[JasonMonette]

Ok, here is the dilly-o. Last weekend my 1981 CJ-7 (See it here) worked fine. I just pulled it out of the Garage, and my brakes had no pressure. I pumped them up to get pressure, starting driving and hit the brakes, nothing, no pressure. I pumped them up, held the pressure on, and the pressure just gave and the pedal went to the floor. I checked the Master Cylinder, it was full. No leaks, no ballooning in the lines. I am stumped. Any ideas???

[gosupes]

Probably the master cylinder. Mine was doing the same thing. Leaking past one of the pistion seals would be my guess.

[GADJIT98]

Jason,

I am assuming you have power brakes on your rig.....if not you will need them with those size tires. You can get everything new for under $200 at NAPA, or go to a yard and get it off a junker, You will want to get the booster & MC for a 94 wranger.

To answer your question, yes, you need to replace the MC on your rig. Now would be a good time to do the stuff above if you need it

Dave

[JasonMonette]

Originally Posted by GADJIT98

Jason,

I am assuming you have power brakes on your rig.....if not you will need them with those size tires. You can get everything new for under $200 at NAPA, or go to a yard and get it off a junker, You will want to get the booster & MC for a 94 wranger.

To answer your question, yes, you need to replace the MC on your rig. Now would be a good time to do the stuff above if you need it

Dave

No they are manual brakes......and the master cylinder is brand new

[GADJIT98]

Jason,

My guess is that you somehow still have fluid bypassing your MC. Even if it is new, there is still a chance that is is still defective. TRUST ME on this one, Go to NAPA and get a booster and MC (should be already put together) for a 94 wrangler. The only part you will have to find is a bracket from one in a junk yard and also 2 adapters from NAPA...I can get you the part numbers if you need them. The total cost is less than $200 brand new, and you will have GREAT breaks.....much better than the manual ones. When I did this mod, it was a great improvement and worth every penny!

Let me know if you would like to pursue this and I will get you as much info as you need. Everything is a direct bolt up with no fabrication needed.

Dave

[lord_byron]

You could also get a master cylinder/booster for the CJ and mount it up. I thought about doing the wrangler master cylinder swap because my brakes were not working very well. Turns out the rears were not working because they were out of adjustment and the wheel cylinders were leaking. I rebuilt both drums and adjusted the rear pads, and I replaced the front pads with performance friction pads. Now my CJ's brakes work nearly as well as my TJ's brakes.

[JasonMonette]

Originally Posted by GADJIT98

Jason,

My guess is that you somehow still have fluid bypassing your MC. Even if it is new, there is still a chance that is is still defective. TRUST ME on this one, Go to NAPA and get a booster and MC (should be already put together) for a 94 wrangler. The only part you will have to find is a bracket from one in a junk yard and also 2 adapters from NAPA...I can get you the part numbers if you need them. The total cost is less than $200 brand new, and you will have GREAT breaks.....much better than the manual ones. When I did this mod, it was a great improvement and worth every penny!

Let me know if you would like to pursue this and I will get you as much info as you need. Everything is a direct bolt up with no fabrication needed.

Dave

Ok, give as much info as you can on how to do the swap. Thanks a ton.

[kaptainkarst]

Originally Posted by gosupes

Probably the master cylinder. Mine was doing the same thing. Leaking past one of the pistion seals would be my guess.

Check your wheele cylinders (especialy if the rear is drum). You will see a small amount of fluid that has leaked on the bottom of the wheel. I just had to have mine replaced with similar but not as dramatic symptoms. I could have honed the old ones and rebuilt them with new rubber etc, but it was just as cheap to buy two new cylinders (while you are in there, replace the shoes and have the drums turned if needed). I purchased the parts myself from Advance Auto and it cost me $70 for ALL of the parts including: Two wheel cylinders, a set of shoes, a hardware kit (includes all of the springs etc for both sides and another pint of brake fluid. I then took all of the parts and Homer to a local garage and they charged me $40 to do the brake job (did not turn drums).

Before ordering parts, you will have to know if you have 10" or 11" brakes. I pulled a tire off the back, and took a wire brush to the outside of the drum and the tolerance was stamped on the drum which indicated the size.

[lord_byron]

Originally Posted by kaptainkarst

Check your wheele cylinders (especialy if the rear is drum). You will see a small amount of fluid that has leaked on the bottom of the wheel.

Also a leaky wheel cylinder will drench the shoes with brake fluid and ruin them. When I rebuilt mine, I got a new set of Bendix pads to replace the ruined ones.

[bods7]

If I were you before I bought anything I would pull my wheels and look at the brakes. Sometimes I thihnk we all get to caught up in giving information out and we put ideas into peoples heads. We can't forget that the best information is given after we know the facts.

Anyhow as someone already said check the wheel cylinder boots. Pull them off the cylinder and look inside them for brake fluid. There shouldn't be any. Also check the front calipers for brake fluid leaking anywhere. While your there check to make sure your bleeders are tight. Since your doing that you may as well have someone press down your brake pedal for you and bleed the brakes checking for air to come out. If all the brakes look good I would guess your problem is in the master.

[JasonMonette]

Ok I checked everything that you guys suggested and still can't figure it out. I think it is time to start replacing things. So if someone can give me some directions and what is needed to convert to power brakes I would appreciate it.

[jadams68]

Go to a junkyard and a get YJ brake booster and master cylinder for $20-$40 and see our writeup.

www.bustedjeep.com

[jeepmor]

Jason,

If it's not leaking fluid anywhere, it is most likely the master cylinder with a bad seal in it, allowing the fluid to slip by as you hit the brakes. When you pump them up, you're forcing the bad seal to flare out and hold pressure. Once you remove the pressure, it equalizes and your back to pumping it to regain pressure.

However, make sure you're not leaking.
1. Reservoir level does not drop with repeated cycling
2. No leaks at calipers or rear wheel cylinders
3. No leaks at connections to calipers or wheel cylinders
4. No leaks at the connection fittings on MC, proportioning valve or where your hard lines connect to the flexible lines at the calipers and rear housing above the differential.

I know you state you have a new Master Cylinder, but that does not preclude it being good. I have bought bad parts from good parts stores like Napa on a couple occasions, especially if they are rebuilt instead of new. I personally avoid Napa parts like the plague. On a related topic, I had a new clutch master cylinder fail on my wife's 85 4Runner in a matter of weeks when I replaced the whole shooting match, master and slave cylinder. So I was assured that it was not due to my work or contamination because it flushed out clean fluid when bleeding out the system. Still had to argue with the Napa guy over it, but he did give me my money back.

I think people might cycle these parts before they put them in and damage the seals before fluid is on them or the manufacturer is not properly lubricating the seals during assembly. Dry o-rings do not move in tight quarters well without lube. An indication of this issue could be a blackish looking brake fluid from the seal particles being generated..... At least that was the case with my wife's hydraulic clutch.

whew, sorry so long, hope it's complete enough for you.

jeepmor

[jeepdaddy2000]

Originally Posted by JasonMonette

No they are manual brakes......and the master cylinder is brand new

Silly question, but I gotta ask...You DID bleed the master cylinder before you installed it?

[JasonMonette]

i didn't install it. it worked fine for a couple of months, then it just stopped working right. I have blead the brakes a couple of times to know avail.