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Hey guys, I got a problem on my hands with my 1989 MJ 4.0 2WD with the BA10/5 transmission. To start at the first of my problems, my clutch pedal started to feel soggy. I checked the fluid level and it was low, so I topped it off. A week or so later it was soggy again and low so I topped it off again. Doing this over and over I decided to check the master cylinder. It didnt look like it was leaking too bad but it was a little bit, so I changed that out and bled it. After I bled it, it felt great, but then after only driving it around the block it went soggy to zero pressure and then there was fluid leaking between the dust pan and tranny. So I figured it was the slave cylinder all along. I then dropped the transmission and replaced the slave cylinder, while I was in there I replaced the clutch and pressure plate as well. Now with everything back together and after bleeding the clutch I get good pressure, but when I start the engine and try to put it in gear it will not allow me to at all, and the clutch pressure starts to slowly fade away. After shutting the engine off it seems like the clutch pressure gradually builds up again. I then bled it again and then pushed in the clutch while I’m gear and had another person try moving the truck. It will not budge. I can hear the clutch moving a little bit by repeatedly pressing the clutch with the engine off. I tried bleeding it several other times and still the same issue occurs. The tranny shifts perfectly while the engine is off and it has fresh fluid. I am stumped on this one guys... as of this moment I am going to try leaving the reservoir cap off over night while the clutch is pressed all the way down to see if any air in the system can work it’s way out. I would really appreciate any of your guys help as I am trying to get this going as soon as possible. Thanks.

I know there are many threads that explain this procedure but another won't hurt from someone elses experience. So, this weekend I am starting the dual diaphragm conversion on my 1989 MJ. To start off, here are the tools and equipment I have so far: 1996 XJ Brake Booster and Master Cylinder (bought off of JC Whitney) $170 (2) 3/16 diameter bubble flared with 10mm fitting brake lines STANDARD flare tool (rented from auto parts store) (1) 12mm thread 3/16 diameter line, fitting (1) Vacuum Tool (4) 10mm stop or lock nuts (1) Line cutter The four 10mm nuts are for the brake booster. The other two bolts on the other side can use the nuts off of the stock MJ booster. I chose to buy the bubble flare lines because the 1996 MC takes bubble flare ends and not double flared. The MJ distribution valve body DOES take double flare though. So, I am going to have to flare one end of each line using the standard flare tool. Also, one of the ports on the 1996 MC takes a 12mm fitting which I will have to slide on the line before flaring again. 1996 XJ brake booster 1996 XJ master cylinder currently being bench bled using vacuum tool Vacuum tool This tool made the bleeding process a little easier. There are many ways to do it. Putting each of the hoses from both fittings into the bottle and pushing the rod in, will have the same effect. I did both methods just to be sure. That is where I am at right now. Tomorrow I will start the upgrade!! :wrench: Also there will be lots of more pictures! :clapping: :thumbsup:

Hi all, I just got my first Comanche a few months ago and it's been an awesome truck for me so far. Until the other day I started her up and the clutch went down to the floor, and I could barely change gears. I checked my reservoir and it was dry, so I topped it off hoping that would do the trick. Nothing. I did some research online (including this site) and figured out it's probably one of the cylinders that went bad. The problem is I'm not sure which one. I'm really hoping it's the master, because unfortunately my truck has the dreaded internal slave cylinder, and I don't have the knowledge or tools to drop the transmission myself. Thing is, there's no visible leaking at either cylinder, so I'm completely lost as to which one I should replace. At this point I'm thinking of just doing the master myself, and if that doesn't fix the problem then I'll take her into a shop. But I would love to spare myself the trouble and cost of replacing parts that don't need replacing.... Any help would be greatly appreciated!! Cary

Attempting to put in my new AX-15 and learned something today. The Master Cylinder for the '92 models uses the same "pin" style fittings as the later models, even though I have an internal slave like the rest of the Comanches. Meaning, I don't need an adapter and a new line to attach my JY slave I salvaged nor do I have to fool with swapping out my master (possibly the rod end is a different size, have not confirmed). Apparently the older Master Cylinder was used until '91 and changed in '92.

I recently finished doing an 8.8 SOA swap in my 1991 Jeep comanche Pioneer 4.0 manual. I need to do something about the brakes because they are seriously lacking in stopping power. Currently all I have done is eliminated the rear proportioning valve. I am going to swap in a 95/96 XJ brake booster, master cylinder and proportioning valve. My question is seeing that the 8.8 has disc brakes do I need to find a brake booster, master cylinder and prop valve from a donor vehicle that also has disk brakes or will a donor with drums work? What would be the best set up to keep the rears from locking up before the fronts under extreme braking conditions? Thanks in advance.

Hey, so looking through the forums, everyone is very concerned with the master cylinder leaking onto the fuse box. Well, this happened to me. A year or so ago, i caught the leak and swapped out the master cylinder and even replaced the clutch because of a leak on that too. The leaking fluid has corroded some of the fuses, and as a result, my brake lights, and turn signals fail to work sometimes. a quick little tap and some finesse with the fuses makes everything work again, but the problem is becoming more and more reoccurring. so, whats the fix for this? new fuse box? where can i get one?