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no brakes!!!

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sounds like its time to make the upgrade to the dual diaphragm one.



That's my plan, and the reason I didn't investigate further. No hissing sound from mine.



you drive it like that?


Heck no. The 88 doesn't really go anywhere. Even more so now that the gas tank won't hold gas. :(

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I'm gonna say its the master cylinder, and possibly the booster as well. I had another vehicle, same thing. I would bleed the brakes and have a nice firm pedal, but once the engine was running it would sink to the floor. If you pumped it a few times quick, it would build a little pressure, but was instantly gone.


Someone then told me, when you bleed brakes on an older car/truck, to put something under the brake pedal so that when you are pressing the pedal you arent bottoming it out. Over time you will wear a 'groove' for lack of a better word, on the shaft of the MC. When you bleed the brakes and or lose brakes and the pedal bottoms out, you mess up that seal and it then leaks and will not hold pressure.


Either way on the other car, once I put in a new MC, brakes worked like new!

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One of my NAXJA friends had this with an '89 XJ. He replaced just about everything in the system, with zero improvement. What finally fixed it was removing the factory proportioning valve and replacing it with an adjustable proportioning valve.


However, I recognize that the MJ does not have a proportioning feature in the front metering block. So some diagnosis is in order. Back to basics: Have you removed the cover from the master cylinder to see if one or the other chamber is low -- or empty? That's the first step. The large chamber feeds the front brakes, the small chamber feeds the rear brakes.


Check it out and let us know.

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:dunno: they were both a little low when i opened it

i filled it to the top, put cover back on, then pumped with engine off

pressure jamminz.gif

started truck..

to the floor :fs1:

i took the cap back off and they were both full

i pumped with cover off and there were bubbles in the front chamber when the pedal was coming UP

does that help a little more?

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sounds like a booster problem. check your fluid level, pad wear, wheel cylinders, and calipers, as well as all the lines and valves. Do you hear a hissing coming from your booster with the truck on and the pedal not being pressed.

i hear hissing from the booster with the truck off and pressing the pedal down...then the bubbles inthe front chamber when pedal is coming up

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just woke up, :chillin: , and went into garage to look at my master...

front chamber is full still

rear is 100% empty! :eek:

looked for leak on floor....hard to see cuz floor is wet from snow falling off trucks....didnt see anything! figured it disipated in the water on the floor.

looks like i gotta track down a rear line leak, huh?

i mine as well put that new brake block on too,(to bypass that crazy brake system in the rear)......

eric.....come up n help :D

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two chambers on my master cylender

front one (small) = rear brakes?

rear one (large) = front brakes?


am i right? :shake:

Yes, the large reservoir is for the front discs.


If the small reservoir went empty, you have a leak. The most probably place is naturally the least accessible -- where the lines run along the frame above the fuel tank.

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Just discovered the same problem with mine. It must have had a pinhole (of course where Eagle said, where the line runs between the gas tank and the bed wall) and I found a puddle that turned out to be brake fluid. SO now I'm midway to replacing the entire line from the MC back.

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