doh! look at what I brought home

[RenoKeene]

It's a good looking truck...rust and all.

[Jack_71C10]

I found a leaking wheel cylinder when I was installing my drop kit, so I replaced it and continued with my suspension. When I was done with the drop my left rear wheel locked up real easy. I replaced master cyl, springs,
hoses all chasing this problem. I didn't think it was my shoes because they were less than a year old. I read an old post about getting grease or oil on the shoes would cause this. A lightbulb in my head went off remembering the leaking wheel cylinder. I bought new shoes - problem solved.

[a2tripp]

Thanks for all the positive replies ans support. I got some studded tires and white steelies that I am going to pop on tomorrow, pretty stoked about that.

Now I know I only had this truck for a day but its ironic that I am so ethusiastic about it. My 72 is in really good condition but I am always hesitant when I am working on it or driving it, mostly because of the fresh paint (money) etc. I guess I have just missed having a real truck, beater, jalopy, whatever you want to call it.

Today was a long day at work but tomorrw I have off and I am determined to get this brake issue resolved.

I noticed today that the pedal is about halfway down before it engages/grabs. In the dirt parking lot when I lock up the tires the front tires are what locks up and causes my grab. So its up there somewhere. I also noticed after going into reverse and locking up several times the I had a little bit up brakes before it grabbed, after driving my way home it was back to normal. It SEEMS that my back brakes are functioning normal before the grabs (maybe not though).

PLEASE CORRECT ME

So my drum/drum has a distribution block, it purpose is to isolate the front/rear in case of pressure loss? if thats the case how could this affect my front brakes grabbing?

Longhorn- how would freeplay make my front grab? I will adjust freeplay tomorrow, it looks like the po has bungee cords as the return spring on the pedal. I have not looked yet but is adjusting freeplay pretty obvious (like a bolt)?

Now the brakes must proportion itself somehow, is this done by wheel cylinder sizes? drum sizes? how?

Are these brakes self adjusting? by going into reverse? When I have the drums reinstalled should they be adjusted to were they just start having resistance?

So I will take the drum off and take a peek for leaks or whatever, any tips or specific things I should check?

A little history: I am going through the PO receipts, time line goes something like this:

a years ago, swapped master cyl, booster
6/13 shoes, 2 wheel cyl
7/13 2 wheel cyl, drums, line, hardware kit, adjusters
7/16 shoes

according to the po everything has been swapped other than the distribution block. This was an existing problem which has stayed with replacing all the brakes. It would seem logical that the problem would be before the distribution block.

Anyhow, I appreciate any input you guys have on this.

Thanks.

[Vintage Windmills]

Originally Posted by a2tripp

T

So my drum/drum has a distribution block, it purpose is to isolate the front/rear in case of pressure loss? i
Thanks.

Nope. I was just reading that the front and rears weren't isolated until later in the 67-72 production when a dual zone master cylinder was incoorporated. Think it was 69 or 70.

Even though the previous owner replaced things doesn't mean he did it wright. If he got fluid on the pads or wripped a piston seal that could be the problem. Although, if both fronts are locking up at the same time, it might be less likely to be a fluid grab issue. Good luck finding problem, let us know what it was when you finally nail it.

[a2tripp]

well what the distribution block for? does the master cylinder have two pistons?

[Vintage Windmills]

Originally Posted by a2tripp

well what the distribution block for? does the master cylinder have two pistons?

I am a little uncertain now after looking at pics of a 67 3/4 ton below. It does appear to be dual piston but I beleve the source was credible where I read about the later upgrade to isolated systems. Maybe the difference is between 1/2 and 3/4 tons? What does your mc look like?

I'm sure someone knows for sure and will chime in.

[a2tripp]

I think my m/c is the same, maybe a larger resevoir, but the way the lines go down to the dis block are identical, I also have a booster

[a2tripp]

Its seems the distribution block is there for safety, isolating the front/ rear, I think the sensor trips a light when theres pressure loss, if thats the case I dont see why that would be causing my issue.

I really wish I had a book or a FSM, even if I order one it willl be a while before it get here. I am on a island about 600 miles from normal civilization. Luckily this forum and the minds on here are way more helpful, thanks for your help!!

[VA72C10]

Nice truck. Hope you resolve the brake issue soon. Take off the drums and take some pictures and post them on here....there's a bunch of knowledgeable guys in this thread who could help out when they have pics to go by.

[RCbowtie69]

Nice buy & a good looking truck.Keep on truckin'

[a2tripp]

well I took a look at everything, made very little progress. First off those bleeders valves are horrible to get to, especially when there rusted and deformed, uh! Anyways got the drums off and like the po said everything is new. No signs of leaky wheel cylinders and everything appears to be hook up right. I bleed the brakes and loosened all the adjustments. It was much better but still locked up. Took a look at the pedal adjustment and got stumped. The PO has a bungee as a return spring but pedal braket does not look like its adjustable, so ??????
So after making a lot of reverse stops I noticed it was better but still not good enough for winter driving. Drove by les scwab on the way home and the manager is a owner of a 68. He said my problem was the adjustment on the drums, that the distribution block is not the cause. He explained to me the if the front brakes are locking up when the pedal is almost to the floor than the rear need to be adjusted, blah blah blah... I told him that I just readjusted the drum so to the point were there was no drag. He swears up and down that this is a common gm drum/drum issues and it was an adjustment issue. So I will drop it off tomorrow and see what he can do....I shamed to do it, but the brakes need to be right to drive on the icy roads up here.

I managed to grab an adapter for my carter afb. mr gasket#1932. not a single person at napa new if this was a squarebore carb to qjet manifold adapter.

[C5Phil]

subscribing--

[a2tripp]

well it been 2 weeks and I am still at a lost with the brakes. So shortly after my last post I adjusted the brakes and brought the front shoes almost all the way in... I had way better brakes but the front still locked up. Took it to les schwab and the first mechanic couldn't figure it out and told me I needed a new prop valve. So out of stupidity I ordered the $100 distribution block and installed it, gues what, the old one was fine, made no difference. So took it back to les schwab because they have another mechanic who knows brakes??????? he had it for 3 days. called me up and it was fixed, resurfaced the new front drums, power bled the brakes, and adjusted the brakes. $300 later I was off. Well the brakes were better, better than they have been. Put about 50 miles on the truck and its back to locking up. So I am out $400 good thing it grows on trees. So after banging my head for not going to disc I am writing this. What could possibly be wrong, This just does not make sense.

Tomorrow I am going to dig back into it, this time in the cab at the brake pedal. I noticed when I was wiring the electric choke that I have a couple of bungees working as a return spring on the brake pedal. Is this a common mod

c'mon drum guys out there, I can't be the only one!

[DaBigKahuna]

I haven't read the whole thread but what kind of shape are the soft lines in? Over the years they can start to swell and reek havoc with brakes.

[a2tripp]

Originally Posted by DaBigKahuna

I haven't read the whole thread but what kind of shape are the soft lines in? Over the years they can start to swell and reek havoc with brakes.

all new

[Vintage Windmills]

How bad are the tires? Even if they show tread they could be old and hard and not grip well. Also maybe try a different set of shoes? Just thinking out loud here. Curious what it will end up being.

[a2tripp]

I swapped to studded tires since I had the truck but both set have had good tread but were probally old. The shoes/drums/hoses/wheel cyl were new napa ones. its just weird....

thanks for the replies everyone