Leaking master cylinder cap. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

grubsster · 11-25-2021, 03:25 PM

Hi all, I have a '66 C10 with a leaking master cylinder cap. It is not over full. For some reason all the fluid came out the rear port. This is a new master that got all ugly from the fluid. I refilled and bled. Now I see why it is getting emptied. Has anyone else had this problem? Any ideas? Thanks in advance...

**MySons68C20** · 11-25-2021, 04:22 PM

New cap and rubber gasket? Tightening the wire hold downs is a pain but took care of the leak on my cap.

**cwcarpenter98** · 11-25-2021, 08:38 PM

I have a similar master. I went a couple years of driving before checking the fluid again. When I did that, a little bit of crustiness had built up on the seal. When I put the cap back on, I noticed that it started leaking. Took it off again, cleaned the crustiness off the rubber on both sides, then took a razor blade to the sealing side on the master to make sure it was clean and flat. I haven't had a leak since doing that

**pjmoreland** · 11-26-2021, 12:58 AM

I installed a new master cylinder last year that is the same style as yours, and the cover leaked right from the beginning. I ordered a MCAK012 cover from opgi.com, and it hasn't leaked since. This cover is overpriced, but it did solve the problem.

https://www.opgi.com/brake-systems/m...l-mcak012.html

grubsster · 11-28-2021, 06:51 PM

Thanks all, new cap, gasket and tightened the hold downs. No more leak!

**MySons68C20** · 11-28-2021, 11:30 PM

Right on!!

SCOTI · 11-29-2021, 02:30 PM

@grubsster.....

Thank you for updating the status.
Would you care to share the p/n or any specific info related toward the 'fix' that can be used for future reference should others see this thread?

grubsster · 11-29-2021, 05:19 PM

Sure, I used the original cap from my old master cylinder which seemed to be of better material than the new master. Installed the retaining clips upside down in the vise and bent both sides inward, at the point where they go in the master, about 1/8th of an inch to "shorten" them a little. Used a 42071 dorman gasket.

Hope that helps.

SCOTI · 11-29-2021, 06:21 PM

Quote:

Originally Posted by grubsster

Sure, I used the original cap from my old master cylinder which seemed to be of better material than the new master. Installed the retaining clips upside down in the vise and bent both sides inward, at the point where they go in the master, about 1/8th of an inch to "shorten" them a little. Used a 42071 dorman gasket.

Hope that helps.

That's good info for the next guy that has a similar issue. Appreciate the feedback.

68PanelTruck · 11-29-2021, 08:32 PM

Thanks for the update. My brand new MC looks like it is seeping from under the cover but only when I fill it all of the way to the top with brake fluid. I will look into these fixes.

grubsster · 11-30-2021, 01:09 AM

Quote:

Originally Posted by 68PanelTruck

Thanks for the update. My brand new MC looks like it is seeping from under the cover but only when I fill it all of the way to the top with brake fluid. I will look into these fixes.

When you are filling, make sure you are allowing room for expansion. I fill mine as in the picture. Others may do differently, but that works best for me.

**youngrodder** · 12-02-2021, 02:58 PM

Those type of caps always leak. Mine was the same way. I spent the $150.00 and purchased a Wilwood MC. Best money spent, but I hate leaks.

I get that you would need to bench bleed the new MC prior to installing then re-bleed your brakes. I know that's what I ended up doing and it was still worth it (to me).

Marc

11-25-2021, 03:25 PM	#1
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 145	Leaking master cylinder cap. Hi all, I have a '66 C10 with a leaking master cylinder cap. It is not over full. For some reason all the fluid came out the rear port. This is a new master that got all ugly from the fluid. I refilled and bled. Now I see why it is getting emptied. Has anyone else had this problem? Any ideas? Thanks in advance... Attached Images

11-25-2021, 04:22 PM	#2
MySons68C20 Senior Member Join Date: Sep 2014 Location: Wenatchee, Wa Posts: 929	Re: Leaking master cylinder cap. New cap and rubber gasket? Tightening the wire hold downs is a pain but took care of the leak on my cap.

11-25-2021, 08:38 PM	#3
cwcarpenter98 Senior Member Join Date: Jan 2018 Location: Hickory Flat, GA Posts: 4,488	Re: Leaking master cylinder cap. I have a similar master. I went a couple years of driving before checking the fluid again. When I did that, a little bit of crustiness had built up on the seal. When I put the cap back on, I noticed that it started leaking. Took it off again, cleaned the crustiness off the rubber on both sides, then took a razor blade to the sealing side on the master to make sure it was clean and flat. I haven't had a leak since doing that __________________ Christian Carpenter 1963 C10 - Frankentruck 283, Muncie 3 speed with overdrive Overdrive wiring here 1963-ish truck bed trailer - Half-Wit 1981 C10 - Penny 305, th350 --> Soon to be 350, Saginaw 4 speed 1995 Dodge Dakota Sport "I'll put it simple: if you're going hard enough left, you'll find yourself turning right." - Doc Hudson

11-26-2021, 12:58 AM	#4
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,974	Re: Leaking master cylinder cap. I installed a new master cylinder last year that is the same style as yours, and the cover leaked right from the beginning. I ordered a MCAK012 cover from opgi.com, and it hasn't leaked since. This cover is overpriced, but it did solve the problem. https://www.opgi.com/brake-systems/m...l-mcak012.html Attached Images

11-28-2021, 06:51 PM	#5
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 145	Re: Leaking master cylinder cap. Thanks all, new cap, gasket and tightened the hold downs. No more leak!

11-28-2021, 11:30 PM	#6
MySons68C20 Senior Member Join Date: Sep 2014 Location: Wenatchee, Wa Posts: 929	Re: Leaking master cylinder cap. Right on!!

11-29-2021, 02:30 PM	#7
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,064	Re: Leaking master cylinder cap. @grubsster..... Thank you for updating the status. Would you care to share the p/n or any specific info related toward the 'fix' that can be used for future reference should others see this thread? __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

11-29-2021, 05:19 PM	#8
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 145	Re: Leaking master cylinder cap. Sure, I used the original cap from my old master cylinder which seemed to be of better material than the new master. Installed the retaining clips upside down in the vise and bent both sides inward, at the point where they go in the master, about 1/8th of an inch to "shorten" them a little. Used a 42071 dorman gasket. Hope that helps.

11-29-2021, 08:32 PM	#10
68PanelTruck Registered User Join Date: Aug 2020 Location: Frankfort, Ill Posts: 143	Re: Leaking master cylinder cap. Thanks for the update. My brand new MC looks like it is seeping from under the cover but only when I fill it all of the way to the top with brake fluid. I will look into these fixes. __________________ It's not rust, it's called patina Trying to bring a 68 Panel Truck back from the dead. 396 Big Block, 4 on the floor, and a whole lot of rust.

12-02-2021, 02:58 PM	#12
youngrodder Registered User Join Date: Mar 2007 Location: Scotts, Michigan Posts: 3,774	Re: Leaking master cylinder cap. Those type of caps always leak. Mine was the same way. I spent the $150.00 and purchased a Wilwood MC. Best money spent, but I hate leaks. I get that you would need to bench bleed the new MC prior to installing then re-bleed your brakes. I know that's what I ended up doing and it was still worth it (to me). Marc __________________ …………...........__________ .................. ((__\|__\|\|___\____ ..;.;;.:;:;.,;..;((_(O))____ (_(O)) 1948 Chevy Truck - Finished SOLD!! 1953 Chevy Suburban "Family Truckster" Completed: Spring of 2021 http://67-72chevytrucks.com/vboard/s...d.php?t=605484 1994 4x4 Blazer - "Field Find" https://67-72chevytrucks.com/vboard/...ferrerid=30857



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