How to Install 14 Inch Brakes on an A-Body (or B/E also)

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Reddartowner

Reddartowner

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What to do when you want better braking than the 11-3/4 mopar units can provide? Pay $2500 for a set of Baer brakes..? Possible, but expensive.

How about adapting a set of 2010 Shelby GT500 14 inch rotors with 4 piston Brembo calipers?

Impossible you say? Read on.

My son's '68 Dart gets autocrossed regularly, and the 11-3/4 inch brakes were just not as strong as he would have liked, especially with the weight of a big block on the front end.
So beginning about a year ago, we began to look into how to adapt a later set of Mustang calipers and rotors to the A-body spindles, due to the common Ford/Mopar bolt pattern.

Long story short, we developed an adapter bracket that bolts to the factory spindles and mounts the 2010 GT500 4-piston calipers, allowing him to run the 14 inch rotors using 18 inch wheels. The car now runs 18x9 inch wheels with 255 series rubber front and rear (255/35 front, 255/40 rear).

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Brake Caliper Right Side Rev E 3D.JPG
 
The first part of this mod is to acquire a pair of '73 or later disc brakes and have the discs machined off so that only the hubs remain. We then installed a set of 3 inch Moroso studs for reliability. We also machined the inner section of the hub next to the mounting flange to fit inside the GT500 rotor with approx. .005 clearance.

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We installed a modified hub onto an A/B/E spindle along with a "cheap" GT500 rotor and caliper for mock up dimensioning. After 3 major iterations and the help of a friend's 3d printer we came up with a working prototype, which then underwent a couple of minor revisions to make it fit cleanly.

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Installation day.....

The bolts securing the adapter to the spindle are 1/2-20. The fasteners securing the adapter to the caliper are 12-1.5 socket head cap screws that fit into the counterbored holes on the adapter.

First the existing setup:

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Removed the existing rotor and caliper and mounting bracket. Also had to reverse the steering arm/lower balljoint bolts to clear the new hub:

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Then installed the new adapter bracket to the spindle using the 1/2-20 bolts. Finally, installed the new rotor and installed the new caliper using the 12-1.5 socket head cap screws:

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Total cost for this project: $1385, not counting pads of your choice. We are using Hawk HPS pads. Wheels are not included in this cost.

Caveat: A word of warning when selecting wheels for this mod. We found out the hard way that not all wheels will fit the 4-piston calipers. You need to check with the manufacturer on this. In the end we selected Forgestar F-14 wheels, 18x9 with 40mm offset. The rear wheels are 20mm offset.
 
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Very, very nice work!!! :thumbsup:

I wonder how different that hub is compared to the aluminum ones that DoctorDiff sells and uses with his 13" conversion kits?
Mopar Billet Aluminum Hub

Any plans on selling the adaptors?
 
If we were to do it again, we'd probably have purchased the aluminum hubs from Dr. Diff. They would be lighter than the ones we made. But at the time, he didn't have any available. The cost to machine the discs off the brakes to create the hubs was about the same as purchasing a pair from Dr. Diff.

From a weight-savings point of view, though, the aluminum hubs savings over the steel hubs is the small end of the hammer. The GT500 discs weigh 26 lbs each.....
 
Reddartowner said:
If we were to do it again, we'd probably have purchased the aluminum hubs from Dr. Diff. They would be lighter than the ones we made. But at the time, he didn't have any available. The cost to machine the discs off the brakes to create the hubs was about the same as purchasing a pair from Dr. Diff.

From a weight-savings point of view, though, the aluminum hubs savings over the steel hubs is the small end of the hammer. The GT500 discs weigh 26 lbs each.....
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I wasn’t trying to knock your effort, just curious. Honestly for a street car I kinda like the idea of not having aluminum hubs, just from a wear and tear perspective. But for some folks it would be easier to just purchase something ready to bolt on, so the aluminum hubs might be a good option.

Any plans to make more of those adaptors? I bet you could get a list together. I’d be interested for sure!
 
Very nice upgrade on the brakes! Like you mentioned wheels can be hard to find that clear these calipers ...even some 19 inch wheels I tried would not clear.
 
67autocross said:
Very nice upgrade on the brakes! Like you mentioned wheels can be hard to find that clear these calipers ...even some 19 inch wheels I tried would not clear.
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Yeah I've noticed that a lot of wheels have "will not clear Brembo brakes" in their descriptions. See it a decent amount since more than a few of the aftermarket 18" wheels I look at are intended for the late model mustangs. Definitely something to consider.

I'd still be pretty interested though! :D
 
Nice. I really wonder if these actually work any better than the Dr Diff 13" Mustang Cobra brakes. I have them, the Mustang Cobra rears, and Hydroboost, and holy crap do they stop. You can basically lock all 4 275-35-18 hard at 55 mph if you panic brake. They also modulate well. For autocross and probably some track duty, I'm sure they're good. And basically every wheel bigger than 17" fits.
 
goldduster318 said:
Nice. I really wonder if these actually work any better than the Dr Diff 13" Mustang Cobra brakes. I have them, the Mustang Cobra rears, and Hydroboost, and holy crap do they stop. You can basically lock all 4 275-35-18 hard at 55 mph if you panic brake. They also modulate well. For autocross and probably some track duty, I'm sure they're good. And basically every wheel bigger than 17" fits.
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Same set up I have now, well, except for the hydroboost. 13" fronts and 11.7" rears, car stops GREAT. But I do have a Challenger that might be getting a big block before it goes back on the road. The DoctorDiff 13" Cobra set up works great, but if the GT500's got 14's and those calipers I would wager it's still an upgrade. :D

Plus I like that someone took the time to engineer their own solution. With the hubs from DoctorDiff available now it makes doing a brake upgrade of your own choosing relatively straightforward. That's not to say easy, even just making a caliper bracket is a ton of trial and error, lots of time and test fitting invested. Which is why I haven't done it myself. Having access to a 3D printer is super handy too!

So @Reddartowner, have you considered making a run of these caliper brackets? You did the hard work already...
 
72bluNblu said:
Same set up I have now, well, except for the hydroboost. 13" fronts and 11.7" rears, car stops GREAT. But I do have a Challenger that might be getting a big block before it goes back on the road. The DoctorDiff 13" Cobra set up works great, but if the GT500's got 14's and those calipers I would wager it's still an upgrade. :D

Plus I like that someone took the time to engineer their own solution. With the hubs from DoctorDiff available now it makes doing a brake upgrade of your own choosing relatively straightforward. That's not to say easy, even just making a caliper bracket is a ton of trial and error, lots of time and test fitting invested. Which is why I haven't done it myself. Having access to a 3D printer is super handy too!

So @Reddartowner, have you considered making a run of these caliper brackets? You did the hard work already...
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Yeah, I mean I have worked in OEM braking systems for 15 years, though the last 9 have been brake controls, not calipers. I'm merely pointing out pros and cons here.

The big advantage of opposed piston calipers like these are volume consumption because they are stiffer, and taper wear. Otherwise caliper output is basically a function of pressure, pad mu, moment arm, and pad area. In a road race or heavy use application the extra mass to take the heat of a bigger rotor helps a lot. Something like street driving or autocross this isn't a huge issue.

So now, we get into piston size, which has a big effect on brake bias. Since we don't have any electronic brake force distribution or ABS like a modern car it's a pretty big deal. The Cobra setup is well matched to the F/R weight distribution and weight of most of our cars because they are largely similar in weight, weight bias, and wheelbase. As a result you get really good proportioning and therefore good braking performance. How will this turn out? Not sure honestly. If the cobra ones aren't enough on your own, the booster will take care of the rest. A 94-04 Mustang cobra is also a hydroboost car FWIW.

At the end of the day the tires are the limit for the brakes anyway, so if you can lock them at will at any time, and have good modulation, they are enough.

The big downside I see here is the unsprung and rotating weight. The cobra setup with the aluminum hubs is lighter than the stock 11.75 iron setup by at least a few lbs from what I remember. The OE brakes are also garbage for anything except cruising around town.

Of course they do look more racey so there's that.
 
To take over for my dad for a bit, for 72bluNblu, I never really had any plans to manufacture these in a larger scale. I have plans to take the new brakes to an autocross next weekend to really test out the caliper bracket design. With that said, I wouldn't really feel comfortable selling them until I have put em through their paces.

For goldduster's response I did manage to calculate the brake bias for this setup and it is a little farther front than I would like it to start. But well have to see when I get it out on the autocross course how she handles. When I was a part of my colleges Formula SAE team I learned a whole lot about braking system, definitely dont know everything, but I know the importance of unsprung and rotating weight on a car. I do have plans to lighten this setup down the road and try to incorporate some adjustable bias into the system maybe in the shape of a bias bar and dual master cylinders. I would definitely like to pick your brain about braking systems as im always trying to learn
 
I've built systems like that before using cut down hubs and factory rotors. We ran a setup like that on a road race Valiant for a while. It worked, but was super heavy. I eventually started having custom aluminum hubs made since the custom hub allowed me to put the wheel where I wanted it. A custom hub also allows you to use different wheels with different center diameters. These days I use lightweight rotors and high quality calipers. Usually Baer rotors and Brembo calipers. Here is the setup I have on my Duster.
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Reddartowner said:
To take over for my dad for a bit, for 72bluNblu, I never really had any plans to manufacture these in a larger scale. I have plans to take the new brakes to an autocross next weekend to really test out the caliper bracket design. With that said, I wouldn't really feel comfortable selling them until I have put em through their paces.

For goldduster's response I did manage to calculate the brake bias for this setup and it is a little farther front than I would like it to start. But well have to see when I get it out on the autocross course how she handles. When I was a part of my colleges Formula SAE team I learned a whole lot about braking system, definitely dont know everything, but I know the importance of unsprung and rotating weight on a car. I do have plans to lighten this setup down the road and try to incorporate some adjustable bias into the system maybe in the shape of a bias bar and dual master cylinders. I would definitely like to pick your brain about braking systems as im always trying to learn
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If you want to read a few chapters on brake design including how to build custom big brake setup for Mopar cars then pick up a copy of my B body book. I covered all of this in the book.

https://www.amazon.com/dp/1934709301/?tag=fabo03-20
 
This is a great thread. Just what I have been thinking about as far as modding a standard rotor. When I asked last, Dr Diff wasn't selling the hub separate from the kits.
I've got a damaged rotor to play with and a full set of 2000 BMW M5 front brakes that use a 345mm x 32mm (~13.6" x 1.25") rotor. They are single piston calipers but were designed to haul a 4000lb sedan down from 185mph Autobahn speeds and served duty well on the Nuerburgring Taxis. I think they will be a nice upgrade for my car.

Did you face the rotor hub at all to move the centerline of the rotor disk? That Cobra disk looks like it has less offset than the old parts.
 
gzig5 said:
Did you face the rotor hub at all to move the centerline of the rotor disk? That Cobra disk looks like it has less offset than the old parts.
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We did not face the modified hub. I did not want to weaken the hub center and risk cracking through where the studs are located. Not a fan of catastrophic failures....

As the front wheel sits now, it is only 1/4 inch from the tie rod end (18x9 wheel with 40mm offset).
 
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You could cut that material on the outer side off using the lathe if you wanted, it doesn't do anything for strength in this case, so it would get lighter.
 
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I’ve been using 14” brakes for years now. In my 35 yrs of Dart ownership, at least a dozen open track events and 2 Optima events, I can say the larger brakes offer a good margin over the 13” setup I had for years prior. The additional pistons, from 2 to 4 and the additional mechanical advantage improve the feel quite a bit. If you haven’t used both on the track, you might not notice, but the difference is real.
The cut down rotor idea works and allows my 18x9s to fit perfectly with 6.38” backspace. Cass (Dr Diff) made these brackets at one time, but no longer. I also believe the alum hubs are Baer pieces. I’m not sure Baer sells component parts like they used to. The SRT rotor is heavy, but it’s a great heat synch. It’s cheap and slotted which means it’s quiet and will last some time. I use Carbo tech brakes. Not cheap, but confidence inspiring. The key issue with this setup is overall stiffness. Pad knock back is something that can be remedied by a floating rotor. The OEs do this, but it’s expensive.
I made a run of 13” brackets a while back that I will advertise at some point.
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And this is why you need to test new designs.....

On run 3 of an autocross at Tavares, Fl on Sunday we had a catastrophic failure of the left caliper adapter. The failure appears to have initiated at the top of one of the counterbored holes (where it is close to the inside corner of the "backbone" on the bracket). So the counterbores will be eliminated on the next revision, and we'll use steel for the brackets, probably 4130.

The good news is the damage was minor... bracket (obviously), trashed caliper, torn brake hose, minor scratches on inside of wheel. Spindle, hub and rotor unaffected.

My son (driving) did say the braking was excellent before the failure.

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Failed Bracket 2.jpg
 
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