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Bench Bleed Power Brake MC Question

619 views 5 replies 5 participants last post by  60Bubba 
#1 ·
I have searched these forums (CJ/TY/XJ/etc) and good ol' Google without a definitive answer, so I'm turning to you kind folks.

I am working on a frame-up restore of my 81 CJ5, and I'm installing the Power Booster and Master Cylinder for the brakes. I purchased the brackets off Craigslist and a new/reman complete booster and master from the local parts store. I have new Classic Tube lines and prop valve and the system is currently "dry".

My question is in regards to bench bleeding. The booster/master came assembled (together). Do I separate them to bench bleed the master? It looks like there's some thread sealer (Loctite) on the threads joining the two. The engine doesn't run yet, so I'm assuming bleeding on the Jeep isn't an option.

I'm fine separating them to do this properly, but I want to make sure I'm not making this any harder than it needs to be. Any clarification you can provide is greatly appreciated!

Thanks - Jonesie
 
#3 ·
I just gravity bled mine. I assumed I'd run into issues with the proportioning valve, but everything came together easier than expected. It took longer than a pressurized system, or the 2 man way, but here's what I did on my 'dry' system

Fill MC
open rear passenger bleeder
wait until you see fluid weeping (best to find something else to work on while you wait)
Close the bleeder screw
Check fluid level, and top off

Repeat at rear driver side

Repeat at front pass. side

Repeat at front drivers side

The above steps got the system primed, and then I had friend to help with the 2 man way to get a stiff pedal. I expect there's still a bit of air in there that'll soften the pedal after I get the engine running, but this got me to a point where I had functional brakes - they may or may not be road worthy yet.

Just my $.02 - hope it helps
 
#4 ·
I know some do the MC while it's on the jeep, but to me it was more accessible and easier to do when it was clamped in a vise.

A couple of things I learned from this forum: first was to do an initial bleeding to where it looks good then let it sit overnite (gives any air bubbles time to migrate) and bleed again to ensure no more air. I used a kit that had clear tubing to connect to the ports on the side of the MC and the other end of the tubes each went back into the top of their respective reservoirs. Just add more fluid to make up for the air venting.

The second thing was getting a seal on the MC lid. When i got my jeep the MC lid was leaking which ruined the paint on the inside surface of the fender. I first replaced the MC with a reman, but it leaked as well. Finally bought a new MC and did what was recommended on this forum which was to smooth the top of the MC where the gasket seats. I used 200/400/800 emery paper in stages to get a very smooth finish without any imperfections and it did the trick, no leaks. I would tape what ever grit i wanted to use to a piece of glass, turn the MC upside down and work it on the paper in various directions. This was after 3 attempts to get a tighter seal to stop the leakage. If you want to do this it's better to do it before you do a bench bleed cause you'll need to do a little cleanup of the MC to remove any leftover dust.
 
#5 ·
Thanks for the help everyone. I mounted the booster and master on the firewall, then pulled the master off to bench bleed it. It was surprisingly easy.

Quick follow-up question that I'm almost too embarrassed to ask...

Does the engine need to be running to bleed power brakes? I don't think it does, but I figured I'd confirm before I waste my time fighting it.

Thanks - Jonesie
 
#6 ·
Nope. You can definitely bleed with the engine off. The vacuum created by the engine is stored in the booster, which just reduces the effort required to press the pedal to force the pads/shoes against the rotors and drums. With one bleed screw opened up, there is little resistance since the fluid you move by pressing the pedal down just squirts out the opening in the bleeder.
 
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