Manual brake problem, need some help

[ScottH]

I just installed a new master cylinder in a 68 which has the manual drum brakes all around. The problem I have is that the pedal is pretty much all the way to the top and hard as a rock. The engine isn't completed yet so it isn't driveable, but I'm concerned that something isn't right with the pedal being so high and hard. I did bench bleed it before installing, and bled all wheels afterwards.

Any ideas or suggestions would be greatly appreciated.

Thanks.

Scott

[LockDoc]

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I'm not sure I can help with this but a couple of things come to mind. If the rod from the pedal to the master cylinder is too long "or" there is no return spring on the brake pedal under the dash it won't let the piston inside the master cyl. return far enough to release the pressure from the brake system. If this is the problem you won't be able to roll the truck back and forth in neutral. The only other thing I can think of is that something may be binding somewhere or you have the wrong master cylinder (I'm not sure there is a difference). Maybe someone with more brake knowledge on our trucks will chime in.....

Some things to think about anyway.

LockDoc

[Jim_PA]

Are they adjusted too tight?

[ScottH]

Thanks guys, all wheels spin fine (up on stands all around right now) and stop when brakes applied.

I've been thinking about this and I think it may be one of two things, or a combination. Like Jim said, I could have over adjusted them. Also when I bled them, the right front had hardly any pressure, just kinda trickled out. From what I've read this could be a bad hose or wheel cylinder. I have to get new bleeders all around so I'll rebleed them again and see if I still have a pressure problem with the right front.
If I do, I'll start by replacing both front hoses as they look to be the oldest part of the system.

Scott

[68gmsee]

Not sure what you mean "all the way to the top." Do you mean that there's no free movement of the pedal before it becomes hard? As was mentioned, the only thing that can cause the pedal from being solid like that is either a bind, bad master cylinder, or brakes adjusted too tight.

When you bled the brakes, did the pedal move almost to the bottom without binding? If that's the case, then the brakes are probably too tight and you can readily check that by rotating the wheels...

[ScottH]

Yupper, pedal went to floor with no problem.

Any suggestion on proper adjustment method? I've always adjusted them until they are dragging slightly - so you can turn them but it takes a little effort to go all the way around.

[68gmsee]

I guess you've got it under control...

One thing that I will say is that these old trucks will have bad hoses. In some cases (mine specifically) they will swell internally and you will have a hard time depressing the pedal because the flow is restricted. I'd replace all of them and don't forget the rear hose above the rear axle going to the frame.

[68gmsee]

Originally Posted by ScottH

Yupper, pedal went to floor with no problem.

Any suggestion on proper adjustment method? I've always adjusted them until they are dragging slightly - so you can turn them but it takes a little effort to go all the way around.

That's the way I've always adjusted mine when I put new shoes on. Then come back after I drive it around for a few days and check it again so they drag ever so slightly.

I check the new brakes periodically about every few weeks for a couple months (depending on your driving) just to make sure that they're worn evenly. Usually, I don't need to adjust them after that but about once a year.

[ScottH]

Thanks very much. I'll update the thread once I get the chance to work on them again. Hopefully with good news!

[PanelDeland]

I would suggest replacing all the brake hoses.Think about 40 years.Think rubber.Think elements.Think about running a 40 year old set of tires.

Brakes and steering are not the place to "Cheap out!"

[ScottH]

Yupper, totally agree, if I'm in there for one I'll do them all.

Thanks.

[HavinSomeFun]

I completly replaced all the break system in my 67. It had been sitting for several years and I didnt trust any of it! I was amazed all the parts were available in the parts store!

[slammed1]

I have done tons of brake systems on many styles of brakes and I have always felt 4 wheel manual drums with no power brakes always had firm pedals that tend to get a little softer as the shoes wear. Personally I feel that a non power boost 4 wheel drum set up tends to have a firmer feel from all the systems I have rebuilt in the past. I have been a frt end/brake/alignment specialist for near 20 years.

[Shyguy]

My son's '70 C-10 has manual drum brakes and has a real firm feel to the pedal, but it stops real well with enough pressure applied to the brake pedal.

I have '71 C-10 with manual disc brakes and it has a firm pedal, but stops with a little less pedal pressure.

Danny

[slammed1]

Its funny that while sitting still and applying pressure to the brakes makes them feel really firm too but once the vehicle is rolling and the same pressures are applied the pedal feels different. I have done completely rebuilt brake jobs and the pedals would hardly move while testing in the shop but once your on the road testing they feel great.