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brake woes

89eliminator

NAXJA Forum User
Location
Delphi, IN
here is the deal...

for the past 8-10 months i have had sub-par brakes. the pedal will travel about 3/4 of the throw until there is enough pressure to slow the truck down.

new parts:
MC (3rd different one in the past time period). bench bled.
rear drums have been COMPLETELY rebuilt. new everything.
no air in the lines, guarantee.

when i hit the brakes, the small chamber in the MC shoots a stream about 1 foot high under full brake pressure (my 92 MJ does not do that). the cap seal cant contain that pressure so it is always leaking fluid.

here is the kicker, ever since i put on Rubi Express brake lines front and rear, the brakes have been crappy. i almost think they are expanding (causing the long brake pedal throw). but i dont see what could be causing the huge pressure in the MC.

so my questions are, is anyone else running the RE SS lines with good/bad feedback? i was thinking about putting the stock lines back on temporarily to see if that changes anything.
 
have you eliminated the mj-specific rear proportioning valve? the one that connects to the rear diff cover? assuming this is on an mj?
 
a MC should not do. there is a small compensation valve that allows for fluid movement in the valve but this closes after about an 1/8in movement of the MC. after that, no fluid should bypass the seals. id say that MC is toast. did you buy a reman or new?
 
a MC should not do. there is a small compensation valve that allows for fluid movement in the valve but this closes after about an 1/8in movement of the MC. after that, no fluid should bypass the seals. id say that MC is toast. did you buy a reman or new?

this is my 2nd reman MC. i thought maybe the 1st reman one i bought was faulty but i guess not. think i should get a new one?
 
If the left front and right front brake cylinders get put on the wrong side, the brakes will not completely bleed. Bleed screw has to be at the top of the brake cylinder. They will fit on either side, but won't work. "I know". Just a thought.
 
before you go throwing parts at it try adjusting the rear brakes as best you can I had the same problem and that seemed to help 80% out of curiosity do you have the hydraulic booster?
 
1. There shouldn't be ANY pressure in the MC reservoir, period.

2. If you are getting pressure in the MC (and what you describe IS pressure) then the MC is bad. As fluids are not compressible, and Pascal's Law is applicable in our dimension, that fountain of fluid is coming internally from the working part of MC.

3. Life lesson: most reman MCs are muy malo--very, very bad. Buy new, what the heck, the life you save may even be your own!
 
so my questions are, is anyone else running the RE SS lines with good/bad feedback? i was thinking about putting the stock lines back on temporarily to see if that changes anything.

I ran RE SS lines front and rear. No issues.
 
Here are some thing s to try

1.open all 4 bleeders do not push brake pedal let it gravity bleed at least 1 can through it .
2.Adjust rear brakes .

3. Check to see if you still have the stock prop valve under the hood . If you do and have added the wilwood you may have added too much or a restriction to the rear .

4. Clean and check the seal on the cap make sure it is in good shape .

FYI the valve at the rear of the truck is a load sensing valve . when the truck gets loaded heavy it add more pressure to the rear brakes
 
1. There shouldn't be ANY pressure in the MC reservoir, period.

2. If you are getting pressure in the MC (and what you describe IS pressure) then the MC is bad. As fluids are not compressible, and Pascal's Law is applicable in our dimension, that fountain of fluid is coming internally from the working part of MC.

3. Life lesson: most reman MCs are muy malo--very, very bad. Buy new, what the heck, the life you save may even be your own!

yes there is definite pressure in the MC. guess i should just lay down the cash and go with a new one...
 
Here are some thing s to try

1.open all 4 bleeders do not push brake pedal let it gravity bleed at least 1 can through it .
2.Adjust rear brakes .

3. Check to see if you still have the stock prop valve under the hood . If you do and have added the wilwood you may have added too much or a restriction to the rear .

4. Clean and check the seal on the cap make sure it is in good shape .

FYI the valve at the rear of the truck is a load sensing valve . when the truck gets loaded heavy it add more pressure to the rear brakes

1) did that, twice.
2) i did adjust the drums with those star adjusters, didnt do anything to help
3) i junked the whole MJ prop valve setup and did my own. the brakes worked for 3 years with the Wilwood valve.
4) its "new"
 
actually the mc will bleed off fluid from the front piston until the back starts building pressure so the front brakes dont lock up before the back does anything again try adjusting your back brakes real good
 
also if you have the vacumm booster there is a reaction disc in between the mc and the booster (smaall plastic disc ) it may have fallen down in the booster when you pull it apart see if that is there
 
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