Brake proportioning of a split bus?

[flemcadiddlehopper]

I am in the process of working out a disk brake set up for my bus using Wilwood Calipers, Pads, Rotors and Master cylinder.

It looks as though 11.75" rotors will fit inside my Empi Wide 5 Wheels.

I am wondering what was the original bus brake proportion front to rear? Or what is the shoe width front and rear as well as the wheel cylinder bores front and rear? So that I may do the math.

Thanks for any input. I will share my plan once I work out most of the details.

Gordo.
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[flemcadiddlehopper]

I dug around a bit and came up with some numbers.

Front wheel cyls of 25mm ?

Front shoe width of 50 mm ?

Rear wheel cyls of 22 mm ?

rear shoe wodth of 43 mm ?


If these numbers are correct or near correct, then the bias is approc. rear has 87% of what front has. Or 56.5% front and 43.5% rear.

Now if I was to go to a 4 wheel disc set up with the biggest brakes I can fit inside my 15" Empi wide 5s, I could fit 11.75" rotors front and rear, both the same. These rotors are 30 vane vented, non drilled or slotted, for smooth and quiet operation. They are also only $33.47 each.

The front calipers that could fit are the Wilwood Dynapro 6 piston lug mount. With a piston area of 3.08"sq. At $299.93.

The rear calipers that fit could be the Dynapro 4 piston lug mount. With a piston area of 3.00"sq. At $213.66.

Now those areas come to the rear being 97% of the front Hydraulically. Which can be dialed out with a proportioning valve.

The pad surface areas for those calipers come closer to the original Bus bias of the rear being 87% of the front.
If I machine the drums down to be mounting hubs for the rotors, all bearing, seals and offset will be stock. All that is required after that is a mounting adapter for the rotors to the hubs and caliper mounting brackets.

I am just working out the logistics of the adapter and bracket machining costs to see if this stays in a realistic budget realm.

Gordo.
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[durfeec]

Is all of this really worth it when there are so many options for an already proven kit? I think the traditional 60/40 braking proportion will work fine for a bus.
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[flemcadiddlehopper]

[Riff Raff]

My calcs show a different bias.
I get 62% front and 48% rear.
That was derived by mutiplying the area of the wheel cylinders by the width of the shoes.
I think using the square of the radius will give a more accurate proportion than using the diameter.

I like the idea of bolting those rotors to a machined down bus drum, but I can't visualize how it can be done with zero offset.
can you elaborate on your idea?
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[mandraks]

[flemcadiddlehopper]

The mounting point for the wheels does not change as they are still bolting up to the existing drum outer face, thus no offset change. Now cut the drum braking surface off of the drum. Machine a flat surface on the inner facing side of the drum. In the case of this rotor make a 2.25" tall aluminum cylinder with an I.D. of 6.0" and an O.D. of 7.5". Tap 8 threaded M8x1.0 holes in a 8 x 7.00" arrangement and counter sink 8 more 10mm holes between to mount it to the drum. The rotor bolts to the aluminum cylinder and the cylinder bolts to the inside face of what was the drum.
This leaves enough space to fit the caliper between the remaining drum face and the rotor, And the inside edge of the rotor will be where the inside edge (that was cut off) of the drum was.

Gordo.
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[Riff Raff]

Ya, 62/38 duh!

Ok, I get the idea, I was thinking there would not be enough clearance between the wheel and the caliper, but the aluminum cylinder accounts for that offset.
Certainly an advantage to run larger diameter rotors.
Sounds like a fun project!
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The greatest obstacle to discovery is not ignorance, but the illusion of knowledge
- Daniel Boorstin

[Malokin Martin]

[flemcadiddlehopper]

Well if I do the math the way you have,I end up with 62.5/37.5 , using the total surface area of the shoes. So, then this new set up would have a brake bias of 57.54 front and 42.45 rear. Using the surface areas of the pistons x surface areas of pads. Rear is 84.9% of the fronts.

This works for me as I have more rubber on the rear anyways. Although the bias can be dialed in too.

Gordo.
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[flemcadiddlehopper]

Oops, my bad...I reworked the numbers given and came up with a stock bias as rears being 86% of what the front is making the ratio 57/43 . Which ends up very close to the disc set up ratio of 84.9% of the fronts at 57.55/42.45 .


Gordo.
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[Merlin]

Calculating and sourcing such specific parts seems like a somewhat overcomplicated procedure to me...

Is there any particular reason why you aren't considering the use of a brake proportioning valve?

[flemcadiddlehopper]

[flemcadiddlehopper]

Wilwood makes this easier to plan out than you think as they provide their customers with a huge amount of info about their products.

Even the rotor hat (adapter) that I need is only $87.00 , saving me time and money having it made. I would just need to machine the inner side of the drum face to mate them.

Gordo.
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[Merlin]

Noted. Best of luck with your conversion. Please keep us posted.

[quote="flemcadiddlehopper"]

[67dubcab]

Looks like a great way to get high performance brakes and keep the wide five wheels.
Matching the master cyl. to the calipers is something most aftermarket systems fail to address, Wilwood has done that for you.

I am running a Tilton proportioning valve on my bus (matching Porsche turbo brakes) and from my research the valve has a set front to rear bias and the adjusting part changes the pressure at which the bias kicks in, stays one to one up to that point. This keeps the rear brakes more in play for more equal pad/disc wear on the street.
I think it is called a pressure knee. During hard braking it goes straight to the non-adjustable bias. The only way I know of to adjust the front to rear bias is a twin adjustable master cylinder.
I have run both 944 single piston and presently the dual piston Brembos (944 turbo) with the matching master cyl. and balance has great.

You can also fine tune brakes with different pads front to rear.

Does the Wilwood rear calipers have a parking brake option?
I am still figuring out my parking brake, and instead of a custom cable to the 944 rear mini drums I may plumb in a rally/drift handbrake, which also helps for those tight corners while autocrossing.
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[flemcadiddlehopper]

Wilwood does offer a single piston e-brake caliper, but I would need to go to a smaller rotor diameter in the rear to fit it. This would also not work well with the big brake plan and biasing.
I plan on using a line lock lever as a parking brake, though technically not an e-brake as it is not mechanical.
Wilwood does make e-brake shoes to fit inside the hat. This may be an option for me to look into.

Gordo.
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Retrograde Garage. Vintage Aircooled, and others.

[weststock69]

Just instalked an adjustable proportioning valve. Easy acces to play.
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[weststock69]

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[flemcadiddlehopper]