Resetting a proportioning valve - The 1947 - Present Chevrolet & GMC Truck Message Board Network

western star · 07-21-2003, 10:24 PM

My dual master cylinder has what I believe to be a proportioning valve on the bottom front of it. It has a little rubber boot over it. I changed a rear brake line and the fluid level dropped out of site. After filling it I made a brake application to bleed the brakes and have no air or fluid coming out of the back line. Would this valve trip some how so as to supply bakes to the front in case of failure and if so how do you reset this valve so as I can bleed my brakes. It's on a 71 Chev 1/2 ton with front discs.

**68 Stepside** · 07-22-2003, 08:25 PM

Yes, the valve can "trip", and not supply fluid to the rears. I would fill the master cylinder back up, put the lid on, and step on the brake pedal (with both feet) fairly hard, and quickly as well. I'm pretty sure that will reset the valve. If it doesn't, I'm sure someone will know the correct way. I know it involves stepping very hard on the brake pedal very quickly, but I don't know if you should crack the bleeders open or not. I don't believe so.

Good luck.

western star · 07-23-2003, 08:54 PM

OK I'll try that and see if it works. I don't have the truck here right now as it's in the body shop for some final work. I'll try your suggestion when I get it home.

*Shane* · 07-23-2003, 09:16 PM

it still amazes me the things you can learn on this board ... I never knew that a proportioning valve had a "resettable circuit" ...

Good call TJ!

cdowns · 07-23-2003, 09:36 PM

that little rubber boot should just pop off there's a pin under it while bleeding the brakes the pin should be held out (theres a special toolto do it ) i made my own out of a piece or sheetmetal

Alex · 07-24-2003, 07:54 AM

cdowns - don't you mean the pin must be held in? In the Chilton manual, during the bleeding process, the pin (metering pin) must be held in. Either use a special tool or have a helper with a screwdriver or similar push it back in when the brake pedal is applied.

western star · 07-24-2003, 10:27 PM

Alex thanks for that tip. Many years of playing with cars and some things just never came up until now. Go figure.

07-21-2003, 10:24 PM	#1
western star Registered User Join Date: Mar 2003 Location: Victoria BC Canada Posts: 198	Resetting a proportioning valve My dual master cylinder has what I believe to be a proportioning valve on the bottom front of it. It has a little rubber boot over it. I changed a rear brake line and the fluid level dropped out of site. After filling it I made a brake application to bleed the brakes and have no air or fluid coming out of the back line. Would this valve trip some how so as to supply bakes to the front in case of failure and if so how do you reset this valve so as I can bleed my brakes. It's on a 71 Chev 1/2 ton with front discs.

07-22-2003, 08:25 PM	#2
68 Stepside huh? Join Date: May 2000 Location: Washington, Illinois Posts: 5,690	Yes, the valve can "trip", and not supply fluid to the rears. I would fill the master cylinder back up, put the lid on, and step on the brake pedal (with both feet) fairly hard, and quickly as well. I'm pretty sure that will reset the valve. If it doesn't, I'm sure someone will know the correct way. I know it involves stepping very hard on the brake pedal very quickly, but I don't know if you should crack the bleeders open or not. I don't believe so. Good luck. __________________ Someday when I'm lonely, Wishing you weren't so far away, Then I will remember Things we said today. RIP El Jay

07-23-2003, 09:36 PM	#5
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	that little rubber boot should just pop off there's a pin under it while bleeding the brakes the pin should be held out (theres a special toolto do it ) i made my own out of a piece or sheetmetal __________________ 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

07-24-2003, 07:54 AM	#6
Alex Registered User Join Date: Jan 2000 Location: Blaine, MN Posts: 798	cdowns - don't you mean the pin must be held in? In the Chilton manual, during the bleeding process, the pin (metering pin) must be held in. Either use a special tool or have a helper with a screwdriver or similar push it back in when the brake pedal is applied. __________________ '72 C/10 LWB 402/400 Blaine, MN

07-23-2003, 08:54 PM	#3
western star Registered User Join Date: Mar 2003 Location: Victoria BC Canada Posts: 198	OK I'll try that and see if it works. I don't have the truck here right now as it's in the body shop for some final work. I'll try your suggestion when I get it home.

07-23-2003, 09:16 PM	#4
Shane Account Suspended Join Date: Jun 2000 Location: over yonder Posts: 14,270	it still amazes me the things you can learn on this board ... I never knew that a proportioning valve had a "resettable circuit" ... Good call TJ!

07-24-2003, 10:27 PM	#7
western star Registered User Join Date: Mar 2003 Location: Victoria BC Canada Posts: 198	Alex thanks for that tip. Many years of playing with cars and some things just never came up until now. Go figure.



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