C15A brakes jamming

[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