Brakes still will not stay pumped up

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?

I had the same problem a while back, it turned out that the master cylinder was no good. Have a look at the thread here: http://www.forabodiesonly.com/mopar/showthread.php?t=4510

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.

You still have air in the system or the rear brakes need to be adjusted,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.

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).

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).

As I recall you also had a hard time accepting it was the Master too:glasses8: .

As I recall you also had a hard time accepting it was the Master too:glasses8: .
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.

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.

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.

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.

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

I kind of did that with the master cylinder. I said that some thing was wrong with the rear brakes.
I just ran out of time to work on it. I took it in yesterday to a local custom shop, a friend of mine who has done work for me before, cheep. He is also going to give me a price on finishing the body and sealing it.
I should know more Friday.

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.


You did not buy it from me. I do not sell parts on Ebay. Also, for about a year now I have only sold brand new master cylinders.

You did not buy it from me. I do not sell parts on Ebay. Also, for about a year now I have only sold brand new master cylinders.

I bought mine probably 2 years ago, I guess that was before you went to only new MC's.

Well, the car been the shop for about a week now and he can't fine anything wrong? He trying to push a powerboost unit on to me, but I tell he there is no room with the 440 in.
I just cant believe that manual brakes only give a half peddle. You can step on the peddle and hit the gas and they will hold the car while the tires spin. The problem I am having is if I am rolling about 10-15 mph and hit the brake, I think the car should stop on a dime. Not cost a car length or more then a slow stop. They never really grab lock if rolling.
What do you guys think? The ones who have done the disk brake conversion, how are your brakes. I have nothing to compair them to, pleasse help.
Thanks
The only good thing is that he said he would finish the body work and put it into seal/primer for under 1K. So I am going to let him finish the body work.

I have 74 disks up front and "C" body brakes on the rear and it stops great now. I had a similar problem with my brakes. I found a couple little leaks and gravity bled my brakes for about an hour, that made a hell of a difference. I have full pedal and it stops almost as well as my 04 Sebring.

JLP

Well, What do you guys think? The ones who have done the disk brake conversion, how are your brakes. I have nothing to compair them to, pleasse help.
Thanks


I converted from 9" manual drums all the way around to the 73-76 disks up front and 10x2.5" drums in the rear. I used the proportioning valve from the 73 Dart doner. The rear drums were turned and new shoes installed with all new hardware and wheel cylinders. Up front, new rotors with rebuilt calipers and rebuilt disk brake MC. I also replaced all the steel lines to the rear of the car and all three rubber hoses.

I had no problem bleeding the system and have a nice high hard pedal.

Compared to the 9" drum system initial bite is not as much with the disks as it was with the drums (this is to be expected since drums tend to be self grabbing) so at slow speeds it takes more pressure on the pedal with the disks to stop the car than with the drums. The big difference is slowing down from speeds above 30 mph. The disks just grab and the rate of slowing down is proportional to the pressure on the pedal. The drums esspecially at high way speed fade with in a couple of seconds and no amount of pedal pressure will increase the rate the car slows down. It also required lifting off the pedal for a second to let things cool down so you could get the breaks to grab again. A couple of times it was quite unnerving and I worried if I would stop in time.

The rebuilt calipers came with pads installed. These sqeaked like hell. Replaced them with a set of Raybetos PG+ pads, that solved that problem plus the work better too.

It still sounds like you have an issue with the rear brakes. If it takes a lot of fluid movement to get the shoes in contact with the drums it can manifiest it self as poor overall braking.

Other areas to look are; I am assuming you have freshly turned drums and either new or turned rotors. Quite often the shoes and or pads will take a couple of hundred miles to bed into the drum/rotors before you get full contact. If the pads/shoes are not chamfered on the leading and trailing edges you may want to take a grinder to them and make a chamfer (make sure you wear a mask). If the hole face of the pad/shoe doesn't make contact evenly you will get a soft felling pedal as the pad/shoe flexes into full contact.

I have tryed to differrent master cylinders, and all the hoses are new except the rear. Before doing the disk brake conversion, the drums work great and the car stop fine. I would think I should be able to get back to what I had before if not better. I am along way for having what I had with the drums.

Can you get steel braided hose line to replace the rubber ones? I think that would help.

SS braided lines will certainly reduce the flexing of the lines but you have something else going on that I don't think the lines will fix. You should have a problem getting a nice high hard pedal.

I would look at the things I mentioned. Also, I negelected to mention to check to make sure you do not have slop in the pedal linkage. That would account for pedal travel but not a lack of stopping power.

I'm having the same braking problem. I just reaplaced the bushing on the passenger side upper control arm and, of course, removed the brake caliper to get the balljoint out. While the caliper was off, the piston basically just fell out (gradually, but it did work itself out). I spent forever getting it back in, and got it all put back together correctly. I topped off the MC, bled the front lines multiple times and it will only hold pressure if I pump it up a bunch.

Best part is, I had to drive back to my mom's house with funky brakes so most of my stopping came from downshifting and E-brake :flower:

I don't recommend coming to Nashville to get bushings pressed out/in, they don't like that sort of thing :angry8:

The car is in the body shop, so I can't mess with the brakes now.
The guy at the shop look at them and could not find any leaks. I am woundering about the calipers now. I bought single piston caliper for a 74 dart at an auto store of a manufacturer that was going to stop selling them. I only bought them because they did not want a core and I didn't have a core to exchange. Could there be something wrong with them, and how could I tell. Should I buy different one and use them as my core?
I really don't know what else to do.
I have tryed:
2 different new master cylinders
new calipers and pads
new rubber hoses front only
hardware kit
new rear pads
1 new rear wheel cylinder
I can't find any leaks

It's enough to make a grown man cry.