HELP! - New MC leaking - from TOP? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

nosto · 07-21-2003, 11:40 PM

I replaced the non-power brake master cylinder last year, but just got the truck on the road last month. After I drive it, I get a load of brake fluid all around the sides of the MC, dripping down on to the steering shaft (and wiping out my new paint @#$^%).

If the truck just sits, theres no leak. It's definitely coming out of the top; I can see it seeping from under the rubber gasket; it's not leaking where the brake lines screw in at all. I've cleaned and sanded the rim of the MC and the rubber gasket is new, clean and flexible. The bail is tight; need a screwdriver to pry it loose.

I'm out of ideas here, short of using Form-a-Gasket, but I suspect there's something else wrong.

BTW: I started out with the brake fluid level pretty near the top, but it's now about 3/4" down, and it still leaks....

TIA

jhow66 · 07-21-2003, 11:50 PM

Did yoy use a chrome lid?

Longhorn Man · 07-22-2003, 04:14 PM

On the 2 trucks I have had on the road, I have had a total of 5 master cylinders. Every one has done that.
When i asked this question on hear about 2 years ago, someone told me that with the master empty and not installed, hold it upside down and run a long file across the top to make it nice and flat.
I tried that, but I have yuet to drive that truck so i can't say if it works or not.

oldtrucknut · 07-23-2003, 08:59 PM

I had a similar problem. I bought a remanufactured MC from Autozone... big mistake. I didn't notice until after it leaked out that the top edge was very rough from not being machined properly. I bought a new MC from Autozone as well, and it leaked a little at first. I tightened the lid holder thingy and put a light coat of brake fluid on the gasket, like you would do on an oil filter. It has not leaked since.

lukecp · 07-23-2003, 09:10 PM

I also have that problem. If i try to fill the MC to the top with brake fluid, it squirts out all over my inner fenders. The front resivour stays full no problem, but the back one is always about 3/8" below being full. The brakes work about the same either way, so i just don't worry about it.

07-21-2003, 11:40 PM	#1
nosto Flamin' Bass Join Date: Aug 2001 Location: Galloway, NJ, US Posts: 315	HELP! - New MC leaking - from TOP? I replaced the non-power brake master cylinder last year, but just got the truck on the road last month. After I drive it, I get a load of brake fluid all around the sides of the MC, dripping down on to the steering shaft (and wiping out my new paint @#$^%). If the truck just sits, theres no leak. It's definitely coming out of the top; I can see it seeping from under the rubber gasket; it's not leaking where the brake lines screw in at all. I've cleaned and sanded the rim of the MC and the rubber gasket is new, clean and flexible. The bail is tight; need a screwdriver to pry it loose. I'm out of ideas here, short of using Form-a-Gasket, but I suspect there's something else wrong. BTW: I started out with the brake fluid level pretty near the top, but it's now about 3/4" down, and it still leaks.... TIA __________________ Rick Olson /nosto/ Galloway, NJ Pics : http://community.webshots.com/user/nosto53 1972 Triumph TR6 - full resto, now with a Toyota 5-speed 1975 F**D F-100 - rusty, but reliable 1982 HD XLH-1000 1967 C-10, shortstep, 350/M21 4spd, nitrogen tank fills fast bags on 4 corners, Toyo 255/45X20s on American Eagle 221 20X8s, shaved locks and handles, antenna, fuel filler, tiny C-notch, rear fuel tank, long headers, Edelbrock, worn 600 Holley, Checkmate flush hard cover, rear pan, custom LED taillights - painted it, too! But don't like it so I'm gonna do it again!!

07-21-2003, 11:50 PM	#2
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Did yoy use a chrome lid? __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-23-2003, 08:59 PM	#4
oldtrucknut 67-72 truck surgeon Join Date: Jul 2003 Location: Indiana Posts: 155	I had a similar problem. I bought a remanufactured MC from Autozone... big mistake. I didn't notice until after it leaked out that the top edge was very rough from not being machined properly. I bought a new MC from Autozone as well, and it leaked a little at first. I tightened the lid holder thingy and put a light coat of brake fluid on the gasket, like you would do on an oil filter. It has not leaked since. __________________ 1969 Chevy C10 1993 Toyota Camry LE 1999 Ford F250 Super Duty 4x4 diesel 2008 Dodge Charger Super Bee 1953 International R182

07-23-2003, 09:10 PM	#5
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	I also have that problem. If i try to fill the MC to the top with brake fluid, it squirts out all over my inner fenders. The front resivour stays full no problem, but the back one is always about 3/8" below being full. The brakes work about the same either way, so i just don't worry about it. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

07-22-2003, 04:14 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	On the 2 trucks I have had on the road, I have had a total of 5 master cylinders. Every one has done that. When i asked this question on hear about 2 years ago, someone told me that with the master empty and not installed, hold it upside down and run a long file across the top to make it nice and flat. I tried that, but I have yuet to drive that truck so i can't say if it works or not.



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