Need help with Master Cylinder problem! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jeff1vol · 12-20-2006, 11:38 AM

My master cylinder is leaking fluid from under the fluid cover. The cover itself looks brand new. The gasket looks decent as well. Could it be the wrong size fluid cap? It looks to be a little bigger than it should be. The master cylinder is a Delco Moraine. Thanks for the help.

Myself · 12-20-2006, 12:28 PM

I had the same problem on my wife's truck. I got a new chrome lid and bail, and a new gasket, problem fixed.

67-72trucks · 05-18-2011, 11:31 PM

Having the same problem. Everything new..Have a leak under the cover and eating the paint off my inner fender..Once leak is fixed i will take the inner fender out and repaint.

67-72trucks · 05-18-2011, 11:47 PM

Anyone one else have this problem?

dmack91 · 05-19-2011, 02:25 AM

I had the same problem. Went to NAPA to get a new cover gasket, and it didn't fit right - too big. Ended up trimming it to fit and it still leaked.

Seems to have a slight forward tilt after I installed my power booster.

I just run it about 2/3 full instead of fully topped off, and it seems to have stopped.

68gmsee · 05-19-2011, 08:39 AM

^ Yeah, don't fill all the way to the top. If the brakes are adjusted properly, and lines bled it doesn't take much fluid to operate the brakes. Hydraulic fluid doesn't compress but it can expand with heat.

I've had the same problem before and most of the time it was the cap and/or gasket. Carefully check the top edge of the master cylinder with a flat ruler and a feeler gauge for any low or high spots. If it looks good then it's either the gasket or cap.

Don't overfill!

Lee H · 05-19-2011, 10:00 AM

Having the same problem. New cover & gasket did not help. Annoying.

67-72trucks · 05-19-2011, 12:58 PM

going to try a new cover and two new metal attaching rods. Mine are lose!!

**leddzepp** · 05-19-2011, 01:16 PM

Make sure the mounting surface on the M/C is clean and smooth, otherwise it will leak. Lightly sanding it helps. I also agree with not filling it all the way to the top.

697498chevy · 05-19-2011, 06:32 PM

Have the same leak . Put on a new top without much help .

mbgmike · 05-19-2011, 07:10 PM

Quote:

Originally Posted by 68gmsee

^ Yeah, don't fill all the way to the top. If the brakes are adjusted properly, and lines bled it doesn't take much fluid to operate the brakes. Hydraulic fluid doesn't compress but it can expand with heat.

I've had the same problem before and most of the time it was the cap and/or gasket. Carefully check the top edge of the master cylinder with a flat ruler and a feeler gauge for any low or high spots. If it looks good then it's either the gasket or cap.

Don't overfill!

I agree.check the top also on a surface plate or flat surface. They can get bent easily and make sure their is nothing between the gasket and cap. EVEN on NEW caps and gaskets. Check your springs also. If they go on easily with just your fingers its too loose. Keep the liquid down at proper level. if still leaks put a real thin layer of rtv sealant on it. Real thin. Should not have to but have seen many come in like this.

67-72trucks · 05-19-2011, 10:29 PM

Checked surface of the master cylinder where it seals. Has no pits and very smooth. I checked to see if the surface was flat with a big file. Looks good. fluid it at proper lever. Will brake fluid eat rtv?

12-20-2006, 11:38 AM	#1
jeff1vol Registered User Join Date: Dec 2006 Location: Fredericksburg, VA Posts: 71	Need help with Master Cylinder problem! My master cylinder is leaking fluid from under the fluid cover. The cover itself looks brand new. The gasket looks decent as well. Could it be the wrong size fluid cap? It looks to be a little bigger than it should be. The master cylinder is a Delco Moraine. Thanks for the help.

12-20-2006, 12:28 PM	#2
Myself Registered User Join Date: Oct 2005 Location: Northern Arkansas Posts: 1,142	Re: Need help with Master Cylinder problem! I had the same problem on my wife's truck. I got a new chrome lid and bail, and a new gasket, problem fixed.

05-18-2011, 11:31 PM	#3
67-72trucks Registered User Join Date: Jun 2006 Location: Michigan Posts: 530	Re: Need help with Master Cylinder problem! Having the same problem. Everything new..Have a leak under the cover and eating the paint off my inner fender..Once leak is fixed i will take the inner fender out and repaint.

05-18-2011, 11:47 PM	#4
67-72trucks Registered User Join Date: Jun 2006 Location: Michigan Posts: 530	Re: Need help with Master Cylinder problem! Anyone one else have this problem?

05-19-2011, 02:25 AM	#5
dmack91 Registered User Join Date: Jan 2011 Location: Redmond, OR Posts: 763	Re: Need help with Master Cylinder problem! I had the same problem. Went to NAPA to get a new cover gasket, and it didn't fit right - too big. Ended up trimming it to fit and it still leaked. Seems to have a slight forward tilt after I installed my power booster. I just run it about 2/3 full instead of fully topped off, and it seems to have stopped. __________________ 68 Chev C20- son has it now 83 K20 - bought from son 70 C20 - in progress

05-19-2011, 08:39 AM	#6
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Need help with Master Cylinder problem! ^ Yeah, don't fill all the way to the top. If the brakes are adjusted properly, and lines bled it doesn't take much fluid to operate the brakes. Hydraulic fluid doesn't compress but it can expand with heat. I've had the same problem before and most of the time it was the cap and/or gasket. Carefully check the top edge of the master cylinder with a flat ruler and a feeler gauge for any low or high spots. If it looks good then it's either the gasket or cap. Don't overfill!

05-19-2011, 10:00 AM	#7
Lee H Registered User Join Date: Jun 2010 Location: Upland Ca Posts: 4,147	Re: Need help with Master Cylinder problem! Having the same problem. New cover & gasket did not help. Annoying. __________________ 1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703

05-19-2011, 12:58 PM	#8
67-72trucks Registered User Join Date: Jun 2006 Location: Michigan Posts: 530	Re: Need help with Master Cylinder problem! going to try a new cover and two new metal attaching rods. Mine are lose!!

05-19-2011, 01:16 PM	#9
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,031	Re: Need help with Master Cylinder problem! Make sure the mounting surface on the M/C is clean and smooth, otherwise it will leak. Lightly sanding it helps. I also agree with not filling it all the way to the top. __________________ 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

05-19-2011, 06:32 PM	#10
697498chevy Registered User Join Date: Jan 2009 Location: South Carolina Posts: 266	Re: Need help with Master Cylinder problem! Have the same leak . Put on a new top without much help .

05-19-2011, 10:29 PM	#12
67-72trucks Registered User Join Date: Jun 2006 Location: Michigan Posts: 530	Re: Need help with Master Cylinder problem! Checked surface of the master cylinder where it seals. Has no pits and very smooth. I checked to see if the surface was flat with a big file. Looks good. fluid it at proper lever. Will brake fluid eat rtv?

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