help....major brake problems

this is on my sons 91 xj with a front 60 and a 14 bolt rear.front and back are 3/4 ton chevy disc brakes.we installed this over 8 years ago and have not had a problem with it ever.this rig is mainly driven on the street.when we installed these axles we swapped to the corvette equal reservoir mc also.
the other day on the way to work he completely lost his brakes.this happened suddenly without warning (he says)
fortunately he was going slow and was able to get to a parking lot and leave it sit.
we went back and worked on it that night and noticed one side of the reservoir was low but not empty.
we filled it and tried to bleed it but every bleeder broke off so I had to try to bleed it by breaking the banjo bolts.this seemed to work and we got a lot of fluid through it but still no pedal at all.
next we went out and bought a rebuilt mc the same as the corvette one we had.
it has to be modded a bit to fit but we did it and bench bled it and got it mounted on.
still nothing right to the floor.in drive there was no brake at all.
next we got it towed home and bought all new calipers and pads.now we were able to bleed it properly with the bleeders at the top.
we got fluid to bleed through them and im confident there is no or very little air at all in the system but they will not hold at all and the pedal still goes to the floor.
its on jackstands now and the wheels are off.with the brake to the floor the rears are not clamping enough to even stop it from spinning.
if we lock it in 4wd the fronts will stop everything from spinning but if I put a bar between the studs I can easily overcome the clamping force.
one thing I did notice uis that the rear rotors were rusted on the faces.i don't thik they hsave been clamping for a while ,even before this major problem.
any ideas as to what the heck is going on here?

the stock "distribution metering" block is still in place.
and we have not added a proportioning at all in the stock system.

Try seeing if you got a leak some where. Also it's possible a flew line has failed internally cheap insurance to replace them.

Form the sound of it it's isolated to the rear axle and it's not applying enough for. If it did this before them there might be a restriction in a line. Inspect for damage.

pushrod backed off or broke?

just for information sake...
bore and stroke of the MC?
dual diaphram booster?

thanks,
I will take the mc off of the booster and look at the rod and stroke tonite.
I believe the mc is 1-1/8 and the booster is single.

thanks guys.
we will look into all of these tonite starting with the pushrod length.ive read to set it properly you take most of the fluid out and then press down on the pedal 3/8 to 1/2 inch and look for the fluid to spout up from the holes at the bottom of the mc.
does this sound right?

thanks again.
last nite we had an emergency and didn't get far with the diagnosis.
I did pull fluid from each reservoir in the mc so it was just under 1/2 filled.then I had him push the pedal just a 1/2 inch down and I saw fluid fountain up from the holes in the bottom of the mc.im sure now that the rod stroke is where it should be or at least within reason.
tonite we will look into it more and ill let ya know how it goes.

thank you all for the advice.
we finally got it last nite.
we opened the large nut(bleeder)on the end of the combination block and pumped the pedal a few times before any fluid came out from around the threads.then we mashed the pedal very hard a few times after we closed that nut back up.finally I tapped the whole area with a wrench to try to free up any trapped air.after all this we bled it again and got quite a bit of air out and finally a pedal.
thanks again for everything!

markg said:

thank you all for the advice.
we finally got it last nite.
we opened the large nut(bleeder)on the end of the combination block and pumped the pedal a few times before any fluid came out from around the threads.then we mashed the pedal very hard a few times after we closed that nut back up.finally I tapped the whole area with a wrench to try to free up any trapped air.after all this we bled it again and got quite a bit of air out and finally a pedal.
thanks again for everything!

Click to expand...

Success!:smoker: