[5STRINGINIT]

Just wondering, how would you know if the prop valve on the breaks is going bad? My breaks were running great for a year, then all of a sudden the break pedal goes to the floor sometimes and then it works fine sometimes. This is off of a 1980 cj7 manual breaks. I have no leaks on the system at all. Thanks in advance.

[bigjoe]

Sounds like the MC is going bad to me. Is it the original one or a refab?

[5STRINGINIT]

it is a rebuilt one, about 4 mths old.

[Fatman]

Might want to pop off the rear drums and check the shoes. Sometimes the self adjusters don't adjust as they should. Prop valves don't go bad very often.

[bigjoe]

Ok so you checked the lines I'm guessing for leaks or weeping right? How about the wheel cylinders in the drums. Maybe one is going. If no leaks there I would rebleed the MC (bench bleed it) and then rebleed the system to see if this helps. Either the MC is bad or there is air in system.

[Mike Romain]

That is a master cylinder failure. The 'rebuilt' ones are a crap shoot these days. If they have to be honed out smooth, no one makes an oversize for their seals so even a new seal has very little wear available before it fails.

The last two out of three I bought have had failed seals or better said 4 out of 6. Thankfully I spotted the leak at the pedal end when bench bleeding them. Only one failed internally.

The 'good' one that is on mine now ahas started for fade on me by slowly going toward the floor now and then.