Proportioning valve for drums? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MightyFine69 · 01-30-2004, 05:12 AM

I know this may sound like a dumb question, but do you need a proportioning valve for four wheel drum brakes? The reason I ask is last September I had to slam on my brakes to avoid hitting a tractor that was turning in front of me and my rear brakes locked up and caused me to spin around and flip over in the ditch. Needless to say my truck if not drivable as it crushed the roof. Oh, by the way, my brakes are manual, not power. I plan on either replacing the cab on my truck or seeing how much it would cost for body work to fix the existing cab. Thanks in advance.

JimKshortstep4x4 · 01-30-2004, 09:00 AM

Drum brake trucks don't come with proportioning valves. I suspect that there is problem with your rear brakes, wheel cylinders leaking or grease on the lining?

Jim

Dave67 · 01-30-2004, 09:13 AM

I don't want to argue with Jim, but my 67 C-20 has drums all around, and a proportioning valve. It looks factory. Was this an option?

70c10 · 01-30-2004, 09:16 AM

Mine has power drums all around and what appears to be a proportional valve. I'll have to double check it.

Wootdog · 01-30-2004, 09:27 AM

I originally had manual drums and there was a proportion valve on my 68. In fact I still have it with the upgrade to power drums. Kerry

JimKshortstep4x4 · 01-30-2004, 09:32 AM

They have a distribution/blocking valve but it is not a true proportioning valve unless someone changed it.

Jim

Longhorn Man · 01-30-2004, 10:34 AM

Jim is correct. ON drum/drum, that block is just a distribution valve, and does not alter the line pressure front to rear.
Rear wheel lock up is pretty much to be expected. You can plum an aftermarket adjustable poportioning valve in to reduce the tendincy to skid. You'll need to open the valve all the way up when hauling to get maximum braking.

Huge bummer about your truck. Were you OK? Obviously you were't hurt too bad, but I'm sure you ended up in the E.R.

MightyFine69 · 02-05-2004, 06:23 AM

Thanks for all the replies. I did go to the emergency room with a sore back. Come to find out I had a compression fracture of my T7 vertebrae. I was in a back brace for three months. I am back to work now, though. I have been really busy, that's why it has taken me so long to respond. I plan on getting the truck fixed this summer, and I am going to get the brakes looked at after that. I think I will plumb in an aftermarket proportioning valve, too. I run 33x12.5 tires on my truck in the summer, and they like to skid when I hit the brakes hard. You wouldn't think that manual brakes would be that easy to lock up.

MOTHERTRUCKERS · 02-05-2004, 11:45 AM

Adjustable prop valves 49.00 shipped to your door.

01-30-2004, 05:12 AM	#1
MightyFine69 Registered User Join Date: Jun 2001 Location: Traverse City, MI Posts: 97	Proportioning valve for drums? I know this may sound like a dumb question, but do you need a proportioning valve for four wheel drum brakes? The reason I ask is last September I had to slam on my brakes to avoid hitting a tractor that was turning in front of me and my rear brakes locked up and caused me to spin around and flip over in the ditch. Needless to say my truck if not drivable as it crushed the roof. Oh, by the way, my brakes are manual, not power. I plan on either replacing the cab on my truck or seeing how much it would cost for body work to fix the existing cab. Thanks in advance. __________________ 1969 3/4 ton 4x4 33's with no lift, gotta love it! A man and his truck, it's a beautiful thing.

01-30-2004, 09:13 AM	#3
Dave67 Junior Member Join Date: Dec 2001 Location: Bethel Park, PA USA Posts: 127	I don't want to argue with Jim, but my 67 C-20 has drums all around, and a proportioning valve. It looks factory. Was this an option? __________________ 67 C-20 LWB 56 Nomad--- nope, sold it 75 Stingray 13 Silverado crew cab 08 Trailblazer (wife's) Pittsburgh, PA

01-30-2004, 09:16 AM	#4
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,856	Mine has power drums all around and what appears to be a proportional valve. I'll have to double check it. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

01-30-2004, 09:27 AM	#5
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,687	Yes it does. I originally had manual drums and there was a proportion valve on my 68. In fact I still have it with the upgrade to power drums. Kerry __________________ 1967 C10 Got it back after three years Boy I sure missed Peppy 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

02-05-2004, 06:23 AM	#8
MightyFine69 Registered User Join Date: Jun 2001 Location: Traverse City, MI Posts: 97	Thanks for all the replies. I did go to the emergency room with a sore back. Come to find out I had a compression fracture of my T7 vertebrae. I was in a back brace for three months. I am back to work now, though. I have been really busy, that's why it has taken me so long to respond. I plan on getting the truck fixed this summer, and I am going to get the brakes looked at after that. I think I will plumb in an aftermarket proportioning valve, too. I run 33x12.5 tires on my truck in the summer, and they like to skid when I hit the brakes hard. You wouldn't think that manual brakes would be that easy to lock up. __________________ 1969 3/4 ton 4x4 33's with no lift, gotta love it! A man and his truck, it's a beautiful thing.

01-30-2004, 09:00 AM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Drum brake trucks don't come with proportioning valves. I suspect that there is problem with your rear brakes, wheel cylinders leaking or grease on the lining? Jim

01-30-2004, 09:32 AM	#6
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	They have a distribution/blocking valve but it is not a true proportioning valve unless someone changed it. Jim

01-30-2004, 10:34 AM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Jim is correct. ON drum/drum, that block is just a distribution valve, and does not alter the line pressure front to rear. Rear wheel lock up is pretty much to be expected. You can plum an aftermarket adjustable poportioning valve in to reduce the tendincy to skid. You'll need to open the valve all the way up when hauling to get maximum braking. Huge bummer about your truck. Were you OK? Obviously you were't hurt too bad, but I'm sure you ended up in the E.R.

02-05-2004, 11:45 AM	#9
MOTHERTRUCKERS Registered User Join Date: Dec 1999 Location: BRADENTON FLA Posts: 3,269	Adjustable prop valves 49.00 shipped to your door. __________________ Rest in Peace Ed. Thanks for all the good times.



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