C15A brakes jamming

[harrygrey382]

The brakes are sticking on my Chev. It's not that you apply and they stick, they are on fairly well, even with the shoes backed right off and hyd. pressure released. Jacked up I can hardly rotate each wheel, and it's really sapping power - can't get into 2nd while moving (lost momentum by the time it's in gear) and won't pull top on a flat. Motor is rebuilt.

I rebuilt (honed, new rubbers, all new lines, new linings) the brakes on my C15A. Problem is that was about 12 years ago. It then sat for "a while". I know alarms bells are now going off about brakes sitting unused with fluid in them. At the time, there were so many things going on, and I was so thrilled to finally be driving it (a rolling chassis with no go pedal or seat) I didn't pay much attention to how it was getting along.

Fast forward 'till now and I'm revisiting all the work I did in the past
I've tried tightening the shoes as hard as I can then backing them off. In my mind, this is pushing the pistons back in the cylinders, then I back them off, in theory creating clearance between the shoe and drum. That is, assuming the pressure is caused by the pistons sticking out. But this doesn't help, they're still just as stiff before.

So now I'm thinking, maybe the linings are too thick or something's assembled wrong (in each wheel, unlikely). Am I missing something or is my logic correct here? I'll have to pull the drums off I know but just getting things right in my head first, and haven't had time yet either...

Pedal feels good btw

[Bruce Parker (RIP)]

I bet the wheel cylinders are 'stale' and not releasing allowing the shoes to retract. Pull a wheel and a cylinder to see what's up. If the bores are clean then clean up all four wheels and the master, re-bleed and away you go. If pitted and full of crap...you'll know what to do.

Typically it goes the other way after a long sit. You apply pressure at the pedal and the rotten seals or pitting causes a pressure loss.

[TCLARK]

Also make sure there is a bit of "play" in the brake pedal when at the top. My CMP will sometimes not let the brake lights go out because all the pressure is not released. I backed off the rod in the brake master cylinder so there was play and problem solved.

[Dave Mills]

Have you by chance overhauled your master cylinder? Maybe just maybe if you have you could have placed the fluid return washer in back the front, upside down, etc. The washer is usually a wave washer, If this little washer is in back the front it will allow the fluid out into the wheel cylinders and will not allow it to return to the reservoir tank, keeping the brakes engaged. When you say you have released the pressure is this from all 4 wheel cylinders or from the master cylinder? Just a thought as I have suffered the same problem with my own repairs, not a C15A but never the less have suffered the same problem.

[hrpearce]

Originally Posted by Dave Mills

Have you by chance overhauled your master cylinder? Maybe just maybe if you have you could have placed the fluid return washer in back the front, upside down, etc. The washer is usually a wave washer, If this little washer is in back the front it will allow the fluid out into the wheel cylinders and will not allow it to return to the reservoir tank, keeping the brakes engaged. When you say you have released the pressure is this from all 4 wheel cylinders or from the master cylinder? Just a thought as I have suffered the same problem with my own repairs, not a C15A but never the less have suffered the same problem.

I agree with Dave it seems that the master cylinder is not allowing the fluid to return.

[Hendrik van Oorspronk]

Originally Posted by harrygrey382

So now I'm thinking, maybe the linings are too thick or something's assembled wrong (in each wheel, unlikely). Am I missing something or is my logic correct here? I'll have to pull the drums off I know but just getting things right in my head first, and haven't had time yet either...

Pedal feels good btw

Did you adjust the bottom mountings of the shoes correct? if not they can stick to the drum.

Hendrik

[Richard Farrant]

Originally Posted by hrpearce

I agree with Dave it seems that the master cylinder is not allowing the fluid to return.

This can be proven easily by releasing a bleed nipple on a wheel and seeing if it will then turn, if it does not then it is a seized wheel cylinder.

[harrygrey382]

Originally Posted by Bruce Parker

I bet the wheel cylinders are 'stale' and not releasing allowing the shoes to retract. Pull a wheel and a cylinder to see what's up. If the bores are clean then clean up all four wheels and the master, re-bleed and away you go. If pitted and full of crap...you'll know what to do.

Typically it goes the other way after a long sit. You apply pressure at the pedal and the rotten seals or pitting causes a pressure loss.

That's what I suspected - that's why I did what I did with the shoe adjusters. I put a lot of force on them to retract the pistons and nothing changed. So either the pistons are seized solid (I guess possible) or there's a mechanical obstruction.

Originally Posted by TCLARK

Also make sure there is a bit of "play" in the brake pedal when at the top. My CMP will sometimes not let the brake lights go out because all the pressure is not released. I backed off the rod in the brake master cylinder so there was play and problem solved.

Hmm not much play, I guess there's a tiny amount but the pedal is right at the top

Originally Posted by Richard Farrant

This can be proven easily by releasing a bleed nipple on a wheel and seeing if it will then turn, if it does not then it is a seized wheel cylinder.

Yep that's what I tried first up, no change. As above I guess you're right it could be a (well 4) very very seized cylinders.

Was liking the idea of the master cylinder return washer in the wrong way round, if releasing the pressure made a difference I'd be right on it. Now I just have to go and pull a drum off... Is going to be fun with these tight shoes

[Lynn Eades]

Probably the (aluminum??) pistons went in dry, and have grown (oxidized)in their bores.

[harrygrey382]

Originally Posted by Lynn Eades

Probably the (aluminum??) pistons went in dry, and have grown (oxidized)

They went in with rubber grease, could they still have oxidised?

[rob love]

12 years on a rebuilt hydraulic system is a long time. Agree with the others who say to try and crack a bleeder screw and see if the pressure leaves, but most likely you need to take er apart and rebuild it again.

Not sure about your neck of the woods, but hydraulic components are dirt cheap these days. Wheel cylinders run around $30-35 each. A Ford master cylinder is about the same price. Unfortunately not the same deal for the chev master cylinders at this point in time.

[chris vickery]

I had a similar problem on my first 12 cab when I had just fully rebuilt the braking system.
My pedal had little free play and the brakes worked great for a little while. After a couple miles of driving the brakes would stick on and the drums were heating up.
Investigation reveal led improper adjustment of the pushrod which was not allowing the fluid to release freely back into the master cylinder. As the fluid got hotter and continued to expand the result was application of the brakes by sheer hydraulic pressure buildup.
Once the pushrod was adjusted the brakes worked perfectly.

[rob love]

Adjustment of the master is critical, as has been mentioned. Another possibility is the collapsing of a flex line internally. They will allow fluid to go to the cylinder, but not back again. If it is the line to the rear axle assy, then both will lock on. To find this out one has to raise the vehicle and determine which wheels are dragging. But again, on a 12 year old rebuilt system that did not get a lot of use, the cylinders would be my prime suspect.

[Phil Waterman]

Hi Harry

Assume that your problem is with the rear wheels?

First my HUP has almost always had a rear brake grab when the brakes are first applied after the truck has been sitting for any length of time. Now if I remember once I pull the truck out of the garage I stab the brakes a couple of times and the problem goes away, suspected cause light rust on brake drums from sitting that cleans right off.

Your problems as other have suggested sounds like miss-adjustment, cylinder sticking in the bore, failure of the brake pressure to release, or two other causes not mention yet.

Weak or wrong length brake springs
Parking Brake, is your parking brake on the drive shaft or on the wheels?

As other have suggested very careful brake adjustment by the book is probably the best approach. Suggest that you block the truck up so all the wheels are free to turn then back all of the adjustments off both top and bottom adjusters and start fresh at each wheel.

You comment or question about something simple like brake linings being to thick would indicate to that the linings are new or really good condition, correct?

One last point, many years ago I had all my cylinders wheel and master sleeved this has ended problems with the cylinders. Now it is replace the rubber parts every 10 years on principle.

Keep us posted on what you find.

Cheers Phil

[chris vickery]

I have switched to using silicone brake fluid in my restoration work.
So far so good, the silicone fluid does not attract moisture like the regular fluid and does not peel paint neither in the case of a leak or while bleeding wheel cylinders.

[harrygrey382]

Thanks guys. Yeah if I'd thought about it back then I would have switched to silicone as everything was new. I get what you're all saying about adjustment, pressures and collapsing flexi lines but releasing the pressure at each wheel cylinder makes no difference. So it can't be a pressure issue. Also after it sitting a couple of weeks same deal.

The park brake is disconncted - I removed all linkage (fitted a 2sp TC with brake drum). But all four wheels are behaving exactly the same anyway. Yep brand new lining. My using the adjusters to try and push the cylinders in then backing right off should rule out springs too.

Another thing I just thought of - the brakes actually work really well. As in at any speed, hit the peddle hard and all wheels lock up instantly, feather the pedal and it stops gently. Release the peddle and it'll release fine (up to a point of course). No wheels drag more than the others.

So nothing is seized. Master cylinder rod still could be out, washer back to front etc. but releasing pressure at each cylinder makes no difference. This is why I was thinking about wrong lining thickness. I just can't remember what the drums were like to get on. I may well be pulling it all apart but won't if I don't have to. It's not about to get registered - I'll just use it about the property for things like firewood and hunting before anything like that

[Richard Farrant]

Originally Posted by harrygrey382

This is why I was thinking about wrong lining thickness. I just can't remember what the drums were like to get on.

When fitting new shoes, especially if relined, they should be laid in the drums to ensure they are radiused correctly. You might need to take a drum off to check unless you remember doing it ............. although 12 years is a long time!

[harrygrey382]

Originally Posted by Ghost

Hello all,

I agree with Rob Love - have you checked the rubber brake hoses?

I have had two instances of the rubber brake hoses swelling & the lines become so restricted they act like a valve. Push on the brake pedal & the brake shoes do as they are designed to do.......... but when you release the brake pedal, the fluid won't return to the master cylinder - thus jamming the brakes on.
I have had this happen to a GMC and a White.
It kept me looking for the problem for ages & the first time it cost me an unnecessary brake rebuild.

It may be worth a check - especially after 12 years.

Rob.

Thanks, sounds logical but doesn't explain why release the pressure at the bleed nipple doesn't release the shoe tension

[Rob Beale]

In the Chev master cylinder there is a tiny hole that allows the fluid back into the reservoir. If the seal in the cylinder is too long, it may be obstructing that hole. You should be able to see it through the reservoir filler hole. A thin wire or needle inserted in the hole will confirm if there is a restriction or not.

Rob

[motto]

If it was a hydraulic problem then opening the bleeder at the wheel cylinder would release the brakes on that wheel at least whether the blockage was caused by a master cylinder fault or a restricted hose.
Yes, it is possible for components to corrode over time even if assembled with rubber grease. A lot depends on the quality of the grease and atmospherics.
I don't know the exact brake set up that is causing problems here but running the adjustment out and back may do nothing to retract the pistons.

David