Brake problems

[CEThomas]

Well I have been fighting with the brakes after I put in the 8.8 axle. I have changed out the master cylinder and brake lines, but just can not get the system to bleed :mad: I have used a vac system, the old fashion way, I have done the master cylender and all 4 calipers :mad: and 2 big bottles later it has not changed :cry: peddle is mushy, brake light comes on when you step on the peddle and brakes are poor at best :nuts: Oh and I have fluid at all 4 calipers :nuts:

 

The prop valve I have came with the 97 booster / master cylender, I did not see the XJ it came out so I do not know if it had antilock. Anyone knows if the prop valve is different on the antilock XJ's?

 

Charles

[CWLONGSHOT]

Stupid question...but are the calipers on the correct sides? Bleeder screws on top/highest point.

 

I ask because I made this error myself. In the heat of the install didnt think and couldnt get all the air out. Went in for a beer and a lil break, my buddie came over and almost in unison we both said DUH, I a dumb @$$ and put the calipers in upside down!!!!

 

CW

[CEThomas]

Stupid question...but are the calipers on the correct sides? Bleeder screws on top/highest point.

 

I ask because I made this error myself. In the heat of the install didnt think and couldnt get all the air out. Went in for a beer and a lil break, my buddie came over and almost in unison we both said DUH, I a dumb @$$ and put the calipers in upside down!!!!

 

CW

 

Yes, wish that was it ;)

 

Charles

[carnuck]

Do you still have that retarded load level valve? If so, it traps air in the return line to the master. Bypass the POS and your brakes should improve. They also need to be driven a bit to seat the brakes (OH! and make sure you don't have a brake pad caught up and acting like a springboard! Found several STOCK XJs and MJs that way with "bad brakes") as the calipers retract after touching the rotors. Did you run a strictly disc brake master? If not, there is a pressure retention valve needs to be pulled out. (under the master cyl line seats)

[CEThomas]

Do you still have that retarded load level valve? If so, it traps air in the return line to the master. Bypass the POS and your brakes should improve. They also need to be driven a bit to seat the brakes (OH! and make sure you don't have a brake pad caught up and acting like a springboard! Found several STOCK XJs and MJs that way with "bad brakes") as the calipers retract after touching the rotors. Did you run a strictly disc brake master? If not, there is a pressure retention valve needs to be pulled out. (under the master cyl line seats)

 

No, we pulled the load level valve out when we got the MJ. All the pads are OK, but do not know about the master. Did 97 xj run drums or disc brakes??? When I pull vac everything is great on the front system but I get a lot of air on the rear. Today at one point we started to get some peddle then the next time I went to bleed the rear we lost what we had and back to where we started.

[CEThomas]

Where would I find the pressure retention valve at???

[JeepcoMJ]

simple problem...you may need a new master cylinder.

 

since newer XJ's have drums in the rear, I *think* that your master cylinder would have a small(er) reservoir for the rear brakes. since that's the case, you may be simply running out of fluid in the rear brakes.

 

anyone else think that may be the case?

[Eagle]

All the XJs use rear drums. I suspect the 8.8 calipers require a LOT more fluid than the old wheel cylinders. The ZJs used rear disc brakes. I would suggest getting the master cylinder and the front combo valve from a disc brake ZJ and using those.

[CEThomas]

Great :roll:

 

Anyone know if the ZJ master will work on the XJ booster??

 

Looks like I will have a 97 XJ master for sale cheep :D

[JeepcoMJ]

yea, it should fit. just grab the zj master and booster and use that instead

[CEThomas]

Thanks,

 

Look for a good deal on a 97 master cylinder and booster ;)

[Eagle]

This is why converting to rear disc brakes doesn't make any sense to me. Even in an XJ, which has more weight over the rear axle under normal conditions, the rear brakes only do a small percentage of the actual stopping. In an unloaded MJ, the rear brakes do almost nothing. Converting to rear discs and then having to deal with the resultant fluid and pressure issues just seems like an exercise in futility.

 

I guess if you're doing the 8.8 conversion and it comes with disc brakes you're sort of committed, but IMHO it's cheaper and easier to use a Chrysler 8.25 out of a 97+ XJ and leave the brakes alone.

[CEThomas]

Well it was a good try, but I just checked the part numbers and the master cylinder # is the same for a 97 xj & 97 ZJ :cry:

[TNT]

Read this

 

http://www.madxj.com/MADXJ/technical/technicalfiles/ARbrakeBoosterUpgrade/BrakeBoosterUpgrade.htm

 

The rear discs will work fine with the booster. Worst case use a ZJ master for rear discs.

[CEThomas]

Thanks, that is the link that I used to do the swap.

 

I have checked part numbers and the 97 XJ master is the same as the 97 ZJ master. So to swap the 97 XJ master with the ZJ will not help :cry:

[TNT]

Some people have had good luck removing the O-ring for the rear brakes in the proportioning valve.

 

IIRC the difference between the XJ & ZJ is the proportioning valve.

[CEThomas]

Where is the O-ring located????

[TNT]

http://www.lunghd.com/Tech_Articles/Suspension_Steering_Axles_and_Brakes/Proportioning_Valve_Mod.htm

[CEThomas]

Thanks

 

Going out and try now :cheers:

[CEThomas]

Well, got the O-ring out and no longer have air on the rear system :cheers:

 

But.........

 

No peddle yet and the brake light comes on every time you push the peddle :cry:

[TNT]

Did you bench bleed the mastercylinder?

[CEThomas]

Yes, but I am thinking that it may have sucked air into it while working on the other problem. :roll:

[TNT]

That's a good possibility. It's simple to redo. I would redo it and then rebleed the system.

[CEThomas]

Going to give it a try :roll: