Oh it stops!

[ah_5500]

Well kinda..
Ive had a local shop doing some work on my 72 K5 Im building. One issue after another and Im pretty much done and tackling it myself, undoing and redoing.
Currently my latest issue is they redid some brake lines, new calipers, and a master and booster. When I got it back the rear would lock up. I don't even know if the front was doing anything the rear would lock up so quick.

Upon inspection they didn't install a proportioning valve. So I sent it back.
This time they replaced all of the lines and added the prop valve.
I go to get the truck and what do you know, the rear is still locking up. Any speed they lock up, even rolling up to a speed bump at 5-10mph they lock and it tries to go sideways. The brakes don't seem to have any resistance like theyre sticking. The mechanic says to just drive it and they should stop, which seems odd to me and dangerous considering the issue.

Im hoping to get some thoughts and opinions and Im going to post a picture up to see if its ran correctly or not.

Additional Info:
The two front lines coming off the prop valve go to the front brakes and the rear to the rear.
The Blazer is 5.3 swapped ( which seems to have its own list of issues too :/ )

[Spf79]

Originally Posted by ah_5500

Well kinda..
Ive had a local shop doing some work on my 72 K5 Im building. One issue after another and Im pretty much done and tackling it myself, undoing and redoing.
Currently my latest issue is they redid some brake lines, new calipers, and a master and booster. When I got it back the rear would lock up. I don't even know if the front was doing anything the rear would lock up so quick.

Upon inspection they didn't install a proportioning valve. So I sent it back.
This time they replaced all of the lines and added the prop valve.
I go to get the truck and what do you know, the rear is still locking up. Any speed they lock up, even rolling up to a speed bump at 5-10mph they lock and it tries to go sideways. The brakes don't seem to have any resistance like theyre sticking. The mechanic says to just drive it and they should stop, which seems odd to me and dangerous considering the issue.

Im hoping to get some thoughts and opinions and Im going to post a picture up to see if its ran correctly or not.

Additional Info:
The two front lines coming off the prop valve go to the front brakes and the rear to the rear.
The Blazer is 5.3 swapped ( which seems to have its own list of issues too :/ )

This sounds crazy, but have you thought about adjusting your rear drums in so that they don't grab as hard and then take it around the block a few times to see how it feels? The shoes will wear funny. Are the drums and shoes new?
I had a set of rear brake shoes that would grab and lock up every time I came to a light, just one side though. I adjusted them out and they were a lot better. I think my shoes had gotten some fluid on them from a bad wheel cylinder at one point. The PO had mentioned he had replaced the wheel cylinders but not the brake shoes because they were clean. I think he lied to me. .

[ah_5500]

Maybe sounds crazy to you but I'm a learner with drums. Im looking into it now online and will be doing some adjustments tomorrow.

Whats your (or anyone's) thoughts on the plumbing of the lines? I thought that there should be one line for the front and one for the rear coming off the valve then they would split at the axles or nearby.

Thanks!

[Spf79]

Originally Posted by ah_5500

Maybe sounds crazy to you but I'm a learner with drums. Im looking into it now online and will be doing some adjustments tomorrow.

Whats your (or anyone's) thoughts on the plumbing of the lines? I thought that there should be one line for the front and one for the rear coming off the valve then they would split at the axles or nearby.

Thanks!

I am no mechanic buddy, I only know what I know because I have not gotten myself killed yet.

I was wondering about your plumbing, I have not seen that set up either. You did say that the mechanic put new lines in?
My front lines come to a tee where my single line from the master connects. ?
I also have a single line to the rear and it is larger than the line going to the fronts.

I'll post pics, they are not great... but you may be able to zoom and see something helpful.

The one item I would check, do you have a proportioning valve for a disk /disk set up rather than a drum/disk set up? I just read a blurb online where a guy was having the same issue as you. It ended up that he had a proportioning valve for an all disk set up. His proportioning valve also has single lines for each front wheel coming from the valve. It's a long shot, but I figured I would mention it.

Good luck!

[chadcampbell00]

That's a distrubution block you have there. I had the same issue with mine and put in an adjustable proportioning valve in the rear break line and turned the pressure down. That made a world of difference

[hemi43]

Your rear wheels locking up has nothing to do with the way it's plumbed. It's a mechanical problem. Like someone already mentioned, adjust your rear shoes, and while you're in there make sure everything is where it should be and that the shoes aren't mounted wrong. There is a leading and trailing shoe, and both have different length friction material. Also, check the contact surface of your drums and make sure there are no lips on the edges which could contact the shoes first. If in doubt, put new drums on it.

Edit; I just looked at your original picture of your master cylinder. Make sure that the lines going to the proportioning valve are correct. Sometimes the front reservoir is the secondary(like my truck), which means this would need to go to the rear brakes. Look at the picture of my Blazer below, and although difficult to see, the output lines cross each other before going into the proportioning valve.

Edit#2; I found a thread from this site showing the OP also has his lines crossed. Scroll down to the picture. http://67-72chevytrucks.com/vboard/s...d.php?t=478154

[hemi43]

I couldn't edit my last post because it timed out.
It should read that the primary side of the master cylinder goes to the rear wheels.

[robs71k5]

Also the plunger in the proportionng valve may have been pushed back and Jammed while bleeding the brakes improperly. You can push it back by pulling the rear line off and with a small Allen key you will be able push it forward into alignment again. The is a thread already on this subject that has loads of info . That sounds very liking to the possible problem.

[ah_5500]

Thanks for the flow of responses.
I removed the rear drums and they were very black, cobwebbed, and dusty. The RR is the one hanging up and it took some hammer persuasion to get it off due to the shoes applying a lot of force on the drum. I adjusted it in and cleaned it all with brake cleaner (trying to avoid mass amounts in the shoes) then clicked them both out some. The RR I adjusted out a lot I felt but it continued to spin very easily and will rotate about 2.5-3 times which I thought 1.5 times is normal?
I drove about a mile down the road it seemed better but the RR locked again (once) and in the parking lot I it was easy to make it do it. It doesn't seem near as bad as it was but still very easily locks/hangs.

Im thinking that I might get new shoes and drums for both sides to eliminate those issues and be preventative...but I think there will still be and issue because it locks up so easily.

Questions
- How will I know if my lines need to be switched between the master and valve/block.
- Whats the difference between a prop valve and distribution block? I thought what I bought is like a factory style non adjustable prop valve?
- If I remove the rear line and push the plunger in will I feel it stop? Will it move easy? I don't want to damage anything.
- Should I only have one front and one rear out of the prop valve? it seems like having two front lines coming from two separate prop valve locations would not be equal pressure to each front wheel.
Thanks

[hemi43]

Originally Posted by ah_5500

Questions
- How will I know if my lines need to be switched between the master and valve/block.
- Whats the difference between a prop valve and distribution block? I thought what I bought is like a factory style non adjustable prop valve?
- If I remove the rear line and push the plunger in will I feel it stop? Will it move easy? I don't want to damage anything.
- Should I only have one front and one rear out of the prop valve? it seems like having two front lines coming from two separate prop valve locations would not be equal pressure to each front wheel.
Thanks

-That all depends on which master cylinder you have. Unfortunately, it will have to be removed to find out which side is the primary . The primary side builds a bit of pressure first, and this goes to the rear drums.

-The distribution block is what is located under the master cylinder. It's job is to prevent your rear brakes from locking up under panic stops, and also houses a switch to turn on the brake warning light if it notices a difference in pressures between the front and rear brakes. It has a built in proportioning valve. Sometimes guys will put a variable proportioning valve for the rear brakes but you wont need this.

-If you remove the rear line (assuming it's the primary side) and push the plunger in, you will bottom out the internal rear brake piston in the master cylinder, then your front brakes will apply. If everything is working properly, the brake malfunction light on the dash should also come on.

-Some prop valves only have two outputs ( front and rear brakes) GM used two outputs for the front brakes and only one for the rear on our trucks.



It's a simple system, and after reading your last post it sounds like replacing the drums and shoes will most likely fix your issue. While you have everything apart, make sure your wheel cylinders are not seized or sticking.
Also, don`t get any contaminants on the new brake shoes. Any oil on there could issues.

[GMC-YA68]

I'd replace the wheel cylinders and make sure your e-brake isn't hanging.

[ah_5500]

Originally Posted by GMC-YA68

I'd replace the wheel cylinders and make sure your e-brake isn't hanging.

Yes those too. I'm thinking tomorrow I'll get shoes drums and wheel cylinders. Should I look into new springs etc also?
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[ah_5500]

Thanks for the wealth of knowledge. My budget is only allowing small purchases currently so I bought a wheel cylinder for the one locking. Hopefully tomorrow I can swap them out.