Master cylinder question

i have a '75 cj with manual brakes, the pedal is spongey, the front cylinders are new, i checked the reservoir and BOTH sides were low. Does this mean that I have a leaky master cylinder? And, if i replace it can i install a power booster? and just use one of the vacuum ports on my high-rise intake manifold? Thanks

 

does this mean you have a leaky master? Not necessarily. You could have lost fluid when changing the cylinders, bleeding the breaks, could have a small leak in a line connections. spongy brakes could be air still in the system either from not getting it all out or entering the system at the leak source. I would fill the master, get the brakes bled, make sure any fluid is off your lines and connections, and let it sit overnight, checking all lines and connections the next morning for any signs or leaks. Power booster-- I don't think you can add a booster to a manual system, I may be wrong though.

 

Replacement OE power brake boosters for the '72-75 era Jeeps are hard to find. if I had a power brake equipped Jeep, I would expect to have my booster rebuilt if needed, simply because the cores are so scarce.

If you could find a '72-75 donor with power brakes, you could take the booster, firewall brackets, and push rod for power brakes. Then you would have to make new brake lines, since the master cylinder location moves forward, ahead of the canister. So even if you have the OE parts, you'd need to do some fabricating.

If you want power brakes, search the archives here for others that have done the conversion. https://www.google.com/search?q=site:earlycj5.net intermediate power brakes

 

"Spongey" is most often air in the system. Needs proper bleeding. Air in the system gives a soft pedal but it will bounce back and will not continue to "sink" after a certain point.

A leaky master might result in air being drawn in when the reservoir empties, but in itself an open leak will result in a 'sinking' pedal that will gradually go to the floor when constant pressure is applied, not sponginess. Sometimes a faulty master seal internally will result in a long pedal travel without resistance before the pedal gets "hard."

At a guess, I'd say start by bleeding the front lines and wheel cylinders completely and definitely.

 

You might want to consider upgrading with a power booster from a later model. Mine came off a YJ. Its not a tough job anf there are many on the forum and other forums who have done this. The difference in braking is nothing short of phenominal. I'll try to rustle up a photo or 2.[/URL][/IMG]

 

Mine is on a chevy small block but that doesn't matter. You are hooking the vacuum line from the booster to the vacuum port at the rear of your carb. This is one of the best upgrades I've made, no more standing with all your weight on the brake pedal. Stops very easy. [/URL][/IMG]

 

an intermediate with an inline six has clearance issues with a yj master. the lines and the air cleaner try to live in the same place...the air cleaner looses.

 

thanks for the info!
my jeep has new front cylinders. i cant't see any leaks, but its oregon and everything is wet all of the time. my pedal slowly goes down when i stand on it, it won't pump up like brakes that need bled. about a conversation: i see that morris has a single diaphragm universal booster, has anyone tried it? Thanks

 

If the pedal sinks you either have an external leak or the master cylinder has an internal leak and is bad. Have you checked the rear wheel cylinders? Rest of the system?


Sent from my iPhone

 

Power brake conversion: has anyone used the single diaphragm booster from morris? does it just bolt up and work? http://www.jeep4x4center.com/9-slim-single-diaphragm-universal-brake-booster-mbm-pb9002.html