January 15th, 2025: added a MUCH more affordable cast iron hub option which saves $249 over the cost of the expensive billet aluminum hubs.
HD12 Brake Upgrade Successor
One of the best front brake upgrades for these cars was developed and provided by @Navy Lifer in the form of his HD12 kit. This was the ultimate in bolt-on convenience for upgraded brakes that stop hard, resist fade, fit in all OEM wheels, and use easily-obtainable service parts. It was pretty cost-effective, too, and easily-reversible to return to stock. Sadly, he ran out of inventory for the brake rotors.
After much research, I've come up with a list of part numbers that allow anyone to replicate the HD12 brake kit. This retains all the benefits of the original kit, but using readily-available rotors and hats in place of the previous one-off rotors and KORE3 hats. I'll list and describe the kit part numbers below, as well as possible add-ons that are worth considering. (I'm not affiliated with Wilwood or KORE3 in any way, I just happily use their products that I purchased at no discount whatsoever)
Core Kit (with cast iron hubs)
Core Kit (with billet aluminum hubs)
The kit with cast iron hubs adds 1/8" of track width (each front wheel gets spaced outward by 1/16"). Those hubs cost $300, which is $249 less than the billet aluminum hubs. They also come with ABS tone rings pre-installed.
The kit with billet aluminum hubs reduces the front track width by a negligible amount, less than 1mm or "0.030. May as well consider it OEM track width. If you want to retain the ABS functionality, you still need to pull the ABS tone rings from the old OEM brake rotors and install them onto the KORE3 hubs. I was able to easily remove the old tone rings with a standard 3-jaw puller, a little heat applied to the tone rings can help them pull off smoothly without breaking.
Note that the part number for rotor hats is different between the two configurations. The cast iron hubs require hats that have a deeper offset. Both part numbers cost the same (currently $101 per hat).
The calipers are readily available at most auto parts stores or on Rock Auto from many different brands (including AC Delco) in both reman and new for very affordable prices.
Pair the kit with your favorite D52 brake pads (any pads that would've fit in your original calipers) and you'll be all set. There's other threads on this forum that have recommendations for adequate pads to suit anyone's needs.
Options and Add-Ons
Brake Rotors
Coleman Racing will make rotors of most shapes and sizes. After some trial and error, I've come up with rotor specs that fit perfectly and allow any thickness of brake pad. Simply call Coleman Racing and tell them you want to order a set of Frank Gore brake rotors. The two choices are RACE or STREET;
RACE - For heavy duty applications to help prevent cracking from extreme heat. HD casting (thicker face), slotted, balanced, stress relieved via heat treatment, directional vents, $394.24 for the pair at current prices.
STREET - If you don't plan to race your car, save a few bucks over the race rotor. Standard casting (same face thickness as stock), plain face, balanced, directional vents, about $280 per pair at current prices.
Wilwood Calipers
In place of the OEM calipers listed above, you can also opt for Wilwood forged billet aluminum dual-piston calipers that will bolt right on. The part number for that is 120-10936 (available in gray, black or red, need 2 because they're interchangeable L/R). Those calipers require a 7/16-20 banjo bolt that's larger than the stock M10, so new front matching flex lines will be needed as well. Note that the stock brake fittings on the hard lines are M10-1.0 bubble flare. A combination of Fragola 352012 hoses and 650205 fittings would combine to make the correct flex line. Technically the dual 2" pistons have slightly less surface area than the huge single piston on OEM calipers, but the reduced flex of the caliper construction and the more even pressure applied to the pad means that they end up providing about the same braking effort as the OEM calipers. Only pads with a smooth backing plate will work (no shim rivets), and you can't use the retaining clip on the inside pad, so it might end up rattling around while not applying the brakes. This is not a safety or performance issue, just a potential annoyance. These calipers do look very pretty. They also might not fit in some OEM 15" wheels.
Solid Bearing Spacer
The factory-original method to mount the hub is to tighten the spindle nut to 12 ft-lb while turning the rotor (to seat the bearings directly against the races), then loosen the nut, re-tighten the nut by hand, and back it off to the closest cotter pin hole. This is intended to provide a bearing clearance of 0.001" to 0.005". However by using a solid bearing spacer, you can not only target a specific bearing clearance (ideally exactly 0.001"), you can also ensure that the bearing shells will never spin against the spindle. There's also speculation that pre-loading the spindle with the nut helps to stiffen it up. All of this provides noticeably more precise steering, longer bearing life, cooler-running hubs, and more predictable braking. Having the bearings with a 0.001" clearance helps prevent pad knock-back, so the brakes will be more likely to grab when you expect them to. Setting it up takes a bit more time and effort than a standard installation. KORE3 sells a bearing spacer kit that you can call and ask for. More recently, PTFB started selling a similar kit for less money that basically does the same thing. It can be found here: Wheel bearing spacers | Pro Touring FBody (I'm not affiliated with PTFB in any way, and I'm not promoting their product over the KORE3 product in any respect other than potential price, I've never used the PTFB bearing spacer. I have 2 sets of KORE3 bearing spacers that I love)
Stainless steel braided hoses
I don't think I need to describe these too much, everyone knows about them. They're available from many sellers and manufacturers. They'll improve the feel of the pedal by reducing flex in the system. They will not increase the amount of total braking force, though they may reduce the amount of pedal pressure needed to achieve the desired braking force, and they'll improve feedback through the pedal so you can better tell what the tires are doing.
Edit history:
5/19/25 - updated the rotor hat part number for the core kit from 170-0208 to 170-0357 after actually measuring the cast iron hub to confirm that its face has actually been machined down. Updated the effect on track width from 1/2" to 1/8" as a result. Updated the Wilwood caliper info to reflect the need for new lines in addition to banjo bolts.
4/11/25 - updated the hardware part number from 230-12020 to 230-12120 (original was a typo).
HD12 Brake Upgrade Successor
One of the best front brake upgrades for these cars was developed and provided by @Navy Lifer in the form of his HD12 kit. This was the ultimate in bolt-on convenience for upgraded brakes that stop hard, resist fade, fit in all OEM wheels, and use easily-obtainable service parts. It was pretty cost-effective, too, and easily-reversible to return to stock. Sadly, he ran out of inventory for the brake rotors.
After much research, I've come up with a list of part numbers that allow anyone to replicate the HD12 brake kit. This retains all the benefits of the original kit, but using readily-available rotors and hats in place of the previous one-off rotors and KORE3 hats. I'll list and describe the kit part numbers below, as well as possible add-ons that are worth considering. (I'm not affiliated with Wilwood or KORE3 in any way, I just happily use their products that I purchased at no discount whatsoever)
Core Kit (with cast iron hubs)
- Aluminum hats: Wilwood 170-0357 (need 2)
- Rotors: Coleman Racing - ask for a "Frank Gore" brake rotor set, either "RACE" or "STREET", call Coleman Racing at 1-866-COLEMAN, see more info below
- Hardware: Wilwood 230-12120 (need 1)
- Cast iron hubs: RPM Automotive Brakes Hub Kit (need 1)
- OEM calipers for a 1994 to 1996 Cadillac Fleetwood commercial chassis (option J55): OEM part numbers 18005246 for right, 18005245 for left
Core Kit (with billet aluminum hubs)
- Aluminum hats: Wilwood 170-0764 (need 2)
- Rotors: Coleman Racing - ask for a "Frank Gore" brake rotor set, either "RACE" or "STREET", call Coleman Racing at 1-866-COLEMAN, see more info below
- Hardware: Wilwood 230-12120 (need 1)
- Billet aluminum hubs: KORE3 GMTS HD (need 1)
- OEM calipers for a 1994 to 1996 Cadillac Fleetwood commercial chassis (option J55): OEM part numbers 18005246 for right, 18005245 for left
The kit with cast iron hubs adds 1/8" of track width (each front wheel gets spaced outward by 1/16"). Those hubs cost $300, which is $249 less than the billet aluminum hubs. They also come with ABS tone rings pre-installed.
The kit with billet aluminum hubs reduces the front track width by a negligible amount, less than 1mm or "0.030. May as well consider it OEM track width. If you want to retain the ABS functionality, you still need to pull the ABS tone rings from the old OEM brake rotors and install them onto the KORE3 hubs. I was able to easily remove the old tone rings with a standard 3-jaw puller, a little heat applied to the tone rings can help them pull off smoothly without breaking.
Note that the part number for rotor hats is different between the two configurations. The cast iron hubs require hats that have a deeper offset. Both part numbers cost the same (currently $101 per hat).
The calipers are readily available at most auto parts stores or on Rock Auto from many different brands (including AC Delco) in both reman and new for very affordable prices.
Pair the kit with your favorite D52 brake pads (any pads that would've fit in your original calipers) and you'll be all set. There's other threads on this forum that have recommendations for adequate pads to suit anyone's needs.
Options and Add-Ons
Brake Rotors
Coleman Racing will make rotors of most shapes and sizes. After some trial and error, I've come up with rotor specs that fit perfectly and allow any thickness of brake pad. Simply call Coleman Racing and tell them you want to order a set of Frank Gore brake rotors. The two choices are RACE or STREET;
RACE - For heavy duty applications to help prevent cracking from extreme heat. HD casting (thicker face), slotted, balanced, stress relieved via heat treatment, directional vents, $394.24 for the pair at current prices.
STREET - If you don't plan to race your car, save a few bucks over the race rotor. Standard casting (same face thickness as stock), plain face, balanced, directional vents, about $280 per pair at current prices.
Wilwood Calipers
In place of the OEM calipers listed above, you can also opt for Wilwood forged billet aluminum dual-piston calipers that will bolt right on. The part number for that is 120-10936 (available in gray, black or red, need 2 because they're interchangeable L/R). Those calipers require a 7/16-20 banjo bolt that's larger than the stock M10, so new front matching flex lines will be needed as well. Note that the stock brake fittings on the hard lines are M10-1.0 bubble flare. A combination of Fragola 352012 hoses and 650205 fittings would combine to make the correct flex line. Technically the dual 2" pistons have slightly less surface area than the huge single piston on OEM calipers, but the reduced flex of the caliper construction and the more even pressure applied to the pad means that they end up providing about the same braking effort as the OEM calipers. Only pads with a smooth backing plate will work (no shim rivets), and you can't use the retaining clip on the inside pad, so it might end up rattling around while not applying the brakes. This is not a safety or performance issue, just a potential annoyance. These calipers do look very pretty. They also might not fit in some OEM 15" wheels.
Solid Bearing Spacer
The factory-original method to mount the hub is to tighten the spindle nut to 12 ft-lb while turning the rotor (to seat the bearings directly against the races), then loosen the nut, re-tighten the nut by hand, and back it off to the closest cotter pin hole. This is intended to provide a bearing clearance of 0.001" to 0.005". However by using a solid bearing spacer, you can not only target a specific bearing clearance (ideally exactly 0.001"), you can also ensure that the bearing shells will never spin against the spindle. There's also speculation that pre-loading the spindle with the nut helps to stiffen it up. All of this provides noticeably more precise steering, longer bearing life, cooler-running hubs, and more predictable braking. Having the bearings with a 0.001" clearance helps prevent pad knock-back, so the brakes will be more likely to grab when you expect them to. Setting it up takes a bit more time and effort than a standard installation. KORE3 sells a bearing spacer kit that you can call and ask for. More recently, PTFB started selling a similar kit for less money that basically does the same thing. It can be found here: Wheel bearing spacers | Pro Touring FBody (I'm not affiliated with PTFB in any way, and I'm not promoting their product over the KORE3 product in any respect other than potential price, I've never used the PTFB bearing spacer. I have 2 sets of KORE3 bearing spacers that I love)
Stainless steel braided hoses
I don't think I need to describe these too much, everyone knows about them. They're available from many sellers and manufacturers. They'll improve the feel of the pedal by reducing flex in the system. They will not increase the amount of total braking force, though they may reduce the amount of pedal pressure needed to achieve the desired braking force, and they'll improve feedback through the pedal so you can better tell what the tires are doing.
Edit history:
5/19/25 - updated the rotor hat part number for the core kit from 170-0208 to 170-0357 after actually measuring the cast iron hub to confirm that its face has actually been machined down. Updated the effect on track width from 1/2" to 1/8" as a result. Updated the Wilwood caliper info to reflect the need for new lines in addition to banjo bolts.
4/11/25 - updated the hardware part number from 230-12020 to 230-12120 (original was a typo).
