Drum master cylinder - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Wootdog · 07-29-2003, 06:00 PM

Is it possible to use a power drum master cylinder off a 70 Chevy custom 10 which had eight lug wheels with a disc/disc setup? I would probably at least need a different proportion valve right? I ask because both the resevoirs are the same size. Wootdog

smokekiki · 07-30-2003, 07:52 AM

Not sure about the master.But I would use an adjustable prop valve.

tom hand · 07-30-2003, 08:03 AM

You could use it and it will work but drum master cylinders have a check valve to keep a certain amount of pressure on the brakes to overcome the springs in a drum setup. If you use it with disc it will cause them to slightly drag causeing uneeded wear and lots of brake dust.

Wootdog · 07-30-2003, 08:19 AM

So I guess it wouldn't be such a good deal at the salvage yard afterall. Thank you Kerry

Wootdog · 07-30-2003, 08:22 AM

I could use the bracket and bolts though right. They should be the same for drum and for disc, right? Kerry

smokekiki · 07-30-2003, 01:47 PM

I didn't want to lead you wrong about the master cyl.I saw an article a while back in super chevy where they put discs on in place of drums.They changed some parts in the master cyl.Must have been the check valve that Tom Hand was talking about.

Frank_Zeller · 07-30-2003, 01:59 PM

There is a residual pressure valve at the outlet of the master to the brake lines. Drum master. With the lines off the master you look inside the line holes into the master cylinder. There will be an orange rubber disc. All you have to do is pull the disc and spring out. Pull the front and rear brake ones out and just leave your drum brake distribution block. Removing the pressure valve to the rear brakes keeps them from locking up.

Wootdog · 07-30-2003, 02:13 PM

So I could use this with a dual disc setup afterall? If so, I will call them and ask what they want for it. Thanks Guys. Kerry

Frank_Zeller · 07-30-2003, 02:21 PM

I'm running the stock 1969 drum master with the residual pressure valves removed and drum distribution block and lines with 71 front disc.

tom hand · 07-30-2003, 02:35 PM

Frank_Zeller is correct but made it sound a lot easier than it is. After you remove the lines you have to remove the flair fittings under them without damage...remove the check valves...and replace the fittings. The fittings are brass and recessed, hard to remove but easy to damage....if you had the MC I would say go for it, but I don't think I would go buy a used MC that you may or may not can modifiy to use. I would go get a new MC from the parts store for an early 70's Corvette that was made for disc/disc from the get go and make that work...that way when you need a new MC you just go to the store and get one as opposed to having to modify a new one...providied you can remember what you bought it for...lol

Wootdog · 07-30-2003, 02:49 PM

My problem is the truck don't have the master cylinder, the power brake booster nor the mounting bracket for mounting to the fire wall. When the truck was torn down for the frame off (my brother had it then) everything was misplaced or stolen. (According to my brother). So guys I am between a rock and a hard place. I guess I could get a new one with all the stuff from one of the vendors. Kerry

Longhorn Man · 07-30-2003, 04:14 PM

Another unmentioned problem, is the fact that discs use more fluid than drums.
Drum brakes use mechanical adjusters, while discs use fluid to maintain the adjusment.
If you use the drum master, and it works, make sure you keep an eye on the brake fluid level, once it is sucked dry, it could really put a damper on your day.

Frank_Zeller · 07-30-2003, 04:46 PM

An appropriately sized sheet metal screw will work for pulling out the brass flairs . Tom you right, it requires time and much patients to get them out. I practiced on an spare master cylinder first.

07-29-2003, 06:00 PM	#1
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,676	Drum master cylinder Is it possible to use a power drum master cylinder off a 70 Chevy custom 10 which had eight lug wheels with a disc/disc setup? I would probably at least need a different proportion valve right? I ask because both the resevoirs are the same size. Wootdog __________________ 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

07-30-2003, 07:52 AM	#2
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,474	Not sure about the master.But I would use an adjustable prop valve. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

07-30-2003, 08:03 AM	#3
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	You could use it and it will work but drum master cylinders have a check valve to keep a certain amount of pressure on the brakes to overcome the springs in a drum setup. If you use it with disc it will cause them to slightly drag causeing uneeded wear and lots of brake dust. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

07-30-2003, 08:19 AM	#4
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,676	Thanks So I guess it wouldn't be such a good deal at the salvage yard afterall. Thank you Kerry __________________ 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

07-30-2003, 08:22 AM	#5
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,676	bracket and bolts I could use the bracket and bolts though right. They should be the same for drum and for disc, right? Kerry __________________ 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

07-30-2003, 01:47 PM	#6
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,474	I didn't want to lead you wrong about the master cyl.I saw an article a while back in super chevy where they put discs on in place of drums.They changed some parts in the master cyl.Must have been the check valve that Tom Hand was talking about. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

07-30-2003, 01:59 PM	#7
Frank_Zeller Registered User Join Date: Jun 2001 Location: Austin, Texas Posts: 796	There is a residual pressure valve at the outlet of the master to the brake lines. Drum master. With the lines off the master you look inside the line holes into the master cylinder. There will be an orange rubber disc. All you have to do is pull the disc and spring out. Pull the front and rear brake ones out and just leave your drum brake distribution block. Removing the pressure valve to the rear brakes keeps them from locking up. __________________ 69 SWB C/10 5-6 drop 700R4 69 Firebird Convert 455 4 spd 70 Torino GT Convert Austin-Texas

07-30-2003, 02:13 PM	#8
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,676	Use it? So I could use this with a dual disc setup afterall? If so, I will call them and ask what they want for it. Thanks Guys. Kerry __________________ 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

07-30-2003, 02:21 PM	#9
Frank_Zeller Registered User Join Date: Jun 2001 Location: Austin, Texas Posts: 796	I'm running the stock 1969 drum master with the residual pressure valves removed and drum distribution block and lines with 71 front disc. __________________ 69 SWB C/10 5-6 drop 700R4 69 Firebird Convert 455 4 spd 70 Torino GT Convert Austin-Texas

07-30-2003, 02:35 PM	#10
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Frank_Zeller is correct but made it sound a lot easier than it is. After you remove the lines you have to remove the flair fittings under them without damage...remove the check valves...and replace the fittings. The fittings are brass and recessed, hard to remove but easy to damage....if you had the MC I would say go for it, but I don't think I would go buy a used MC that you may or may not can modifiy to use. I would go get a new MC from the parts store for an early 70's Corvette that was made for disc/disc from the get go and make that work...that way when you need a new MC you just go to the store and get one as opposed to having to modify a new one...providied you can remember what you bought it for...lol __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

07-30-2003, 02:49 PM	#11
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,676	RE vette master My problem is the truck don't have the master cylinder, the power brake booster nor the mounting bracket for mounting to the fire wall. When the truck was torn down for the frame off (my brother had it then) everything was misplaced or stolen. (According to my brother). So guys I am between a rock and a hard place. I guess I could get a new one with all the stuff from one of the vendors. Kerry __________________ 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

07-30-2003, 04:14 PM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Another unmentioned problem, is the fact that discs use more fluid than drums. Drum brakes use mechanical adjusters, while discs use fluid to maintain the adjusment. If you use the drum master, and it works, make sure you keep an eye on the brake fluid level, once it is sucked dry, it could really put a damper on your day.

07-30-2003, 04:46 PM	#13
Frank_Zeller Registered User Join Date: Jun 2001 Location: Austin, Texas Posts: 796	An appropriately sized sheet metal screw will work for pulling out the brass flairs . Tom you right, it requires time and much patients to get them out. I practiced on an spare master cylinder first. __________________ 69 SWB C/10 5-6 drop 700R4 69 Firebird Convert 455 4 spd 70 Torino GT Convert Austin-Texas



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