MC bowl going dry? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BIGBLU 72 · 11-18-2009, 05:02 PM

My master cylinder's back bowl kept running dry and thus losing my brakes. so i noticed fluid around the back of the MC where it mounts to the booster. i replaced the MC and drove the truck but the pedal never came back and when i checked the bowl the fluid was gone again????? I traced all the lines and couldnt find any leakage anywhere? where else could i be losing fulid?? i was thinking maybe a wheel cylinder but thats alot of fluid to lose in an hour i would think? what do yall think?

71tahoe · 11-18-2009, 05:25 PM

It may be the wheel cylinders. Or you could have gotten a bad MC new out of the box. You should take off the rear drums and check to see if there is any leakage there to be sure.

Longhorn Man · 11-18-2009, 08:23 PM

if you lost that much fluid out a cylinder, you'd know at a glance, the inside of the tire would be soaked. Look under the truck at the inside sidewall, and if they are dry, then go get another master cylinder.

BIGBLU 72 · 11-18-2009, 09:38 PM

thats the strange thing! i cant find anywhere that a leak has occurs, even directly after driving?? Could it be leaking into the Booster???

rico7769 · 11-18-2009, 09:49 PM

see if a buddy can watch as you press the pedal. Fill it again, listen under the hood for a "squishing" sound from the MC, and then press it again while someone listens/watches the rear. Had the same prob with ours. Doesn't take much to get rid of the back bowl with shot wheel cylinders. Even with drums I didn't see a ton of fluid on the inside sidewall of the tires. Figure how much fluid it takes to fill the lines as you empty them out three to four times of pressing the pedal to the floor. Math will tell you how quickly it can be dumped down to nothing. Hope that works

BIGBLU 72 · 11-18-2009, 11:39 PM

Thanks for the info!

tim21391 · 11-19-2009, 12:55 AM

could of bought a bad mc?

jkeady · 11-19-2009, 01:55 AM

Dumb question, maybe, but I have to ask: did you bleed the master cylinder properly?

Longhorn Man · 11-19-2009, 06:28 PM

yes, it is probably going into the booster

BIGBLU 72 · 11-19-2009, 08:38 PM

Is it leaking into the booster real bad?

Longhorn Man · 11-19-2009, 11:19 PM

yeah. if there is no fliud in the M/C, then you have no brakes.
and once brake fluid gets in there, it will destroy the rubber diaphram and one day it'll pop and you'll lose power assist... usually when you need it the most too.

BIGBLU 72 · 11-19-2009, 11:37 PM

oh yeah that sounds real bad lol! is there any way to get it out once it gets in there?

11-18-2009, 05:02 PM	#1
BIGBLU 72 Registered User Join Date: Dec 2008 Location: Ashland, KY Posts: 700	MC bowl going dry? My master cylinder's back bowl kept running dry and thus losing my brakes. so i noticed fluid around the back of the MC where it mounts to the booster. i replaced the MC and drove the truck but the pedal never came back and when i checked the bowl the fluid was gone again????? I traced all the lines and couldnt find any leakage anywhere? where else could i be losing fulid?? i was thinking maybe a wheel cylinder but thats alot of fluid to lose in an hour i would think? what do yall think? __________________ 68 C10 LWB 2/4 drop 406/th400/3.73posi 04 Silverado SS LQ9 6.0/4L65e/4.11posi AWD

11-18-2009, 05:25 PM	#2
71tahoe Registered User Join Date: May 2006 Location: Jonesboro, AR Posts: 916	Re: MC bowl going dry? It may be the wheel cylinders. Or you could have gotten a bad MC new out of the box. You should take off the rear drums and check to see if there is any leakage there to be sure.

11-18-2009, 08:23 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: MC bowl going dry? if you lost that much fluid out a cylinder, you'd know at a glance, the inside of the tire would be soaked. Look under the truck at the inside sidewall, and if they are dry, then go get another master cylinder.

11-18-2009, 09:38 PM	#4
BIGBLU 72 Registered User Join Date: Dec 2008 Location: Ashland, KY Posts: 700	Re: MC bowl going dry? thats the strange thing! i cant find anywhere that a leak has occurs, even directly after driving?? Could it be leaking into the Booster??? __________________ 68 C10 LWB 2/4 drop 406/th400/3.73posi 04 Silverado SS LQ9 6.0/4L65e/4.11posi AWD

11-18-2009, 09:49 PM	#5
rico7769 Hybrid67 Join Date: Jan 2009 Location: Martinez, GA Posts: 195	Re: MC bowl going dry? see if a buddy can watch as you press the pedal. Fill it again, listen under the hood for a "squishing" sound from the MC, and then press it again while someone listens/watches the rear. Had the same prob with ours. Doesn't take much to get rid of the back bowl with shot wheel cylinders. Even with drums I didn't see a ton of fluid on the inside sidewall of the tires. Figure how much fluid it takes to fill the lines as you empty them out three to four times of pressing the pedal to the floor. Math will tell you how quickly it can be dumped down to nothing. Hope that works __________________ Keep em' Running! All show.....no go

11-18-2009, 11:39 PM	#6
BIGBLU 72 Registered User Join Date: Dec 2008 Location: Ashland, KY Posts: 700	Re: MC bowl going dry? Thanks for the info! __________________ 68 C10 LWB 2/4 drop 406/th400/3.73posi 04 Silverado SS LQ9 6.0/4L65e/4.11posi AWD

11-19-2009, 12:55 AM	#7
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: MC bowl going dry? could of bought a bad mc? __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

11-19-2009, 01:55 AM	#8
jkeady Registered User Join Date: Apr 2004 Location: Salem, OR Posts: 127	Re: MC bowl going dry? Dumb question, maybe, but I have to ask: did you bleed the master cylinder properly? __________________ Josh '70 Custom Camper / 20

11-19-2009, 06:28 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: MC bowl going dry? yes, it is probably going into the booster

11-19-2009, 08:38 PM	#10
BIGBLU 72 Registered User Join Date: Dec 2008 Location: Ashland, KY Posts: 700	Re: MC bowl going dry? Is it leaking into the booster real bad? __________________ 68 C10 LWB 2/4 drop 406/th400/3.73posi 04 Silverado SS LQ9 6.0/4L65e/4.11posi AWD

11-19-2009, 11:19 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: MC bowl going dry? yeah. if there is no fliud in the M/C, then you have no brakes. and once brake fluid gets in there, it will destroy the rubber diaphram and one day it'll pop and you'll lose power assist... usually when you need it the most too.

11-19-2009, 11:37 PM	#12
BIGBLU 72 Registered User Join Date: Dec 2008 Location: Ashland, KY Posts: 700	Re: MC bowl going dry? oh yeah that sounds real bad lol! is there any way to get it out once it gets in there? __________________ 68 C10 LWB 2/4 drop 406/th400/3.73posi 04 Silverado SS LQ9 6.0/4L65e/4.11posi AWD



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