[dallen]

Hi all. I have a 1986 CJ7. When I bought it, it had rear disc brakes. I didn’t install them or have them installed so I know very little about them. My problem is the brake pedal goes all the way to the floor when I first start out. After I pump them once or twice everything is OK except when I am wheeling. If I am going up or down a Simi steep hill the brakes need to be pumped. This does not happen every time though. I have bleed the breaks several times with no change. I can not see any leaks and I don’t use or loose any fluid. I could really use some help with this one. Thanks.

[jadams68]

It sounds to me that if someone did a disc brake conversion on your CJ, that they may not have used a proper disc brake master cylinder.

[CJeep]

Assuming the the PO did not chage the master cyclinder or proportioning valve, you may have some headaches ahead of you.

While the fronts do most of the stopping, the rear (stock) drums account for most of the pedal movement. It take a lot less fluid to move disc calipers compared to drum brake shoes.

My guess would be that a new proportioning valve would fix your problem, but I have no idea what the right proportions need to be. I'd check with an expert, hot rodders do a lot of drum-disc conversions, but it may require a good deal of trial and error.

[rustyCJ]

contact SSBC or SBSC or something like that, they are the most common manufacturers of aftermarket disc conversions for jeeps. i contacted them about how to convert my rear to disc, they will beable to answer all of your questions.

[dallen]

Thanks for all your help. I think I need to look into a bigger master cylinder.

[crotz83]

i have the same exact problem with my scrambler, i doesn't seem that the front discs' pads wear hardly at all...i need some help with this subject as well, for the record i don't dig headaches i would just like a fix if anyone knows...i don't think the master cylinder has been changed on mine....is there anything dealin with vaccuum from the engine that affects brake pressure?? just a question

[jadams68]

Crotz,

Yes, if you have power brakes. The Vacuum booster draws air from a tube coming out of the engine intake manifold. Vacuum is created while the engine is running (no kidding) and when you press the pedal down, the input rod is pushed forward in the booster which blocks a port in the diaphragm and opens another port causing the vacuum to shove the push rod into the master cylinder.

[crotz83]

okay, well i have a 350 chevy ....maybe i should check for this vaccuum connection then....any other ideas??

[RockJeep]

go to the parts store and tell them you want a Master cylinder for a 68 corvette w/4 wheel discs. should bolt right up, about 15 bucks plus a core charge. it should have an almost equal resevoirs, also its got a longer stroke bigger bore, 1", and should solve your problems. if your rear brakes start to drag on the street at all you can get a willwood adjustable proportioning valve for the rear and tune the brake pressure.
later
bob
p.s. for some serious stopping power swap in a hydraboost setup from a diesel.

[Jeep Daddy]

I don't think you need a larger master cylinder - just get a new one to start with. Those are symptoms of a bad master . . . plain and simple. Lets assume that the brakes were converted corectly by the PO and that they worked properly after the conversion. Unless you know that the PO got rid of the Jeep because he couldn't figure out his brake problem.

So, I'd just get a new MC, be sure to compare the old one to the new one and swap it out. Should only take about 15 minutes to swap out, then bleed. Make sure you bleed all the wheels starting with the farthest wheel.