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Disc/Drum vs Drum/Drum master cylinder
#1346933 Tue Feb 18 2020 01:45 AM
Joined: Feb 2001
Posts: 1,343
T
Tommy Offline OP
Shop Shark
What would happen if a disc/drum cylinder was used in a drum/drum system?


Tommy
59 apache 1/2t
261 short stepside
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1346939 Tue Feb 18 2020 02:08 AM
Joined: Jan 2013
Posts: 1,807
Shop Shark
You would need a proportioning valve.

Like This

https://www.jegs.com/i/JEGS/555/631290/10002/-1

Chris

Last edited by ndkid275; Tue Feb 18 2020 02:11 AM.
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1346962 Tue Feb 18 2020 03:15 AM
Joined: Sep 2019
Posts: 58
O
Wrench Fetcher
Tommy,
My understanding is that if you would be sending heavy brake fluid pressure to the wheel cylinder, which a disk brake caliper could handle fine after a certain degree of brake pressure.
The proportioning valve is supposed the govern the pressure going to the wheel cylinders brake side. Without you could comprise the line and get a possible leak...

Steve


1948 1/2 Ton 6-volt 216
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1346965 Tue Feb 18 2020 04:03 AM
Joined: Feb 2004
Posts: 21,019
H
Boltergeist
The only real difference is the size of the reservoir chambers. A disc brake reservoir is larger because more fluid is needed to operate the large diameter pistons of the calipers. The portion of the MC that operates the calipers will also need a much lower pressure residual pressure valve, 1 or 2 PSI instead of the 10 PSI or so that the drum brake wheel cylinders need to keep the cylinder cups expanded and avoid air leaks.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1347027 Tue Feb 18 2020 03:59 PM
Joined: Jul 2000
Posts: 1,038
G
Shop Clutterist
What are you planning to do?

I have a Camaro rear end and Camaro disc brakes up front. So, I used a Camaro m/c. I'm pleased with the brakes because they work well because everything matches.


Gord
----
1954 1/2 ton 235 4 speed
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1347079 Tue Feb 18 2020 10:31 PM
Joined: Feb 2001
Posts: 1,343
T
Tommy Offline OP
Shop Shark
I'm updating the master cylinder on my truck, I have drum brakes. I some times think about putting disc brakes on the front and was thinking I would just put the disc/drum master on now . Howe ver I will due the drum/drum master.


Tommy
59 apache 1/2t
261 short stepside
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1347080 Tue Feb 18 2020 10:55 PM
Joined: Jan 2016
Posts: 567
S
Shop Shark
Not sure how you would handle the pressure differential between disc vs drum.
Generally, drum brakes require about 400 to 500 psi, discs 800 to 900 psi. So the disc side of the master cylinder runs at about twice the drum side. Some modern disc run 1500psi to the discs.

Proportioning valve manages the pressure front to back in disc/drum.

If disc/drum master was used in drum/drum .........front drums would lock up prematurely and be super sensitive.

Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1348278 Sat Feb 29 2020 02:18 AM
Joined: Feb 2018
Posts: 292
J
Shop Shark
I put disks up front on my 47 and a new dual reservoir master cylinder. Not power. I've got to push the pedal pretty hard and far down but it stops just fine. Opp said I didn't need a proportioning valve. Is there a way to check if I'm getting proper braking front and rear?

Sorry to jack your thread Tommy, seemed relevant tho.

Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1348319 Sat Feb 29 2020 03:13 PM
Joined: Jun 2011
Posts: 3,630
E
Shop Shark
Find a limited traction road-ice, mud, etc., have a buddy stand on the side and watch which wheel locks up first when brakes are applied hard.

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Re: Disc/Drum vs Drum/Drum master cylinder
Tommy #1348320 Sat Feb 29 2020 03:15 PM
Joined: Feb 2000
Posts: 4,177
J
Shop Shark
Just take your truck to a local empty parking lot and stand on the brakes from about 30 mph. You should have even braking if everything is right. Likely you are going to have rear wheel lock up due to the weight bias to the front. The " simple " solution is to add an adjustable proportioning valve back by the rear axle. Then do some more brake testing while adjusting the valve till you get hardly any lock up but still have adequate stopping power. https://www.speedwaymotors.com/Speedway-Purple-Adjustable-Brake-Proportioning-Valve,23498.html I use this same valve, it does what it suppose to do, limits the pressure to the rear brakes.

Last edited by Joe H; Sat Feb 29 2020 03:16 PM.
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