pressure.

Do you think I have a bad master cylinder? Would a power bleeder help fix this and how would I do that?

Mon Jun 30, 2008 2:31 am

are the brakes adjusted correctly?

you dont have to bench bleed the MC. just crack the brake lines open at the MC and bleed them then bleed the wheel cylinders.

also what has been your procedure for bleeding the brakes?

i'd also like to add that i have experienced non-german brake parts, expecially wheel cylinders be bad right out of the box.

Mon Jun 30, 2008 9:55 am

Not sure what you mean by "If I push on brake the pedal it will go to the floor with pressure."

But this thread may help.

http://www.thesamba.com/vw/forum/viewtopic.php?t=293046

Mon Jun 30, 2008 10:27 am

I bled the passenger side rear first, go a lot of foam and bubbles. then the left rear. THen Passenger side front then drivers side.

What I am saying is that when I push on the brake it goes about 3/4 way to floor. The next pump is solid, but I was told if you continue to push on the brake and it goes to the floor the MC is bad. and that is what happens. THe MC was new and has had no driving, as I have just been trying to get a good safe pedal.

I will try cracking the connections at the MC to see if I get out the air.

I did replace all 4 Wheel cylinders. Each wheel has been adjusted to so that it just rubs slightly but turns ok.

Poor car can't run or stop. it is becoming a lifetime project. Thanks.

Fri Jul 04, 2008 3:16 pm

As a follow up...I pressurized the brake system and found leaks where the pressure sensors are on the MC. I thought they were tight and did not want to strip the threads, but I got a few more good turns.

Also I adjsuted each of the wheels to where they would hardly turn and bled each WC.

It seems I now have the hardest pedal I ever had on this car. I left the pressure on for the night and see what is left in the morning. It was dropping but I am not sure if that is not due to the connections on the bleeder to Reservoir.

Fri Jul 04, 2008 3:46 pm

I left the pressure on for the night and see what is left in the morning. It was dropping but I am not sure if that is not due to the connections on the bleeder to Reservoir.

Or the reservoir hoses to the top of the master cylinder. I don't think either of those are high-pressure connections, so you may be right.

but I was told if you continue to push on the brake and it goes to the floor the MC is bad. and that is what happens.

That just means that brake fluid is getting out somewhere. I replaced most of the components in my brake system; slave and master cylinders, hoses, and main front to back brake line. Adjusting the first time, and bleeding, it was pretty soft. I got everything together, put the wheels on, drove it one, the brakes weren't up to what I felt was safe, so I jacked it back up and adjusted again. The brakes moved quite a ways and the pedal was much firmer and braking was much better.

If I pushed down hard on the brake pedal and held it, I could tell it was dropping after a minute. I had to wait that long to convince myself that I wasn't imagining it. I found the leak--I hadn't fully tightened the hard brake line connection to the right rear slave cylinder. I found it because it was leaking very slowly, but when I did the above test repeatedly I found brake fluid on the backing plate. So leaks elsewhere cause the pedal to drop.

I found that you have to adjust and bleed a couple of times to get it tight, and at least couple of times while adjusting EACH wheel, go to the cab and push the brake pedal down a couple of times, to re-seat and re-center the shoes. I think that's very important.

Fri Jul 04, 2008 10:02 pm

Thanks, I noticed that the pedal is still hard but not as high, I have her up on jacks so I will look for more leaks. This evening I see the MC area is still dry, need to check slaves.

I can't drive her as I am waiting for engine parts, but I am enrcouraged that the pedal is much better. I was surprised how tight the wheels have to be adjusted though

Fri Jul 04, 2008 10:19 pm

I'm having the same trouble with the brakes. I'm gonna tighten em up a little tighter tommorrow. I know I have no leaks. I have been keeping the clumps of hair i've been pulling out of my head. So when I do get it on the road I can enjoy the breeze blowing through it.

Sat Jul 05, 2008 12:30 pm

Take this with about a POUND of salt because this is ENTIRELY speculation:

I've gone through a lot of the same stuff that veedubbug and roadster49 are talking about here. My sequence:

-replace most of the brake system
- filled with fluid
- bleed (can with tube and pump brakes method)
- adjust on stands
- drove car, brakes very weak
- car back up, bleed and adjust brakes again. This time, after each adjustment, pump brakes a couple of times and re-check
- My front wheels now make slight scraping sounds when they turn
- pedal only goes 1/4 of the way down and stops, very firm

NOW MY SPECULATION:

I think that some of the issue here may be that the original master cylinders for all-drum brakes may have come with residual pressure valves in the master cylinder. That valve would leave some pressure in the brake lines and keep the shoes right next to the drums.

However, you don't want RPVs in master cylinders when you're putting on disk brakes.

Since a lot of people put on disk brake kits, it makes more sense for the manufacturers to make something that works with all brake types, thus the non-RPV master cylinders have become the standard.

Now you can buy RPVs for brake lines. I have not done this. I don't know what the threads are or whether or not this would ultimately be a good idea.

However, that may be the issue here. Perhaps the RPVs would reduce the amount of drift in the brakes and make them easier to keep in adjustment.

In the absense of this, with the current system of the master cylinder letting ALL the pressure off the slave cylinders, I think the only way to keep short pedal travel is to keep the shoes really close and tight.

Now the possible downside is that I don't know how much drag this is creating for driving the car. Turning the wheel by hand it's definitely noticable. Pushing the car on the ground, I don't notice it at all. Driving I don't notice it. Finding out for sure will require doing a careful mpg comparison, and I haven't driven it enough since the brakes were re-done to be able to make that measurement.