Master Cylinder Cover Leaking Brake Fluid How to stop? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

petey-pablo · 01-12-2010, 03:50 AM

I have noticed my inner wheel well wet under my Master Cylinder when I go for a drive then I would wipe it down.My pain is now alittle ruined I thought it was the fittings that were loose so I tightend them but it wasn't, today I found out it was the cover I touched it then it started to make a noise like escaping air from the back of it. So now I know where the fluid is leaking from. Do I just need to buy a new cover or is there a reason why it is leaking through here? This was a new Master Cylinder any help would be greatly appreciated Thanks Pablo.........

unclewatts · 01-12-2010, 04:05 AM

It could be many things. A) pressure building up inside the reservoir forcing fluid out. B) cracked or missing rubber gasket. C) warped or defective cover D) weak hold down wires E) overfilling reservoirs.(should be no less than 1/4" from top). Actually it could even be a bad casting on the body of the MC. Top edge should be perfectly smooth and flat with no pitting. Hope this helps.

**mikey531** · 01-12-2010, 05:35 AM

I had the same problem, I got a new gasket and it still leaked. What I had to do was bend the wire bails to hold the cover on tighter. It hasn't leaked since.

petey-pablo · 01-15-2010, 05:27 AM

Quote:

Originally Posted by mikey531

I had the same problem, I got a new gasket and it still leaked. What I had to do was bend the wire bails to hold the cover on tighter. It hasn't leaked since.

I bent down to tighten the wire hold downs,Hope this solves my problem. It messed up my paint on my wheel well I am just glad it wasn't worse then it is. I think I might have filled it alittle too much but not sure.I haven't driven it much as I just got the truck back from the exhaust shop so I will find out this weekend. Thanks guys

1964Chevy · 03-24-2013, 07:19 PM

Hey petey-pablo did bending the wire solve the problem
Here is my story. Last April bought MC and booster with proportioning valve from LMC.
Since day 1 the MC cover leaked, I bent the wires and it still leaked.
Pulled it off and bought new MC, tried to install the booster from LMC but it was the wrong one.
Bought a reconditioned booster and installed it, bleeding the brakes with the new MC and booster and it still leaks.........
I'm curious if it worked for you or if it was something else. PS, I also hear it sucking or blowing air out of the top gasket and then see the leak.

68gmsee · 03-24-2013, 08:14 PM

Some new, after market master cylinders are cheaply made. I had one that leaked like that and wound up getting one at a junkyard in real good shape that worked.

I had another one that did the same and it had a rough surface on the top. I placed it on a vise and laid a flat file across the top at an angle and filed it smooth. Another way is to turn it upside down on sand paper taped to a completely flat surface. If you do this be sure and use brake cleaner to flush and clean the inside out completely.

**leddzepp** · 03-24-2013, 08:19 PM

I had the same problem, and used sandpaper as described above. No more leaks.
Posted via Mobile Device

1964Chevy · 03-25-2013, 08:21 AM

I'll try to flatten the top. Thanks for the info.

01-12-2010, 03:50 AM	#1
petey-pablo "THE GREEN GOBLIN" Join Date: Mar 2008 Location: Fremont Ca. Posts: 1,025	Master Cylinder Cover Leaking Brake Fluid How to stop? I have noticed my inner wheel well wet under my Master Cylinder when I go for a drive then I would wipe it down.My pain is now alittle ruined I thought it was the fittings that were loose so I tightend them but it wasn't, today I found out it was the cover I touched it then it started to make a noise like escaping air from the back of it. So now I know where the fluid is leaking from. Do I just need to buy a new cover or is there a reason why it is leaking through here? This was a new Master Cylinder any help would be greatly appreciated Thanks Pablo......... Attached Images __________________ Petey-pablo "THE GREEN GOBLIN" 1972 Cheyenne 10 Short Fleet Side Front 2.5inch Spindles with 2inch Springs Rear 4inch drop Springs. 454BBC TH400,Posi 1971 Cheyenne 10 Long Fleet Side 454BBC TH350,Posi Sold Drive it like you stole it! Petey-pablo@sbcglobal.net

01-12-2010, 04:05 AM	#2
unclewatts 70 Chevrolet=Obsession Join Date: Jun 2009 Location: nice ca Posts: 1,067	Re: Master Cylinder Cover Leaking Brake Fluid How to stop? It could be many things. A) pressure building up inside the reservoir forcing fluid out. B) cracked or missing rubber gasket. C) warped or defective cover D) weak hold down wires E) overfilling reservoirs.(should be no less than 1/4" from top). Actually it could even be a bad casting on the body of the MC. Top edge should be perfectly smooth and flat with no pitting. Hope this helps. __________________ I'm Just like my truck. Old, Ugly and Grouchy. Except my truck starts easily in the morning and doesn't smoke! IT'S NOT EASY BEING GREEN! -Kermit the frog 1970 Chevrolet C-10 Longbed Stepside : 350, Muncie M20, 3.08 GM corp. positraction Forest green exterior/light green interior(Where all my money goes) 1996 Toyota Corolla (Parts runner) Last edited by unclewatts; 01-12-2010 at 04:08 AM.

01-12-2010, 05:35 AM	#3
mikey531 Senior Member Join Date: Jul 2009 Location: Exeter, NH Posts: 794	Re: Master Cylinder Cover Leaking Brake Fluid How to stop? I had the same problem, I got a new gasket and it still leaked. What I had to do was bend the wire bails to hold the cover on tighter. It hasn't leaked since.

03-24-2013, 07:19 PM	#5
1964Chevy Registered User Join Date: Jan 2012 Location: Denton, Texas Posts: 92	Re: Master Cylinder Cover Leaking Brake Fluid How to stop? Hey petey-pablo did bending the wire solve the problem Here is my story. Last April bought MC and booster with proportioning valve from LMC. Since day 1 the MC cover leaked, I bent the wires and it still leaked. Pulled it off and bought new MC, tried to install the booster from LMC but it was the wrong one. Bought a reconditioned booster and installed it, bleeding the brakes with the new MC and booster and it still leaks......... I'm curious if it worked for you or if it was something else. PS, I also hear it sucking or blowing air out of the top gasket and then see the leak. __________________ If your strength is small, don't carry heavy burdens. If your words are worthless, don't give advice. Chinese Proverb

03-24-2013, 08:14 PM	#6
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Master Cylinder Cover Leaking Brake Fluid How to stop? Some new, after market master cylinders are cheaply made. I had one that leaked like that and wound up getting one at a junkyard in real good shape that worked. I had another one that did the same and it had a rough surface on the top. I placed it on a vise and laid a flat file across the top at an angle and filed it smooth. Another way is to turn it upside down on sand paper taped to a completely flat surface. If you do this be sure and use brake cleaner to flush and clean the inside out completely. __________________ 68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...

03-24-2013, 08:19 PM	#7
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,019	Re: Master Cylinder Cover Leaking Brake Fluid How to stop? I had the same problem, and used sandpaper as described above. No more leaks. Posted via Mobile Device __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

03-25-2013, 08:21 AM	#8
1964Chevy Registered User Join Date: Jan 2012 Location: Denton, Texas Posts: 92	Re: Master Cylinder Cover Leaking Brake Fluid How to stop? I'll try to flatten the top. Thanks for the info. __________________ If your strength is small, don't carry heavy burdens. If your words are worthless, don't give advice. Chinese Proverb

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