69 Chevelle SS front disc brake bleeding
 

Lately I have been going through the brakes on my Chevelle including flushing the brake fluid with fresh DOT 3. When I went to bleed the front brakes I never got what I would characterize as acceptable flow without bubbles. I used a hand pump Mighty Vac bleeder. When I finished as best I could with the bleeding I had an acceptably firm pedal. The front wheels spun relatively freely after several cycles of applying the brakes. When I test drove the car (did not exceed 30 mph) it drove and coasted nicely........for the first 10 minutes, then the front calipers began to bind increasingly worse as time went on. They were not overly hot by the time i got back to the house, i.e. I do not think that I "boiled" the brake fluid. I had my master cylinder rebuilt recently by White Post. I rebuilt my pressure metering valve (located next to and below the master cylinder) myself with a rebuild kit. I also lubricated the bushings and pins on the calipers to ensure that they were not binding. I learned something new when I read the chassis repair manual (see attached photo) where they recommend depressing the plunger on the pressure metering valve when bleeding the front brakes. I haven’t tried this yet but wanted to get input from some of the Masters out there on things I might have missed. Thanks

I have no personal experience with White Post, but have heard nothing but good things about them.

Hard to diagnose without being there, but my first thought was the a residual pressure valve was installed under the brass fitting on the disc brake port on the master.

The first thing I would check though (because it is easier) would be to make certain there is sufficient free play at the pedal, AND make certain the pin between the booster and the master is not too long. If it is just 1/8 inch too long, it is pre-loading the master.

You can check both of those without breaking into the hydraulics.

'

What brand and how recent are the Flex lines...collapsing inside?
:hmmm:
~ Pete

.

Lynn, thanks for chiming in. Yes, I checked the pedal for free play and have confirmed that the pin coming out of the front of the booster is not preloading the master cylinder.

Pete, until recently I had the original flex hoses on this car. But, I replaced those with In-Line brand and am confident that they are not collapsing. Thanks

Sam,

"Recommend depressing the plunger on the pressure metering valve when bleeding the front brakes."

Absolutely.....this is a must.

Dan

Well, I bled the brakes again and decided to follow the manual and depress the plunger – imagine that! Well that certainly is a new one on me, but then again I have only owned this car for 12 years now! Yeah Dan, I expect you bled a few 69 SS front brakes before. Took the car out for a 25 minute spin using the brakes frequently and no binding of the front calipers! Yippee! Thanks all.

Learned long ago about depressing the plunger on the valve. I had a ‘69 Pace Car that “taught” me.

I guess that I am curious why my initial NOT depressing the plunger on the pressure metering valve led to the front calipers to clamp down on their own while driving.

This is why I questioned the flex lines.
Glad things worked out, hope all's good from here!
:beers:
~ Pete

.

Too Late to add anything to this,but just went through bleeding my own brakes recently with a similar outcome.