XJlimitedx99

10 hours deep into bleeding my brakes. I'm just going around in circles at this point.

Replaced the master cylinder (with a Durango MC, not XJ) and all hard lines last week. Got into vacuum bleeding them and have had no success. I tried many different steps. My main issue through the process was not getting fluid to the rear circuit. This lead me to believe my pressure safety switch in the combination valve was stuck. I disassembled the valve and manually returned it to center. Confirmed it is not triggered by testing continuity at the switch. Went on attempt to vaccuum bleed at the right rear and then also at the proportioning valve and just got a ton of air.

I've never had to bleed a system from empty before. Is there something I'm missing?

Some things I have checked/was aware of:

-Bled the MC, twice. First time didn't do a great job. Second time I made a more-robust setup with tubes that went back to the reservoir and got a bunch of air out of it.
-MC piston is not stuck depressed. I read about how a MC can be damaged during bleeding from actuating too far. I removed the MC and confirmed the piston is bottomed out in its neutral position.
-Pressure safety valve not triggered (as stated).
-Lines not kinked/blocked.
-Vacuum bleeder sealing on bleed nipples.
-No leaks in system (that I could find).
-Cap off reservoir.

I began by gravity bleeding the system to all four corners. Got fluid dripping at each one. Tried to bleed the rear with no success. Moved to the front just to see if it would work and got fluid to both front calipers. Assumed I had a leaky fitting in the rear circuit so I stomped on the pedal to push pressure through the system hoping it would reveal a leak. It did not reveal any leaks but it did trip the pressure safety valve, which took me hours to learn about, diagnose, and fix.

Just before I came inside I attempted to bleed the fronts again for s+g and found something very strange. With relatively strong vacuum on the bleed nipple I was not pulling anything from the caliper. It would pull fluid up a few inches then get stuck. If I really pumped the vacuum it would work its way up higher but it was not pushing fluid out as it should've been.

Does this have something to do with the fact I'm vacuum bleeding rather than pushing pressure through the MC? Anything I'm grossly overlooking? What gives? I'm extremely frustrated.

tech

Ok what is the bore of the Durango MC and what was the bore of the xj MC ?

XJlimitedx99

XJ = 1.000"
Durango = 1.125"

I went Durango to push more fluid in anticipation of swapping to full-sized axles. Saw several threads where people installed the Durango MC with no modification.

Aside:
I am aware the larger bore will reduce my braking pressure with my current calipers. I wanted the larger bore to retain a factory-like amount of pedal travel after going to larger calipers all around compared to the OEM's front caliper/rear wheel cylinders.

RockyMtn96XJ

I wouldn't think the bore size would have any effect on static pressure and just trying to move fluid from the reservoir to the bleeders. Personally I've never vacuum bled brakes, always did it using the 2 person method so I could press the brake pedal and "push
" the fluid to the calipers, while the other person is opening and closing the bleeder valve to allow the air to escape after each pedal push. From what I read, I didnt see where you have tried that method yet, unless I was speed reading and over looked it. Maybe give that a whirl and see if it works...

tech

Have you checked the rod in the booster is the right and not to short?

RockyMtn96XJ

or its smaller in diameter and fluid is leaking by.... if that's even a possibility. I may sound dumb asking that hahahaha

4.3L XJ

I have had this kind of issue on my pickup when I put a 14 bolt in it. I did find a leaking fitting though. But what I would suggest is a two person bleed. I have not had real good success with vacuum bleed due to air getting around the brake bleed fitting. What I would suggest is a two person bleed. Get your girl friend/wife/significant other and giver her a big kiss and tell her to operate the pedal on command. Down to the floor with your finger off the end of the bleeder. Up with finger on the end. Repeat and you will eventually start getting some movement. Once you can get enough fluid through to one side, the other will go easily. Remember, you are compressing air at first and it will not seem like you are doing much, but the more you go the more you will be able to detect some loss of air until you get fluid at the bleeder

RockyMtn96XJ

Yeah

XJlimitedx99

I have not tried conventional bleeding at this point, but that is the next step. Gonna have to phone a friend to get someone over here to lend a hand.

Yes, the Durango MC and XJ MC look identical as far as the rod, mounting, and fittings.Also, after the last time I bled the master I have not depressed the pedal or actuate the piston in the master in any way.

You got a write-up you for this step?

awg

have you actually tried to use the brakes after a gravity alone bleed ?...especially if that is done for a fair while, I have found that is usually all I need to do,
although it is better to do it a 2nd time, after using the brakes hard.

another method is to make a bicycle pump and inner tube arrangement to pressurise the resevoir

XJlimitedx99

Negative. I had never actually gravity bled brakes before. I'm not entirely sure what it should look like. The first time I did it, there was basically a steady stream of fluid flowing from each bleeder. After taking the MC off, reinstalling, and gravity bleeding again, I'm just getting drips out of the bleeders. Very slow drips.

Should fluid readily flow from the fittings on the master when there is nothing other than gravity affecting it? I.e., holding it in your hand while full of fluid?

bluejeep2001

It might be as simple as the bleeders internally rusted...I had "speed"bleeders installed in my 01 and after I replaced the main rear brake line I couldn't get the fronts to "bleed" When I took the line off the bleeder and fluid gushed out ...I knew what had happened

bluejeep2001

Yes fluid will steadily weep out under gravity alone if there are no obstructions. Its not a shooting stream but will empty the cylinder in a short while. Do you have antiskid and might that effect the bleeding

XJlimitedx99

Let the Jeep sit for 2 days then bled it conventionally with the 2 person method, no problems.

I still have no idea why I was having so much trouble before

318SixPack

You may not have been holding your tongue right. Review some Michael Jordan video for reference.