MBM 4 wheel disc brake conversion master cylinder question

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Confusedcuda

Confusedcuda

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Installed the MBM 4 wheel disc brake conversion set on my 1968 plymouth barracuda, from classic industries. What master cylinder do I need to use? My friend says just get one for 10'' Abody disc in front and drum rears should work. Some I look at say "not for 4 wheel disc" Anybody done this conversion on their Abody before? Thanks
 
You actually want a 4 wheel DRUM Mc. But 37 other people will chime in and tell you otherwise. So good luck on your quest. :(
 
I was going to say that, it's the drum rear, disc front that changes things. Stay with your MC.
 
The difference "generally" between drum and disc masters is:

Older drum cylinders had same size front/ rear reservoirs, this is not a big deal
Newer drum cylinders had off size reservoirs "I guess" because they were case in "disc" era
Disc cylinders do NOT have residual pressure valves for the disc section. Generally all drum masters have residual valves

Size: Larger piston gives you more difficult braking effort, but less pedal movement
Smaller of course, opposite
 
Last question, I don't want to hyjack. Can a drum Master (68 Dart) be used with stock keysey hayes disc set up ?
 
Kendog 170 said:
Last question, I don't want to hyjack. Can a drum Master (68 Dart) be used with stock keysey hayes disc set up ?
Click to expand...
disc brakes usually require more fluid than drum brakes, so while it's possible, you'll probably "run out of pedal" and have to deal with "brake fade" ~ it may work ok at first but if you are "leaning" on them (stop and go traffic) you're taking a chance. There's a lot of really good brake science out there these days ~ going forward fast is only the first half of the equation.
 
Kendog 170 said:
Last question, I don't want to hyjack. Can a drum Master (68 Dart) be used with stock keysey hayes disc set up ?
Click to expand...
I used my stock 67 drum master on the 73/74 single piston brakes. I did poke a nail through the residual valves to rupture the valve. I have 4X wheel disc, they are as mentioned, front, and factory Lincoln Versailles rear (Ford 9")
 
So your doing rear brakes like this?

20200712_180635.jpg


20200712_180339.jpg
 
67Dart273 said:
I used my stock 67 drum master on the 73/74 single piston brakes. I did poke a nail through the residual valves to rupture the valve. I have 4X wheel disc, they are as mentioned, front, and factory Lincoln Versailles rear (Ford 9")
Click to expand...
Where are the residual valves? I just changed my brakes from drum/drum to all disc also, and heard a late 90's caravan master would work good? Should I just keep the drum/drum mc and remove residual valves, or change master cylinders? And to what mc?
 
Chuck Schoolcraft said:
Where are the residual valves? I just changed my brakes from drum/drum to all disc also, and heard a late 90's caravan master would work good? Should I just keep the drum/drum mc and remove residual valves, or change master cylinders? And to what mc?
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I have 4 wheel discs on my 68 fastback , keep the stock splitter/residual valve , I run a 15/16'' 1987 diplomat master cyl. , stops well , but I cant lock them up . If I ever get the urge , I might go to a 7/8'' master cyl. .
72blunblu has a lot of experience in these matters ----- could also call doctor diff too .
 
Chuck Schoolcraft said:
Great, thank you. Do you need any adapter or anything to mount it? And is the rod from the pedal the same? Mine are manual also, if that matters?
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I had to use an offset block anyway , (raised port heads are big), its a 4 to two conversion, 1/2'' thick, modified the rod to the same 1/2'' to allow for the block.
 
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