blistovmhz
NAXJA Forum User
- Location
- Vancouver, BC
Before everyone jumps to "have you tried *obvious answer here*", yes, I have.
A buddy picked up an 86 XJ with an old carbed chev 4.3. We've got everything else working pretty tip top, but brakes are ****ing eluding me.
He had another of his buddies bleed the system. They found lots of air but by the time they were done, there was absolutely no affect on braking.
I take a little more methodical approach.
Original situation:
Pedal stroke at 2" provides enough pressure to stop the front wheels from being spun by hand, but rears haven't even moved. Verified by pulling drums. The Cylinders have not moved a nanometer with 2" stroke. At 3" stroke, the fronts are about as stiff as they're going to get, and rears still haven't moved. At just shy of 4" stroke, the pedal is rock hard and the rears start expanding slightly, but not enough to stop me from spinning them by hand. At exactly 4" stroke, the prop valve pops and of course the rears cannot possibly go any further.
So I bled the entire system (in the correct order, through about 5 full reservoirs of juice). Found that the fronts and rear driver all bleed normally, but rear passenger always ends up with air in it. Suspected cylinder was drawing air on retraction, and replaced it. No longer draws air, bleeds fine, but ZERO affect on pedal stroke.
Pull the MC and bench bleed it, reinstall, re-bleed entire system, zero affect.
Install new MC after a very serious bench bleed, re-bleed system, zero affect.
Bleed the combo valve (I'm not sure if it's bleeding properly due to it's location, but no more air coming out). Zero affect.
Replace some rear lines for no reason. Zero affect.
With engine off, first pump gets about 2" stroke. Second about 1", and third the pedal barely moves 1/4". With engine on and booster helping, pedal feels like it's not even connected to anything until it hits 2-3" stroke, then ramps up quickly to 4". Again, just before the prop pops, the rears haven't moved at all, but front pressure is as high as it's going to get. Above 4" the prop pops and pedal gets super stiff immediately.
Logically, we've got air in the rear circuit. That explains why the prop is popping before the rear cylinders have any pressure. Like, at 2" stroke, I can pull the drums off by hand easily. At 3" stroke, I can force them off.
Yes, the rear shoes are adjusted properly. We've even tried adjusting them so they're too tight to turn by hand before applying brakes. Zero change in pedal travel or overall braking performance.
Sorta at my wits end here. I always get the most ridiculous problems, but I'm the guy everyone comes to when they can't figure something out, and this one's got me stumped. We've got a buddy bringing over a pressure bleeder as a last resort. I suspect it'll work, but even if it does, I don't like not knowing why a brake system wouldn't bleed properly.
Am I missing something and just derping out? I'm not about to discount the possibility that' i"ve just suffered a stroke and am not thinking clearly.
A buddy picked up an 86 XJ with an old carbed chev 4.3. We've got everything else working pretty tip top, but brakes are ****ing eluding me.
He had another of his buddies bleed the system. They found lots of air but by the time they were done, there was absolutely no affect on braking.
I take a little more methodical approach.
Original situation:
Pedal stroke at 2" provides enough pressure to stop the front wheels from being spun by hand, but rears haven't even moved. Verified by pulling drums. The Cylinders have not moved a nanometer with 2" stroke. At 3" stroke, the fronts are about as stiff as they're going to get, and rears still haven't moved. At just shy of 4" stroke, the pedal is rock hard and the rears start expanding slightly, but not enough to stop me from spinning them by hand. At exactly 4" stroke, the prop valve pops and of course the rears cannot possibly go any further.
So I bled the entire system (in the correct order, through about 5 full reservoirs of juice). Found that the fronts and rear driver all bleed normally, but rear passenger always ends up with air in it. Suspected cylinder was drawing air on retraction, and replaced it. No longer draws air, bleeds fine, but ZERO affect on pedal stroke.
Pull the MC and bench bleed it, reinstall, re-bleed entire system, zero affect.
Install new MC after a very serious bench bleed, re-bleed system, zero affect.
Bleed the combo valve (I'm not sure if it's bleeding properly due to it's location, but no more air coming out). Zero affect.
Replace some rear lines for no reason. Zero affect.
With engine off, first pump gets about 2" stroke. Second about 1", and third the pedal barely moves 1/4". With engine on and booster helping, pedal feels like it's not even connected to anything until it hits 2-3" stroke, then ramps up quickly to 4". Again, just before the prop pops, the rears haven't moved at all, but front pressure is as high as it's going to get. Above 4" the prop pops and pedal gets super stiff immediately.
Logically, we've got air in the rear circuit. That explains why the prop is popping before the rear cylinders have any pressure. Like, at 2" stroke, I can pull the drums off by hand easily. At 3" stroke, I can force them off.
Yes, the rear shoes are adjusted properly. We've even tried adjusting them so they're too tight to turn by hand before applying brakes. Zero change in pedal travel or overall braking performance.
Sorta at my wits end here. I always get the most ridiculous problems, but I'm the guy everyone comes to when they can't figure something out, and this one's got me stumped. We've got a buddy bringing over a pressure bleeder as a last resort. I suspect it'll work, but even if it does, I don't like not knowing why a brake system wouldn't bleed properly.
Am I missing something and just derping out? I'm not about to discount the possibility that' i"ve just suffered a stroke and am not thinking clearly.