Master Cylinder Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jakes-66-K10 · 09-14-2005, 03:57 PM

Will a 3/4 ton 1972 master cylinder work OK with drums?

I'm preparing to swap spindles to 72 disc brakes, but it may need to wait until next summer. I was looking at my current master cylinder and it's pretty sludgy inside, and smaller in size than the 72 cylinder. So I was curious if I can put on the new, bigger 72 cylinder in it's place, but add the disc brake prop. valve and other components later. Anyone ever tried this?

70GMCer · 09-14-2005, 05:46 PM

I put what I think is a 3/4T mc on my 70 and worked great. I'm also waiting to install the disks later. The mc I have is the double diaphragm from a 72 and was told it was from a 3/4 T. I used the existing drum Prop valve.

Longhorn Man · 09-14-2005, 07:22 PM

70GMCer... did you actually use the master cylinder off the 72 also, or just the booster. You make reference to both.
Personally, i would not do that, the disc master cylinder creates much more pressure on the front side of the system, also, the lines aren't the same.
Watch the 3/4 ton master cylinder on a 1/2 ton truck. The resivours are switched around.

70GMCer · 09-15-2005, 06:02 AM

No, relax.....I just used the booster...I should have said that........

Jakes-66-K10 · 09-15-2005, 04:13 PM

Yeah, just to help clarify - I did what sounds like 70GMCer did too. I already have a 72 booster assembly in place, it works great. It sounds like I can't just put the 72 master cylinder in place of the existing 70 cylinder because of brake lines? What if I use the 72 brake lines down to the junction box?

My undestanding about sending more pressure to the front wheels was from the proportioning valve? If I used this newer M.C. and keep the existing drum prop. valve, think that will work?

cableguy0 · 09-15-2005, 04:48 PM

the block on your drum setup is just a distribution block its doesnt affect pressure. you CANNOT use a disk master on a drum setup it will lock the brakes up constantly and make the truck unsafe. disk brakes work on much higher pressure and less volume.

jhwkns · 09-15-2005, 10:17 PM

M/C's are cheap.. Ten bucks or so for a reman.. To me it would be worth that just to not have to deal with the brake lines, and proportioning valve issues twice.

**VetteVet** · 09-15-2005, 11:34 PM

here's a great article on disc brakes.

http://www.hotrodheaven.com/tech/bra...kes1_index.htm

09-14-2005, 03:57 PM	#1
Jakes-66-K10 Registered User Join Date: Aug 2004 Location: Idaho Posts: 640	Master Cylinder Question Will a 3/4 ton 1972 master cylinder work OK with drums? I'm preparing to swap spindles to 72 disc brakes, but it may need to wait until next summer. I was looking at my current master cylinder and it's pretty sludgy inside, and smaller in size than the 72 cylinder. So I was curious if I can put on the new, bigger 72 cylinder in it's place, but add the disc brake prop. valve and other components later. Anyone ever tried this?

09-14-2005, 05:46 PM	#2
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	I put what I think is a 3/4T mc on my 70 and worked great. I'm also waiting to install the disks later. The mc I have is the double diaphragm from a 72 and was told it was from a 3/4 T. I used the existing drum Prop valve. __________________ 1997 GMC Sierra Ext 1965 Mustang

09-15-2005, 06:02 AM	#4
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	No, relax.....I just used the booster...I should have said that........ __________________ 1997 GMC Sierra Ext 1965 Mustang

09-15-2005, 04:48 PM	#6
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	the block on your drum setup is just a distribution block its doesnt affect pressure. you CANNOT use a disk master on a drum setup it will lock the brakes up constantly and make the truck unsafe. disk brakes work on much higher pressure and less volume. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

09-15-2005, 10:17 PM	#7
jhwkns Registered Cruiser Join Date: May 2002 Location: Las Vegas NV Posts: 2,230	M/C's are cheap.. Ten bucks or so for a reman.. To me it would be worth that just to not have to deal with the brake lines, and proportioning valve issues twice. __________________ I intend to live forever. So far, so good.

09-14-2005, 07:22 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	70GMCer... did you actually use the master cylinder off the 72 also, or just the booster. You make reference to both. Personally, i would not do that, the disc master cylinder creates much more pressure on the front side of the system, also, the lines aren't the same. Watch the 3/4 ton master cylinder on a 1/2 ton truck. The resivours are switched around.

09-15-2005, 04:13 PM	#5
Jakes-66-K10 Registered User Join Date: Aug 2004 Location: Idaho Posts: 640	Yeah, just to help clarify - I did what sounds like 70GMCer did too. I already have a 72 booster assembly in place, it works great. It sounds like I can't just put the 72 master cylinder in place of the existing 70 cylinder because of brake lines? What if I use the 72 brake lines down to the junction box? My undestanding about sending more pressure to the front wheels was from the proportioning valve? If I used this newer M.C. and keep the existing drum prop. valve, think that will work?

09-15-2005, 11:34 PM	#8
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,723	disc brake article here's a great article on disc brakes. http://www.hotrodheaven.com/tech/bra...kes1_index.htm __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

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