Is the master cylinder designed to leak?

I bought and installed a remanufactured master cylinder in my Jeep. The problem is that when I apply the brakes, it squirts brake fluid out of two notches in the cap, which may be vents, but I'm not sure. It looks like these are part of the cap design, but for an unknown purpose (to me). One is located at the front right and the other is at the back left. They're triangular shaped. Is the cap supposed to have these or does it seem like I have a defective master cylinder? Thanks.

 

No it should not leak, if you post a pic of your cap it would help
sounds like a defect

 

Compare it to your core? Hope you haven't turned it in yet. Should not geyser enough to throw fluid out, if it was assembled and bled correctly.

JMO - rebuilt master cylinders are ju... uh, unpredicatable in their quality. Take it back and use the credit for a new part.

 

Generally the notches in the cover are used to retain the rubber gasket under the cover. The gasket should have two tabs on it that snap into those notches. Does your cover have that gasket? The gasket completely fills the cover and has bellows built into it to allow the fluid level to change. If the cover is there and the gasket is properly installed, the MC won't leak.

 

X2 and also on the fact that rebuilt parts are usually a gamble. It should not leak at all. Take it back, but don't throw it at them, they hate when you do that and are not as helpful afterwards.

 

R)
Also remember the counter people didn't rebuild the product, they are just there to try and get you parts. Counter people can be your best friends or worst enemies in the Automotive world. Nickmil

 

Sounds like shoddy MC assembly work. It must thave been rebuilt on a Monday or Friday.

 

It does have the gasket and has two notches in the cover which hold the two ends inside the cap. Also has the bellows. I already returned it for a new one so I didn't get a pic, but if you positioned the cap vertically and looked at it from the top, the triangular notches were at the upper left and lower right on the cover. The parts store that I go to took it back without a problem and I should have the new one in the Jeep by the weekend. Hopefully the new one won't leak so I can pass inspection.

 

To answer your original question: The little notches are indeed vents to allow air in on top of the bellows. When you step on the brakes fluid is obviously pumped to the wheel cylinders/calipers. This fluid has to be replaced temporarily with air, but since air has moisture (very bad for DOT 3 or 4 brake fluid) a bellows is used to separate the brake fluid from the air itself. The air comes in & exits from the vents as the bellows goes up & down in the fluid.

I have that same problem, but to a lesser degree. After all the paint was disolved off of the firewall I realized I had a leak somewhere. It turns out that the bellows had cracks in it from age & flexing & a small amount of brake fluid would get above the seal/bellows & eventually dribble out the vents & run down the firewall. I just found this out & will be getting a new seal/bellows ASAP.

 

Thanks a lot. I appreciate your response. The new master cylinder I just put on is totally different from the first one and there are no vents on the new cap.

 

I'll bet there are vents on it somewhere, the laws of physics don't change. There has to be some provision for the movement of the fluid to the wheel cylinders/calipers. Sometimes they're disguised quite well, just look at the old caps on the frame mounted MC's, hidden quite well!

 

Never seen one with vents. Generally the fit between the gasket and the lid is loose (at the notches) so air gets in and out there.

 

Oops...what I meant to say was that there were no vents on the cap near the gasket. The new mc has one vent, but it's at the top, which is well above the gasket. No leaks yet.

I would think that the fit between lid and gasket has to be tight so that the fluid stays inside.