What Master Cylinder for 4 wheel disk brakes?

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loganscuda

loganscuda

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I have willwood discs in the front and foreign discs in rear (Ferd discs on 8.8 rear end). I currently have power brakes and my master cylinder is leaking from the cover. I want to replace it. I have a proportioning valve from a disc/drum car 73 Duster. And an adjustable proportioning valve.
I am also thinking of going manual. The car in question is 67 Barracuda originally manual drum
 
I've done my share of brake conversions but I would never want to recommend something only to have it hurt someone. That said, speedway motors had some very helpful videos in the past. Wilwood if I recall had some good information too.

I may be wrong but in my opinion power brakes, due to the vacuum assist, are not as hard to size as a manual master cylinder simply because the vacuum compensates for the input force. On the Factory Five Racing Cobra I built, which had manual brakes, I think I tried 3 different piston diameter masters before I finally found one that had a comfortable braking performance for the amount of foot force. Nothing worse than standing on the brake pedal and the car feels like it won't stop. Good luck.
 
What you’re looking for is a master with no residual pressure valves that are in a master that has drum brakes. These can actually be removed from a drum brake master, and/or also removed from the rear circuit on a disc/drum master. You’ll likely have to run a proportioning valve on the rear circuit to regulate a good split between front and rear stopping power.
 
I am a streeter
I like my 15/16 M/C with a booster off an early F-body. This combo has a nice progressive feel to it, and locks up nice when I stand on it, lol.
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I run 235/60-14s on the front and 295/50-15s on the back
On the front are the KH 4-piston fixed calipers and
on the back are 10x2 drums with 7/8ths w/cs, so
this set-up requires NO additional proportioning.
I run 1.03 T-bars and a big swaybar on the front.
At the back are de-arched HD springs, with a second mainleaf installed. The car is lowered to 5.75" to the lowest part of the K-member.
This set-up has just the right amount of weight-transfer on hard braking, and those 295s out back, when working hard, are like dragging a puller-sled. This allows me to come into a corner, braking really hard, and still be able to steer around it. Whereas if the car still had the factory proportioning, she wouldda locked up, jumped the curb, and been in who-knows-what-kind of trouble. I have not, in 23 years, broke a period aluminum wheel.
Yes there are times (braking hard in turns) when I suspect the rear is a tad heavy, but, with the 295s back there, it is easy to modulate the pedal and avoid trouble.

If you have big and littles like I do, don't be afraid to make the back actually work, lol; just be sure to stop experimenting before the back locks up first!

BTW
I sure wouldn't throw away the Master for a leaking cover. Especially if you are running Dot-5/silicone, which will find every stinking place it can, to leak from. If the leaky lid is all that is wrong with it, I would just fix it.
 
AJ/FormS said:
I am a streeter
I like my 15/16 M/C with a booster off an early F-body. This combo has a nice progressive feel to it, and locks up nice when I stand on it, lol.
-----------------------
I run 235/60-14s on the front and 295/50-15s on the back
On the front are the KH 4-piston fixed calipers and
on the back are 10x2 drums with 7/8ths w/cs, so
this set-up requires NO additional proportioning.
I run 1.03 T-bars and a big swaybar on the front.
At the back are de-arched HD springs, with a second mainleaf installed. The car is lowered to 5.75" to the lowest part of the K-member.
This set-up has just the right amount of weight-transfer on hard braking, and those 295s out back, when working hard, are like dragging a puller-sled. This allows me to come into a corner, braking really hard, and still be able to steer around it. Whereas if the car still had the factory proportioning, she wouldda locked up, jumped the curb, and been in who-knows-what-kind of trouble. I have not, in 23 years, broke a period aluminum wheel.
Yes there are times (braking hard in turns) when I suspect the rear is a tad heavy, but, with the 295s back there, it is easy to modulate the pedal and avoid trouble.

If you have big and littles like I do, don't be afraid to make the back actually work, lol; just be sure to stop experimenting before the back locks up first!

BTW
I sure wouldn't throw away the Master for a leaking cover. Especially if you are running Dot-5/silicone, which will find every stinking place it can, to leak from. If the leaky lid is all that is wrong with it, I would just fix it.
Click to expand...
I have replaced the lid on it before. I’m running Dot-4.
 
What diameter master cylinder bore do you have, and do you like the feel? ? Are the wilwood calipers the 11 inch disc / 4-piston ones?
 
This is what I just installed. 1 1/8 bore. 11” willwood in the front and ford explorer in the back. What a big difference in stopping it made. Much better feel and response. McKellar's Modified Rides
Call this guy up he help me tremendously when I was at the MATSLV. You will have to get the adapter to go from 4 bolt to 2 bolt.
This picture is not correct but close. It was $70.00 I think for it.
 
Last edited:
He’s in Bakers Field CA. Has a lot of Abody parts not just brakes. But he specializes in brakes for Abody
 
loganscuda said:
This is what I just installed. 1 1/8 bore. 11” willwood in the front and ford explorer in the back. What a big difference in stopping it made. Much better feel and response. McKellar's Modified Rides
Call this guy up he help me tremendously when I was at the MATSLV. You will have to get the adapter to go from 4 bolt to 2 bolt.
This picture is not correct but close. It was $70.00 I think for it.
Click to expand...

Thru years of testing, comparing, and replacing, - unless you have a power booster, that M/C would be terrible compared to 15/16 or smaller, in effort, feel, and modulation for a spirited driver.
jmexperience
Good luck
 
loganscuda said:
I have a power booster. Works a hell of a lot better that the one I took off.
Click to expand...

The original post was asking about manual, - there's a world of difference, so I wanted to be clear about which sizes of master cylinders you were comparing, and if in fact you were not using power as asked.
You might try a 15/16 from drdiff, see what difference you find in performance feel, - you may toss the power, as many do.
Good luck.
 
I went with Dr Diif rear brake kit. 15/16 MC. Works perfectly

20191201_152412.jpg
 
You'll need a different MC depending on power or manual so make that decision first. If you go manual brakes you'll want something in the 15/16 range. If you stay with a booster then you'll want something bigger, probably over an inch in bore size.

Brakes are a hydraulic system so you need to know the size of the caliper pistons before you pick the size of the MC pistons. The piston sizes need to be matched to work together. Big pistons in the calipers require big pistons in the MC to move the fluid. Small pistons in the calipers need small pistons in the MC. You can't pick one without knowing the other. Well okay you can, but you'll be picking blind so you'll probably make a mistake. Kind of like picking a cam without knowing anything else about the engine.
 
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