'75 Duster B body front brake upgrade impressions wanted

DionR said
I actually checked my spreadsheet before posted just to make sure I wasn’t doing something wrong. But will see if I can compare mine to yours and see if I see something.

Ft/inches really isn’t much different that ft/lbs, just 12 times bigger. :rofl:

I will admit it wasn’t my choice for units, but it works out and is what Marian did in the HR article.

But I will compare later when I get back home.

Will be back. :thumbsup:

Uh, ft/inches is length/length. I don't care who used it, it's not a unit of force. Probably a typo, but whatever. Just because it's in a magazine doesn't mean much. Inch-Lbs is what you're talking about.

DionR said
Ok, I can match your numbers (for the most part) by taking my effective rotor diameter and converting it to feet, and thus returning lb/ft (or ft/lbs). In the end, the calculation is really only useful if the units are the same when comparing. So, don't see anything wrong in my calculations, other than not doing the conversion to feet on the effective rotor diameter.

If I convert to feet, I get the following numbers:

10.87 w/ 2.6" piston - 1627
11.75 w/ 2.6" piston - 1783
10.87 w/ 2.75" piston - 1820
11.75 w/ 2.75" piston - 1745
13" w/ Cobra calipers - 1286
13" w/ C5/6 calipers - 1453

One place that can significantly upset any comparisons between your numbers and mine is the way the swept area is dealt with. In my spreadsheet, it was simpler to use the total rotor diameter and the width of the pad at the centerline to calculate the effective rotor diameter. I did this because I didn't have one to measure from and it was easier to find the pad dimensions and assume it was at the edge of the rotor. I know they are probably 1/16" or more down, but I figured it was good enough to compare the numbers between my calculations. Looks like yours requires you to input the effective radius, so you must be coming up with a number somehow, and we ended up not matching there.

So in my calculations, my effective rotor diameter ended up being 9.1935" for the 10.87 rotor and 10.0735" for the 11.75" rotor. This is a pretty good departure from your numbers. I got to my numbers based on a pad width of 1.6765". Now, it's been 9 years since I started this spreadsheet, so I can't say for sure where I got it other than probably RockAuto since I think I got a fair amount of info off that site. I think I probably took a picture from one of the pad manufactures that had dimensions on it and scaled the width.

An image like the fourth in this link - More Information for CENTRIC 10200840

In regards to the 1000psi at the piston, it was a general number I read about some time ago when I was looking at building my own custom brake setup and trying to get a handle on a direction. As I recall, the point was that the pressure out of the MC should be 1000 psi and the whole MC bore size and pedal ratio was a different calculation and I didn't really care since most of that was pretty well fixed by then. But I am reaching way back to remember what all was going on. My only point is, that the 1000psi number is similar to the coefficient of friction in that I standardized on a value so that I could look at the specifics of the rotor size and piston diameter(s).

Lastly, I have looked for bigger piston calipers and have come up pretty blank. All of the Cobra calipers I have found online are 1.5" (38.1mm) pistons. I used the C5 calipers on my swap because they us 40mm pistons, and just recently discovered that the later Challenger calipers look to be a direct swap for my C5 calipers and have 42mm pistons. I did find 51mm piston calipers but they are on GM pickups and appear to be significantly larger over all and thus don't swap. I would love to step up to a 45mm piston caliper that bolts to my existing abutment. Not argue that they aren't out there, only that I can't find them.

Yeah my diameters are wrong. I subtracted from the diameter like it was a radius. I measured a set of pads I have

So the effective diameters for the 10.87's should be like 9.095" and the 11.75's should be 9.975" based on that. I'm sure there's some pad variation out there anyway so that makes them basically the same as your numbers. My numbers in my previous post above are wrong. Should be more like this...

Screen Shot 2020-12-24 at 12.51.56 PM.png

Screen Shot 2020-12-24 at 12.51.56 PM.png

As for the mustang calipers, these are listed at 45mm.
2002 FORD MUSTANG Power Stop L4723 Power Stop OE Replacement Calipers | Summit Racing

These are listed at 40.3mm
More Information for CARDONE 184885

I didn't measure mine, I suppose I could ask Cass. I assumed they were 40mm because the later PBR calipers were (2000 up I think?). Of course, that's not the only thing that goes into braking performance. The 13" cobra style kit uses aluminum hubs, and even with the 13" rotors that assembly is quite a bit lighter than the 11.75". Which is all rotating mass the caliper also has to stop. And the efficiency thing about multi-piston fixed vs. single piston sliders we talked about before. Honestly, and this is just my subjective opinion, I think the difference between the 10.87's and 11.75's was probably bigger than the 11.75's and the 13" cobra style kit. The 13's were an improvement IMO, but it was not as dramatic. And it could just be that they "feel" better, because again that's just my subjective experience. That could be pad compound, it could be the change in the size of the piston area changing the pedal feel, it could be the reduction in flex with the fixed calipers, who knows.