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After WJ brak mod cant get brake system to pressurize properly

S

stockli

NAXJA Forum User
Location
Ft. Collins
89 Limited
4.0
aw4 trans

The master went bad on my 89 so we swapped in a WJ booster and followed the write up from this site.

The problem we are having is we cant get the system to pressurize. Wave bled the system over and over again but no matter what we still get tiny tiny bubbles out of the front calipers. We can pump the pedal up and it holds pressure with the jeep off, but when running the pedal will push almost to the floor. Not low enough however to trip the brake idiot light.

We bled the master and nothing is leaking. We are at a loss, Im hoping someone can steer us in the right direction.
 
If you flared the new brake lines yourself, check to make sure it is a straight and good otherwise it won't seal properly and will leak and not keep pressure.
 
images
 
Are you using a suction type bleeder? that is what i have used in th past and have great results. try also flushing the old fluid out.
 
gravity bleed... crack the caliper screw just till its open and just let it sit for 20-30 mins .. go back and tighten it up do a quick pump and press .. should b no bubbles .. fill to desired level and done.


common misconception is u have to pump the brakes to bleed em.. u dont it will bleed its self if u open the screw and wait till fluid drips out the screw on its own u know its bled .. takes a lil longer but u can pound some beers while u wait lol
 
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Did you bleed the proportioning valve? Lots of nooks and crannies inside that valve to trap air.
Did you bleed the MC on the bench as opposed to on the truck? If you didn't have the MC level when you bleed it, you can trap air at the ends of the piston.
I find two or three very slow pumps of the brake pedal works better than rigorous pumping (rigorous pumping can cause bubbles to form in the fluid) before holding NEAR the floor (pushing pedal all the way to the floor can cause the piston cups to abrade and then leak internally--I always put a block of wood under the pedal to keep it ~1" off the floor).
I use the vacuum pump method in the onset to insure fluid to all cylinders, then switch over to to "pump and hold" method.Like was already noted, using vacuum alone can give false indication of air in system (sucks air around bleeder screw threads).
After properly bench bleeding the MC, I would crack the connections at the porp valve, and insure bubble-free fluid at each connection, then move on to the rear right, followed by the rear left, then the fronts.
 
We didnt bleed the prop valve, I thought it would bleed with the rest of the system through depressing and holding the brake pedal all the way around.

How do you bleed the prop valve?

Also the connections on the prop valve would leak if they were not flared properly correct? We have zero leads even under heavy load.

We know there is air in the system as the pedal will push almost resistance free to the floor when the jeep is running and the booster is assisting the brake system.
 
Push the pedal much slower. I can bleed my system till the day I die if I'm pushing hard/fast and I will continue to get bubbles, but if I bleed the same system pushing slowly, the bubbles decrease a lot in size and quantity.
 
kastein said:
Push the pedal much slower. I can bleed my system till the day I die if I'm pushing hard/fast and I will continue to get bubbles, but if I bleed the same system pushing slowly, the bubbles decrease a lot in size and quantity.
Click to expand...

This. Don't be overly vigorous with the pedal.

Start at the RR, then LR, then RF, then LF wheels.

You can crack the fittings at the proportioning valve while there is pressure on the pedal to try and get any air out--the output fittings (LF/RF/Rear).
 
wanaB4x4 said:
gravity bleed... crack the caliper screw just till its open and just let it sit for 20-30 mins .. go back and tighten it up do a quick pump and press .. should b no bubbles .. fill to desired level and done.


common misconception is u have to pump the brakes to bleed em.. u dont it will bleed its self if u open the screw and wait till fluid drips out the screw on its own u know its bled .. takes a lil longer but u can pound some beers while u wait lol
Click to expand...

X2 works pretty good but if the MC is not bench bleed properly then no amount of line bleeding is going to help.
 
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Stockli and myself worked on the brakes again last night. We bled the prop valve and re-bled all 4 wheels in proper order. There are no air bubbles in any of the lines and we must have put 2 or 3 of the big bottles of fluid through this thing by now. Still NO pressure on the brake pedal until half an inch or so from the floor. I think the next thing we're going to do is flare some new lines and bench bleed the master again and then bleed the prop valve and then all 4 wheels. If anyone has any more advice I am open to suggestions.
 
You could take steps to isolate the problem by putting plugs in the MC to verify it's OK. Plug both the front and rear ports; you should have a rock hard pedal. If no, then the MC needs bench bleeding, or has internal leak. If yes, leave the front circuit plugged, and connect the rear system to the MC. If the pedal is now soft, and goes near the floor, you've isolated the problem to the rear system. If the pedal is still hard, connect the front circuit and test again.
By the use of plugs on the MC and prop valve, and clamps for soft lines, you should be able to determine where the problem is located.
 
DrShaggford said:
Stockli and myself worked on the brakes again last night. We bled the prop valve and re-bled all 4 wheels in proper order. There are no air bubbles in any of the lines and we must have put 2 or 3 of the big bottles of fluid through this thing by now. Still NO pressure on the brake pedal until half an inch or so from the floor. I think the next thing we're going to do is flare some new lines and bench bleed the master again and then bleed the prop valve and then all 4 wheels. If anyone has any more advice I am open to suggestions.
Click to expand...
This may sound stupid, but have you wiped down all hydraulic connection points (hard lines, soft lines, banjo bolts, etc) and pumped the brakes to verify there are no leaks? Doing this while the car is running would probably be a wise idea to ensure you have the assistance of the brake booster when applying pressure.

Otherwise, a bench bleed of the master cylinder as you suggested would be the next logical step (though I'm sure you're sick of paying for fluid by now, lol). This should only be necessary if the fluid reservoir was ever sucked completely dry while bleeding the system.
 
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