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#1 |
Senior Member
![]() Join Date: Dec 2003
Location: Pampa, Texas
Posts: 1,554
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Manual Disc/Drum Master Cylinder??
I'm converting my 68 to disc up front, but keeping the drums in the rear. i currently have manual drums all around... Do i need to swap my master cylinder out?? If so, just a 71/72 master work?? do i need to get a proportion valve or is it built into the master??? I'm not carving corners or running autocross here... I just wanna stop.
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#2 |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Manual Disc/Drum Master Cylinder??
Is it manual or power brakes?
Yes a 1972 master and combo valve will work. Just bolt in and go.
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#3 |
Senior Member
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Location: Pampa, Texas
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Re: Manual Disc/Drum Master Cylinder??
Staying with Manual brakes for now.
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#4 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
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Re: Manual Disc/Drum Master Cylinder??
The use of a Proportion Valve has nothing to do with power or manual brakes.
With a drum/drum system, you are delivering the same pressure to the rear wheel cylinders as is delivered to the front wheel cylinders. If you are pushing on the pedal hard enough to deliver 400 psi to the front wheel cylinders, you are also delivering 400 psi to the rear cylinders. 1200 psi to the front, 1200psi to the rear. ![]() If you replace the front drums with discs and don't add a proportion valve to the rear circuit, you will be providing too much pressure to the rear, at higher pressures. At 400 psi front and rear, the brakes will work fine. At higher pressures, the rear drum brakes will lock-up at much lower pressures than the front disc calipers will lock. A proportion valve reduces the rear pressure at a proportional rate, but only above a threshold pressure point. In the example below, the Valve allows the same pressure, front and rear below 600psi. At higher pressures, say 1200 psi, the valve reduces the rear pressure to 750psi. It works the same with manual or with power booster. A proportion valve would still be required and work the same with a dual master cylinder or with an older Single master cylinder. ![]()
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#5 |
Registered User
Join Date: Apr 2015
Location: Silver City, NM
Posts: 60
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Re: Manual Disc/Drum Master Cylinder??
I’m looking to do a disc upgrade as well. Planning on keeping manual brakes as well. Are the master cylinders off power and manual drum brakes the same as long as I get a disc/drum master and proportioning valve?
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#6 | |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,963
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Re: Manual Disc/Drum Master Cylinder??
Quote:
Here is a thread about a 66 dual res conversion (not a disk brake conversion, it's all drum, so there's no need for a distrib block/prop valve, or for any 3/16" lines). Might provide some helpful pics. http://67-72chevytrucks.com/vboard/s...d.php?t=487384 Also keep in mind the decisions you'll need to make before pitching in - i.e. 5 vs 6 lug, etc. If you think you'll ever want to go with power brakes, save money in the long run and do it all now. CaptainFab sells a great pb booster bracket that is snug to the firewall and uses stock gm boosters. Just a thought. If you want to stay 6 lug, you'll likely need aftermarket rotors. Also keep in mind that stock 64 6 lug steelies will not normally clear the caliper in front - 71 or newer K5/K10 wheels are what you really need to stay with stock steelies. ID them by having 4 cap nubs rather than 3. If you want to switch to 5 lug, there are kits available, and it can provide more wheel style choices. But keep in mind you then will also probably want to swap to 5 lug rear axles so you only need 1 spare tire...Kits are available for that also and aren't that expensive. Last edited by jocko; 11-21-2018 at 08:11 PM. |
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#7 |
Senior Member
![]() Join Date: Aug 2016
Location: Loris South Carolina
Posts: 428
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Re: Manual Disc/Drum Master Cylinder??
Sorry to revive this thread but I am having trouble finding a 71/72 manual mc for my truck, I'm swapping the body onto a 1972 frame that came with discs up front and have upgraded the braking system so it has wilwood dual piston calipers up front (yes I know that these are overkill for my truck but I got a good deal on them) and 14 bolt drums in the rear, I have everything fitting nice enough to roll the frame around the shop and I'm about to start swapping the body over but I need to upgrade from the drum mc that came on the 69. I would like to stay with manual brakes but like I said I'm having trouble finding the manual mc for my truck. It's a c20 frame. Does anyone know where I can find one?
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#8 | |
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Join Date: Sep 2011
Location: Ark City, Kansas
Posts: 3,332
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Re: Manual Disc/Drum Master Cylinder??
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#9 | |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,963
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Re: Manual Disc/Drum Master Cylinder??
Quote:
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#10 |
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Location: Albuquerque NM
Posts: 7,848
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Re: Manual Disc/Drum Master Cylinder??
were manual disc brakes even an option in 71-72?
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#11 |
Registered User
Join Date: Apr 2015
Location: Silver City, NM
Posts: 60
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Re: Manual Disc/Drum Master Cylinder??
Hey sorry forgot to mention mine is a 64.
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#12 |
Registered User
Join Date: Sep 2011
Location: Ark City, Kansas
Posts: 3,332
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Re: Manual Disc/Drum Master Cylinder??
Manual discs were an option in 71 and 72.
Get a 71 or 72 manual brake master cylinder, and the 71 or 72 proportioning valve to go with it. Do NOT use a drum brake m/cyl. I have both a 67 and 68 C10, plan to go with manual disc on both. Only thing I am not sure on is rod from brake pedal to m/cyl. I did not get those when I got my salvage parts.... |
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#13 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,963
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Re: Manual Disc/Drum Master Cylinder??
70 402, what 68Gold/White said is good advice. You indeed want a 71-72 "manual brake" mc. Best way to identify is that the hole in the piston that your brake rod lever fists into is deep - just like the one you'll be removing. A "power" 71-72 mc would have a shallow indent in the mc's piston. I'd use a standard distribution block/combo valve from a 71/72. It will provide the same level of notification and circuit isolation your 68's current mc does. On the other hand, if you want to be able to "tune" the front-to-rear bias once it's all installed, an aftermarket proportioning valve would be an option also.
Btw, is your 68 a C10 or C20? Make sure you specify when ordering, the mc's are different. Last edited by jocko; 11-21-2018 at 08:02 PM. |
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#14 |
Senior Member
![]() Join Date: Aug 2016
Location: Loris South Carolina
Posts: 428
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Re: Manual Disc/Drum Master Cylinder??
I would have to look at the brake line kit I got to know which size it is, I know it is for a 72 c20 but I'm not sure if it's all the same size line or not as it's been awhile since I looked at the lines since putting them on. I would like to add a proportioning valve and don't mind if it doesn't look correct. And the reason I'm hesitant is because I am planning on keeping the 250 in my truck for the time being and upgrading to something with more power later on down the road, but I don't know if the 250 would have sufficient enough vacuum to run a power brake booster, and I don't want to run any kind of hydroboost system
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#15 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,388
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Re: Manual Disc/Drum Master Cylinder??
Unless you've done something crazy with a cam or carburetion, the 250 will pull enough vacuum for power brakes. One thing to consider though, is if the engine quits, you have no power steering and the booster will take about 3 pumps until you have no assist. the fuel pump quit on my Astrovan many years ago, and my wife barely managed to steer it off the freeway and get it stopped. If she'd been in bad traffic, it could have been ugly.
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#16 |
Senior Member
![]() Join Date: Aug 2016
Location: Loris South Carolina
Posts: 428
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Re: Manual Disc/Drum Master Cylinder??
Ive had that problem with brakes and steering before which is why I don't want a hydroboost system, and I am going to put a Chinese Weber 32/36 dgv 2 barrel on it, and I'm going to port and polish the head. Other than that I'm leaving the motor alone. I'd be willing to try power brakes if y'all think I would have enough vacuum pressure to power it but I would like to stay with manual brakes for the simplicity of it if I can
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#17 |
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Location: Simi Valley, CA
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Re: Manual Disc/Drum Master Cylinder??
The only difference between the power and manual brakes is the (not much) higher pedal effort. It's not as high an effort as if you have power brakes and the engine quits. You should be fine either way you go. I don't think that the carb you are putting on is going to be a problem. It looks like it is progressive linkage, so won't be too much carburetor. How many CFM is it, BTW?
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#18 |
Senior Member
![]() Join Date: Aug 2016
Location: Loris South Carolina
Posts: 428
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Re: Manual Disc/Drum Master Cylinder??
I think it's somewhere around 350-400 cfm. I'd have to double check on that though.
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#19 | |
Who Changed This?
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Location: Simi Valley, CA
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Re: Manual Disc/Drum Master Cylinder??
Quote:
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#20 |
Senior Member
![]() Join Date: Aug 2016
Location: Loris South Carolina
Posts: 428
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Re: Manual Disc/Drum Master Cylinder??
Awesome, also I checked the brake lines on the frame and I do have the 3/16" lines up front and 1/4" for the rear so I should just need the prop valve, the brake booster/master cylinder, the rear brake shoes, and the emergency brake cables to finish everything off. Thanks for all the help
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