I am at my wit's end and would appreciate any help!! I have spent several months (yes months!) trying to get my brakes to work on my 69 SS 396. The original master cylinder was re-sleeved and rebuilt and the original front calipers are rebuilt. At first I kept getting air in the front brake (secondary) piston and I traced this to air being sucked in past the seal in the proportioning valve below the cylinder. I have temporarily bypassed the valve, and still the pedal goes to the floor. I noticed the front caliper pistons were retracting slightly when I released the pedal. I installed a different set of calipers and they did they same thing. I then installed a check valve in the front outlet port of the master cylinder and the pedal was hard as a rock after 2 pumps, but the front brakes also would not release. I thus had to remove the check valve and the pedal goes to the floor. There is no air in the system. I am using silicone dot 5 fluid. HELP!!!
Jim

It's supposed to be very hard to get the air out of DOT 5 fluid. It holds the air in little bubbles. Since it takes a couple pumps then the pedal is hard with a check valve, it sounds to me like you're compressing air. Or the master cylinder isn't working properly.

Tim.

It's not supposed to be hard, it is hard. I found that the Dot 5 seems to hold a lot of air in it. When I tried bleeding my brakes, I would push the pedal down and then open and close the bleeder. Then, I release the pedal and the pedal comes back but there is no pedal and I found if I work it slowly up and down air comes out of the hole in the master. Some of the time, the master cylinder wouldn't even spring back all the way.

In the end, it was seeming like the fluid would hardly go through the little hole leading from the reservoir to the cylinder. Small hole and very thick or high surface tension fluid or something like that. This was leading to air being left in the master during the next bleeding attempt. So, I drilled the hole slightly larger so the fluid would easily pass through it. The brakes then bled and they work ok now.

Funny thing was that the back brakes seemed to bleed OK. I think the hole on the drum brake side was considerably larger, which was the reason I decided to drill out the disk side.

The best thing to do with that fluid is to make sure not to shake or disturb it much when handling it so it doesn't get air in it.

Peter

Best thing to do is not use DOT 5 but if your insistent on it best bleeding method is pressure bleeding from the master cylinder. I beleive it was car craft that made a make shift pressure bleeder, archive thier web site for details. Dot 5 is very complicated to deal with and generally not worth the effort except in race only applications.

if you have time,try gravity bleed i found it to be the best.....

You said, that you buy passed the valve under the m/c. if you are talking about the round valve right under the m/c, it is called a pressure metering valve.
this is used so that you have equal brake pressure to the front and rear brakes.
you have to hold in the rod that sticks out of the back of the valve when you bleed the brakes. other wise they will never bleed right. use a small c-clamp to hold the rod in and then bleed.
passenger rear first then driver rear, passenger front and driver front.

I have always had trouble bleeding my 69. What I finally did was to jack up the back of the car to reduce the angle of the master cyl. Otherwise, one or two pumps of the pedal & your sucking air..

Just my .02 graemlins/thumbsup.gif

Thanks for all the suggestions!! I am going to try them all this week-end and see what works. If I can get a solid pedal I will let you know.
Jim

Originally posted by Peter F.:
It's not supposed to be hard, it is hard. I found that the Dot 5 seems to hold a lot of air in it.I said "supposed to be" because I used DOT5 and had zero problems.

Filled the master and gave it a few pumps (in the car witth rear jacked up to level the master)) and tapped it a bit to get the bubbles out. Then gravity bled to all the wheels. Couple pumps out each bleeder and it was done.

Tim.