I have put 3 on from advance auto, None work. Anybody got a dependable supplier. I'm sure its the MC Cause it just pushes a little out and sucks it right back when release the pedal. I've been through the whole system. I need a good local supplier( makes it much easier to return faulty products) Thought some of you probably had experienced this and could point me in the right direction. I'm 100 percent sure its the MC.
HI, I'm with HackFab you have to bench bleed it or you well never get the air out. no way 3 master were bad. you ether have other problems or you didn't bench bleed it.
good luck
tim
I did bench bleed the master cylinder. I know when it releases it should suck back a small amount to release pressure on the brakes. I put a piece of clear tubing on just for bench bleeding and testing. It actually sucks the tubing flat when released. I put my finger over the outlet port to feel it bluid pressure and when the pedal is released it sucks back a lot. So much so that the spool will not spring return until I remove my finger. I can actually here the spool snap back when I remove my finger. That can not be right. Some how it has to make up the fluid lost when bleeding?
I've also got an 85 CJ7 and replaced the MC a couple of years ago. I ended up with one from NAPA. It was a new one, not reman, cause I'd had some troubles getting the lid to seal with the reman.
Have you bench bled an MC prior to this situation? Reason I ask is, from my experience, when you push the plunger in it's a hard push, but goes in relatively easy and reaches a point where it feels you've reached the end of the stroke, but really haven't. Push harder at that point and it'll go further. When I did the bleed I had the MC in a vise and used a bleed kit that had 2 clear pieces of tubing routed from each outlet and looped back to it's respective reservoir. As you push the plunger in you can see air bubbles come out the tubes and back to the reservoir where they rise to the surface and leave. As air is removed, just keep the reservoirs near full by added brake fluid. If you're not getting any of this venting action (bubbles coming out of the tube and going to the reservoir) from the rear tube (the one for the large reservoir-disc brakes) then you're not pushing the plunger far enough in.
HI ... sounds like the master is working fine.. when you put your finger over the tubing it did NOT spring back because it could NOT draw back with the tube plugged off. It has to draw back thru the tube NOT the master and if you plug the tube its not going to work... If it draws back thru the master then the seals are bad in the master.. The master pushes and pulls the fluid thru the lines NOT the master its self or the brakes would not work. You would step on the brakes and if the full pressure does not go thru the lines you would have NO brakes
good luck
tim
Thanks for the replies guys. Not to be repetitive but man I have done everything to this, replaced mc 3 times. bench bleed, replaced proportional valve. vacuum bleed. I have great front brakes just no rear brakes. I have checked brake shoe adjustment. Held the little pin in on the proportional valve. I just get a few drops of fluid when I have someone press the brake pedal and try the bleed screw. I have experience bleeding brakes before. Never had this much trouble. I don't know whats going on?
Condition of brake lines? Pinched? Rusted? Old rubber lines?
Rear brakes need 10 pounds of residual pressure to keep the shoes close to the drums. Most Disc/Drum master cylinders have that built into them. But not getting fluid to the wheel cylinder (where the bleeder is), is an indication that something from the master (assuming it is fine) back is fawked.
Possibly you have a bad wheel cylinder? Trust me, just because they are 'new', doesn't mean they are good....
How old is the rear brake hose? Maybe the hose is almost swollen shut not allowing the fluid through. Did you have fluid before you started replacing parts?
Okay, there is a lot of confusion going on. I guess my post aren't very clear. I am getting hardly any fluid out of the master cylinder. I checked flow/pressure at the wheel cylinder and had hardly any so I took the rear brake line straight off the master cylinder and there is hardly any fluid or pressure at the outlet of the master cylinder. This why I believe the master cylinder is the problem. To me this rules out brake lines, proportional valve, wheel cylinders. I have repeatedly bleed the master cylinder with the bleed kits. I seem to have flow though the bleed kit with no restriction, but as soon as I use my finger over the outlet port and have someone press the brake pedal, very little pressure and flow. I can basically hold it back with my finger.
Well, maybe you did get 3 bad MCs. Can't really suggest a better supplier... I've used re-mans from AZ, O'Reily, and Advanced without any issue (I think most of them come from the same re-builder anyway).
I had 2 Dorman MCs fail from the box. I've also learned bench bleeding takes patience and can be a slow and methodical process. Mine took many complete strokes. Did I understand that your MC rear reservoir is not pushing fluid, but your back brakes are not working?
I changed my master cylinder again on Sunday and seemed to have finally made some progress. I now have rear brakes Although my brae light is on and the pedal is a little softI think with some more brake bleeding it will be fine. I was in a rush to get it put on and probably didn't get them bleed as well as I should. Things are looking up:0
i just did this on 81cj7 for a buddy and used a cardone select from RA. it said it was new not reman. i have bench bled many mc but this one was a booger.....like posted above it took several times of i'm done....no wait it will push a little more and yep couple bubbles came out.....clamped in the vise and my brother still helped hold it cause i was sure i was gonna flip it out of the vise.....got it installed, bled brakes good, drove it a day and then rebled.
HI, maybe the bleeders are plugged? try taking them out and have someone push the pedal and see how much comes out?? hold your finger over the hole to prevent to much air being sucked back in when the pedal is released. Maybe take a paper clip size wire the poke the hole a little if no fluids comes out, might have some build up (corrosion).. Same with the bleeder you can just poke the holes and make sure there clear.
good luck
tim
Had the same issue with brake light tripped in combination/proportioning valve after changing MC and bleeding. That brake light works with both the parking brake and combination/proportioning valve. After a couple of good panic stops (hit the pedal hard), I heard it trip and off goes the brake light! Good luck.
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