Brakes still will not stay pumped up

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67barracuda

67barracuda

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I have done a front disk brake swap with a new manual MP master cylinder with proportioning valve. I continue to bleed the brakes and I get no air out the the bleeders only fluid. I have to pump the brakes about 3-4 time to get a really hard peddle, but if I let it sit for while, it will be soft again. I acts like there is still air in the line, but I have blead the many times, I even bought an one man vacume brake bleeder. Is there something I am missing?
What should I try next?
 
Make sure the rear brakes are adjusted right and the drum turns 1 turn and stops.If the calipers are installed right with the bleeders on top and you have bleed the four wheels to the piont of no air in the fluid,clap off the 3 flex lines and pump the pedal.HOld the pedal and see if it slowly goes to the floor,if so,the master is loosing presure,replace it,Mrmopartech
 
If I up the pump the peddle and keep pressure on it, it will stay and I do not loose peddle. Only if I release the peddle and let it sit a minute, dose it loose the peddle pressure. And when I mean it looses pressure, I still have half peddle.
 
67barracuda said:
If I up the pump the peddle and keep pressure on it, it will stay and I do not loose peddle. Only if I release the peddle and let it sit a minute, dose it loose the peddle pressure. And when I mean it looses pressure, I still have half peddle.
Click to expand...

That's exactly what was going on in my case. I'd pump it up, it'd be fine, then get off it and a few second later it'd go almost down to the floor. In my case it was the master cylinder, even though the one I had was new (a rebuild, actually, but never installed).
 
mikelbeck said:
That's exactly what was going on in my case. I'd pump it up, it'd be fine, then get off it and a few second later it'd go almost down to the floor. In my case it was the master cylinder, even though the one I had was new (a rebuild, actually, but never installed).
Click to expand...

As I recall you also had a hard time accepting it was the Master too:glasses8: .
 
onehellofadart said:
As I recall you also had a hard time accepting it was the Master too:glasses8: .
Click to expand...
Yep, that's right... It was new, there was no reason for it to be bad. But that's what it turned out to be!
 
Mikel when you say new is that a new rebuilt one or a new/ new one?

as i have had problems with rebuilt MC and water pumps and I will not use them any more just for that reason.

I will spent the extra $$ for new/new.
 
abodybill said:
Mikel when you say new is that a new rebuilt one or a new/ new one?

as i have had problems with rebuilt MC and water pumps and I will not use them any more just for that reason.

I will spent the extra $$ for new/new.
Click to expand...

It was a rebuilt one, I bought it from Greg @ MagnumHP.
 
I may have bought my master cylinder for that same greg guy?
I bought it on ebay, the guy had 3-4 listed, but it was sometime ago and I got mine pretty cheap.

I think I will bleed them again and pick up a new master cylinder.
 
Did you bench bleed the master before you hooked up the brake lines? Are you losing any fluid anywhere? I agree that it sounds like a bad master cylinder though.
 
67barracuda said:
I may have bought my master cylinder for that same greg guy?
I bought it on ebay, the guy had 3-4 listed, but it was sometime ago and I got mine pretty cheap.

I think I will bleed them again and pick up a new master cylinder.
Click to expand...

I picked up a new one at Autozone (I think), and it came with a lifetime warranty.
 
Is your caliper upside down (i.e. the bleeder on the top or the bottom)? silly question but easy to do if you swapped sides.

-Daty
 
I went out a bought a new master cylinder and bench bled it last night. I will install it today and bleed the brakes one more time. I wil also look for leaks, but I wasn't loosing any fulid before.
No, the capliers are right, bleeders on top... I already fixed that mistake.
 
I installed a proportioning valve when I did the brake swap, where should I it be set to start out. If it is closed to much, will it cause what I am seeing?
 
New master cylinder didn't make think any better, but I did find a bad wheel cylinder. I will replace it tonight and hopefullly things will be better than.
 
OK, here's where I am at now.
I tryed a new master cylinder with no inprovments. So I put the old one back on.
I replaced the wheel cylinder, no help.
I started off removing both lines and plugging the ports with the given caps for bench bleeding the master cylinder. The peddle was nice and firm was as you would expect from a good master cylinder.
Next, I pluged off the rear port on the master cylinder closest to the firewall and left the front line in. Trying to eleminate which set of line is having the problem. The brake peddle was fine nice and firm.
So I witched them around plugging the front one port and hooking up the rear line back to the master cylinder. The brakes were soft as the problem I have been having but could be pumped up as before.
So I think I have it narrowed down to the rear brakes, but where do I start looking?
 
look at the flexible line from the body to the rear axle, it may be soft/leaking, check the connections around the brass tee, and check the rear line for kinks.

Have you looked inside both rear drums and verified everything is clean and assembled correctly? something may have slipped out of position.

-Daty
 
I bought a new master cylinder for my Duster and it did the same thing, turns out it was by-passing...I drove it for a while till I figured out it was a bad master cylinder...replace it.
 
Also make sure the rear shoe are adjusted up fairly tight and that the e-brake cables are not hanging and keeping the shoes from fully returning into the wheel cylinder
 
The e brake is disconnected from the frame.
I removed both drums and made sure everything was moving and not hanging up, it was freely moving.
I did remove the rearend and had to disconnect the seel line from the rubber hose when I relocated the springs. I will check that again.
I tryed a rebuilt master cylinder once already, I guess that could have been bad. I'll buy another one and try that. This time I'll buy the complete unit not just the cylinder part.

Thank
Mark
 
It's not over yet.
I put on a NEW complete mater cylinder and reservoir, and bench bled it.
Rebled the brakes lines once again.
The peddle is about half what I would expect. The brakes are better now, but they are also about half of what is need to stop the car? I double checked for leaks, could not find any.
I very close to leting someone else find the problem, I just running out of time.
 
when you press down the brake pedal does the pedal sink slowly?
if so it probably air in system or small leak, if there is leak , the fluid
in resovoir should go lower, if same then problem is air in lines and
in master cylinder.
start bleeding master then back brakes then front brakes. as you progress
the pedal should get firmer and not sink as much.
hope this helps.
 
You have three rubber flex lines for the brakes -- one at each front wheel and one from the frame to the rear end. Clamp these off (they make special tool for this, vise grips will work but are hard on the hoses). If you now have a full pedal, the problem is at one of the wheels -- if it is still low. the problem is from the clamps forward. If it is in the wheels, remove 1 clamp at a time till the pedal falls away -- that is the problem wheel.

HTH.

Brian Gordon
 
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