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Unread 07-30-2012, 02:29 PM   #1
kengeigerjr
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Brake fluid leaking out of master cylinder cap

Have an 81 Cj5 and I had the master cylinder replaced about 6 months ago. I have not had any problems until recently, but the brake fluid is leaking out the cap of the master cylinder. It seems as though there is too much pressure in the brake line. Little help?

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Unread 07-30-2012, 02:39 PM   #2
CALOcruiser
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The leaking master cylinder cap has nothing to do with pressure. The seal in the remanufactered master cylinders are notoriously bad. You probably have a remanufactured unit. Remove the lid and make sure the surfaces are clean. Also make sure the brake fluid level is 1/4" or so below the top. Over filling will make it leak more. Make sure the lever across the top supplies good pressure to the lid.
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Unread 07-30-2012, 03:49 PM   #3
brokeagain007
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Would a leaking Master Clyinder "lid" cause power brakes to be weak? I have front disk and drum rear on my 81 cj8. Sorry to intrude kengeigerjr!
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Unread 07-30-2012, 04:01 PM   #4
keith460
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No, a leaking MC lid would not cause brakes to be weak. It's just a cover for the brake fluid reservoir.
I've had my 'new' MC leak as well and has ruined the paint on the inner fender well too. I had polished the top of the MC where the cover would go on while I had it off using very fine wet sandpaper placed on top of a sheet of glass. But it still leaked a little due to the lest then soft ride from the lift kit and all the bouncing around the Jeep does. I now keep my fluid level about a 1/2" below the top and that has seemed to help.
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Unread 07-30-2012, 04:27 PM   #5
kengeigerjr
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No big deal @brokeagain007, that's what this awesome forum is for. Thanks for the help I'll remove some fluid and clean the surface of both the lid and rim of the MC, and I'll report back.
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Unread 07-30-2012, 06:13 PM   #6
brokeagain007
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I'll do the same, thanks for the advice. I think mine used to have paint, right now its just about every rattlecan color out there. haha
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Unread 07-30-2012, 07:02 PM   #7
brokeagain007
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I got another question for ya'll. It's probably just ignorance, but if a leaking master cylinder isn't the root of my weak brake issue, what could it be? My set up is power brakes disk in front drum in rear. I am running the stock master cylinder for now, but am about to do the upgrade to a corvette one. I have good pads on all four wheels, I bled each line individually, and checked all components for anything worn out or broken. Nothing but the leaking master cylinder. My only other thought is that it may have something to do with the vacuum lines leading to the brake booster. Those may be leaking. I have yet to mess with them. For the mean time, I put the brake pedal to the floor and run backwards through the gears using the engine to help slow me down.
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Unread 07-30-2012, 07:03 PM   #8
skizriz
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Had a problem with mine leaking as well. I ended up taking the rubber gasket out of the cap, and used another rubber piece I had laying around to cut a strip to fit inside of the cap, between the good rubber gasket and the cap.
Double layer of rubber gasket between the MC and cap if that makes sense.Kind of a thicker gasket.
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Unread 07-31-2012, 04:31 AM   #9
CALOcruiser
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Quote:
Originally Posted by brokeagain007
I got another question for ya'll. It's probably just ignorance, but if a leaking master cylinder isn't the root of my weak brake issue, what could it be? My set up is power brakes disk in front drum in rear. I am running the stock master cylinder for now, but am about to do the upgrade to a corvette one. I have good pads on all four wheels, I bled each line individually, and checked all components for anything worn out or broken. Nothing but the leaking master cylinder. My only other thought is that it may have something to do with the vacuum lines leading to the brake booster. Those may be leaking. I have yet to mess with them. For the mean time, I put the brake pedal to the floor and run backwards through the gears using the engine to help slow me down.
If you pump the brake pedal, will the braking improve and the pedal get firmer? Did your MC ever run out of fluid in one reservoir? You may not have all the air out of the lines.
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Unread 07-31-2012, 07:32 AM   #10
brokeagain007
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Pumping the pedal does not seem to change anything. One of the reservoirs did when a seal in the rear blew out. I can't remember what the thing was called. I'll try to bleed the lines again maybe that will help.
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Unread 08-04-2012, 12:20 PM   #11
CALOcruiser
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If there is air in the lines, it won't brake as well, but usually pumps up to firm the pedal. Unless there is a lot if air. Be sure to bleed them starting with pass rear, then drivers rear, pass frt, drivers frt. I always open bleeder valve when pressing pedal, the close bleeder before pedal comes up. That way it doesn't suck anything back up the tube. Two person job. Don't let the reservoirs go dry! You'll have to start over if it does.
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Unread 08-28-2012, 09:43 AM   #12
brokeagain007
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Sorry for the delay, just got back to college and it's been a big adjustment again haha anyways, I inspected the master cylinder and it was plugged up with crud. A new master cylinder and a lot of bleeding later, everything is perfect! thanks!
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