brakes still problematic

56chevtrk

56chevtrk

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So as said I have been having problem getting decent brakes on my 56 Chev pickup.

My braking system is actually a stock 1980 C10 front disc and rear drum set up with a new
"corvette style" booster and master cylinder.

I was just out with one of my sons doing the two person pedal pump & hold while I crack individual bleeders thing.

I have good solid fluid flow from all wheels. The pedal feels good!

I then start the engine while resting foot on brake pedal and feel the pedal drop a bit telling me the booster is working and then basically loose all pedal firmness.

Does not seem to be any fluid leaking anywhere!

On a side note and certainly related when pushing lightly on the brake pedal with M/C reservoir cover off you can clearly see fluid pushing up in the front reservoir (discs) but no fluid movement in rear reservoir at all!

Is that normal? Should there not be fluid movement in the back reservoir as well?

I think I have been careful pushing the brake pedal as I have a thick piece of plywood under the pedal to hopefully prevent going to far and maybe turning a seal inside M/C.

Last time I checked vacuum off of engine it seemed low but I can't remember right now what it was. Could low vacuum cause this kind of problem?

Not to sure what to try next!!!
 
Both are new but I guess that does not mean that that could not be happening. Who knows how long it was sitting on the shelf or if I rolled a seal in the M/C. Maybe thats why I am not seeing fluid movement in the rear reservoir!

These are new because I first purchased a firewall mount booster & M/C 15 or so years ago and by the time I got to testing it the M/C was leaking - into the booster. That was visible as it was leaking out the front of the booster but I also saw it inside the booster.

If I disconnect the M/C from the booster I should be able to see fluid inside the booster once again if it is indeed happening again!

Or at least see fluid coming out of the M/C!

I will look tomorrow. Good start.
 
Just a thought here, and I expect you have this covered anyway. I'm wondering if you have the firewall and pedal mount adequately braced so that the firewall is not flexing under a hard brake application. The description of your problem does not really point to this as you say the pedal is softer with the engine running than with it off. Just that the cab was not originally designed for firewall mounting so additional bracing is required.
 
Yes the first firewall mounted booster and M/C came with a template and firewall under dash brace that also locks in the steering column.

I got lucky when I ordered my second booster & M/C in that I only had to drill 2 new holes through the firewall and bracing behind and under the dash.

So I think we are good on that front. Thanks for helping.
 
Just a thought,but if you find yourself having to buy a new booster you might want to look into a hydraulic booster like a astro van or one ton ,or diesel pick up. it will run of the power steering pump
 
chimp koose said:
leaking brake fluid into the booster ?
Click to expand...
Pulled the M/C off today and checked booster. Everything is dry as a bone. No fluid moving into booster. I guess that does not mean that fluid is not moving past seals inside the M/C though.

I tried something else and had interesting results. This after I removed the M/C and bench bled it again. I think it was okay.

After mounting the M/C on the booster again I disconnected both brake lines and plugged the M/C with some fitting I fabricated.

I then have a great pedal with engine not running. But again as soon as I start the engine I loose most of the pedal! I am also hearing a swoosh or hiss when I press on the pedal. In my research it says my booster could be leaking. When I do another test - holding my foot on brake pedal and starting engine the pedal drops a bit just like its suppose to so that tells me the booster is working - I think!!!

Any ideas anybody?
 
I also checked my vacuum today and at idle I only have 12. It climbs up past 16 or 17 when I rev engine up and back off. I know that is pretty low and I am having trouble finding definitively what the Ramjet 350 is suppose to be maintaining. I am seeing references to some Chev small blocks producing lower vacuum numbers even without any sort of high lift cam in it.
 
Interesting problem, I’m watching the thread to see if I can learn something. Keep us informed.
 
Are you sure the MC is the correct dia for a booster? A small dia MC will have to stroke a long way to provide enough volume to activate 1/2 ton brakes. Im guessing the bore dia would be somewhere around 1.125 "
 
After a very quick look it appears that a 1" MC bore diameter is standard on C10 but the booster size I have may be smaller than stock.

I am going to keep looking at a few other parts sites and see what they are listing.

This was after looking at Summit's - the one I am most familiar with - website and M/C & boosters for ca. 1980 C10.
 
I run a 15/16 without a booster disc/drum but probably smaller volume than your system. Takes firm pressure to haul it down or lock'em but not stupid.
I'm thinking you could run a bigger Dia master?
Fred
 
A few years ago i had my work truck in for somthing I can’t remember...anyways the guy doing the work had the same truck as mine but he noticed my brakes were way better than his. Mine had a dual diaphragm booster where he only had a single. He went and got the same as what I had and his brakes where much better...maybe?
 
I don’t think that the size of the MC is going to cause the problem that you have, it will affect how much pedal pressure is needed but not a sinking pedal.
 
JohnnyBgood said:
A few years ago i had my work truck in for somthing I can’t remember...anyways the guy doing the work had the same truck as mine but he noticed my brakes were way better than his. Mine had a dual diaphragm booster where he only had a single. He went and got the same as what I had and his brakes where much better...maybe?
Click to expand...
I am going to confirm whether mine is single or dual diaphragm. I think it is already dual!

Thanks
 
Rusty Olds said:
I don’t think that the size of the MC is going to cause the problem that you have, it will affect how much pedal pressure is needed but not a sinking pedal.
Click to expand...
I tend to agree. After a bit more research I am seeing both 1" and 1 1/8" diameter M/Cs in 1980ish Chev C10.

The booster I have seems smaller than what I am seeing in OEM applications.

Thanks for your help.
 
I think that the fault needs to be found first then see how good the brakes are. The size of MC/booster can then be considered, or even the amount of vacuum you have. But the sinking pedal is the prime issue.
 
When not running,, I had a "hard" pedal; when running, a "soft" pedal until at speed, then the pedal was okay.
Had to install a vac reservoir as the intake manifold was producing low vacumm at idle for the power brakes to work properly.
 
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Rusty Olds said:
I think that the fault needs to be found first then see how good the brakes are. The size of MC/booster can then be considered, or even the amount of vacuum you have. But the sinking pedal is the prime issue.
Click to expand...
Agreed.

I do have another booster that came with the first kit I purchased, probably the same size, and I am going to see if it will bolt up to my M/C and see if it makes any difference. Would not be the first time a brand new part has malfunctioned!!!

Other than that I am going to re-check that my callipers are correct and that my rear drum brakes are adjusted properly as either of those can affect proper brake function.
 
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