Brakes Help!

[polarbear]

Alright, so i have a 1988 mj, 4 cyl ax4 2wd, recently i was driving and went to hit the brakes and the pedal went to the floor with very little resistance, after one pump they began to bring me to a stop. I have replaced the calipers, rear wheel cylinders, brake booster and master cylinder, and i still have the issue... any suggestions??

[AeroNautical]

First, the obvious. Check for leaks in all of your lines. Have you bled your brakes recently? When applying the brakes, do any of your soft lines flex or bend? I had/have a similar problem, and fixed it by bench bleeding the master cylinder. I have to do it again because I didn't get all of the air, but it made a huge difference. There is also a bypass (failsafe) line going to the rear brakes, used to eliminate the proportioning valve and give the rears 100% braking power if the fronts fail. If there is air in this line, it has to be bled a specific way. 

[Eagle]

Does your MJ still have the rear height-sensing proportioning valve, with two steel lines running from the front distribution block (just under the master cylinder) to the rear of the vehicle? If so, after doing all the brake parts replacements, did you follow the factory procedure for bleeding the safety bypass hydraulic circuit to the rear axle?

[polarbear]

I did bench bleed the master, and did a complete bleed at all wheel points (started furthest from master and working towards it). And I didn't do anything to the proportioning valve, not really sure what to do with it. I can say that the front brakes are what feels to be failing to brake the truck with the first pump (leading to the second pump and the front brakes then working)

[Eagle]

I did bench bleed the master, and did a complete bleed at all wheel points (started furthest from master and working towards it). And I didn't do anything to the proportioning valve, not really sure what to do with it. I can say that the front brakes are what feels to be failing to brake the truck with the first pump (leading to the second pump and the front brakes then working)

 

Then you did NOT follow the factory-required bleeding procedure, and there is probably air trapped in the bypass line for the rear brakes. I've posted the procedure, quoted verbatim from the FSM, on this forum previously. Try that and see if it helps.

[polarbear]

Could you send me a link to the procedure? Icant seem to find it anywhere.

[Eagle]

I found this one before I could find the procedure I copied from the FSM.

 

http://comancheclub.com/topic/40428-brake-bleeding/

[HOrnbrod]

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

[88 pioneer Olympic]

i want to delete this valve how'd i do that

[DTA]

i want to delete this valve how'd i do that

http://comancheclub.com/topic/51268-load-height-sensing-valve-delete-bypass/