More Brake Troubles - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bbarooo · 01-09-2009, 12:25 PM

I know there have been alot of brake questions lately but I'm stumped.

I did the brakes on a 72 C-10 replacing everything but the rear brake hose and proportioning valve. I could only get a trickle of pressure out of the rear brakes but the pedal felt good so I drove it(with the brake light on). The light went off for a while and came back recently. I checked the fluid and the front brake reservoir was overfull(spit out when I released the cap) and the rear was empty. Anyone had this happen to them?

bbarooo · 01-09-2009, 12:29 PM

I have also since replaced the rear hose and swapped the prop valve with one I knew was good with the same results. No pressure in the rear brakes and no gravity bleed on all 4.

cdowns · 01-09-2009, 12:59 PM

did you clamp the pin on the combination valve like it says to do in the service manual?

nac593 · 01-09-2009, 01:07 PM

cdowns, could you explain the manual's procedure. I couldn't find it in my book.

windmill · 01-09-2009, 03:33 PM

You need to change the proportion valve. These will go bad on the inside. make sure you get one with disc-manual brakes witch is a 70-30. but if you go disc-disc you will need the 50-50.

bbarooo · 01-09-2009, 03:41 PM

cdowns...I read that in the service manual but I'm not sure where to find that pin or how to clamp it. Any advice?

windmill...I swapped the valve with a functioning 72 and it didn't change anything.(accept to give me another truck with no brakes) And that one bled ok a few months back.

nac593 · 01-09-2009, 04:13 PM

bbarooo, can you explain what the manual said as far as clamping it?

windmill · 01-09-2009, 04:56 PM

Ok i see where you changed it. start from the pportion valve and make sure you have fluid come out their for the rear brakes. if so , go to the next place and check for pressure their.(before the rubber hose) the hose could be bad on the inside.

cdowns · 01-09-2009, 05:36 PM

the pin on the combination valve is normally toward the front/sometimes its covered by a small rubber bulb

i clamp it in place to keep it centered with a cclamp,there is a special GM part#tool to do it tho i've never seen one

70GMCer · 01-09-2009, 05:46 PM

If the prop valve is stuck, clamping that pin/rubber plunger will not work. I've been told to drive the truck to around 10 or 15 mph and then slam on the brake pedal hard. This will most likely release that valve. You might have to do this a couple times. I didn't know about this until someone on here told 70c10 to try that. Damn if it didn't work. Then bleed the brakes. Also, the dash brake light will stop coming on.

bbarooo · 01-09-2009, 06:22 PM

nac593...the service manual I have only says to clamp it in place using the special tool

windmill...thanks for the voice of reason. The hose is now new as well but the pressure must get lost somewhere. Have you ever worked on something so long you forgot how it works? Yours is a sure way to find it.

70GMCer...thats a good one to try first, I don't even have to get dirty.

Thanks for your help!!

01-09-2009, 12:25 PM	#1
bbarooo Registered User Join Date: Sep 2004 Location: So. California Posts: 121	More Brake Troubles I know there have been alot of brake questions lately but I'm stumped. I did the brakes on a 72 C-10 replacing everything but the rear brake hose and proportioning valve. I could only get a trickle of pressure out of the rear brakes but the pedal felt good so I drove it(with the brake light on). The light went off for a while and came back recently. I checked the fluid and the front brake reservoir was overfull(spit out when I released the cap) and the rear was empty. Anyone had this happen to them? Last edited by bbarooo; 01-09-2009 at 12:26 PM.

01-09-2009, 12:29 PM	#2
bbarooo Registered User Join Date: Sep 2004 Location: So. California Posts: 121	Re: More Brake Troubles I have also since replaced the rear hose and swapped the prop valve with one I knew was good with the same results. No pressure in the rear brakes and no gravity bleed on all 4.

01-09-2009, 12:59 PM	#3
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: More Brake Troubles did you clamp the pin on the combination valve like it says to do in the service manual? __________________ 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

01-09-2009, 01:07 PM	#4
nac593 Registered User Join Date: Sep 2007 Location: san diego,ca Posts: 125	Re: More Brake Troubles cdowns, could you explain the manual's procedure. I couldn't find it in my book.

01-09-2009, 03:33 PM	#5
windmill Registered User Join Date: Jan 2007 Location: Sylvania, Alabama Posts: 288	Re: More Brake Troubles You need to change the proportion valve. These will go bad on the inside. make sure you get one with disc-manual brakes witch is a 70-30. but if you go disc-disc you will need the 50-50. __________________ 72 swb pickup http://i124.photobucket.com/albums/p...k/100_0958.jpg 1967 chevelle ss 1966 mustang getting a l33 ls motor 1969 chevy dump truck 1989 mustang 6.0 ls best time of 1.29 at 5.91 https://www.youtube.com/watch?v=JtbooZoGZmQ

01-09-2009, 03:41 PM	#6
bbarooo Registered User Join Date: Sep 2004 Location: So. California Posts: 121	Re: More Brake Troubles cdowns...I read that in the service manual but I'm not sure where to find that pin or how to clamp it. Any advice? windmill...I swapped the valve with a functioning 72 and it didn't change anything.(accept to give me another truck with no brakes) And that one bled ok a few months back.

01-09-2009, 04:13 PM	#7
nac593 Registered User Join Date: Sep 2007 Location: san diego,ca Posts: 125	Re: More Brake Troubles bbarooo, can you explain what the manual said as far as clamping it?

01-09-2009, 04:56 PM	#8
windmill Registered User Join Date: Jan 2007 Location: Sylvania, Alabama Posts: 288	Re: More Brake Troubles Ok i see where you changed it. start from the pportion valve and make sure you have fluid come out their for the rear brakes. if so , go to the next place and check for pressure their.(before the rubber hose) the hose could be bad on the inside. __________________ 72 swb pickup http://i124.photobucket.com/albums/p...k/100_0958.jpg 1967 chevelle ss 1966 mustang getting a l33 ls motor 1969 chevy dump truck 1989 mustang 6.0 ls best time of 1.29 at 5.91 https://www.youtube.com/watch?v=JtbooZoGZmQ

01-09-2009, 05:36 PM	#9
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: More Brake Troubles the pin on the combination valve is normally toward the front/sometimes its covered by a small rubber bulb i clamp it in place to keep it centered with a cclamp,there is a special GM part#tool to do it tho i've never seen one __________________ 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

01-09-2009, 05:46 PM	#10
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: More Brake Troubles If the prop valve is stuck, clamping that pin/rubber plunger will not work. I've been told to drive the truck to around 10 or 15 mph and then slam on the brake pedal hard. This will most likely release that valve. You might have to do this a couple times. I didn't know about this until someone on here told 70c10 to try that. Damn if it didn't work. Then bleed the brakes. Also, the dash brake light will stop coming on. __________________ 1997 GMC Sierra Ext 1965 Mustang

01-09-2009, 06:22 PM	#11
bbarooo Registered User Join Date: Sep 2004 Location: So. California Posts: 121	Re: More Brake Troubles nac593...the service manual I have only says to clamp it in place using the special tool windmill...thanks for the voice of reason. The hose is now new as well but the pressure must get lost somewhere. Have you ever worked on something so long you forgot how it works? Yours is a sure way to find it. 70GMCer...thats a good one to try first, I don't even have to get dirty. Thanks for your help!!



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