The best 12 bolt disc brake conversion depends on the axle, vehicle, bolt pattern, and parking-brake needs. The Speedway Motors kit with a parking brake is best for buyers who want that feature in a bolt-on package, while the JEGS kit is aimed at 1964–1972 GM A-body applications. A separate Speedway bracket suits buyers replacing or sourcing only brackets. Confirm axle and vehicle fitment before ordering; a “12 bolt” description alone does not establish compatibility.
| Product | Best suited for | Key fitment note |
|---|---|---|
| Speedway Motors conversion kit | Mid-size GM cars | Not for full-size cars, pickups, or 7.5-inch 10-bolt axles |
| Speedway Motors kit with parking brake | Buyers seeking a parking-brake-equipped kit | GM 10- and 12-bolt rear axles |
| JEGS A-body kit | 1964–1972 GM A-body owners | Check rear shock placement |
| GM truck-pattern kit | Specified 1964–1987 applications | 5-on-5 bolt circle |
| Speedway Motors caliper bracket | Buyers needing brackets only | GM metric caliper spacing |
Speedway Motors Mid-Size Rear Disc Kit
This bolt-on kit is designed for GM 10- and 12-bolt rear ends in mid-size cars. It includes two caliper brackets, two vented rotors, two GM metric calipers, and installation hardware. It is best for a mid-size car owner seeking a package with the principal brake components and brackets included.
Why it was selected: The listed contents and vehicle category make it a clearly defined option for a mid-size GM application. Limitation: The seller says it is not suitable for full-size cars, pickups, or 7.5-inch 10-bolt axles. Check the exact axle before choosing it.
Speedway Motors Kit With Parking Brake
This bolt-on conversion is described for GM 10- and 12-bolt rear axles and includes an integrated parking-brake feature. Listed components include 11-1/4-inch vented rotors, loaded GM metric calipers with pads, brackets, brake lines, and hardware. It is best for buyers prioritizing a parking brake and a kit that lists brake lines among its contents.
Why it was selected: Its feature list identifies both the parking-brake function and several included installation components. Limitation: The provided details do not specify every vehicle or axle configuration it fits. Verify application, wheel clearance, and parking-brake connections before purchase.
JEGS GM A-Body Conversion Kit
This kit is listed for 1964–1972 GM A-body disc-brake conversions and is described as a bolt-on option for most 10- and 12-bolt rear axles. It is best for an A-body owner whose axle and suspension layout match the stated application.
Why it was selected: The year range and vehicle category provide useful fitment guidance for classic GM buyers. Limitation: It is specified for standard shock applications with both rear shocks either forward of or behind the axle housing. Confirm shock orientation and axle details; “most” does not mean every configuration.
GM Truck-Pattern Rear Disc Kit
This listing describes a rear axle-end conversion kit for 1964–1987 GM 10- and 12-bolt applications, with cross-drilled rotors and a 5-on-5 truck bolt circle. It is best for a buyer whose axle and wheel bolt pattern match those details.
Why it was selected: The truck-pattern specification distinguishes it from car-oriented kits. Limitation: The supplied description does not provide a more detailed vehicle list or a full component inventory. Confirm axle-end measurements, rotor pattern, and included hardware with the seller before ordering.
Speedway Motors GM Caliper Bracket
This is a bracket, not a complete disc-brake conversion kit. It bolts onto GM car 10- and 12-bolt rear-end housings and is listed for GM metric calipers with 5.45-inch center-to-center bolt spacing. The description also notes compatibility with GM emergency-brake calipers such as part 91031046.
Best for: Builders replacing or sourcing a bracket while obtaining the remaining conversion parts separately. Why it was selected: It is a relevant component for a 12-bolt conversion and clearly states caliper spacing. Limitation: It does not supply the rotors, calipers, or other parts needed for a complete conversion.
Buying Guide: Choosing a 12 Bolt Disc Brake Conversion
How do you confirm axle fitment?
Identify the vehicle year and model, rear axle type, axle-end configuration, and wheel bolt pattern before comparing kits. A 10- or 12-bolt label is not enough by itself: the listed products have distinct restrictions, including mid-size car use, A-body fitment, and a 5-on-5 truck pattern. Compare the product’s application notes with the actual vehicle and axle.
Should you choose a complete kit or individual parts?
A complete kit can simplify sourcing when it lists brackets, rotors, calipers, and hardware together. Check whether brake lines and parking-brake components are included rather than assuming every kit contains them. A bracket-only part is appropriate when the other components are already selected, but it is not a substitute for a full conversion package.
What else should you check before ordering?
- Confirm rotor bolt circle and wheel clearance for the intended setup.
- Check rear shock position when considering an A-body application.
- Verify whether the kit supports the desired parking-brake arrangement.
- Review the included parts list and ask about unclear fitment details.
Frequently Asked Questions
Will every 12-bolt disc conversion fit any GM 12-bolt axle?
No. Vehicle type, axle-end details, bolt pattern, and suspension layout can affect fitment. Use the kit’s application notes and verify the specific axle.
Is a caliper bracket a complete conversion kit?
No. The Speedway Motors bracket listing is for a bracket only. Rotors, calipers, and other required components must be sourced separately.
Which listed kit includes a parking brake?
The Speedway Motors 10- and 12-bolt rear disc conversion listing specifically identifies a parking-brake feature.
Does the JEGS kit fit every GM A-body?
The listing identifies 1964–1972 GM A-body applications and specifies standard shock arrangements. Confirm the vehicle, axle, and shock layout before purchase.
What does 5-on-5 mean for the truck-pattern kit?
It identifies a five-lug wheel bolt circle with a 5-inch pattern. Confirm that this matches the vehicle’s wheels and axle before selecting the kit.