What is this on my Brake Booster??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

aboyer · 05-01-2006, 08:41 PM

Can someone tell me what is the item that is left side of the master cylinder?
(The left side facing in the picture)

I have a 68 Chevy with front disk brakes. There is a prop valve on the opposite side, but I am not sure what this is on the other side.

It doesn't seem orginal equipment, so if anyone can help me out, I would appreciate it.

Adam

1LoC10 · 05-01-2006, 08:51 PM

vacuum hose I think

**truckdude239** · 05-01-2006, 08:55 PM

think he talking about this in the yellow i have no clue other then maybe tailier brake

Longhorn Man · 05-01-2006, 08:55 PM

That was probably for the old school trailer brake control. Have you folowed the lines?

69face · 05-01-2006, 08:59 PM

it's a trailer brake or the solenoid for a second emergency brake which is usually used on tow trucks and heavy duty trucks.

wibilly · 05-01-2006, 10:29 PM

the line looks like it comes from the master cyl then right to the proportioning valve do you suppose it is some kind of external residual valve? the end of the bracket on the mc looks factory but the line appears to be rebent

Solver · 05-01-2006, 10:45 PM

My guess would be that because someone added the disk brakes (not available in 68) and they kept the original proportioning valve for drum brakes that this is an equalizing valve for the disks to be proportioned properly.

rauto13 · 05-01-2006, 10:52 PM

on my 70 Camaro, there was a setup like that from the factory, I was told it is to equalize the pressure for the front disk vs rear drums. On the Camaro, the "proportioning" valve is just really a distribution block. That is what I was told anyway.

stope4 · 05-01-2006, 11:27 PM

What you think is the proportioning valve must be a distribution block only. The item that is circled is known as a proportioing valve. I thought 67-72 trucks only used one piece combination proportioing/distribution blocks.

Livrat · 05-01-2006, 11:58 PM

The block with the all the brake lines going into it is the distribution block.. which is factory for the drum brakes.. the one you are asking about is a "porportioning valve" for a disc brake setup.. it looks like a factory GM on off of a 68 - 70 Chevelle,Camaro,Nova
One thing I noticed is your master cylinder is a drum brake unit and will not function correctly with disc brakes as it does not have an internal "residual pressure valve" that the disc brakes require.. it keeps a small amount of pressure on the calipers... you may find that you will always have to pump the brakes to get a good pedal..

That setup could/may be dangerous!!.. The porportioning valve may not be calibrated correctly for the larger truck rear wheel cylinders and brake size..(a porportioning valve limits the fluid pressure to the rear wheel cylinders) plus the master cylinder might not have the correct piston diameter to put the correct pressure to the disc brake calipers.. (disc brake calipers take different pressure to engage than the original drum brake wheel cylinders)

In my opinion I would get the correct 71 - 72 truck disc brake booster, master cylinder, combination distribution/porportioning valve and lines that way you KNOW it will work like it should..

70GMCer · 05-02-2006, 06:10 AM

I had the same thing on my 67 Chevelle w/disks

Bob Moore · 05-02-2006, 01:36 PM

I agree with LIVERAT and 70GMCer. The Camaro,Chevelle, and Corvette people would probably pay a good penny for that piece. I have not seen one in the junkyards for a loooonnnngggg time. Listen to LIVERAT and get the proper parts and sell that piece to partially offset the price of safety.

Good luck - Bob

aboyer · 05-02-2006, 10:57 PM

Thanks for the tips. I am planning on switching the rear drums to disk, in the coming months. Maybe someone could help me out with this, but I was planning on purchasing a new brake booster/master cylinder 71-72, then I would also need a new prop valve for the rear disk brakes.

I believe this is correct, but want to make sure. Let me know if this sounds good.

Adam

72armyswbtruck · 05-03-2006, 08:38 PM

WOW, you learn something new everyday...

05-01-2006, 08:41 PM	#1
aboyer Adam B Join Date: Jul 2005 Location: Westfield Posts: 151	What is this on my Brake Booster??? Can someone tell me what is the item that is left side of the master cylinder? (The left side facing in the picture) I have a 68 Chevy with front disk brakes. There is a prop valve on the opposite side, but I am not sure what this is on the other side. It doesn't seem orginal equipment, so if anyone can help me out, I would appreciate it. Adam Last edited by aboyer; 01-02-2008 at 01:42 PM.

05-01-2006, 08:51 PM	#2
1LoC10 Insert Title Here Join Date: Feb 2006 Location: Dyer, Indiana Posts: 5,679	Re: What is this on my Brake Booster??? vacuum hose I think __________________ BOBBY _69 SWB_ 1000 pics of 67-72's>> http://s193.photobucket.com/albums/z...-72/?start=all <<

05-01-2006, 08:55 PM	#3
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,238	Re: What is this on my Brake Booster??? think he talking about this in the yellow i have no clue other then maybe tailier brake Attached Images __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

05-01-2006, 08:55 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: What is this on my Brake Booster??? That was probably for the old school trailer brake control. Have you folowed the lines?

05-01-2006, 08:59 PM	#5
69face Registered User Join Date: Feb 2006 Location: northridge Posts: 534	Re: What is this on my Brake Booster??? it's a trailer brake or the solenoid for a second emergency brake which is usually used on tow trucks and heavy duty trucks. __________________ ""A bagged vehicle is only as good as it's wheel/tire combo!" -getlowness! my build thread http://67-72chevytrucks.com/vboard/s...=223747:metal: I'M SO SO CAL!

05-01-2006, 10:29 PM	#6
wibilly Senior Member Join Date: Nov 2005 Location: northwestern wi Posts: 2,111	Re: What is this on my Brake Booster??? the line looks like it comes from the master cyl then right to the proportioning valve do you suppose it is some kind of external residual valve? the end of the bracket on the mc looks factory but the line appears to be rebent __________________ common sense isn't so common anymore

05-01-2006, 10:45 PM	#7
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	Re: What is this on my Brake Booster??? My guess would be that because someone added the disk brakes (not available in 68) and they kept the original proportioning valve for drum brakes that this is an equalizing valve for the disks to be proportioned properly. __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

05-01-2006, 10:52 PM	#8
rauto13 saving one more Join Date: Sep 2005 Location: Pryor Creek, Oklahoma Posts: 3,066	Re: What is this on my Brake Booster??? on my 70 Camaro, there was a setup like that from the factory, I was told it is to equalize the pressure for the front disk vs rear drums. On the Camaro, the "proportioning" valve is just really a distribution block. That is what I was told anyway. __________________ 72 Chevy longbed - now for parts 69 Chevy short fleet - needing some love 70 RS Camaro - needing more love driver - 96 GMC X-cab

05-01-2006, 11:27 PM	#9
stope4 Registered User Join Date: Jan 2006 Location: Houston Posts: 434	Re: What is this on my Brake Booster??? What you think is the proportioning valve must be a distribution block only. The item that is circled is known as a proportioing valve. I thought 67-72 trucks only used one piece combination proportioing/distribution blocks.

05-01-2006, 11:58 PM	#10
Livrat Member #1049 Join Date: Jun 2000 Location: Troy Montana Posts: 3,940	Re: What is this on my Brake Booster??? The block with the all the brake lines going into it is the distribution block.. which is factory for the drum brakes.. the one you are asking about is a "porportioning valve" for a disc brake setup.. it looks like a factory GM on off of a 68 - 70 Chevelle,Camaro,Nova One thing I noticed is your master cylinder is a drum brake unit and will not function correctly with disc brakes as it does not have an internal "residual pressure valve" that the disc brakes require.. it keeps a small amount of pressure on the calipers... you may find that you will always have to pump the brakes to get a good pedal.. That setup could/may be dangerous!!.. The porportioning valve may not be calibrated correctly for the larger truck rear wheel cylinders and brake size..(a porportioning valve limits the fluid pressure to the rear wheel cylinders) plus the master cylinder might not have the correct piston diameter to put the correct pressure to the disc brake calipers.. (disc brake calipers take different pressure to engage than the original drum brake wheel cylinders) In my opinion I would get the correct 71 - 72 truck disc brake booster, master cylinder, combination distribution/porportioning valve and lines that way you KNOW it will work like it should.. Last edited by Livrat; 05-02-2006 at 12:02 AM.

05-02-2006, 06:10 AM	#11
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: What is this on my Brake Booster??? I had the same thing on my 67 Chevelle w/disks __________________ 1997 GMC Sierra Ext 1965 Mustang

05-02-2006, 01:36 PM	#12
Bob Moore Registered User Join Date: Feb 2004 Location: Tacoma WA Posts: 1,365	Re: What is this on my Brake Booster??? I agree with LIVERAT and 70GMCer. The Camaro,Chevelle, and Corvette people would probably pay a good penny for that piece. I have not seen one in the junkyards for a loooonnnngggg time. Listen to LIVERAT and get the proper parts and sell that piece to partially offset the price of safety. Good luck - Bob __________________ 67 C-20 LWB, tilt, speed alert, vac, 454, T400 67 C-10 SWB, factory air with more to follow

05-02-2006, 10:57 PM	#13
aboyer Adam B Join Date: Jul 2005 Location: Westfield Posts: 151	Re: What is this on my Brake Booster??? Thanks for the tips. I am planning on switching the rear drums to disk, in the coming months. Maybe someone could help me out with this, but I was planning on purchasing a new brake booster/master cylinder 71-72, then I would also need a new prop valve for the rear disk brakes. I believe this is correct, but want to make sure. Let me know if this sounds good. Adam

05-03-2006, 08:38 PM	#14
72armyswbtruck Registered User Join Date: Feb 2004 Location: Idaho Posts: 4,033	Re: What is this on my Brake Booster??? WOW, you learn something new everyday... __________________ "Remember, They can Kill You, but they can't eat You, That's against the law!!!!!!!!!"



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