Airheart 175 and Mustang rear discs

[Mr T Bucket]

What size master cylinder bores would you go with if:

You're building what might turn out to be a really bitchin' T bucket, or, at least it is in your mind. 18" wire wheels up front with Airheart 175 discs and because you would really like to stop quickly you want discs in the back as well as integrated parking brakes, and the fact it'll look really cool with all the fancy hardware out in the open back there and besides, you would want to fully use the 29/18.5 Prostreet Radial rolling stock . Due to space limitations and the fact that it might be difficult to find an OEM master cylinder that would work reasonably well with that setup AND having to add the somewhat unsightly adjustable proportioning valve just won't do, you're planning on running a dual remote mounted master cylinder setup, similar or pretty closely related to Gerry UK's ride complete with bias/balance bar and whatnot.

The Airheart 175's have a 1.75 inch piston. The '94-'04 Cobra rear calipers have a 38mm, or 1.5 inch piston. If your choices for master cylinder bore diameters were .75, .875 or 1", which would you use and for front or back. I'm thinking for the front, use a 7/8 (.875) and a 3/4 (.75) for the rear.

Estimated/anticipated pedal ratio right around 6:1.

 

[blownt]

I'd just go with a 68 Mustang non power brake master cylinder. It is a 1" bore. That is what most are using prolly. Can get a new one from O Reilly for under $50, or it was when I bought the last one.

 

[ellis8500]

Another good choice is a '75 Corvette manual brake MC. It is designed for all around discs. The Mustang MC might be designed for front disc, drum rear. With 4-wheel discs you should use a MC designed for that. Just my opinion. With your selection of calipers, you will have about 58% of the stopping power on the front.

 

[GAB]

Chris
How many pistons do the Cobra calipers have? Are they a fixed or floating mounting design? Disk brakes depend on line pressure for their operation unlike drums that get a self energizing assist from rotation of the drum... so higher pressures are the order of the day and those are the result of smaller bore master cylinders. But in this instance, the difference in volume might be a factor if the rear calipers are multiple bores (like 2 or 4 piston models). I suspect that Mr. Bills calculation of 58% of the braking on the front is based strictly on the caliper area dimensions and does not take into account the rear caliper design and the vast difference in tire size front to rear and weight distribution. The balance bar arrangement might prove to be valuable for working with this setup.

I had a fellow bring over a motorcycle caliper the other day that was a 6 piston that used a 1/4 thick rotor and it looked like it might be worth considering for an upgrade from the Airheart setup. It is a solid mount and the mounting is offset. I made him mounting brackets for a pair of them for the V-8 motorcycle that we built a few years ago. Just something to think about.

 

[blownt]

I got 4 wheel discs and the 68 Mustang master cylinder is just fine.

 

[Ted Brown]

I use a 3/4 to the ft. and 7/8 to the rear with rear drums, you want to be able to push the pedal without too much foot pressure, and be able to adjust it all so that in a panic stop, all 4 lock up about the same time... IMHO

 

[Mr T Bucket]

Thanks for the replies, guys. I had thought about the Vette master cylinder but was really intrigued by the balance bar discussion on the Ted Brown's brake pedal thread especially with George's computer renderings. So much so, I picked up a pair of used Wilwood pedal assemblies off ebay the other day. One is a dual master setup with the balance bar and the other is a single master. Got em for the same price as if I'd bought just a new balance bar, so I've got the stuff to do the twin setup. George, the Cobra calipers are a single piston floating design. Got some mounting plate/bearing retainers from Currie Enterprises and I think I got the rotor centering adapters from them too. I guess what it comes down to, is if with the 3" wide front tires and the 18.5" back tires and my particular brake caliper choices, I might have to just try it one way and see how well it works. I can always change out one of the masters if needed. Shoot! Late for work. Maybe I'll post some pics tonight. George, I'm on vacation next week. Might have to look you up.

 

[Ted Brown]

Testing testing testing is the name of the game when building your own style car, if it is not a proven kit or design, testing is the only way to tell what works and what does not, because every car is different in many ways. Use a back road or big parking lot??? and test every thing, in many ways and at different speeds... Like I always say, drive it naked until it proves itself... and still later you will find something that still needs to be changed.

 

[GAB]

Chris,

You are more than welcome to visit. Just give me a call at 816-734-8211 as it is a long way to come and not find anyone here. I know...our daughter and her family live in Gardner!

George

 

[Mr T Bucket]

George, it was a pleasure meeting you in person the other day. Thanks for letting me come by to check out the Master Metal Manipulator's Mecca. What a great shop! Like I said, I'll be in touch.