Help! Master Cylinder Leaking - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Chevypoor · 05-29-2011, 08:13 AM

Our 69c10 has a manual brake master cylinder that is leaking down the firewall! It was replaced less than 2 years ago. It will also sometimes leak around the cover.

The master cylinder that was on the truck when we got it appeared to be doing the same thing.

The truck still stops fine.

Is this a common problem with manual brakes? Hopefully someone here has an answer as this is making a mess of things.

cdowns · 05-29-2011, 08:29 AM

a good master cylinder does not leak

vin63 · 05-29-2011, 09:14 AM

Quote:

Originally Posted by Chevypoor

Our 69c10 has a manual brake master cylinder that is leaking down the firewall! It was replaced less than 2 years ago. It will also sometimes leak around the cover.

The master cylinder that was on the truck when we got it appeared to be doing the same thing.

The truck still stops fine.

Is this a common problem with manual brakes? Hopefully someone here has an answer as this is making a mess of things.

If it is leaking around the cover, double check the seal between the lid and the master cylinder for tears, installed incorrectly/upside down, etc. If it is leaking from underneath the cover, it is probably leaking down the firewall when you accelerate and the fluid sloshes backward.

SCOTI · 05-29-2011, 10:17 AM

Along w/inspecting the under-cover (lid) seal quality, the fluid level should also not be exceedingly high.

It's common when pads/shoes get worn that the pistons extend farther out to compensate & the fluid level drops. People tend to add more fluid & then once the system is serviced there's more fluid volume than needed.

Chevypoor · 05-29-2011, 01:13 PM

It is leaking around the cover but also at the back where it bolts to the firewall. When you open the cover the fluid is about a 1/4" from the top of the resevoir. There is no evidence of any brake fluid on the "cab" side of the firewall.

SCOTI · 05-29-2011, 01:58 PM

Quote:

Originally Posted by Chevypoor

It is leaking around the cover but also at the back where it bolts to the firewall. When you open the cover the fluid is about a 1/4" from the top of the resevoir. There is no evidence of any brake fluid on the "cab" side of the firewall.

The hydraulics are all contained in the engine compartment/underhood so if there's evidence of brake fluid leaking (wrinkled paint is the dead give-away if it's not wet) it has to be from the unit or the lines.

I would inspect the lines & fittings around the master cyl carefully since the prob continues despite using a diff master cylinder.

Chevypoor · 05-29-2011, 06:36 PM

Thanks guys, I double checked everything again and it appears to be leaking from around the cover. Any thoughts on how to get a tighter seal? Can I adjust the bale? Or can I get a new seal or cover?

05-29-2011, 08:13 AM	#1
Chevypoor Registered User Join Date: Jul 2008 Location: Richmond, VA Posts: 56	Help! Master Cylinder Leaking Our 69c10 has a manual brake master cylinder that is leaking down the firewall! It was replaced less than 2 years ago. It will also sometimes leak around the cover. The master cylinder that was on the truck when we got it appeared to be doing the same thing. The truck still stops fine. Is this a common problem with manual brakes? Hopefully someone here has an answer as this is making a mess of things. __________________ 1990 S10 Reg. cab 2wd 2.5/ 700r4, lowered, soon to be a TBI 350/ 700r4 1993 2500 Reg. cab 4wd 6.5 turbo diesel/ 5spd, bigger turbo, Bull Moose pump, cold air intake, and a few other mods 1969 C10 Reg. cab 2wd 305/350, RHS heads, Voodoo Cam, Gilmer drive, 2400 stall, and lots of other goodies!

05-29-2011, 08:29 AM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Help! Master Cylinder Leaking a good master cylinder does not leak __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

05-29-2011, 10:17 AM	#4
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,094	Re: Help! Master Cylinder Leaking Along w/inspecting the under-cover (lid) seal quality, the fluid level should also not be exceedingly high. It's common when pads/shoes get worn that the pistons extend farther out to compensate & the fluid level drops. People tend to add more fluid & then once the system is serviced there's more fluid volume than needed. __________________ 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.*

05-29-2011, 01:13 PM	#5
Chevypoor Registered User Join Date: Jul 2008 Location: Richmond, VA Posts: 56	Re: Help! Master Cylinder Leaking It is leaking around the cover but also at the back where it bolts to the firewall. When you open the cover the fluid is about a 1/4" from the top of the resevoir. There is no evidence of any brake fluid on the "cab" side of the firewall. __________________ 1990 S10 Reg. cab 2wd 2.5/ 700r4, lowered, soon to be a TBI 350/ 700r4 1993 2500 Reg. cab 4wd 6.5 turbo diesel/ 5spd, bigger turbo, Bull Moose pump, cold air intake, and a few other mods 1969 C10 Reg. cab 2wd 305/350, RHS heads, Voodoo Cam, Gilmer drive, 2400 stall, and lots of other goodies!

05-29-2011, 06:36 PM	#7
Chevypoor Registered User Join Date: Jul 2008 Location: Richmond, VA Posts: 56	Re: Help! Master Cylinder Leaking Thanks guys, I double checked everything again and it appears to be leaking from around the cover. Any thoughts on how to get a tighter seal? Can I adjust the bale? Or can I get a new seal or cover? __________________ 1990 S10 Reg. cab 2wd 2.5/ 700r4, lowered, soon to be a TBI 350/ 700r4 1993 2500 Reg. cab 4wd 6.5 turbo diesel/ 5spd, bigger turbo, Bull Moose pump, cold air intake, and a few other mods 1969 C10 Reg. cab 2wd 305/350, RHS heads, Voodoo Cam, Gilmer drive, 2400 stall, and lots of other goodies!



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