The Stovebolt Site Forums The Parking Lot Big Bolts Brake Advice?

All right, I think I already know the answer, but since I hate troubleshooting with a checkbook, I thought I would ask here first.

'64 C60, 292, 4+2. I have had her for about a year now. When I first got her home the brakes would almost put you through the windshield. I could have 10 ton of gravel on the back and those brakes would still bring you right to a full stop in a hurry! then they started to fade. They got a little weaker and a little weaker. So I decided to have a look and see what was going on and where to go.

The bleeder valves looked as if they had not been touched since it was made. Rusted and crudded in place to the point of being useless.. So, started there and got new valves installed to bleed the system get some clean fluid in and go from there.

Fast forward a bit. I have nothing now. No brakes. The first time you touch the pedal it mushes slowly to the floor and does nothing. Let it come back up? Now you are pushing on a rock and it won't move at all. And stil no brakes.

What's the call?

I would be looking at the master and booster, including the vacuum available to the booster.

I am thinking the booster is smoked. But I was really hoping someone would tell me something different cheap and easy!

Hope is not a plan, son. ;{)

Is there a vacuum booster mounted behind the master cylinder, or a Hydrovac somewhere along the frame, usually on the driver's side behind the cab? Either way, it sounds like you've got a failed booster. Did you just get the bleeder screws changed, or the complete wheel cylinders?
Jerry

Don't forget to check the vacuum check valve between the engine and the booster. There may be a vacuum reservoir tank somewhere too.

There is no booster behind the master cylinder. I have the under the driver side frame mount version. There is nothing damp or showing signs of leaking on the inside of the tires/wheels. so I didnt open things up and change the wheel cylinders. I just changed out the bleeder valves.

Vacuum check valve and reservoir tank? AH!!!! So there may be even some slight sliver of hope! I doubt it! But, at least it is something I can wish for as I wait for weather to clear and crawl under the old girl again. I know I am going to be looking at a bad booster.

So then the question becomes deal with a bad booster? Or look into upgrading the entire system?

The booster could have a stuck valve or piston or a torn diaphragm, none of which would show on the outside or cause a leak. The master could be stuck.

If the fluid came out clean from the start of the bleeding process, the hydraulics could be OK. My guess is it was rusty brown and all the cylinders at the wheels, master and booster are loaded with crud. I got lucky with mine, the master and booster had been replaced shortly before my purchase. All the wheel cylinders were toasted, only one leaked externally.

All fluid was amazingly clean and clear. I was shocked to be honest. No fluid stains on the firewall inside or out to show the master cylinder leaking. I can't see the master being stuck. I get full pedal on that first push. It goes all the way to the floor. When it comes back up, the second push is like hitting a rock and it won't move. With truck running or off, either way, when I pull the lid off the pot I can work the pedal freely to the floor and back as I bled the system. So to me the master is OK. Am I missing something? Clear fluid, no leakage on the firewall, full pedal on fist pump OR with an open system during bleeding. Buckle everything up, sealed system? Once to the floor and then you have a rock. In my head I am thinking booster.

And in my head I am also thinking power steering pump unit and hydraulic booster/master cylinder from a mid 80s one ton swapped in would be pretty cool.

You could test your theory of failed hydro-vac. Disconnect the brake line that comes from the M.C. at the hydro-vac, connect that line to the tee that feeds the rest of the truck. Now you have a manual system and if all is well after bleeding you should have solid braking and no loss of fluid. I'm running my '57 two ton in that manor and the brakes are good even with a full load of hay on it.

Surprisingly enough, NAPA stores can usually order a rebuilt hydrovac unit for most of these old trucks- - - -they're still in use enough for the rebuilders to keep turning them out. They're not cheap, but having good brakes set up the way they came from the factory is good insurance- - - -especially in case of an accident when some ambulance chaser lawyer starts questioning why the brake system was modified as he sues you for everything you own.
Jerry

If the pedal goes to the floor then gets hard, I look for miss-adjusted shoes, as in too loose. You are pushing them freely to the drums on the first stroke, pumping them up. This is very common with drum brakes to a lesser degree than you describe. Have you adjusted the brakes properly, per the book?

Your description of gradually fading brakes over time is consistent with need for a brake adjustment. When bleeding the brakes, did you bleed the hydrovac? Supposed to bleed that first and it usually takes a pressure bleeder or a lot of patience on the part of the wife/helper. Air in the Vac probably wouldn't cause the hard pedal symptom you describe but when the dust settles on that problem, if you have mushy pedal, bleed the hydrovac, then do the wheels from farthest to nearest the hydrovac in that order.