Brake (bleeding) Problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

OhioDan · 10-21-2004, 04:09 AM

Just installed new brake lines throughout. New calipers, and rear drum brake parts are all new. Started to bleed brakes, and had no problems with the calipers. Can't get fluid between master cyl. and rear wheel cyl's. Tried to vacumn bleed and tried to back bleed. No luck. could proportioning valve be bad? Reason I ask, is that the front bled so easy and all the problems I'm having with the rear. Any ideas or suggestions would be appreciated. Thanx.

**Palf70Step** · 10-21-2004, 06:45 AM

Is fluid getting to the junction at the rear axle? If not, check it at the input to the rear hose. If you have fluid flow there than I think your hose is bad. If you still lack fluid then check the master cylinder. Maybe the reservoir for the rear isn't pumping. If you have no fluid at the rear but master cylinder output seems good then I would say it is your proportioning valve.

tom hand · 10-21-2004, 07:07 AM

The proportioning valve keeps fluid from going to the rear brakes to keep them from locking up. There is a pin under a rubber boot that needs to be held in while bleeding the brakes....A good sized "zip tie" should hold it in for you

cheyenne10 · 10-21-2004, 11:26 AM

Great idea. I heard there was a tool for this but haven't found one or even seena picture of one yet.

**Palf70Step** · 10-21-2004, 01:02 PM

Kool I wish I knew of that too. I didn't realize or guess ever need to do that step with the proportioning valve.

flip66 · 10-21-2004, 01:58 PM

had the same problem I had to start at where the rubber line connects to the line on the frame and start there. I had someone push down on the pedal and put my thumb over it before they let off kind of messy but it worked.

OhioDan · 10-21-2004, 05:12 PM

Everything from Master cyl. to the shoes is new. Think I got a bad hose? I suspected the proportioning valve, because it's the only thing that's not new in the system. Oh, I tried to push in the pin as you said, but couldn't get it to move. Can they be rebuilt or serviced? Will check this weekend. Thanx.

Brainchild · 10-21-2004, 08:03 PM

Did you bench bleed the master cylinder real good before installing it?Maybe the back resevoir,which is actually the front I think,is in need of bleeding again.

And try holding the button on the valve too

LONGHAIR · 10-22-2004, 12:42 AM

That valve is not likely to move by hand. It is controlled by the internal pressure in the lines. It is there to cut-off the fluid supply to the lines if one should break/leak. (This causes lower pressure on that end) That is the point of the newer dual reservoir systems. The simplest way I have found to free it up is to open the bleeders on the side that does have pressure, in this case the front. Then press the brake pedal, when it reaches the floor you will hear or feel it pop. It may take a few pumps...... Then pump the pedal slowly a few times. Let the truck sit a while with ALL of the bleeders open, making sure to not let the master cylinder get empty. Then tighten all of the bleeders again. Now, start over bleeding......but start at the right rear (furthest from the M/C) and work your way to the front.
You are never going to get a brand-new (dry) system bled by starting from the front.....this will happen every time.

10-21-2004, 04:09 AM	#1
OhioDan Registered User Join Date: Apr 2002 Location: New Carlisle, Ohio,USA Posts: 1,404	Brake (bleeding) Problem Just installed new brake lines throughout. New calipers, and rear drum brake parts are all new. Started to bleed brakes, and had no problems with the calipers. Can't get fluid between master cyl. and rear wheel cyl's. Tried to vacumn bleed and tried to back bleed. No luck. could proportioning valve be bad? Reason I ask, is that the front bled so easy and all the problems I'm having with the rear. Any ideas or suggestions would be appreciated. Thanx. __________________ LIFE AIN'T EASY WHEN YER FAT AND GREASY! GMC= Got More Class! 1970 GMC LWB, Fleetside, 350/4spd, Flowmaster "40's", 2002 GMC 16" Rallies, cowl hood,and added a bunch of options that weren't there when I started.

10-21-2004, 06:45 AM	#2
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,249	Is fluid getting to the junction at the rear axle? If not, check it at the input to the rear hose. If you have fluid flow there than I think your hose is bad. If you still lack fluid then check the master cylinder. Maybe the reservoir for the rear isn't pumping. If you have no fluid at the rear but master cylinder output seems good then I would say it is your proportioning valve. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

10-21-2004, 07:07 AM	#3
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	The proportioning valve keeps fluid from going to the rear brakes to keep them from locking up. There is a pin under a rubber boot that needs to be held in while bleeding the brakes....A good sized "zip tie" should hold it in for you __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

10-21-2004, 11:26 AM	#4
cheyenne10 Senior Member Join Date: Apr 2000 Location: Oregon Posts: 2,512	zip tie!!!!! Great idea. I heard there was a tool for this but haven't found one or even seena picture of one yet. __________________ Bob

10-21-2004, 01:02 PM	#5
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,249	Kool I wish I knew of that too. I didn't realize or guess ever need to do that step with the proportioning valve. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

10-21-2004, 01:58 PM	#6
flip66 Registered User Join Date: Jan 2004 Location: Garland TX Dallas area Posts: 658	had the same problem I had to start at where the rubber line connects to the line on the frame and start there. I had someone push down on the pedal and put my thumb over it before they let off kind of messy but it worked.

10-21-2004, 05:12 PM	#7
OhioDan Registered User Join Date: Apr 2002 Location: New Carlisle, Ohio,USA Posts: 1,404	Everything from Master cyl. to the shoes is new. Think I got a bad hose? I suspected the proportioning valve, because it's the only thing that's not new in the system. Oh, I tried to push in the pin as you said, but couldn't get it to move. Can they be rebuilt or serviced? Will check this weekend. Thanx. __________________ LIFE AIN'T EASY WHEN YER FAT AND GREASY! GMC= Got More Class! 1970 GMC LWB, Fleetside, 350/4spd, Flowmaster "40's", 2002 GMC 16" Rallies, cowl hood,and added a bunch of options that weren't there when I started. Last edited by OhioDan; 10-21-2004 at 05:15 PM.

10-21-2004, 08:03 PM	#8
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	Did you bench bleed the master cylinder real good before installing it?Maybe the back resevoir,which is actually the front I think,is in need of bleeding again. And try holding the button on the valve too __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

10-22-2004, 12:42 AM	#9
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	That valve is not likely to move by hand. It is controlled by the internal pressure in the lines. It is there to cut-off the fluid supply to the lines if one should break/leak. (This causes lower pressure on that end) That is the point of the newer dual reservoir systems. The simplest way I have found to free it up is to open the bleeders on the side that does have pressure, in this case the front. Then press the brake pedal, when it reaches the floor you will hear or feel it pop. It may take a few pumps...... Then pump the pedal slowly a few times. Let the truck sit a while with ALL of the bleeders open, making sure to not let the master cylinder get empty. Then tighten all of the bleeders again. Now, start over bleeding......but start at the right rear (furthest from the M/C) and work your way to the front. You are never going to get a brand-new (dry) system bled by starting from the front.....this will happen every time.



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