1982 Master Brake Cylinder Leaking - JeepForum.com
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post #1 of 12 Old 06-24-2020, 03:55 PM Thread Starter
c82cj
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1982 Master Brake Cylinder Leaking

My master brake cylinder is leaking is there somewhere that I can just buy the rubber gasket to replace? It seems crazy to replace the entire piece when the rubber would solve the issue. I have looked on Quadratec and Collins Bros with no luck

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post #2 of 12 Old 06-24-2020, 04:54 PM
MrPeter63
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You can get a Master cylinder rebuild kit from just about any parts store, or try Rock auto.
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post #3 of 12 Old 06-24-2020, 05:20 PM
shadoow
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post #4 of 12 Old 06-24-2020, 07:10 PM
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It leaks there probably due to a poor fly cut of the surface where the gasket is suppose to seal it. It is notorious for the MC to leak from the bouncy ride of a CJ and leaked brake fluid on the drivers side inner fender removes the paint. Have seen this countless times in the past, me included.
The fix is to remove the MC, or buy a new one, set some 600 grit wet/sand paper on a piece of glass and place the MC upside down on the sandpaper and polish the gasket surface until smooth.
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post #5 of 12 Old 06-25-2020, 05:42 AM
shadoow
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X2 on what Keith said. I did this years ago after fighting a gasket leak for awhile & polishing the gasket surface on the MC fixed the leak. Been leak free for years.
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post #6 of 12 Old 06-25-2020, 11:59 AM Thread Starter
c82cj
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Quote:
Originally Posted by keith460 View Post
It leaks there probably due to a poor fly cut of the surface where the gasket is suppose to seal it. It is notorious for the MC to leak from the bouncy ride of a CJ and leaked brake fluid on the drivers side inner fender removes the paint. Have seen this countless times in the past, me included.
The fix is to remove the MC, or buy a new one, set some 600 grit wet/sand paper on a piece of glass and place the MC upside down on the sandpaper and polish the gasket surface until smooth.
I have a few questions and sorry in advance if they are all dumb. I am definitely still learning.

Any chance you have pics?
Are you saying that I need to sand the inner side of the lid or the entire cylinder or the outside?
Why sand on glass?

Thanks!
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post #7 of 12 Old 06-25-2020, 12:31 PM
John Strenk
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Quote:
Originally Posted by c82cj View Post
I have a few questions and sorry in advance if they are all dumb. I am definitely still learning.

Any chance you have pics?
Are you saying that I need to sand the inner side of the lid or the entire cylinder or the outside?
Why sand on glass?

Thanks!
Just the surface where the gasket meets the body of the master, sorry, 'primary' cylinder.

mc-sanding.jpg

Glass is used because it's probably flatter than the top of you workbench.
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post #8 of 12 Old 06-25-2020, 12:32 PM
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What you're doing is polishing the gasket surface of the master cylinder. I taped a sheet of emery paper to a square of glass. You use the glass because it provides a very flat surface. I started with maybe 400 grit to get the imperfections down faster then switch to 600 or above to polish the surface flat. Just turn the master cylinder upside down and start moving it around the sanding surface. I also used blue paper towels in the master cylinder reservoir cavities to limit intrusion of dust. It'll probably take awhile, but worth the effort.

Once done you'll have to thoroughly clean the master cylinder to get any residue out it then bench bleed it before putting into the jeep.


oops ! John, we musta been typing at the same time....
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post #9 of 12 Old 06-25-2020, 01:23 PM
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Quote:
Originally Posted by c82cj View Post
Any chance you have pics?
Are you saying that I need to sand the inner side of the lid or the entire cylinder or the outside?
Why sand on glass?

Sorry, no pictures of actually doing it but pic below should give you the idea.

Taking the MC off the Jeep, clean out the fluid and pull out the piston cylinder if you can.

Turn it upside down on a piece of fine sandpaper that is laying atop a glass, because the glass will be the flattest surface you will find readily available.

Wet the sandpaper and start moving the MC around in a figure 8 on top of the sandpaper.
Polish until all traces of a fly cut are gone and the gasket mating surface should be close to a mirror finish but not necessarily.

Results will be a new blemish free surface that will seal against the gasket and be leak free no matter how much you bounce around in a stiff riding CJ.
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post #10 of 12 Old 07-06-2020, 11:52 AM Thread Starter
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I am going to replace my master cylinder and am wondering if I need to replace the brake booster or if that is fine. Also any recommendations on which MC to buy? I am guessing go with Crown but I can't tell which one I have. 2 caliper is my guess but I am truly guessing here.
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No Top No Doors please
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post #11 of 12 Old 07-06-2020, 12:56 PM
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Go With Raybestos, Bendix or similar American made product.

Here's a video, there are many informative brake instruction videos online.


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post #12 of 12 Old 07-07-2020, 12:09 AM
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You have a stock Cj setup for disc front, drum rear.

You do not need to change the booster if it is working, the master just unbolts from the front with the two nuts removed.

When you put it back on it will probably be fine but if you are having "problems bleeding" and the pedal goes to the floor with the engine on, but seems fine with the engine off, it will be the clearance between the shaft poking out from the booster and the back of the master cylinder. They should just about touch (10 thou clearance I think), but I have had one which did not. The end of the shaft is adjustable.When replacing a master cylinder it is a point worth remembering.
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