So,EVERYTHING in the brake system is new except front calipers,and the RWAL valve is bypassed and unpluged behind the glove box

it seems to stop decent(only been up to 25 MPH in my sub so far) but the pedal is really soft and the bottom 10 percent of the pedal travel does all the stopping. With a couple strokes of the pedal it gets a little stiffer but not much.
I have 27in vacuum at the booster check valve and it drops to about 12-15 when you let off the pedal then builds back to 27.

I have all the air bled from the lines.

When I bench bled the master cylinder I would still get an occasional small bubble out of it but I probably stroked the piston in that thing no less then 150 times.

Is this a case of a bad master cylinder out of the box??

Any input is much appreciated

 

It sounds like a bad master cylinder. I just went through this ordeal last week. The one I got from autozone was bad out of the box so I went to oreillys and got the cheap one and it seems to work fine now.

 

I got 2 in a row from Napa. Got the last one from Car Quest.

 

I've gone through this twice.... with my previous 93, and my new 92. Same thing each time.


First was rebuilt masters. I'll never buy another. Everyone I bought turned to crap, so I went with new. just bought it at a local Napa for about $61 plus tax

Part Number United M2326 It's new.... not rebuilt. Much better product, IMO The sealing surface / top mating surface of the lid is machined flat, where the rebuilt crap was all rough and rounded. You need a flat surface to have the seal work properly, and keep the dirt and contaminants such as water vapor from entering. Brake fluid is hygroscopic, which means it absorbs water from the atmosphere... which degrades it. Any open containers of brakefluid are trash, as they're contaminated.

So.

Bought a rebuilt booster @ the same time for about $90 plus tax and core

United # 54-73360

Installed both, in both trucks, and found to have the same problem you're describing. Low pedal, just about 10% off of floor. Drove me nuts.

Readjusted the rear brake shoes.... brought the pedal up a little, but it still felt as though I was just using rear brakes to stop. After about 5 minutes of driving it and being aggravated at myself for going through all of this again, I put the "brakes on" and decided to test vacuum. Identical to yours, except that when the pedal went to the bottom, I only had about 1 hg of vac... then it bounced right back up again.

Turns out that after "one more bleeding" all the way around, including the rwabs unit, the pedal magically stayed up, and presented itself as a normal working functional part of the truck.

Seems as though, the previous bleedings did not get all of the air out. Final bleeding did.



BTW,

From your description, either your masters are bad from the getgo, or you are damaging them in the bench bleeding process (don't ask me how I know this).

After trial and error, and re-reading several times the instructions that came with the master) here's what I learned...

1. You need to plug both outlets on the master.....or run tubes off of them with adapters to the master reservoir. This is essential. Fluid dripping out of them, does not get the air out. I guarantee it... that it will not be bled properly without replenishing tubes, or actual plugs to block the holes. Didn't work for me without them.

#2. Even more important, you do NOT PUSH THE PLUNGER IN MORE THAN ONE INCH MAXIMUM !!! You'll tear the seals inside the master that separate the two chambers......Again.... Please don't ask me how I know this. I measure and use a blunt end tool to push them in 3/4" max as I'm afraid to damage another master by over depth pushing of the plunger. It can tear it almost immediately. and you'll be back buying another master. Within 4-10 strokes, the master should be rock hard, and you shouldn't be able to manually push in the plunger any longer. If you're dong ~150 strokes, you're not doing it correctly, and that's where your problem lies. BTW, the plugs didn't come with the master, as I had a set from a previous encounter.

#3. Bleed as normal. If the pedal is still mush, bleed again. Make sure when you open each bleeder that you only allow a small amount out and quickly close the bleeder. I used to allow a large amount of fluid out, and I found that as I was doing that, the person in the truck was flooring the pedal, causing more damage to the master. Short quick openings, allowing enough fluid and air to escape to see what you're getting out.... works best for me.


Since I follow this procedure, I now have really good brakes...... for dodge brake systems, that is.

 

Ok NJTman,got another reman master cylinder

So before bleeding the brakes but after bleeding the master and mounting it to the truck, I read your post. So I umounted the 2nd reman master,made a set of lines to bleed back into the resevoirs and tried the bleeding of the master all over again.

The first time I bled it with plugs in(and leaking) it got rock hard after a few strokes (5-10) but, not feeling confident it was done properly, I went for the second time around.

Just about the time I thought I had all the air out this thing started pumping air bubbles into the front resevoir like crazy.

Is this one toast now too?

I went with the 2nd reman cause it was Sunday and that's all they had.Ordering new not reman right now.

 

New master cylinder
not reman

I used my homemade bleeder lines, back into the resevoir, and bench bled the new one. Taking great care not to push the piston more than 3/4" and it never got rock hard.

So I mounted it to the truck anyways.Ihave less pedal now then I did before, and after bleeding the lines the only one I got any air out of was the driver rear, and lots of it! Still didn`t get it all out after ALOT of bleeding.

So, another bad master?
Am I bleeding it wrong?
Could this master be pumping air into the system and it`s all going to the driver rear?
The pedal is not stiff or solid at all but will stop the truck at an idle in drive

 

if you used bleeder lines and routed them into the master cyl you won't get a hard piston you watch to make sure airbubbles aren't coming out of the lines and you got all the air out of the master, Not sure how you bleed the lines but start at the left rear and open the line have someone push down slowly and before they get to the bottom close it and repeat the process till air is out of that line. if you pump the pedal to bleed the brakes you break up the big airbubble into alot of little ones... If you can put an automatic bleeder that might be the best way now to make sure you get all the air out....also don't forget to bleed the rwal....if you replaced any brake lines make sure you have all the connections tight i've left one loose before and it was towards the front and didn't leak alot but it would suck air and seemed like i wasn't getting anywhere till i found that. also as long as the master is full it can't pump air into the system you'll just get a pedal that will drop after its been pumped up.

 

Did you bypass rwal hydraulics or just unplug the electrical connector at the valve? I have seen these valves stick causing pressure to drop to rear brakes and it will not set a code for this.

 

I don't have a RWAL valve in the system anymore and everything is new except the front calipers.
Now with the NEW master installed there is barely enough brakes to stop the truck at a slow roll. Soft pedal and when I try bleeding more, the fronts don't have much pressure when I crack the bleeders. The brake light in the info center also comes on when I press the pedal.

I'm at a loss here! It just a dern hydraulic brake system. How hard can it be

 

There is more than 1 size push rod that comes on these mc's. There is a thread on this site that describes the correct 1, I'll try to find it ...Mark

 

i wish they had an airbrake system to put on these trucks that would be awesome....

 

One thing contrary to the instructions. Never bleed a MC off of the truck. If you depress it an 1/8 of inch to far you can damage the seals in the MC. Mount it in the truck and use the pedal to bench bleed it with the little hoses. Mopar MC are only machined most of the way, if a seal goes to far it gets tore, and using a screwdriver or other tool your guessing, but on truck pedal only goes so far. seen many ruined.