Bastardized Brake Bleeding?

This is probably really a basic shop question, but I'm thinking it may have something to do with the parts swap.

Basic system is a '90 w/o ABS. Over time, I've swapped the front lines with SS, the rear line with SS, replaced calipers/wheel cylinders with no issues. A couple of years ago, I swapped in a WJ master and booster. I never had an issue bleeding the system and getting a firm pedal.

Over the long weekend, I swapped in a set of ZJ rear calipers for the stock drums (I did not change the proportioning valve spring) as part of an axle swap (see next post). I welded studs to the axle tubes to mount the soft lines, so they both make a u-shaped loop which extends over the height of the caliper (I know this is bad, but the only way I could fit the line). Since I made this change, I have been unable to bleed/flush the lines anywhere to get to the point where the brakes get pressure and work at all. I know there is fluid movement since the rear pads are now against the rotors, but there's got to be an air pocket somewhere.

I have tried vacuum bleeding at the calipers (using an a/c vac pump, so I know there was strong vacuum), and have also tried a pressure bleeder (set to around 10psi). The fluid comes out clear from all calipers with no bubbles, and I have moved at least 1 quart of fluid through the system. There are no obvious fluid leaks anywhere; I checked all the connections, and do not see the level dropping in the reservoir.
The soft lines are used, but they are only a couple of months old ( I got the receipt for them along with the axle); at any rate, they can't possibly bulge that far to soften the brakes without exploding, can they?

Is there any place where the air can be trapped? Any special trick(s) to release the air? I'm thinking of unmounting the calipers and re-bleeding, making sure that the bleeder valve is the highest point of the system, and perhaps rapping on the caliper in case it will help dislodge something. Is there anything else I am missing? Any hints appreciated!

What method are you using to bleed the brakes?

This is how I do it.

I get a 20oz bottle. Preferably the Mt. Dew bottle that I just finished drinking from.

Fill it about half way with Fluid.

Find a clear plastic hose that fits over the bleeder valve and put the loose end of it in the clear bottle of brake fluid.

Have a friend, preferably a Brunette with long legs and a nice bottom, pump the brakes a few times and hold the pedal 1" off the floor. No more, no less. Not ON the floor.

While she's holding the pedal still you open the bleeder and let it flow untill it stops moving. Close the bleeder. Then she can start pumping again.

Repeat the pump, hold, bleed process a few times on each wheel until the bubbles stop and the pedal gets firm.

Always start with the bleeder closest to the master cylinder.

Seems simple but the key is in the bottle. You SEE bubbles that you wouldn't normally see without the bottle and the hose.

Now that I've typed all of this you may already be doing this.

Tell the Brunette I said Hello.

Haha! Sorry; my brunette pumps, but not brakes.
I've been using a Motive powerbleeder, which gets rid of the helper requirement. It pressurizes the reservoir and forces the fluid through the master. I have not been draining into a partially filled bottle though. I run the bleeder hose up and then into a drain pan, so any air that comes out should float up and be visible in the drain line.

keeping the bleeder smothered in brake fluid seems to help me ....hose with brake fluid in it ,installed tightly on the bleeder going to a bottle.....route the hose up a little so the fluid stays at the bleeder and you can watch the air bubbles as you bleed and with fluid there,no air gets sucked back in...

obaa-xj said:

I welded studs to the axle tubes to mount the soft lines, so they both make a u-shaped loop which extends over the height of the caliper (I know this is bad, but the only way I could fit the line).

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get rid of the upward loops in the brake hoses, even with pressure you're going to have a very hard time (read: next to impossible) pushing air downward out of those spots. I would say with 95% certainty this is your problem.

go ahead and gut the proportioning valve too. it will allow more fluid to flow to the calipers. did this with my 8.8 swap and it works well.

I dont want to offend you but are the calipers on the correct side? Had to help a YJ cuz they couldnt get a pedal after replacing a caliper. When I went to bleed I noticed they had 2 right calipers. Did not know it was possible to mount 2 of the same side calipers

I'll try unmounting the calipers when I bleed them, and keep the bleeders at the highest point. Hopefully, there is no internal cavity that I am trapping air into.
I did check to make sure I had the calipers mounted correctly. I compared them against pics on rockauto and autozone, and I think I have them identified correctly (the bleeders are in different locations, and I have them mounted so the bleeder are located high).
Do I really want to just remove the spring completely from the prop valve? I thought swapping in the ZJ spring was the ticket? I do want to make sure the fronts lock up before the rears.

The ZJ internals is what you want. Cap, spring, plunger and i-ring. Don't gut the valve. That is just bad advice.

GrimmJeeper said:

get rid of the upward loops in the brake hoses, even with pressure you're going to have a very hard time (read: next to impossible) pushing air downward out of those spots. I would say with 95% certainty this is your problem.

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x2 Thats what I was going to day

i wouldnt unmount the caliper when you bleed them the piston will just shoot out. and i thought you were suposed to start with the wheel farthest from the master cylinder.

Farthest from the master cylinder was always my understanding as well.

I usually bleed RR, LR, RF, LF. I just saw another thread where it said rear discs need more fluid, so I'll swap the ZJ prop valve internals (cap, spring, plunger/seal) first. Thanks for reminding me about the piston popping out; I'll be sure to put in a wood block or something first before doing this.

obaa-xj said:

I usually bleed RR, LR, RF, LF. I just saw another thread where it said rear discs need more fluid, so I'll swap the ZJ prop valve internals (cap, spring, plunger/seal) first. Thanks for reminding me about the piston popping out; I'll be sure to put in a wood block or something first before doing this.

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Anyone have pictures of which parts are needed. I just did this swap and need to mess with the master cylinder now.

when i have issues with brake bleeding..i usually jack up whatever end is causing me greif..make sure the Res is topped right up, pull the bleeders right out and throw a few buckets under the drums/rotors..

go for a beer and let gravity do its thing...come back and restart the bleed procedure..starting with the furthest from the M/C using whatever tubing i have and a beer bottle about 1/3 full of clean fluid to start (so you can see the bubbles like stated above) it also helps if your partner or you make a timing mistake, stops ya from sucking a big gulp of air back into the system.

when i pressure bleed my buggy (has line lock, cutting brakes, twin masters and twin reserviors and 4 willwood calipers) i set my air psi to 2lbs and it gets the job done without the worry of blowing out any seals

If the fluid got too low in the MC (happened to me after ZJ rear disk brake swap) there could be air in the MC passages. Pull the MC, clamp in vise in level position and pump fluid through the MC until fluid is bubble free. Reinstall MC and rebleed lines. There are some cheap MC bleeding kits that make this easier.

Good luck.

Cody90XJ said:

Anyone have pictures of which parts are needed. I just did this swap and need to mess with the master cylinder now.

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I don't have any pics, the parts are not on the master cylinder; they're in the prop valve. It's the silver block that the lines from the master cylinder attach to. The pieces you want to swap are behind the red bleeder cap on the front of the prop valve (it'll have a rubber cap on it). You want to swap the cap (the plastic bushing inside it has a different diameter than stock and centers the spring), the spring, and metal plunger that the spring goes onto (there should a black plastic/rubber washer on the plunger).

You did a ZJ disc swap? Buy 2 sets of front speed bleeders for your XJ, rip all the bleeders out, install the speed bleeders. While the old bleeders are still in the rear calipers, use a dremel (not an angle grinder, too much metal removed too fast) to resurface the caliper right around where the bleeder screws in, you want to remove approx. 1/2 to 1mm of material (or c-hair, for those not familiar with metric.) Screw the new bleeders in, if the hex head bottoms out on the caliper face before tightening you need to shave off a little more material.

XJ drums are some wonky metric thread that speedbleeders don't seem to be made for (in the right length and taper point, anyways.) ZJ rear calipers use the same thread (3/8-24) and a *tiny* bit longer bleeder than XJ fronts, so I use the above method. Used it on a handful of jeeps now without a single issue as long as I was careful to brakleen off all the metal filings from the surface grinding before swapping the bleeder out.

Sorry, said that wrong, Fartherst from the MC. Not closest. Ya'll were right.

I got it figured out. Was super easy. Insalled the parts and power bleed the propotioning valve and wow a frecking difference.

If you've done this swap without the valve work then your missing out on a ton of braking performance. I can get a little lock up on the rear tires now with 35's. I call that a WIN!!!!