Brake Master Cyl. ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

70GMCer · 08-30-2005, 04:03 PM

Will a 1972 Pwr Disk master cylinder w/prop valve work on a drum brake system? I plan on changing the front brakes to disk in the future, but for right now, I have a 72 master cyl and need to get my brakes back working again. My old ms cyl went south and hate to buy a new one, when I plan on changing it in the fall. I am all ready using the power booster from the same disk set up, and was working great........

thanks..........

neonlarry · 08-30-2005, 04:08 PM

You may be able to get by with the master, but the brakes might be a little sensitive. The fronts will push more fluid than your nomal one. But you need to use your old drum\drum p-valve. It is different than the disc\drum one.

**hotrodmtodd** · 08-30-2005, 04:30 PM

Steve,
I agree with Larry on this one. Change the master, leave the p-valve swap until spring. People will tell you all kinds of stuff on this subject, how this or that has been working on their truck for 20 years, etc. I have a few of those testimonials MYSELF. But it is BEST to use the CORRECT stuff and not just the CHEAPEST fix. ESPECIALLY on a TRUCK, too much rear brakes is a BAD THING. If you ever do a REVERSE fishtail (during DE-celleration) you will know JUST what I mean. Don't forget to bench bleed the MC. Take care, Mike

PS If you are trying to avoid doing the lines TWICE, it will be TOUGH, unless you just go ahead and do the WHOLE swap now. (I'm assuming that's why you are asking)

**dennislbrooks** · 08-30-2005, 04:31 PM

Just leave out the proportioning valve and use the existing junction block until you get the disc on. ---Then test your braking before getting into hazardous traffic situations.

70GMCer · 08-30-2005, 05:26 PM

thanks to all the above advice......I'll try that with my drum brake prop valve. I did know about the bench bleeding......I don't drive this truck too much and just need to patch this, until I get all the hardware together for the swap......I tell ya, I get one thing completed, and something else goes kaput......but, that's the hobby, right?

again, thanks.....

08-30-2005, 04:03 PM	#1
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Brake Master Cyl. ? Will a 1972 Pwr Disk master cylinder w/prop valve work on a drum brake system? I plan on changing the front brakes to disk in the future, but for right now, I have a 72 master cyl and need to get my brakes back working again. My old ms cyl went south and hate to buy a new one, when I plan on changing it in the fall. I am all ready using the power booster from the same disk set up, and was working great........ thanks.......... __________________ 1997 GMC Sierra Ext 1965 Mustang

08-30-2005, 04:08 PM	#2
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	You may be able to get by with the master, but the brakes might be a little sensitive. The fronts will push more fluid than your nomal one. But you need to use your old drum\drum p-valve. It is different than the disc\drum one. __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

08-30-2005, 04:30 PM	#3
hotrodmtodd 'Burban Legend Join Date: Apr 2005 Location: Mingo Junction OH Posts: 913	Hats Off To Larry Steve, I agree with Larry on this one. Change the master, leave the p-valve swap until spring. People will tell you all kinds of stuff on this subject, how this or that has been working on their truck for 20 years, etc. I have a few of those testimonials MYSELF. But it is BEST to use the CORRECT stuff and not just the CHEAPEST fix. ESPECIALLY on a TRUCK, too much rear brakes is a BAD THING. If you ever do a REVERSE fishtail (during DE-celleration) you will know JUST what I mean. Don't forget to bench bleed the MC. Take care, Mike PS If you are trying to avoid doing the lines TWICE, it will be TOUGH, unless you just go ahead and do the WHOLE swap now. (I'm assuming that's why you are asking) __________________ '67 Chevy Iron City Beer Truck (9ft step) '67 Chevy Panel Truck 467 '68 Short Fleet 305v6 '68 McLaren Ramp Truck '68/'68/'70/'71 Burbs 292/366/402/454 '69 C-30 dump '71 C-50 dump and church bus '71 4x4 454 '72 Blazer (w/pop-up camper) $15 x-hooks '66 Chevy II 194/Weber '68 El Camino" 305v6 '69 Skylark 455 Buick '70 Chevelle 427 '71 Cutlass W-31 '71 GTO 400 2x2 "The 51" Chopped '51 Chevy (409) my first car OK Toad, we'll take 'em all... John Milner

08-30-2005, 05:26 PM	#5
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	thanks to all the above advice......I'll try that with my drum brake prop valve. I did know about the bench bleeding......I don't drive this truck too much and just need to patch this, until I get all the hardware together for the swap......I tell ya, I get one thing completed, and something else goes kaput......but, that's the hobby, right? again, thanks..... __________________ 1997 GMC Sierra Ext 1965 Mustang

08-30-2005, 04:31 PM	#4
dennislbrooks Senior Member Join Date: Feb 2004 Location: Williamsburg, Ohio Posts: 1,766	Just leave out the proportioning valve and use the existing junction block until you get the disc on. ---Then test your braking before getting into hazardous traffic situations.



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