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Possible Master Cylinder Issue

luvherinmyjeep32

NAXJA Forum User
Location
Pennsyltucky
I thought I posted this last night but I guess not...

It seems like my 89 XJ stopping power has been lacking more so than usual lately.

I noticed the front pads were worn badly so I replaced them and no difference. The rotors are in spec.

After I changed the pads last night and no difference in stopping, I went to check the fluid and noticed the back of the fluid reservoir was wet, as if some fluid was leaking out from the reservoir cover. There are no pedals from it but it is definitely wet. The fluid level was good but I had just put new pads on, which I believe would put more fluid back in the reservoir.

I'm going to keep my eyes on this.

After that, I went to the grocery store and I noticed, that while I was at a stop the pedal was slowly sinking. When I first came to the stop it was fine, but then it would very slowly creep to the floor. I could then pump the brakes back up. Once the pedal got close to the floor, pushing it a little would cause it to bottom out and the BRAKE light would come on. Pumping the brakes back up would turn off the light.

The jeep stops fine on level ground or going up hill when I have time and distance, but when I really need to stop or I'm going downhill, I have to stand on it and it seems to almost bottom out and I'm still rolling a little. It used to lock up the front brakes at this point. FYI I'm running skinny 32"'s on aluminum rims.

Maybe a bleeding is in order.

Or maybe I need to swap in the 95 XJ master cylinder I have sitting in the garage from the old beater.

Thoughts?
 
could be a bad master or the rear brake cylinders are leaking.

did you adjust the rear brakes and did you inspect the rear brakes to see if they are functioning properly? also look to see if the cylinders are leaking.

a booster and master swap is always a good idea on the 89 with a single diaphram booster. i did the wj booster ans master swap on my 89 and it made a huge difference.
 
I don't see any fluid coming from the rear drums but I will inspect them tonight.

Is the 95 XJ master cylinder and booster similar the WJ upgrade? I was under the assumption they were. Been awhile since I researched that upgrade.
 
If I do the WJ MC upgrade, should I use my stock proportioning valve (disc/drum) or the one form the WJ (disc/disc) since I'm not upgrading my rear brakes to discs (yet).
 
I noticed, that while I was at a stop the pedal was slowly sinking. When I first came to the stop it was fine, but then it would very slowly creep to the floor. I could then pump the brakes back up. Once the pedal got close to the floor, pushing it a little would cause it to bottom out and the BRAKE light would come on. Pumping the brakes back up would turn off the light.

A slowing sinking pedal is a classical example of a MC that is leaking internally. You need to replace it.

If you do not already have a late model, dual-diaphragm booster, now is the time to do it.
Do not wait; this is a serious safety issue.
 
I did the WJ swap on my 89 trail rig and with stock drums in the rear I can lock the 35's up very easily. I can say it is without a doubt the best "on street" performance mod I have done to it.
 
The quarter inch spacer isnt really all that required. You have to bend the pinch seam on the frame out of the way, and then space it out just enough to where it doesnt hit.

I've gotten away with no spacer some times, I've had to use 2-3 washers others, its all play by ear.
 
UPDATE

While changing the pads I guess something must of happened to the front right brake hose because it was leaking. I didn't get the new MC and booster yet so I wanted to go ahead and replace the hose. I'm trying to bleed the new hose and I'm not getting fluid to there or the other front corner. The pedal has good pressure so I'm thinking only the rear brakes are working.

Is something going on with the proprtioning valve or did the MC die?
 
UPDATE

While changing the pads I guess something must of happened to the front right brake hose because it was leaking. I didn't get the new MC and booster yet so I wanted to go ahead and replace the hose. I'm trying to bleed the new hose and I'm not getting fluid to there or the other front corner. The pedal has good pressure so I'm thinking only the rear brakes are working.

Is something going on with the proprtioning valve or did the MC die?
It could be a prop valve issue but if you didn't do anything to it then it's unlikely. It could also be your bleeding technique, what method are you using?
 
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!) 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.

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:

 
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