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Old 07-26-2020, 11:32 AM   #1
jerry shook
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Default Disk brakes

Can I use my original master cylinder after putting disk brakes on front it is a 40 ford.
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Old 07-26-2020, 11:47 AM   #2
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Default Re: Disk brakes

yes
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Old 07-26-2020, 12:17 PM   #3
Bob C
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Default Re: Disk brakes

I say no as the drum brakes require more residual pressure than the disk brakes.
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Old 07-26-2020, 12:44 PM   #4
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Default Re: Disk brakes

Before you do anything else read all the info. here:
https://www.google.com/search?q=disc...hrome&ie=UTF-8
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Old 07-26-2020, 01:31 PM   #5
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Default Re: Disk brakes

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I say no as the drum brakes require more residual pressure than the disk brakes.
You need to put in 2psi residual valve for front and 10psi for rear.

https://41fordwoodie.weebly.com/earlyv8discs.html
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Old 07-26-2020, 01:36 PM   #6
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Default Re: Disk brakes

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Can I use my original master cylinder after putting disk brakes on front it is a 40 ford.
Yes, you CAN use the original M/C, but that doesn't necessarily mean that the marriage will be a happy one. If you have decided to retain the original SINGLE-piston M/C, two major considerations come to mind.....'pressure', and 'volume' displacement.

The NECESSARY hydraulic pressure required to expand brake shoes against a rotating drum surface....AND EFFECTIVELY STOP THE VEHICLE....is derived as a result of several factors. Brake pedal ratio, comfortable levels of foot force required of the average human, master cylinder AND wheel cylinder diameters, as well as total available stroke of the M/C are some of the major considerations for determining whether or not a particular M/C is compatible with any given 'system'. Generally, the SMALLER the diameter of the bore in a M/C, the easier it will be to push the pedal and still produce the same amount of pressure at the brake cylinder(s). BUT....the M/C (and the brake pedal) must "stroke" a greater distance to displace an equal volume of fluid. Choosing a M/C with the 'wrong' diameter CAN POSSIBLY make it impossible for the average human to apply enough pressure to the foot pedal to reasonably stop the vehicle, OR....by ending-up with a M/C bore that is too small in diameter, the pedal will have to travel so far to move the same VOLUME of fluid (to move the brake shoes) that the pedal hits the floor before enough fluid can be displaced.

When it comes to DISC brakes, the disk brake PADS at each caliper USUALLY 'drag' on the rotor WITHOUT brake pressure applied. In other words, when brake pedal pressure is applied, the pad (and caliper PISTON) effectively does not move any notable distance. Rather, the pressure exerted on the pads to squeeze against the rotating disc is increased, similar in effect to first placing your thumb and index fingers together, and then squeezing them together harder with more applied pressure. Nothing really moves, but the difference in 'squeeze' is readily evident. The trouble with disc brake calipers is that they generally require much greater pressure (for comparable effect) than a 'replaced' drum and shoe brake had required. That is why you normally see dual-piston M/Cs with differently-sized bores for use on disc/drum brake systems. And for vehicles with disc brakes and the higher pressure required, MOST will have a "power brake" booster of some sort to help the driver apply the requisite amount of force needed by the disc brake calipers.

So, brake cylinder sizing is definitely NOT a 'hit or miss' deal. I believe I would do some research and attempt to come-up with a dual-piston M/C with bore diameters that match the stock early Ford for the rears, and with a bore for the DISC part of the cylinder that is maybe 1/16" SMALLER in diameter than the bore in the M/C on the disc's donor vehicle, which should help in view of the fact that you aren't going to use a booster.

One more thing to be aware of though, is that you must ascertain that the replacement M/C chosen is capable of "FULL-STROKE" via the brake pedal BEFORE the pedal reaches the floor.

Not meaning to scare you here with all of this rhetoric, but an arbitrary "Yes" is probably not a reasonable answer! But what do I know? DD
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Old 07-26-2020, 02:25 PM   #7
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Default Re: Disk brakes

I agree with COOP entirely......I have disc fronts, Ford drum rears on my "40 coupe. It would be foolish to not change the MC for one that is designed to this purpose. I used a BOSS 429 MC (15/16 bore), but if I were doing it again I would use a Corvette MC. The Mustang MC works very well, but the cover needed to be modified to fit under the floorboard.....the GM one does not.
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Old 07-26-2020, 03:15 PM   #8
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Default Re: Disk brakes

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I agree with COOP entirely......I have disc fronts, Ford drum rears on my "40 coupe. It would be foolish to not change the MC for one that is designed to this purpose. I used a BOSS 429 MC (15/16 bore), but if I were doing it again I would use a Corvette MC. The Mustang MC works very well, but the cover needed to be modified to fit under the floorboard.....the GM one does not.

hotrodart ...Thank you for your vote of confidence in my little shpiel. One thing for first-timers to be aware of with the Corvette M/Cs....there are TWO different M/Cs used on these cars, as ALMOST all '65s and ALL '66-'82 Corvettes had 4-wheel disc brakes, and MOST had vacuum brake boosters. There were some late '60s and early '70s Vettes that were ordered with NON-power brakes, and those so equipped used a M/C with differently-sized bores than the ones with power brakes. One Vette that I owned and restored was a '69 with NON-power brakes. Even with the correct M/C installed, you still had to climb on that pedal pretty good to stop that thing.....one of The General's "un-better" ideas. Just some handy info to throw out there. DD
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