Replacing master cylinder

93redzj

93redzj

Well-Known Member
Joined
Aug 29, 2005
Location
Albemarle
I attempted to replace the MC on my jeep today, 94 ZJ V8 with disc brakes front and rear, after installed the system didn't seem to want to be bled properly and after cranking the jeep the brake booster seemed to have sucked all of the brake fluid out of the rear part of the reservoir and now there is brake fluid in the booster....what did I do wrong here??
 
I attempted to but it wasn't going so well so I was gonna install in and bleed the lines, starting at passenger side rear. Would this not work?

I did also break lines loose once MC was installed and had a helper pressing brake pedal in an attempt to bleed the MC that way as well and no fluid bled out
 
I've never installed one without bench bleeding it first. Theoretically starting back left and working your way around us the correct way to bleed, but if you left a ton of air in the MC you'll be bleeding forever.
 
93redzj said:
I attempted to replace the MC on my jeep today, 94 ZJ V8 with disc brakes front and rear, after installed the system didn't seem to want to be bled properly and after cranking the jeep the brake booster seemed to have sucked all of the brake fluid out of the rear part of the reservoir and now there is brake fluid in the booster....what did I do wrong here??
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You've got a bad master. You'll need to replace it again. If fluid is getting into the booster the Masters seal is messed up.

Sent from my XT1254 using Tapatalk
 
Ah ok, I guess it's not gonna hurt to exchange it. I'll also take the next one to my dads and bench bleed as he has a vice I can put it in while doing so.
 
Changed out MC got it hooked up correctly this time, seems to be a good brake pedal and all, went to address my rear brakes and this is what I have on the passenger side that appears to be locking up on me....and I can't get caliper piston to depress, it seems to be seized up. Calipers are less than two months old
 

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Fwiw check the soft line that drops to the axle. They can collapse and not allow fluid to travel one way or the other causing either a locked up or non functioning situation. Or, it could have been a bad caliper from the parts house.
 
My front passenger side caliper wasn't that old, and I had to replace it recently. Looked exactly like your situation. The piston was stuck in full extension, but never gave any indication while driving. I couldn't compress it. I replaced it and all is good.
 
skyhighZJ said:
Fwiw check the soft line that drops to the axle. They can collapse and not allow fluid to travel one way or the other causing either a locked up or non functioning situation. Or, it could have been a bad caliper from the parts house.
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Yeah I've checked that soft line to see if it's got any debris in it restricting flow one way or the other, there didn't seem to be anything there. And yeah I think they are reman calipers from autozone.

I also couldn't compress the piston back in like I normally could so I took caliper completely off and took a C clamp to it to press it back in.
 
Well I broke down and took it to a shop for his opinion. He thinks brake system is contaminated and that some trash in the rubber hoses of the brake system is preventing the fluid from flowing back, causing prssure to stay on system. He reccomeded changing out all 4 calipers, the rubber hoses and flushing system. So it looks as if that's what I'll be doing next
 
skyhighZJ said:
Fwiw check the soft line that drops to the axle. They can collapse and not allow fluid to travel one way or the other causing either a locked up or non functioning situation. Or, it could have been a bad caliper from the parts house.
Click to expand...
It appears you could have been right sir
 
Well not that I wanted you to have to spend more cheddar but it can be a sneaky bastard sometimes and people overlook the rubber lines as the culprit.
 
Well I thought I had checked it good enough, my dad had mentioned wiggling the line around and listening for any kind of crackling noise as a potential indicator of trash in the rubber line. I did that but didn't notice anything. But the professional said otherwise lol
 
When in doubt, replace the lines. Usually one of the first things I do with a project car. Cheaper than the advil you'll waste on the headache you'll get while chasing the problem and trying to convince yourself that "those lines look fine!" Manufacturers suggest replacing the lines and flushing the fluid every so often. They don't last forever, especially if the fluid has been compromised by exposure to air and moisture.
 
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