Brake Bleeding Help for ABS System on 00XJ

[CJR]

Recently blew a badly rusted steel brake line. Replaced all the steel brake lines(10 pieces) with stainless steel brake lines from InLine Tube (nice quality!) and also replaced the rear wheel cylinders.

After reading several manuals, including FSM, my son and I can't get brake fluid to the rear brakes. The Combination Valve(located by MC) contains; pressure differential valve, a brake switch, and a rear proportioning valve. Likewise the Combination Valve is not repairable and if defective it must be replaced as a unit. We're not getting any Codes, but I suspect the rear proportioning valve, in the Combination Valve, is not working properly or one of the lines on the ABS is not connected to the proper circuit. Any help would be appreciated on this problem.

Also, I can't find any hydraulic schematic showing where the lines, connected to the ABS, go to what circuits. A schematic would be nice to verify that we connected all the hydraulic lines properly.

Thanks, in advance, for any help to solve this problem.

Best regards,

CJR

 

[Tim_MN]

When the system has a large fluid loss, the proportioning valve can overextend and get stuck. Cherokee owners say that you can disassemble the prop valve, clean and re-center spring loaded valve inside, and that will fix the issue.

The Factory Service Manual says that the ABS system needs to bled with a dealership DRB-III Scan Tool, however the brakes should work normally, they just will not have functional ABS. I always depress the brake pedal and keep it depressed with a 2x4 when working on the brakes. This shuts the valves to the ABS unit and prevent air from entering the ABS unit.

 

[CJR]

Problem solved! My son and I got the ABS brake bleeding figured-out. With the help of a couple of videos and readings here's what worked for us:
1. Some manuals stated ignition had to on before bleeding, so we tried that and found it didn't help.
2. We concluded that EVERY brake line connection to the MC, Combination Valve(Proportional Valve), and ABS Modulator had to be bled before we bled the wheels.
3. So WITHOUT the ignition on, one of us pumped the brake, while the other loosened EACH connection to bleed off trapped air.
4. We then detected brake fluid at all the wheels and bled all the lines in the proper sequence.
5. After every wheel bled, the MC was refilled.
6. Next we put the rear axle up on jackstands so the rear wheels were free to rotate.
7. The engine was started, revved to about 55 MPH and the brakes hit HARD. This was done five(5) times.
8. The rear wheel adjusters were adjusted to get a slight resistance on the rear wheels when rotated in Neutral.
9. The brakes were again bled in the proper sequence.
10. The engine was again started, revved t0 55 MPH and the brakes hit HARD; five(5) more times.
11. The brakes were bled again in the proper sequence and the XJ was then tested on the road.
12. After a week of driving, the brakes will be bled again. Since the tightened annealed ends of the SS lines will have some slight spring-back so that the sealing circular line-contact, on the end of the tube, may not be fully in contact and have a slight leak. A week of driving (i.e road vibration) and reseating of each connector should give a good stable circular line-contact for proper metal-to-metal sealing on each tube end. Hope springs eternal!

Thanks Tim MN for responding!

Best regards,

CJR