Brake problem ARRRGH

[Ax-man]

I am about ready to pull my hair out with one of our trucks. Super late model, don't laugh from the 70's, C-50 Chevy with hydralic brakes with a hydravac.

What causes a brake pedal to push back up from the floor if you have your foot on the pedal like when your stopped at a light or trying to hold the truck on a slight incline. After this happens the pedal goes stiff and hard the brakes hold but don't hold the way they should. The truck stops good with the intial push on the pedal , but if the pedal is held too long or gets pumped a second time too quick it gets stiff and hard.. Is it in the brake system or is a brake booster problem.

We just got through doing a major overhaul on the rear brakes because we have never did anything to them since we have had the truck,way out of adjustment with frozen, with almost bald adjusters,sluggish slave cylinders, ect.ect. the brakes are working much better, but we still have this annoying rising pedal problem. We didn't do anything to the front brakes, because we did some work on them a few years ago, but I can't remember exactly what we did to them. I jacked the front ot the truck up to see what is going on with the front brakes through the inspection slots, they are working but it doesn't seem like there working quite the way they should, I got a feeling our problem is in the front brakes.

Why I am asking questions this same truck some times has a problem with running on after the key is turned off, or will back fire a little. Is this a timing problem or is it a carb related problem, (Quadra junk 4 barrel carb ) air fuel set to rich or the float set to high???

Larry

 

[Marco]

Could be air in the system, can be hard to get it all out especially if the hydravac is under the cab and not next to the master cylinder. If the hydravac unit is under the cab it may have a bleed screw too.

 

[DDM]

Make sure the vacuum hose feeding the hydrovac doesnt have any leaks. Like dryrot. Ive had trucks do the same in the past but cannot remember what the cause was.

 

[Ax-man]

You guys might have hit the nail on the head, cause I really haven't checked out the hydravac, it is under the cab and if it is similar to a Fords there is a bleeder on it, forgot there was a bleeder on those darn things, I have only changed one in all the time I have been in biz, they are a Royal PITA if you have to work on one.

I bet it is one or the other, before we called it quits for the day, I had the truck out of the shop idling with my foot on the pedal and sure enough the pedal came up, but I heard the RRR's pick-up a little as the pedal was coming up which made me think the problem may be in the booster.

Thanks guys, you gave me a nudge in the right direction.

Larry

 

[begleytree]

Only time I saw the brake pedal come up on me was when the vac line was blocked/clogged.
dieseling prob, your carb should have an elect idle sol. on it. when you start the engine, you give the gas a slight push to open the butterflies and let the elect idle hold. when you shut it off, power is cut from the sol and that allows the butterflies to close off, and the engine to stop. sometime the sol is unhooked or defective, and the carb must be idled up to keep the engine running. this allows the dieseling. sometimes guys don't know what the sol is for, and will adjust the idle with the idle screw, instead of setting the idle screw to completely close the butterflies, and take a wrench and adjust the sol plunger for idle. Sometimes folks also remove the 2Bbl and replace it with a 4bbl thinking the truck will run better. it won't, it'll run about the same or slightly worse, and use twice the gas it did on the 2bbl, cause the 2bbl has bigger jets, and the 4bbl has to run the primaries and some secondaries to do the same amount of fuel dump. this is assuming you have the 350, not the 366. the 366 came factory with the 4bbl
also sounds like your timing is slightly advanced, or your carb is loading up.

What is this truck? 350 4bbl 4 spd with the usual low 7.17:1 rear gear ratio? runs about 55mph at 3K rpms? or is it the 366 with factory 4bbl? or is it the super six, 6 cylinder
-Ralph

 

[Ax-man]

Hey Ralph,

The truck is a C50 ( 2 ton ) Chevy dump, with a 350 4bbl, 2 speed rear end. Weak motor for that size truck IMO.

I'll take a look at that solenoid see what is going on, I have had many Chevy's over the years, I know what your talking about. I just have to get off my duff do a little checking and investigating , I just hate working on trucks any more these days, always have to keep after them, get one problem fixed and before you know it more pop up. Always something. :bang: