Leaky master cylinder

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shadow 21

shadow 21

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My master cylinder is leaking fluid from the top where the cap goes on, replaced the master cylinder and still having the same problem, dropped the fluid level about a 1/2 inch from the top still leaking, any ideas on what is going on? I have manual brakes, disc on the front and drum on the back. Thanks for any help. I replaced the rear wheel brake cylinders about a month ago, but the master cylinder was leaking then also'
 
Bolt-on top or with a bail clip? Did the new MC come with a new top AND a new rubber bellows/gasket piece? If you reused the old rubber, if there is any rust embedded in the edges where it contacts the edges of the MC it can cause seepage.
 
nm9stheham said:
Bolt-on top or with a bail clip? Did the new MC come with a new top AND a new rubber bellows/gasket piece? If you reused the old rubber, if there is any rust embedded in the edges where it contacts the edges of the MC it can cause seepage.
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It is a reman master cylinder with bail clip, it came with a top and a new rubber bellows/gasket, no rust,
 
chk the top for warpage.
Wipe it dry as well as the master cyl.
Wet the top rim of the master with fluid and set the lid on loose.
Pick it up as see where it got fluid on the rubber seal.
Tweak and repeat.

You also can make the bail tighter if needed.
 
If you keep getting frustrated, you could change to a 2-bolt alum MC, using a 4-2 bolt adapter plate (ebay). Finding a manual MC type is harder though. At least later ones have a better sealed reservoir. If yours is leaking fluid, it must also be letting in atmospheric air, which brings moisture and rusts your whole brake system internals. Leaking glycol is also a great paint remover.
 
Just went by the auto parts store and they ordered me a new top for my master cylinder, it will be here tomorrow, maybe that will fix my leak, I will let everyone know if it works, thanks for all the response.
 
Maybe you have air in the system and it is like a geyser in there. But yeah- sounds like a bad gasket or loose cap.
 
Replaced master cylinder again, adjusted up the rear brakes, bleed the air out of the system, just made a 30 mile trip and no brake fluid leaking, thanks for all the help. I think the problem was a warped cap, but just replaced the whole thing since it has that life time warranty, again thanks for all the help, have a good one!:burnout:
 
This is more common than you think on these masters ... i had the same issue ... i lowered fluid slightly and replaced cap and resolved my issue ...
 
seem like every year I have to replace the mc leaks after they sitting all winter . just odered on yesterday again
 
rrvolare said:
This is more common than you think on these masters ... i had the same issue ... i lowered fluid slightly and replaced cap and resolved my issue ...
Click to expand...

These should not leak under ANY condition. They should be a perfect seal. If they leak, as mentioned, it's likely rust/ roughness or a warped cover or poor gasket. "Modern" problems, IE Chineseo, cheap third world rebuilts, etc.................
 
A lot of reman'ed master cylinders have a rough porous cast iron surface where the seal meets. I ended up getting a new master cylinder from Rock Auto and that solved my problem.
 
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