Master Cylinder Leaking, losing fluid at the booster

So I noticed my M/C is leaking right where it bolts to the booster. The leak is slow but noticeable. It is leaking straight down, where the brake fluid has done a number on some of the paint, including inside the drivers side wheel well.

So, I'm going to replace it soon, maybe this weekend, but since this fluid is coming out steadily, enough to eat a bunch of the paint off, should I look for any other damage? Should I look to see if it damaged anything inside the booster? There is still plenty of boost, but I would hate to think that the leak destroyed a diaphragm or something in there.

Anyone recommend a good replacement master cylinder? I see brand new and rebuilt ones at the online parts places, auto zone, etc. Are the brand new ones worth the 3-5x more for the price?

Thanks

Oh yeah its an 88 XJ Wagoneer Limited, 4.0, auto, 242, 3.55s, no ABS, 127k miles, all original except for some replacement vacuum lines, sensors, etc.

Well if its an 88 and you have to reoplace the master anyways... Look into the dual diaphram booster of anewer cheroke. Iput one from a 95 on my 89 and one on my buddys 86. Its alittle wotrk but well worth it. Do a search on here about it and it will resault in alot of hits.

If it's leaking INside the firewall it can do a pretty good number on your fuse block, if it hasn't already. I'd check that out too.

Is it worth it to go through the trouble of switching the booster and master cylinder? I only have 235s, and I drive so slow that really the brakes are fine for me. With the new booster, and a new master cylinder, does it just stop faster and have better feel?

Nothing wrong with rebuilt master cyls. The only thing that wears out is the rubber inside, which they replace when rebuilding.

i recently installed the MC and booster from a 98 on my 93 with 6.5" of lift and 33's. works great. much improved.

I second checking the fuse block. It can really melt one into a twisted mess that will cause you headaches troubleshooting electrical unless you replace it (if it is melted)

Jim

I checked the fuse block and it is good. Hopefully I can do the MC today. Any last minute pointers? I will bench bleed it, but this will be my first solo MC on any rig.

You should probably flush out the whole system if it wasn't done within the last year or so.

Here's the best way to bleed 'em from an old post.

I'll just copy and paste mine from an earlier thread, but this is for an evening bleed, not a morning one.

"I did em that way for MANY years too. Called the kids or the old lady out and told em "pump it up and hold it down", and opened up the bleeder until the pedal went way down. There is a way easier way, but it takes longer. I use it whenever I replace brake cylinders or calipers, but mostly it's just to change the brake fluid, which I do whenever I change shoes or pads. Ideally you change brake fluid at least every other year. If you worked on old cars and saw rusty pistons, you'd know why, but people also say that old brake fluid boils and won't stop you right.

The best way is the GRAVITY method. The only problem is it takes a lot of beer and you don't want to drive right after. (CAUTION: YOU MUST BE 21 TO BLEED YOUR BRAKES THIS WAY!)

1.) Get the car in a position where you can open up the bleeders. I always like to break them loose with a 6 point socket being careful not to break them off. If you can, spray them with breakaway or similar a day before.)
2) Starting with the bleeder futhest away from the master (pass. rear), open it about 1 turn. You can put a little hose and cup on it if you want to keep the old fluid from running all over. Make SURE to keep the master cylinder topped off with fluid and DON'T let it get down to where air gets back into the master cyl. Let it flow this way until the fluid comes out of the bleeder clean. This will take at least 2 cups or so of brake fluid. Using gravity alone, you can drink 2 beers while topping off the master cylinder for the first corner. (CAUTION: Do not store brake fluid in beer cans or put beer into master cyinder. Drinking a little brake fluid however will probably not kill you. Beer in your brake lines might.) Snug up bleeder good when you're done.
3.) Proceed to drivers rear and repeat. It won't take as long because the long brake line has already been purged of the old fluid. So you have to drink your beer faster.
4.) Pass front. Drink even faster.
5.) Drivers front. Etc.

Patience can be substituted for beers, but that's no fun.

This prevents the rubber pieces from going any further than they are used to and self destructing.
:cheers: "