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Old 07-01-2022, 08:28 PM
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Default Manual disc. brakes on an "A" body?

Which master and proportioning valve would I use? My 70 Skylark is manual drum right now and I want to convert to manual disc. The engine has a wild cam that makes lousy vacuum.

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Old 07-01-2022, 09:00 PM
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no knowledge to add but would love to hear you report back on how this works out in terms of pedal effort and stopping power. pretty sure i have low t since i run a sissy hyd roller but i stare at the solid rollers on the butler site thinking one day maybe i can get my levels straightened out and be a real man again.

anyway, off to drink some chamomile tea. toodles!

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Old 07-01-2022, 09:36 PM
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I used this on my 71:

https://www.rockauto.com/en/moreinfo...t=1836&jsn=484

Note the rear reservoir supplies the front circuit.

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Old 07-01-2022, 09:38 PM
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my original 70 W-30 car was factory manual disc
and
so is my 68 GTO 4 piston no power ... both manual transmission cars

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Old 07-01-2022, 09:50 PM
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Typical manual brake systems will use anywhere from a 7/8” to 1” bore master with disc brakes. It does really depend on what calipers you are running though.

Most GM manual brake pedals will have somewhere around a 7:1 pedal ratio. You can use this information along with your caliper piston area to determine how much pressure you’ll mathematically have at the brake pad.

The brake pad is the part of that equation that is often overlooked. While clamping force is necessary, most manual disc brake systems will need a fairly aggressive pad compound as well. You need the extra bite from the pad to make up for what you’re missing from a vacuum booster.

I would start here. http://www.wallaceracing.com/brake-master-cyl-calc1.php

You can determine your actual pedal ratio and if you know what calipers you are going to run, you can calculate your master cylinder bore size requirements.

Rules of thumb are that smaller bore masters require less pedal effort at the expense of longer travel, while larger more master cylinders require more pedal effort but will require less pedal travel.

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Old 07-01-2022, 09:59 PM
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Some time back my daily driver ‘64 Tempest (455/TH400/2.56 gears) had 12” disc brakes on 1978 B-body spindles and the stock 9-1/2” rear drum brakes.

The master was a 1975 F-body 1-1/16” bore using the prop valve and mounting bracket from a similar year 2nd gen F-body.

Pedal pressure required wasn’t anything crazy nor excessive, it was easy to modulate the brakes and they would stop you quickly if you needed them to.

My new manual brake setup for the Tempest uses a 15/16” bore GM (Malibu ?) master coupled with 2008 Corvette Z06 6 piston and 4 piston calipers and the corresponding 14” and 13.4” rotors. Also using a Wilwood adjustable prop valve and a gutted distribution valve. I had the option of using either the 7/8” Wilwood aluminum master or the 15/16” GM unit according to Tobin at KORE3 who sold me the brake setup. Haven’t finished my project yet (retiring soon so no more excuses ) but I’m sure I’ll be fine again with the manual disc brakes.

My ‘64 GTO bracket race car had basically the same master and prop valve the Tempest had at first, along with ‘69 GP spindles and 11” discs combined with 11” rear drums on the Ford 9” rear end. Stopped just fine and again the pedal pressure required wasn’t off the charts.

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Old 07-01-2022, 10:50 PM
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I've used 15/16" and 1 1/16". I like the feel of the larger bore better, but I think 1" probably would be "just right". The 15/16" has really easy pedal effort, but a kind of spongy feel. The 1 1/16" requires more effort but has a better feel. More positive feedback maybe...? I've had a few emergency stops, with no issues. However, someone who's never driven a car the size and weight of an a body with manual brakes might have a "code brown" moment. Today's power assist brakes that most people are used to would probably cause this to be culture shock so to speak.

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Old 07-02-2022, 02:23 AM
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Stock calipers and rotors.

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Old 07-02-2022, 04:28 AM
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I'll go out on a limb here since I really don't know for sure about the '70 model year, but my '67 A-body brake arm had two holes available. The bottom hole allowed a shorter throw and required additional pressure and was used for power brake applications. The power brakes nullified the additional force and allowed a short throw for power brakes. The top hole gave a better ratio for manual brakes, but it does require additional pedal travel. So just check and insure the rod is attached to the top hole for manual brakes.

I prefer what is always referred to as the "Corvette" master cylinder, but it is also the same master that came stock on my '67 GTO that came with the optional front disk brakes. Just look for something that pretty much says for front disk, rear drum setups. The 15/16" bore master cylinder is what I have been using, but 1" does work but with just a little more pedal pressure needed.

I personally like the manual proportioning valve that Summit, Jegs, and many others sell that goes in the rear brake line and limits pressure to the rear drums. Disk brakes require more pedal pressure and the rear would be locked solid on anything more than a medium stop. I dislike the pre-set proportioning valves because the adjustment is really never correct. The manually adjustable valve allows you to dial in more or less pressure to the rear. I am now going through this with my '65 wagon where the tech at Master Power talked me into a set pressure combination valve. His claim that they figured out the split was totally inaccurate and the rears should be doing much more of the stopping. Probably the same valve they sell for a pickup truck conversion, and they simply blew it. Now I've got to go back in and remove the combination valve and go to the simple adjustable valve for the rear. I've installed the simple valve on my drag car, my son's drag car, and at least a half dozen disk conversions for our GTO club members.

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Old 07-02-2022, 08:59 AM
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I bought a kit from the Right Stuff for my 72 Lemans.

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Old 07-02-2022, 06:30 PM
KEN CROCIE KEN CROCIE is offline
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what lust for speed said Same sutup on my 64 GTO

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Old 07-02-2022, 11:02 PM
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Quote:
Originally Posted by b-man View Post

My new manual brake setup for the Tempest uses a 15/16” bore GM (Malibu ?) master coupled with 2008 Corvette Z06 6 piston and 4 piston calipers and the corresponding 14” and 13.4” rotors. Also using a Wilwood adjustable prop valve and a gutted distribution valve. I had the option of using either the 7/8” Wilwood aluminum master or the 15/16” GM unit according to Tobin at KORE3 who sold me the brake setup. Haven’t finished my project yet (retiring soon so no more excuses ) but I’m sure I’ll be fine again with the manual disc brakes.
I have a nearly identical manual setup on my '65 GTO. I did use the Wilwood M/C, but also C6 Z06 brakes front and rear from KORE3. The pedal pressure is just fine, it is a little more effort than power brakes, but totally acceptable.

I've had the KORE3 manual disc brakes now for about 4-5 years and am very happy with this setup. The pedal feel is very good and easy to modulate the brake pressure.

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Old 07-02-2022, 11:06 PM
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I used the Right Stuff front disc setup with GM D52 calipers and a Wilwood 1” master with adjustable proportioning valve and it works very well, plus a 10# residual valve going to the rear drums.

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