67 Corvette PB J56 Brake Problem

[72-SS-L48]

Hi Guys,

I just did breaks on a 67 J56 PB cars. The proportioning valve was rebuilt and the booster is brand new. We bled the front brakes and they are perfect. After pumping the pedal and holding it, the pedal sinks to the floor releasing the air when we opened the bleeder.

The problem is the rear brakes. We have fluid to them, but we cannot get pressure. After pumping on holding the pedal even when someone opens a bleeder in the rear the pedal remains hard and does not sink to the floor as it should, releasing the air.

We swapped a master cylinder, that is not the problem. We also changed the proportioning block, that did not change anything. We pulled the proportioning valve off the car and took it apart again, that looks to be ok.

What are we overlooking? Any help is appreciated.

Best,
Dave

[PeteLeathersac]

Are the rear flex lines new?.
If not it's possible they've internally collapsed and/or there's blockage at a rear splitter/joiner block?.
When rebleeding it may be best to start w/ the furthest wheel from the master first...RR then LR to RF and LF last..

Good luck!.
<<GRAEMLIN_URL>>/beers.gif
~ Pete

[72-SS-L48]

Pete,

Thanks for the post. I'm thinking it has to be either the rear hoses or a bloackage some-where. Also to clarify, when I bled the brakes I started on the passenger side rear then moved to the driver side rear and so on to the front.

Best,
Dave

[napa68]

Dave,
Given the details, I would crack the hose open on the one side to see what it does to change the pedal feel and also see what kind of volume you get. Do you think you could have a pinched hard line? BTW, why did you do the brake job in the first place?

Tim

[72-SS-L48]

We did an engine compartment detail on the car. The owner (a friend of mine) expressed some brake trouble. Turned out to be a leaking proportioning valve and a bad booster.

-Dave

[Mr. Chevy]

Be careful if you are using anything reproduction in the system. From the master cylinder, booster to the valves... Problem could lie with that also, but like Pete said I would change the flex hoses out first and try it...

I can tell you first hand that some reproduction master cylinders are JUNK and I'm sure some boosters and valves are not far behind... Your better off rebuilding an original core and using it...

Rich

[L30M20]

Adjust the rear shoes up until they are dragging the drum,not to tight, just so you can somewhat spin the drum/axle, there must be resistance against the shoes/piston in order the create the pressure needed to bleed properly. Good Luck! C

[Fast67VelleN2O]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: L30M20</div><div class="ubbcode-body">Adjust the rear shoes up until they are dragging the drum,not to tight, just so you can somewhat spin the drum/axle, there must be resistance against the shoes/piston in order the create the pressure needed to bleed properly. Good Luck! C </div></div>

1967 Corvette has rear disc brakes, not drums.

[72-SS-L48]

Hi Guys,

I replaced the rear brake hoses today. While everything was apart I removed the blocks, cleaned them and blew out the lines. Put everything back together and pressure bled the system. Whatever it was, we solved it. The car has 100% brakes right now.

Thanks for your help,
Dave

[TimG]

Just did my brakes on my '65 Corvette three weeks ago, same problem on my front caliper. We changed both lines and they work fine. Mine were original 45 year old hoses.