Brake proportioning valve bad?

[madmaxp01]

I've got a frustrating problem. I wonder if anyone could offer me some advice.

I own a '67 CST10 with a 327ci, and drum brakes all around.

As I was leaving my driveway, I felt the brake pedal sink to the floor.
I discovered the short rubber brake line going to my passenger side brake had burst.

No problem. I changed the line.

As my friend worked the pedal to help me bleed the lines, I noticed very little fluid coming from my front bleed screws (less than from my rear bleeders). After a long time of bleeding, I started the truck to test the brake power. There was hardly any pressure under the pedal. It would travel all the way to the floor board. It would have been suicidal to drive it.

Both my master cylinder and booster are under 4 months old.

Is it possible that the proportioner valve could have blown as the brake hose burst?

Any advice would be much appreciated. Thanks!

[rico7769]

Had a similar prob with our 67 gmc custom. Pressed to bleed the brakes in order and got "dribble" out of the lines. Had my brother stomp them one good time and it shot out. Lots of "crap" gunked up in the line. We had just changed over eveything from the MCyl to the wheel cylinders and couldn't figure out why for us either. Do you have a dual reservoir mast cyl? Prop valve distributes pressure to the correct specs like 80/20 Front rear,etc. There are ways to reset them too if they are the culprit and the valve is stuck to one side if I'm not mistaken. Check the site and do a search, not too long ago there was a write up about resetting the prop valve by jacking up the truck in a certain order with the wheel cylinder bleeder valve open to get it to "pop" back into place.

[Tx Firefighter]

4 wheel drum brake trucks do not have proportioning valves. All that unit below the master cylinder is is a splitter. Prop valves became in use in 71 when they went to front disc brakes.

[madmaxp01]

Tx firefighter: Maybe I'm using the wrong term, sorry.

Yes, i do have a dual reservoir master cyl. I'll have to look into the resetting of the valve/splitter(?).

[Tx Firefighter]

Start bleeding it at the master cylinder, loosening and flushing at each connection from master to wheel. I'd suspect you got air into the master cylinder when the line ruptured.

[66_k10_manny]

I just installed front disc brakes complete with mc and booster on my 66 k10. Kept the rear drum. I installed a new proportioning valve complete with new lines and bled the system. My front brakes grab great but the rear brakes are locking up real easily. My pedal also feels kind of spongy. Do you think I might have a similar problem with air in the system or having to reset my proportioning valve?