C15A brakes jamming

[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