1969 Mustang Restomod Brakes (Brake Experts Needed)

Help me fix some Disgustang Brakes (Early Mustang Content)

An acquaintance of mine purchased a 1969 Fastback Mustang Mach I clone, with a big block 429 and Four Speed.

Car was originally built as a manual brake car – and has the original pedal box (and manual pedal) in it.

Car has CSRP Front Spindles, which use ~1975 Ford Granada Calipers and Rotors

Link to Spindles:

https://www.discbrakeswap.com/Mustang%20Disc%20Brake%20Conversion%20Kits%20SWAP2.html

Link to Existing Calipers:

https://www.rockauto.com/en/catalog/ford,1975,granada,5.0l+302cid+v8,1129777,brake+&+wheel+hub,caliper,1704

Front Calipers are single piston, 66mm bore

Front Rotors are 11.03 diameter, with a .875 nominal thickness

Rear has a 9” with the dreaded Generic Cadillac-style rear disc swap calipers (85 Eldorado) and 11.25 inch diameter rotors with a .980 nominal thickness

Link to similar 9” rear disc setup:

https://leedbrakes.com/i-23438950-rear-disc-brake-conversion-kit-ford-9in-large-bearing-new-style-torino.html

Rear Calipers are single piston, with 54mm bore (and new, and adjusted properly)

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According to the owner, it always had “acceptable” brakes – up until on the way over to my Dad’s shop, the clutch z-bar rubbed a hole thru the hardline going to the rear brakes

He brought it over to install aluminum valve covers, and during install of said valve covers, it was noted that the incoming cast iron master cylinder wouldn’t clear the valve covers, so it needed to be replaced

However, whomever “restored” this thing last installed a generic, universal GM style booster and 1-3/16” bore C3-era Corvette master cylinder and prop valve.  They drilled 2 new holes in the firewall to mount the booster / master, and used 2 of the existing holes in the firewall.

Long story short, after a lot of parts swapping, finding a bad booster, a stuck prop valve (turns out “acceptable brakes” means no rear brakes working at all!)  and the aforementioned manual pedal in the power system, and the clearance issues with the big block and valve covers, all parties are in agreement to move to a manual brake system and ditch the janky aftermarket booster.

That said, I'm unsure as to appropriately size the master cylinder bore , and need the hive mind’s knowledge on how to size it appropriately

To further complicate things, long term, the owner wants to move to 99-04 Mustang GT calipers up front, and explorer rear disc using these kits:

https://www.discbrakeswap.com/Mustang%20Disc%20Brake%20Conversion%20Kits%20SWAP%204.html

https://www.quickperformance.com/Ford-9-Inch-Rear-Explorer-Disc-Brake-Kit-With-Shoe-Style-Park-Brake_p_4023.html

The "future" upgraded brakes use Twin Piston Calipers with 45mm bores up front, and a single piston caliper with a 47.9 mm bore in the rear

Ideally, I’d like to find a master cylinder that would work OK for both – but if that’s not possible, I understand.

If anybody has any other suggestions as to brakes on this thing – please speak up.  Only real constraint on this is that he wants everything to fit under a 15” wheel

Got me at the last sentence  ".......`15" wheels"

Wildwood would be a resource

Good Luck

From what I know...

The brake booster is basically a force multiplier. If you put 10 lbs of force into the pedal and you have a 4x booster, that's the equivalent of 40 lbs of force. Simply deleting the booster and doing nothing else will result in a 4x increase in driver effort for a given amount of brake torque. You can decrease the area of the master cylinder to drop that required force at the expense of extra pedal travel. You can also play with the pedal ratio in the same way.

I don't know what the boost ratio of that generic booster was but it's probably in the 5-10X ballpark. If you can find that, it might help you start calculating what you want to do to the master size. What did the Mustang originally have when equipped with manual brakes?

Your twin 45mm piston calipers have almost the same area as your single 66mm does, so that's not an issue. Your planned new rears are significantly smaller so that's going to require a brake bias adjustment when installed.

Contact Shaun at Street or Track, a vintage Mustang suspension, steering, braking and drive train company

https://streetortrack.com

Toss it all.

Street or Track

Mike  Maier

Opentracker Racing.

Get a complete kit from any of them and install a complete package.

I could tell you what I did,but 15" wheels

Keith Tanner said:

From what I know...

The brake booster is basically a force multiplier. If you put 10 lbs of force into the pedal and you have a 4x booster, that's the equivalent of 40 lbs of force. Simply deleting the booster and doing nothing else will result in a 4x increase in driver effort for a given amount of brake torque.

i would grab a booster, master, and pedal assembly from an S197 and figure out how to make it fit.  IIRC (i worked on this system 20 years ago), that booster is about 5.6:1, and the pedal is around 3.5:1, and it is pretty close to properly sized for those calipers. Definitely plumb an adjustable prop into the rear circuit and use that to tune your balance. Fronts should lock a little before the rears on dry pavement.