Stopping Power - The 1947 - Present Chevrolet & GMC Truck Message Board Network

wxman1 · 06-08-2003, 06:28 PM

I've got a 1969 C/10 1/2 ton P/U. From what I've
read disc brakes were not an option until
1971. The truck has drums all the way around. However, the truck has the large disc brake master cylinder and the proportioning
valve. At first I thought that this was the brake
warning failure switch, but it looks more like a
proportioning valve. So, the only thing I can
conclude is that one of the previous owners
put a circa 1971-72 booster-master
cylinder-proportioning valve on it, possibly
from a junkyard.

This is the first vehicle that I've driven in a
long time that had drums all the way around.
While the drums will stop the truck, I can't
lock up the brakes. Some would argue that's
a good thing. At any rate they just don't stop
the truck as fast as I would like or as fast as I
think they should.

Well, at any rate, I replaced the booster and
master cylinder with like kinds. I also replace
the front drums. The brakes have been bled
all around and the peddle is firm, not spongy
at all.

So the only component left is the
proportioning valve. Does anybody know how
to adjust this thing in order to get more
braking up front?? Pix included at URL below.

Proportioning Valve

**PICKMUP** · 06-08-2003, 10:36 PM

I would recommend you install the correct MC & prop valve...and not try to modify or "make work", the wrong one. I just don't like to modify and experiment with brakes, when the right stuff is readily available. My 2cnts.

Pelon916 · 06-09-2003, 01:40 PM

i have a '69 with drums all around.. it took me a little while to get used to the slower stopping, but now it works fine for me.
if the brakes are adjusted properly they should stop you smoothly and not pull to either side in a hard stop... but they still feel like they aren't doing enough.. heh.

Frank_Zeller · 06-09-2003, 02:06 PM

4 wheel drum brakes dont have a proportion valve. Its just a metering block that can sense if one of the reservoir looses pressure. The Disc got the proportion valve that limited pressure to the rear brakes plus offset the front disc brake engagement until the back brakes had a little pressure.

The Disc master has the same size lines into it. The 4 wheel drum masters will have a built in residue pressure valve to the fronts.

The Disc master will only have this for the rears.

Frank_Zeller · 06-09-2003, 02:09 PM

Just saw your pic....that is a Disc Master and Disc Proportion valve. There is no real adjustment. But sometimes these can trap air and need to be bleed with the rest of the system.

06-08-2003, 06:28 PM	#1
wxman1 Senior Member Join Date: May 2002 Location: mt juliet, tennessee, usa Posts: 237	Stopping Power I've got a 1969 C/10 1/2 ton P/U. From what I've read disc brakes were not an option until 1971. The truck has drums all the way around. However, the truck has the large disc brake master cylinder and the proportioning valve. At first I thought that this was the brake warning failure switch, but it looks more like a proportioning valve. So, the only thing I can conclude is that one of the previous owners put a circa 1971-72 booster-master cylinder-proportioning valve on it, possibly from a junkyard. This is the first vehicle that I've driven in a long time that had drums all the way around. While the drums will stop the truck, I can't lock up the brakes. Some would argue that's a good thing. At any rate they just don't stop the truck as fast as I would like or as fast as I think they should. Well, at any rate, I replaced the booster and master cylinder with like kinds. I also replace the front drums. The brakes have been bled all around and the peddle is firm, not spongy at all. So the only component left is the proportioning valve. Does anybody know how to adjust this thing in order to get more braking up front?? Pix included at URL below. Proportioning Valve

06-08-2003, 10:36 PM	#2
PICKMUP "Trucks with Class" Join Date: Jul 2000 Location: OLYMPIA, WA, USA Posts: 8,126	I would recommend you install the correct MC & prop valve...and not try to modify or "make work", the wrong one. I just don't like to modify and experiment with brakes, when the right stuff is readily available. My 2cnts. __________________ Email: frankeham@comcast.net Phone: 360-956-7170

06-09-2003, 01:40 PM	#3
Pelon916 Registered User Join Date: May 2003 Location: Sacto, CA Posts: 39	... i have a '69 with drums all around.. it took me a little while to get used to the slower stopping, but now it works fine for me. if the brakes are adjusted properly they should stop you smoothly and not pull to either side in a hard stop... but they still feel like they aren't doing enough.. heh.

06-09-2003, 02:06 PM	#4
Frank_Zeller Registered User Join Date: Jun 2001 Location: Austin, Texas Posts: 796	4 wheel drum brakes dont have a proportion valve. Its just a metering block that can sense if one of the reservoir looses pressure. The Disc got the proportion valve that limited pressure to the rear brakes plus offset the front disc brake engagement until the back brakes had a little pressure. The Disc master has the same size lines into it. The 4 wheel drum masters will have a built in residue pressure valve to the fronts. The Disc master will only have this for the rears. __________________ 69 SWB C/10 5-6 drop 700R4 69 Firebird Convert 455 4 spd 70 Torino GT Convert Austin-Texas

06-09-2003, 02:09 PM	#5
Frank_Zeller Registered User Join Date: Jun 2001 Location: Austin, Texas Posts: 796	Just saw your pic....that is a Disc Master and Disc Proportion valve. There is no real adjustment. But sometimes these can trap air and need to be bleed with the rest of the system. __________________ 69 SWB C/10 5-6 drop 700R4 69 Firebird Convert 455 4 spd 70 Torino GT Convert Austin-Texas



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