Brake System Help-Pedal goes to the Floor!

[duwem]

My 1950 3100 1/2 ton Chevy truck is in storage for the winter, BUT I want to see if I cant get some help so I can get parts lined up for the spring.

Truck has a stock single circuit master cylinder (under cab mounted, bone stock) and stock 4 wheel disk brakes.

Fluid level is fine and does not go down.

Brake cylinders were replaced not too long ago (before I bought it but they are still shiney)

master cylidner looks like a repacement as well, its rusty, but does not look old. Most of the brake lines have been replaced (again before I bought it)

It stops FINE if you use the brakes often, but what happens is if I drive for 15 minutes without using them, when I go to stop the pedal goes to the floor, I release it and hit it again and they are nice and firm.

It didnt always do that. I put about 600 miles on the truck last summer (first summer I owned/drove it) and at first they would work all the time, but towards the end of the summer they started to do the to the floor.




Few things I'm possibly thinking:

-Brake shoes wore enough that the wheel cylinders need too much travel to engage the brakes and the pedal goes to the floor to fill them then the second push finishes the job??

-I need to add a 2-3psi residual valve right off the master cylinder. That may fix it, but why now and not when I first started driving it??

-Internal leak in the master cylinder (no way to know, maybe you guys do?)??

-Air in the lines?? (have not had anything apart at any point)




I need to fix it because at some time the second push to stop will be too late.

[Rude Dude]

Four wheel disc brakes weren't stock, I would change the master cylinder to a four wheel disc set up. If it is stock master cylinder it is to small. Try changing the master cylinder to math the disc seventys corvette work good. The inline brake valve 2psi for disc and 10 psi for rear drum brakes, and you need a porportional valve adjuster to run brake fluid so front brakes grab slightly before rear. Or get the integrated one that has all built into one. like this

http://www.classicperform.com/Store/...cks/MCPVS4.htm

[Rude Dude]

Didnt catch it at first I think you meant to say drum brakes all around. First peel back the rubber boots on wheel cylinders all four make sure they are not leaking if no leaks try bleeding the air out if that doesnt help. Replace the master cylinder.

[_Ogre]

i will assume you meant stock drum brakes.
if your mc is holding pressure on the second push then i suspect you need to learn how to adjust your brake shoes.
when your wheel cylinders were changed, all the brake hardware should have been taken apart and lubed/freed up.

there is a star wheel adjuster that you need to manually turn thru a slot in the backing plate to get the shoes out to the drum.
the easiest way for you to see this is to remove one drum, confirm that the brake hardware is free and lubed and check how the brakes adjust.
if your star wheel is not free, disassemble it and lube it with a little anti seize lube.
adjust the brake shoes out until you hear a little drag on the drum as you manually turn the wheel.

[54foster]

I think to help you out we need more information. You said the truck has 4 wheel stock disc brakes and I'm pretty sure that wasn't a stock option. If it has drums it sounds like you may need to adjust the drums, follow Ogre's advice and adjust them until you hear just a bit of drag. I would also try bleeding the lines, but if it worked fine before you put it up and it now has air in the lines you have another problem.

[duwem]

Its 4 wheel DRUM, sorry.

[54foster]

Originally Posted by duwem

Its 4 wheel DRUM, sorry.

Have you every adjusted drum breaks, and do you have the tools for it? If not you may want to let someone look at them, but I would start out with adjusting them, if they work fine with repeated use it sounds like something is either sticking or shoes need adjusting. Although we are talking about brakes, if you have a local shop you trust I wouldn't hesitate to let them look it over. Nothing scary then stepping on the brake pedal and the truck not stopping.

[Wheelie]

Possible issues:Not adjusted properly, they should have light drag.also your drum runout is excessive causing the shoes to "pump up" the wheel cylinder. Brake line too close to heat somewhere. Those are at the top my list to check.
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[OrrieG]

Stock drum system should not need a residual valve. I drove these trucks when they were relatively new and the double pump was a sign that they needed adjusting. Even the 60's ones with self adjusters that were supposed to work when you braked in reverse got gummed up and seized.

[duwem]

Seems like you guys are saying this is the first thing to do:

Sounds like I need to spin the adjuster star wheels till I feel some drag while hand rotating each of the wheels and see if that solves it.

[mr48chev]

Originally Posted by duwem

Seems like you guys are saying this is the first thing to do:

Sounds like I need to spin the adjuster star wheels till I feel some drag while hand rotating each of the wheels and see if that solves it.

My old high school auto shop teacher taught me to tighten the star wheel until you can't turn the wheel and then back off 11 clicks and do it on each wheel.

Adjust them tight and back off the same number of clicks (star wheel clicking against spring or tab) on each wheel.

I can't remember which way works to tighten them up and which works to back them off though. Even though I've done hundreds of brake jobs in my life that part always seems to get me.

I've found over the years that after these trucks sit for several months you often need to bleed the brakes as they tend to want to draw in a bit of air past the cups in the cylinders if things are worn a bit. Brake systems like to be driven and used on a regular basis and start acting up when guys let rigs sit for months on end.

[_Ogre]

Originally Posted by OrrieG

... Even the 60's ones with self adjusters that were supposed to work when you braked in reverse got gummed up and seized.

any drum brake does this to me.

my 97 dodge ''self adjusters'' quit working within 30 days of the warranty running out

[OrrieG]

I just remembered that they rotate (click) outward easy, but you need to use a second smaller screw driver to release the rod that goes in the grooves to get them to reverse when you go to far. Knowing this will save a lot of frustration, most manuals do not tell you about this, just to adjust it.

[Helilog56]

Your master cylinder needs an overhaul...!!!!!
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[mr48chev]

Originally Posted by OrrieG

I just remembered that they rotate (click) outward easy, but you need to use a second smaller screw driver to release the rod that goes in the grooves to get them to reverse when you go to far. Knowing this will save a lot of frustration, most manuals do not tell you about this, just to adjust it.

A piece of welding rod with one end rolled around in a loop as a handle works great for that task. I kept one in the tool box for years for the purpose when I was doing several brake jobs a day.

You have to back off a bit and turn the wheel to get the "feel" you want on those setups.

I used to have a tool like this http://www.etoolcart.com/brakeshoead...toolgauge.aspx that you adjusted to the inside of each drum and then held over the shoes while you adjusted them out but didn't think it did the job I wanted it to and traded it back to the tool truck one day. It was handy for getting the shoes close before putting the drums on though and I should have kept it for that.

[duwem]

Where the 1950's originally auto adjusters or not? My guess is not but wondering if anyone knew.



Is there a duel circuit master that is a bolt in replacement for the orignal?

[Rude Dude]

No unless you fab a braket to mount, also you need to use a master cylinder that came after 1967 Chev Truck that has dual chamber for drums brakes all around.

Originally Posted by duwem

Where the 1950's originally auto adjusters or not? My guess is not but wondering if anyone knew.



Is there a duel circuit master that is a bolt in replacement for the orignal?