Brake bleeding issue

[Brly]

I just finished up putting a newer front axle in my truck and can't get pressure on the front brakes. The rear drum brakes were left alone, I just had to cut down the brake line to make a new attachment to the proportioning valve. Rear brakes are working. Front calipers are re-manufactured. New disc/drum master cylinder and proportioning valve. I bled the MC on the truck, hooked the lines up to the calipers and gravity bled with no issues. Started bleeding the calipers with speed bleeders and couldn't get pressure, so I went back to standard bleed nipples at the calipers and made a small improvement. I was getting brake fluid through everything easily. I've been over every fitting on the front brake system at least 6 times and there are no leaks. The calipers are on correctly, bleed nipple up. Thought the MC was bad, so last night I disconnected the front brake output from the MC and plugged it, got a hard pedal right away. So I hooked that line back up and plugged the front brake output at the proportioning valve, hard pedal right away. Connected that line and then plugged the hard line at the frame where it connects to the rubber hose. Had a little air from disconnecting/reconnecting the other parts, but it came up to a hard pedal pretty quickly. It has to be the caliper. I thought there may be a leak at the caliper piston, but I see no brake fluid anywhere on the disk or caliper. I bought a Mityvac yesterday thinking it was just air in the caliper that I couldn't get out. Put a big bottle of brake fluid through everything with the Mityvac and still have a soft pedal. Beat on the calipers with a rubber mallet while the Mityvac was pulling fluid through. Never got any big bubbles. The pedal does get hard when it's almost to the bottom, but that's the rear brakes, I can hear them tighten up. The last thing I was going to try tonight is pushing fluid from the caliper back through the system to the MC with a big syringe. I've done that on motorcycles before and worked well. What am I missing?

[BCRAWLER]

Just to confirm that you centered the proportioning valve. Also are the two bowls the same size on master?

[Brly]

Yup, I screwed the proportioning valve tool in before I started bleeding and it's still there. My understanding is that I wouldn't be getting any fluid through the system if the valve had closed? Front bowl on the MC is larger than the rear. Front brake system is connected to the large (front) bowl.

[RamJetFSJ]

Rear brakes adjusted correctly?

[Brly]

That did cross my mind. The rear drums do not have automatic adjusters on them. Haven't driven the truck a lot, but I can see if they need adjusting. Even if they're out of adjustment, shouldn't I still get a hard pedal if the front brakes are working correctly? Or does it have something to do with the proportioning valve?

[Brly]

Just came in from the garage. Pushed two big syringes of fluid through each side from the caliper to the MC. Checked the rear drums and they were adjusted fine. Put some washers between the MC and booster to make sure the brake rod wasn't too far out, putting a preload on the MC piston. Nothing worked. I wedged the brake pedal down and tried to turn the rotors by hand and couldn't move them, so I'm getting some pressure, but the pedal is still soft for almost 2/3 of it's travel. I'm out of ideas. Hate to take it to a shop.

[cmaje72]

What happens when you plug the the rear lines at the master? Do you get pedal? What master did you use?
I know you said you bled the master on the truck but try this. Put a bubble level on the master and jack up the rear of the truck until the bubble is pointing towards the windshield. Tap the master a bunch of times with a wrench and slowly pump to see if any more bubbles come out of that rear reservoir.

[Brly]

Haven't tried plugging the rear circuit. When I plugged the front circuit, I got a hard pedal immediately, no changes to the rear. Based on that, I assumed the MC was OK and rear circuit was OK. Is that correct?
This is the MC I got: https://www.ebay.com/itm/Disc-Drum-Mast ... Swvs9al5qJ
Checked with a level a while back. Sitting on all 4 tires, the MC is tilted down towards the front (bubble in the level to rear of truck). I can jack the back up more to see if that's it. I see where you're going here. Will work on the rear system tonight.
I have tapped on the MC, calipers and brake lines with a rubber mallet all through the bleeding process. Haven't seen any bubbles in the MC for a days.
Appreciate the help guys.

[RamJetFSJ]

If the rear brake adjustment is way loose, you will get a lot of pedal travel before they engage. You mentioned it got hard near the end.

I never really got a hard pedal on my brakes either, but it stops. It’s not a modern rig. Have you test driven it?

What about the rubber lines? They can get old and balloon under pressure, reducing pedal feel.

Also, it’s pretty common to get a bad rebuilt master cylinder or prop valve right out of the box these days...

[RamJetFSJ]

How did you bench bleed the Master Cylinder on the truck? It’s really easy to ruin one using the pedal, rather than my hand.

Also, since your going to discs I’m front, have you confirmed the correct port is going to the front (usually the larger of the two reservoirs)?

[Brly]

RamJetFSJ - Understand about the rear brake adjustment now. They weren't loose. Haven't test driven it yet. Rubber lines are a year old, show no signs of defect anywhere. I don't think I damaged the MC when bleeding. Used the hoses that came with the MC and pumped the pedal. I understand pushing too far can damage it. Plugging the MC front output gave a hard pedal and it's not leaking into the booster, so I think it's OK. I have confirmed the MC/Prop valve are connected correctly.
I think cmaje72 is suggesting that there may be air in the rear brake circuit causing the soft pedal. I got hung up thinking it's the front, and it could be the rear. I'll sort that out tonight.

[SJTD]

How does bleeding a new master on the vehicle damage it?

[RamJetFSJ]

How does bleeding a new master on the vehicle damage it?

It’s called bench bleeding for a reason. Your supposed to do it on the bench by hand. It’s easy to over travel the system with the extra leverage the pedal provides when there is no pressure in the system. I also gravity bleed the lines as much as possible before doing the pump and hold bleeding method.

[SJTD]

What prevents this over travel when bleeding the rest of the system on the vehicle with no pressure in the system.

[cmaje72]

RamJetFSJ -
I think cmaje72 is suggesting that there may be air in the rear brake circuit causing the soft pedal. I got hung up thinking it's the front, and it could be the rear. I'll sort that out tonight.

Yep just another thing to check so you can definitely rule out issues with the rear. I bled 2 master cylinders last weekend and it took a while to get all the air out of the rear res. It sounds like you are good though.
What front axle did you install? The master you listed in the post above has a 1" bore I think stock disc brake FSJ's had 1 1/8" masters. Also I went to the website of the manufacturer of that master and in their tech section they show that you should have a 10lb residual valve installed in the rear for disc/drum. Possibly since its a universal master they don't have one built in. Heres a link:
http://mbmbrakes.com/typical-brake-syst ... gurations/

[Brly]

cmaje72 - I started looking at the rear circuit last night. I do have a 10 psi RPV in the rear circuit. Had them on both lines when it was drum/drum. Saw that one of the brass reducer fittings going into the RPV was cracked. The tube nut threads were messed up also, so I took it out and made a new line from the proportioning valve to the RPV, but didn't get everything put back together yet. Probably cracked it by over tightening the tube nut. However, I don't think that's the issue. I'll put it together tonight, but then I'm going to plug all of the MC outputs and make sure I get a hard pedal. Then connect the rear circuit and see if it builds pressure. If it does, I'll connect the front circuit and see what happens. I expect the pedal to go soft when the front is connected. Has to be air in the front somewhere, it's the only explanation I can think of.
The axle is a Dana 44 from a 1987 Dodge Ramcharger and has stock replacement calipers.
The MBM site has some good info, been there before.

[Brly]

Got it. After cmaje72 mentioned the bore size, I did some quick reading and decided to pick up an 1 1/8" bore on my lunch break. Napa had a new one in stock for about $45. Before I took the other MC off, I plugged both ports and got a hard pedal. Bench bled the new MC, put the RPV back into the rear circuit and hooked the lines up. Burped out a little air and got a hard pedal right away. Didn't test drive tonight, but I will tomorrow.
Seems strange to me that the small change in bore size would make that big of a difference, but I don't know what else it could've been. The first MC tested OK, so I'm not sure.
Really appreciate all the help!! Thanks!!

[cmaje72]

Glad I could help! I have been dealing with some brake issues on my cobbled together CJ7 lately so its all fresh in my mind. Caddy calipers are my arch nemisis...

[Brly]

Drove it around some tonight. Brakes are working, little more travel on the pedal than I'd like though. Probably have to adjust the brake rod out a little. Should be all set.