Brake combination valve question

[earl84]

I have been just barely getting my truck on the road and driving a little. Working through MANY little things slowly but surely.
Anyway, took it out today, and the front end had kind of a shimmy. Did not feel through the steering wheel at all. Took it to the local tire store and jacked it up to check the balance on the wheels, even though I really didn't think this was the cause, but I felt like eliminating the easy things first. When we jacked it up, the front tires were not turning freely at all. The brake calipers were grabbing the rotors. Front end swapped for a 79 C20, used the 66 brake booster, 79 master cylinder, hard lines from a 1/2 ton and all new rubber lines and all new brake components. The guy at the store seemed to think the combination valve might be bad. I got it home and took the master cylinder loose from the booster to try and eliminate a bad adjustment on the push rod as the culprit. When totally loose, the tires could turn easier, but pads were still grabbing the rotor.
Do you think this combination valve is bad? I am having a hard time locating a new one. I do not have the wire hooked up for the light. I also read something about having to center the valve??? Any help would be appreciated.
Oh, I took the temp of the rotors and they were up about 300 degrees. They were brand new. Do you think they are still good? Should I have them turned? I have not checked runout on them yet, too damn hot, haha.

[earl84]

Adjusted the actuating rod in the booster, will have to drive tomorrow and see if that was my problem. It was a little long, by maybe 1/2 inch at most, but maybe that was enough to cause the brake dragging.

[Ozzy2013]

Curious if that was it.

[Jeff La]

Did you put new hoses to the calipers, the calipers may not be releasing quickly.

[Captainfab]

The '66 booster has the long intermediate pushrod. The '79 master cylinder should use the short intermediate pushrod. You need to change to the short intermediate pushrod.

[earl84]

Originally Posted by Ozzy2013

Curious if that was it.

Me, too, gonna take it out here in a little bit for a drive.

Originally Posted by Jeff La

Did you put new hoses to the calipers, the calipers may not be releasing quickly.

I did install new hoses, and initially used the old calipers. One of the first times I drove it, I knew the front right was not releasing all the way, because it got quite warm, so I bought two new calipers, and that' what is on there now.

Originally Posted by Captainfab

The '66 booster has the long intermediate pushrod. The '79 master cylinder should use the short intermediate pushrod. You need to change to the short intermediate pushrod.

Where do I get the short intermediate pushrod? I actually think I have this licked, when I made the swap, I cut the pushrod quite a bit, redrilled and tapped it to work. I think I just had it adjusted poorly, really poorly. Hoping my new adjustment is the issue and I can check this off the list and move on.

BTW, thanks for the replies everyone.

[earl84]

Well, that made a world of difference!! Shimmy is pretty much gone. When I got back home, the passenger side tire spun freely, the driver's side hung up a little bit. Gonna make one more slight adjustment and try again. Yesterday's temp gun said 300 degrees on the rotors, today was about 160, progress. Gotta work on something else today, though, so test drive will have to wait.

[earl84]

Thought I made the adjustment and solved my problems, but it still drags on the rotors when the truck gets warmed up. Not as bad, but the shimmy still shows up, (although not nearly as bad), once it gets warmed up. The calipers seem to not be letting go all the way. Do the combination valves go bad? I already replaced the calipers, but maybe they are bad new parts, it happens. What else could cause this to happen? Bad master cylinder? Bad hoses? Keep in mind, the entire brake system is new EXCEPT for hard lines and this combination valve. Any help is appreciated.

[davbowen]

there needs to be a small amount of play in the pedal before it makes contact with the booster and or the m/c. mine was similar about dragging. I took the booster to m/c rod and cut off 1/16" and that gave me the play needed. I also had to relocate the brake pedal rod down about 1" lower.

[earl84]

I made another adjustment, and went for a drive. It still is getting better, maybe I just need to make a major adjustment and go from there. I thought I had measured it accurately, but apparently, I am not doing a very good job of measuring.
Also, what did the lowering of the brake pedal rod do for you? Thanks for the reply.

[davbowen]

I added a power booster and the pedal when half way to the floor when running before engaging the brakes. if you do a search here you can a lot of info about doing it.

[earl84]

I seem to remember reading about that now. I had power booster already, so didn't think I needed to change the attach point for the brake rod. I could be wrong, it wouldn't be the first time, or the last, haha.