Standard Brake Setup? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

wxman1 · 08-16-2002, 07:38 PM

I'm putting a link in this message to an image that I shot of
my brake booster in the engine compartment of my 69 C10
P/U. The booster is mounted to a bracket that is mounted to
the firewall. Most power boosters I've seen mount directly
to the firewall with the actuator rod extending through the
firewall to the brake pedal.

http://mywebpages.comcast.net/wxgeek/p8160014.jpg

Is this a standard brake setup? Or maybe this is a distant
cousin?

Jim M.

*Zkast* · 08-16-2002, 07:40 PM

Thats the normal setup for Front disc/Rear drum on these trucks...

wxman1 · 08-19-2002, 07:53 PM

Thanks for the reply Zkast...but the truck has drums all around...
no discs on the front. Also...what is the purpose of the device
to the right of the master cylinder?

The data plate on the door pillar says the truck is a 1969...but
I'm beginning to think this may be a 71/72 front clip. Possibly it
had discs on the front originally?

Jim M.

kaycee · 08-19-2002, 08:02 PM

That is a porpotioning valve to the right, it controls the pressure to the front and rear brakes.

**MikeB** · 08-19-2002, 08:21 PM

It's a box stock 69/70 power drum brake setup. On 71/72 models with front discs, one of the brake lines is smaller (3/16") than the other (1/4").

da-burb · 08-19-2002, 09:07 PM

I could just be adding to the confusion, but the proportioning valve looks like 71-72 to me. Of all the boosters I have, every 71-72 has the brake warning light plug-in on the top of the valve and the 70 and older units have it mounted on the bottom of the proportioning valve. Just my observance.

6869704X4 · 08-19-2002, 09:30 PM

Whats the line coming out the back of the pro valve and going across the firewall?

wxman1 · 08-20-2002, 01:42 AM

If I understand this device correctly (proportioning valve)...
then the 2 lines coming out of the valve (one out the bottom
and one out the end) go to the front drums and rear drums.
I guess my question is "Why is this thing necessary?"
I've heard that if you have discs in front and drums in the rear
that you have to use this device to re-distribute the hydraulic
pressure from the master cylinder. The theory is (I think)
that the front discs being more efficient than the rear drums
would need less hydraulic pressure. The assumption being that
if you had the same hydraulic pressure that the front end would
"dive" excessively during a hard stop.

However...the truck doesn't have discs up front...its got drums
all around. So then why is this thing necessary?

Jim

Longhorn Man · 08-20-2002, 01:49 AM

Couple things...I think you have the wrong booster and prop valve at a minimum... maybe master cylinder too.
Esp when you look at that brake hose routing, that's just sick.
You are very close on your asumption as to why a proportionaing valve, just a little backwards.
The drums take up much less effort to work, and the discs require ahigher pressure, therefore, the prop valve actually restricts the fluid pressure to the back, esp on a vehicle with 80% of its weight on the nose like an unloaded pick up.

Jwill41 · 08-20-2002, 08:43 AM

But, would you need the valve for 4 wheel drums? Why?

colohusker · 08-20-2002, 09:09 AM

Basically the same reason as with discs. When you apply the brakes, the weight transfer loads the front end with 75 - 90% of the weight, depending onhow fast the brakes are applied, payload, etc. If you didn't have a proportioning valve and it was split evenly between front and rear, you'd end up locking up the rear tires every time. I don't know what the stock valve for power drums splits it between f/r, but the disc one is supposed to be 70/30. Just my nickels worth...

*Fast68Chevy* · 08-20-2002, 02:13 PM

it wasnt a valve until 71, before then it was simply just a distribution block with a warning valve piston assembly, in 71 they came to be technically called a combinatin valve, in that it has proportioning system and warnign system in it,

im afraid to look at the pic, from what i have read it sounds like a mess..

good luck

palallin · 08-20-2002, 04:31 PM

The Master Cylinder and valve look very wrong--I won't even comment on the brake line routing--but the bracket and booster look exactly like the ones that were in my '67.

A funny truck, that '67: PB from the factory but not PS.

08-16-2002, 07:38 PM	#1
wxman1 Senior Member Join Date: May 2002 Location: mt juliet, tennessee, usa Posts: 237	Standard Brake Setup? I'm putting a link in this message to an image that I shot of my brake booster in the engine compartment of my 69 C10 P/U. The booster is mounted to a bracket that is mounted to the firewall. Most power boosters I've seen mount directly to the firewall with the actuator rod extending through the firewall to the brake pedal. http://mywebpages.comcast.net/wxgeek/p8160014.jpg Is this a standard brake setup? Or maybe this is a distant cousin? Jim M.

08-19-2002, 08:02 PM	#4
kaycee Registered User Join Date: Jan 2000 Location: Wyoming USA Posts: 2,449	WXMAN That is a porpotioning valve to the right, it controls the pressure to the front and rear brakes. __________________ 2001 Silverado K-1500 2005 FXDWG stage3 69 CHEVY Short/Step 327/4L60 373 posi 63 IMPALA 327

08-19-2002, 08:21 PM	#5
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	It's a box stock 69/70 power drum brake setup. On 71/72 models with front discs, one of the brake lines is smaller (3/16") than the other (1/4"). __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

08-19-2002, 09:07 PM	#6
da-burb "Ochre Ogre" Join Date: Apr 2000 Location: Springfield, MN Posts: 3,558	I could just be adding to the confusion, but the proportioning valve looks like 71-72 to me. Of all the boosters I have, every 71-72 has the brake warning light plug-in on the top of the valve and the 70 and older units have it mounted on the bottom of the proportioning valve. Just my observance. __________________ Bowtie Truck Stop Inc. Mid-West GM Truck Restoration Parts Supplier Your Key Parts, Auto Metal Direct, Dynacorn, and Goodmark dealer. like us @ www.facebook.com/BowtieTruckStop 1971 C-10 Suburban (Ochre) 1971 K-10 Suburban (Ochre) 1972 C-10 Suburban (Ochre) 1972 K-20 Suburban (Yellow- that just aint right!) Springfield, Minnesota 56087

08-19-2002, 09:30 PM	#7
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Whats the line coming out the back of the pro valve and going across the firewall? __________________ The more I learn about women, the more I love my truck.

08-16-2002, 07:40 PM	#2
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	Thats the normal setup for Front disc/Rear drum on these trucks...

08-19-2002, 07:53 PM	#3
wxman1 Senior Member Join Date: May 2002 Location: mt juliet, tennessee, usa Posts: 237	Thanks for the reply Zkast...but the truck has drums all around... no discs on the front. Also...what is the purpose of the device to the right of the master cylinder? The data plate on the door pillar says the truck is a 1969...but I'm beginning to think this may be a 71/72 front clip. Possibly it had discs on the front originally? Jim M.

08-20-2002, 01:42 AM	#8
wxman1 Senior Member Join Date: May 2002 Location: mt juliet, tennessee, usa Posts: 237	If I understand this device correctly (proportioning valve)... then the 2 lines coming out of the valve (one out the bottom and one out the end) go to the front drums and rear drums. I guess my question is "Why is this thing necessary?" I've heard that if you have discs in front and drums in the rear that you have to use this device to re-distribute the hydraulic pressure from the master cylinder. The theory is (I think) that the front discs being more efficient than the rear drums would need less hydraulic pressure. The assumption being that if you had the same hydraulic pressure that the front end would "dive" excessively during a hard stop. However...the truck doesn't have discs up front...its got drums all around. So then why is this thing necessary? Jim

08-20-2002, 01:49 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Couple things...I think you have the wrong booster and prop valve at a minimum... maybe master cylinder too. Esp when you look at that brake hose routing, that's just sick. You are very close on your asumption as to why a proportionaing valve, just a little backwards. The drums take up much less effort to work, and the discs require ahigher pressure, therefore, the prop valve actually restricts the fluid pressure to the back, esp on a vehicle with 80% of its weight on the nose like an unloaded pick up.

08-20-2002, 08:43 AM	#10
Jwill41 Registered User Join Date: Aug 2002 Location: Farmers Branch, Tx Posts: 1,009	But, would you need the valve for 4 wheel drums? Why? __________________ http://www.picturetrail.com/jwill41 67 1/2 ton GMC short step side 68 1/2 ton Chevy long fleet side 72 1/2 ton Chevy Suburban 99 1/2 ton Chevy Suburban founder (and only member) of the primer/clearcoat club

08-20-2002, 09:09 AM	#11
colohusker Registered User Join Date: Apr 2002 Location: Longmont, CO Posts: 436	Basically the same reason as with discs. When you apply the brakes, the weight transfer loads the front end with 75 - 90% of the weight, depending onhow fast the brakes are applied, payload, etc. If you didn't have a proportioning valve and it was split evenly between front and rear, you'd end up locking up the rear tires every time. I don't know what the stock valve for power drums splits it between f/r, but the disc one is supposed to be 70/30. Just my nickels worth... __________________ ------------------------------------------------ I say it's only money, my wife says it's only a truck.... '71 C10 Deluxe, factory ac, ps, pb, should be done by 2102 Longmont, CO husker95@hotmail.com

08-20-2002, 02:13 PM	#12
Fast68Chevy Account Suspended Join Date: May 2000 Location: IL Posts: 0	it wasnt a valve until 71, before then it was simply just a distribution block with a warning valve piston assembly, in 71 they came to be technically called a combinatin valve, in that it has proportioning system and warnign system in it, im afraid to look at the pic, from what i have read it sounds like a mess.. good luck

08-20-2002, 04:31 PM	#13
palallin Registered User Join Date: Jul 2002 Location: St. James, MO Posts: 1,238	The Master Cylinder and valve look very wrong--I won't even comment on the brake line routing--but the bracket and booster look exactly like the ones that were in my '67. A funny truck, that '67: PB from the factory but not PS. __________________ '69 Longstep K-10: 327/SM465/T-221/Closed Knuckle Dana44/12-bolt.

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