Brake bleeding issue

[cavenut]

Ok, first off I might be a newbie here but have worked on many many cars. So here is my issue. I purchase a 1986 cabriolet for my daughter. Its a great ride. But before I turn it over to her I wanted to replace the brakes. I removed the front calibr. and checked them. I thought the things where good and just put on new pads. But I removed them and cleaned them (off car) Returned them after I had the rotors turned and checked ( they are on the correct side), EZ Cheesy. Then I bleed the brakes. Keep in mind I wanted to clean the fluid too and had push lots of fluid thought the lines, it was like pushing mud out, 3 qts (4liters). I used the buddy system, my son pumped and I worked the refill and bleed. When I was done I took it out for a quick run and checked out the brakes. All went well, I lock the brakes 3 times and worked good no pull. But a block later the pedal went to the floor. I puppied it home. Bleed the brakes just in case there was more air. Brakes where hard as a rock.But when I start the car and hit the brakes they go to the floor. So I bleed them again, rock hard then start the car and boom the brake goes to the floor. I don't get it. I checked a lot. The clutch looks to be straight cable so its not in the mix. This ones got me. I hope there is something all the folks out there know. I have worked on any a car but never a VW and this has really got me wondering.

[Briano1234]

If you didn't bench bleed the master cylinder then it may still have air in the system.

if you can manually pump the brakes rock hard and they hold firm with out bleeding off, then apply vacuum boost and they sink to the floor.
I would have to say that you have a defective brake master cylinder.

If you didn't take the rears off to check I have seen where you can blow out the rear wheel cylinders. (you did bleed all 4 brakes).

I have had issues before with the master cylinder being a bad re-manned
The rear wheel cylinders are like 14 bucks each, and they do go bad too. Are you loosing any fluid?

Here is a thread that you can build your own power bleeder.
viewtopic.php?f=27&t=2135

Works good, and brake bleeding becomex a one man issue.

[cavenut]

Briano,
I never touched the Master cyl. just the front calibers. I guess by locking the brake hard I could have done something to either the rear seals or the master. I don't have any leaks so its going to be a search. I guess I'll start by pulling the rears and checking them. Any idea why that would damage the master cyl. ? Oh and yes I did bleed all four in the correct order.

[Briano1234]

Briano,
I never touched the Master cyl. just the front calibers. I guess by locking the brake hard I could have done something to either the rear seals or the master. I don't have any leaks so its going to be a search. I guess I'll start by pulling the rears and checking them. Any idea why that would damage the master cyl. ? Oh and yes I did bleed all four in the correct order.

I have seen that seals will just crap out. Hell I got 2 remanned ones from the autojobber that were bad.
I have also seen when you "stomp" on it a caliper can get "cocked" and not retract under the suction of the mc, and that it causes a false
feeling as it wont go back out, so that when you press it again there is like an air bubble between the mc, and the caliper that you can't over come.

[gull]

Sometimes an old M/C will fail during the bleeding procedure. The brake pedal doesn't go to the floor in normal driving, so there's a section of the master cylinder where the piston normally doesn't travel. It can get pitted there over time, due to corrosion from not changing the fluid often enough. When you bleed the brakes and use the full stroke, the piston seals travel over the pitted section and get torn up.