Combination valve malfunction??

[slikside]

I've done a search, and found some good info, but none of the scenarios were exactly the same as mine, so here goes.

'72 C10 disk/drum. Just finished a complete brake system overhaul. The only part between the pedal pushrod and the pads that isn't new/rebuilt is the combination valve....but it is new to this truck.

I sent the calipers, master cylinder, combination valve, and vacuum booster out to be overhauled. The shop said that my combination valve was shot, but they had one just like it and gave it to me for the price of overhaul. The pin on the metering portion was in, and they said it would pop out after the bleeding process. Well, the bleeding took a while, but we have a firm pedal. Hooked up the wire to the warning switch and had the red brake light on. Pushed hard on the pedal, and the light went out. But here's the thing, the pin on the metering valve has never popped out. It was clamped during bleeding as the procedure calls for.

I do have brakes, but they feel about the same as they did before all this work! Very difficult to get it locked up on the pavement. Found a little dirt road nearby and slammed on the brakes there. The rears are locking up (not prematurely) but the fronts are not.

I have the factory service manual and have read all about this valve. I'm thinking this "replacement" valve I got might not be any better than my original, which they said was junk. The truck just doesn't stop as well as I think it should, and even though my brake (idiot) light is extinguished, that pin on the metering valve has never popped out.

So what do y'all think? I appreciate all your input.

[ole dollor]

slikside: if you have good brakes just drive it a while and get ever thing seated in, if the peddle is real hard check the vacuum to the booster and make sure its getting full vacuum and hooked up properly ....

[BurnoutNova]

I've had the prop valves go bad on me, I'd get a different one and try it. Or, do as ole dollor said and make sure the pads and shoes are seated all the way.

[slikside]

Originally Posted by ole dollor

slikside: if you have good brakes just drive it a while and get ever thing seated in, if the peddle is real hard check the vacuum to the booster and make sure its getting full vacuum and hooked up properly ....

I do feel the brakes are "good enough to drive around", even if I think they should work a little better than they do. But what do you mean by getting everything seated in?? Today I took the rear brake drums off because I wanted to check how the new rear axle grease seals I put in were holding in the oil/grease.....doing good there. I notice that the new shoes on the back are wearing in in various places....is that what you mean? I have put about 15-20 miles on it so far...a lot of it on the freeway, checking the brakes there too. Pedal is good, not spongy. Vacuum was about 17.5" before I hooked it up to the booster. I hooked it up, and then pushed hard on the pedal, and that's when my brake light went out....but the pin on the prop valve did not pop out.

Originally Posted by BurnoutNova

I've had the prop valves go bad on me, I'd get a different one and try it. Or, do as ole dollor said and make sure the pads and shoes are seated all the way.

Again, not exactly sure what seated in means. I know the rears are adjusted properly. I can pull the drums easily as they just skim off the shoes on their way off. I jacked up each front wheel individually and spun them as fast as I could, and had my daughter apply the brakes. Wheel stopped right away, and I could not turn it while she held pressure. So the front brakes are working to some degree, I just don't know if it is to their full potential.... I think not because I have yet to be able to lock them up. A new prop valve is in the back of my mind, but I think I'm going to call the shop that rebuilt it, and see if they have any suggestions.

And I'm still open to any and all opinions....please.

[ole dollor]

seated in means that the brake shoes lining wear to match the drum all the way around ...a long time ago we had a machine that ground off the extra lining of the shoe so it would be the same all around and seat in faster...took all the high sides off the shoe....you would match the shoes to the drum...like you said the lining on the shoe was just touching in a few spots....hope this helps.

[slikside]

Originally Posted by ole dollor

seated in means that the brake shoes lining wear to match the drum all the way around ...a long time ago we had a machine that ground off the extra lining of the shoe so it would be the same all around and seat in faster...took all the high sides off the shoe....you would match the shoes to the drum...like you said the lining on the shoe was just touching in a few spots....hope this helps.

Ok, ole dollar, I've got it now. What I'm seeing now is the beginning of that seating process....the wearing in of the shoes to fit the drums. And, when fully seated, those brakes will be even more effective....right?

I'm guessing that this is a non issue with front pads due to how the caliper is mounted and pad to disk angle??

[slikside]

Also just got off the phone with the outfit that rebuilt/supplied the new/old combination valve.....they said that not all pins will pop out, and that as long as it isn't leaking, there really isn't any concern. Since I was able to equalize the pressure between the front and rear brakes (as evidenced by brake warning idiot light going out), I am inclined to believe them. In my search before starting this thread, I found a case where the pin would not pop out, AND he was UNABLE to get his brake warning light to extinguish. That guy eventually got a new valve, and that solved his braking issues.

So I think I'm just going to go with this for a while, and keep an eye on that valve. The shop provided a 6 month, unlimited milage warrantee on parts that they rebuild, so if it starts leaking anytime before that (or after) then I know I need to replace it.

[ole dollor]

good news...now you can take it out and have some fun....but not to fast for awhile....let the shoes seat in good.....

[slikside]

Originally Posted by ole dollor

good news...now you can take it out and have some fun....but not to fast for awhile....let the shoes seat in good.....

Yep, will do. Thanks for your input ole dollor!