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Very low brake pressure

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steve from staten island

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My saga with my brakes continues. Ive found out i have almost no pressure to the front discs. I have flow put when manually bleeding the brakes(power) engine running the flow was not forceful at all.
I bought a gauge that fits into the bleeder to check pressure, granted the car was not running but pumping and holding the pedal as hard as i could gave me hardly any movement on the dial of gauge. Everything is new and i just installed a dual diaphragm booster. I will checking the master but seeing that the back brakes are ok, could i have a restriction somewhere. Could it be the distribution block? Something with the pressure valve for the warning light?
I was talking to Cass from Dr Diff and even he said i should have a few hundred psi at the least with the motor not running and he thought it could be a restriction as its both calipers. Any thoughts and thanks
 
Steve if there is no pressure at the master the problem is with the master or between it and the pedal. Did you adjust the booster rod to master cylinder. The booster rod needs to touch the master piston without moving it. At this point wasting time downstream of the master is fruitless.
Check the above. Make sure the master has been properly bled of air and try again. And don't let the master run dry.
 
I bench bled the master and it seemed fine. I do get fluid out of the calipers when i bleed them but its not enough pressure. This is why we were thinking a obstruction somewhere, mostly the block were the lines tie in that has the low brake warning .
Either way there is not enough pressure at the caliper according to the gauge installed in the bleeder port.
I'm trying to rig up something to test the master itself. Will let you know what i find and thanks
 
steve from staten island said:
the block were the lines tie in that has the low brake warning
Click to expand...
Might want to look over that low brake warning. If I remember right, that warning switch works off a built in valve. If brake fluid gets too low, and pressure, that valve moves...and does two things. Activates the warning light, and blocks flow on the bad side. Pretty sure, when that happens, the valve must be manually moved back into place.
 
miller said:
Might want to look over that low brake warning. If I remember right, that warning switch works off a built in valve. If brake fluid gets too low, and pressure, that valve moves...and does two things. Activates the warning light, and blocks flow on the bad side. Pretty sure, when that happens, the valve must be manually moved back into place.
Click to expand...
Nope. Valve will center its self when pressure lets just say equalities.
 
Did you replace the front rubber brake lines? Also air compresses. Could also be a reason for a bad reading.
 
I don't think that warning light block will block anything either. It just moves to a ground point when the pressure is not balanced.

As other have said, start at the MC and work your way out. Real easy thing to do is crack the fittings at every connection from the MC out. If fluid forcefully comes out your getting pressure, if it doesn't then that's something to dig into.
 
I dont have the factory proportional block, just the distribute block with the low brake warning switch....
Tomorrow i will check the master with a gauge setup. Every part on the brake system is new. If the master is putting out then i have to have a blockage somewhere. We already know i dont have enough pressure at the caliper, why is the question.
To all who have volunteered information and help,, thank you very much
 
steve from staten island said:
just the distribute block with the low brake warning switch....
Click to expand...
If you have a service manual for the car, check in the brakes section. If the distributor block is stock for the car, should have an open drawing of it, showing the internals, and how things work. Just trying to help out...
If it's not stock for the car, can turn into a guessing game.
 
miller said:
If you have a service manual for the car, check in the brakes section. If the distributor block is stock for the car, should have an open drawing of it, showing the internals, and how things work. Just trying to help out...
If it's not stock for the car, can turn into a guessing game.
Click to expand...
Thanks i need all the help i can get. Im going to get to the bottom of this problem. Im going to check the master. I made up a very short piece of brake line, connected to a gauge. I will have someone slightly touch the brake to push fluid to the top of the fitting, thereby bleeding air. At that point i will screw on gauge, start engine and press as hard as i can on the pedal. If i have no pressure as i had before at the caliper, I'm getting another master.
If i do have pressure than its in the block....Wish me luck LOL
 
1000 PSI at the Master when i stand on the pedal. Pedal is solid..... Next to bleed front calipers and see what pressure is at calipers....NEVER GIVE UP, LOL and thanks for the advise. Will keep you informed
 
Sounds like air in the caliper. What is the orientation of the bleeder? Is it straight up 12 o'clock? If not you may need to take the caliper off , rotate it until the bleeder is @ 12 then bleed it.
Had to do that on my wife's car, the dang bleeders on the rear point at 10 and slightly down...I even used a vacuum pump and still had air in the rears...
 
Thanks Mike, the bleeders are at the top. I checked the master and i have a 1000PSI standing on the brake pedal. If i increased the RPM trying to get the vacuum higher it improved slightly. I hooked up the master, bled the brakes again and checked the pressure at the caliper and had 800 to 900 PSI. I do not think i have enough pressure coming out of the master. Given the engine vacuum could be better, it was 13, and as it warmed up it went up to 15.
Talking to Cass at Dr Differential he told me he had many guys with the same set up that i have and the same problem. He recommended a 15/16 bore master, mine is 1 1/32 . So we'll see what that does.
 
That was my next question, was the mc bore sized correctly....read up on how that's calculated and its more than I wanted to know. ....
 
Mike67 said:
That was my next question, was the mc bore sized correctly....read up on how that's calculated and its more than I wanted to know. ....
Click to expand...
According to Cass at Doctor Diff, he was explaining to me about caliper bore sizes versus master cylinder bore sizes. The two have to work correctly with one another. The other thing is these front brake conversions, you have to be carful all the components are matched properly together.
What i didn't realize was how much engine vacuum plays into all of this.
 
Understood, I was reading about the formula used to calculate. You have to find your pedal ratio and the length of the stroke...blah blah blah...more than I wanted to calculate
 
Do you already bore the mc? am curious because I don't want that problem, am pin pointing all the parts I need to do my front disk brake conversion and so far only mopar parts, at Ieast all the front disk assembly (a body ) , new brake lines and new mc and vacuum booster .
 
The disc swap in Mopar Action said don't use master cylinders with a bore over 1" for manual brakes. Larger bores required excessively high pedal pressure. Whether this applies to power brakes I don't know.
 
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