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3/4" Bore or 7/8" Bore Master Cylinder For Disc Brakes?

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Randyz

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I'm confused. I've been around Spridgets for many years and I'm planning to build two Bugeyes with disc brakes. One will use a later pedal box with separate brake and clutch cylinders for a single circuit brake system as found on '67 cars. The other will use a combined brake/clutch cylinders. Years ago I bought a combined master cylinder for a '62 Mk II Sprite with drum brakes. I never finished that car, so I planned to get that cylinder sleeved to 3/4" for my new project. I have also bought two pairs of later Morris Minor 3/4" bore rear brake cylinders. Today I read on the BugeyeGuy website that he actually prefers the 7/8" bore master cylinders for disc brake cars. Any opinions would be appreciated. Thanks.
 
My first BE was set up that way. 7/8 master and disc brakes. You will get less pedal movement and require a harder push to stop. Guess if he likes ti that way its all up to him. I prefer the 3/4 master and changed rear brakes.

Kurt.
 
You can use a 7/8" master cylinder for disc brakes but the fluid geometry is wrong and you will have a 33% increased pedal effort as a result. With the rear 3/4 cylinders, your pedal will be even harder. In addition, you'll find that your clutch action will also be significantly improved by having the 3/4" master cylinder coupled with the original 7/8" slave. This is especially true of the spring clutches used in the 948 and 1098 engine. You don't mention which engine you will be using. These are facts, not opinions, and I dozens of testimonials confirming the improvement. In case you are not familiar, I have been providing these master cylinder conversions since 2006. You can contact me offlist if you are interested, but I assure you these are the best and most reliable available today. Some picture samples of the finished product below.

I'm not sure why you'd go to the trouble of changing pedal boxes for the separate single circuit setup as there's no advantage functionally. You will also need different pushrods for the 3/4" tandem unit.

IMAG0809.jpgWP_000786.jpgWP_002674.jpeg

Randyz said:
I'm confused. I've been around Spridgets for many years and I'm planning to build two Bugeyes with disc brakes. One will use a later pedal box with separate brake and clutch cylinders for a single circuit brake system as found on '67 cars. The other will use a combined brake/clutch cylinders. Years ago I bought a combined master cylinder for a '62 Mk II Sprite with drum brakes. I never finished that car, so I planned to get that cylinder sleeved to 3/4" for my new project. I have also bought two pairs of later Morris Minor 3/4" bore rear brake cylinders. Today I read on the BugeyeGuy website that he actually prefers the 7/8" bore master cylinders for disc brake cars. Any opinions would be appreciated. Thanks.
Click to expand...
 
3/4" is the way to go. Love mine (for both disks and clutch).
 
A little more info. Both cars will be 1275's with ribcase gearboxes. The only reason one car will have a later pedal box is because a previous owner already cut the hole in the foot well for that modification. I have a '62 Midget racer that was similarly modified to use the '67 single circuit system with disc brakes and later rear backing plates and I've been very happy with it. I figured I'd keep the early rear backing plates on these two cars and use the later Morris Minor 3/4" bore wheel cylinders. I've already bought the wheel cylinders. Now I need to send my master cylinder off to Gerard for a re-sleeve.
 
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