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GM 8.5 / 8.6 10-Bolt
Common light-duty GM rear-axle family. The 8.5 and later 8.6 designations matter when ordering gears, carriers and bearings.
- Often encountered in half-ton GM applications.
- C-clip axle retention is common in this family.
- Verify exact year/application, spline count, brakes and carrier before parts ordering.
GM 9.5-Inch
A distinct GM rear axle family used in heavier applications. Do not confuse it with the 10.5-inch full-floating 14-bolt.
- GM service information treats 9.5-inch axles separately from 8.6, 10.5 and 11.5.
- Confirm semi-float/full-float construction and donor application.
- Good candidate when the original light-duty axle is no longer appropriate for the truck's use.
GM 10.5-Inch 14-Bolt
The classic heavy-duty GM 14-bolt family. It is a different assembly from smaller 14-bolt axles and should be identified by more than the cover.
- Commonly recognized as the heavy-duty full-floating 14-bolt.
- Large physical size affects clearance, wheel/brake choices and swap packaging.
- Measure spring-pad spacing, pinion location, wheel bolt pattern and driveshaft interface before a swap.
GM 11.5-Inch HD
Later heavy-duty GM trucks use an 11.5-inch rear axle family. GM service specifications list it independently from 10.5-inch axles.
- Designed around HD truck duty rather than light-duty performance swaps.
- Weight, brakes, hubs and packaging are major considerations.
- Use the donor's exact service information for setup and lubricant requirements.
GM 12-Bolt
The familiar 8.875-inch 12-bolt exists in passenger-car and truck forms. Those versions should not be treated as automatically interchangeable.
- Strong aftermarket support makes it relevant to classic C10 and performance builds.
- Confirm truck vs passenger housing and application before ordering internals.
- Gear setup requires pinion depth/preload, backlash and contact-pattern verification.
Ford 8.8
A common performance-swap family with broad aftermarket support. Donor width, pinion offset, spline count, brakes and bolt pattern vary.
- Do not buy from the “8.8” name alone—measure the donor.
- Plan spring/link mounts and driveshaft flange/yoke adaptation.
- ABS/tone-ring and parking-brake compatibility can matter on street builds.
Ford 9-Inch / Aftermarket 9-Inch
Popular where builders want extensive gear, differential, housing and axle choices. Aftermarket housings make custom width and mounting easier.
- Third-member design simplifies ratio/differential service.
- Custom housings can solve width and mount-location problems.
- Strength depends on housing, center section, pinion support, differential and axle package—not the name alone.
Ratio, Tire & Transmission Work Together
Rear gear choice should be evaluated with transmission ratios and actual tire diameter. A deep first gear such as the 6L80's changes launch multiplication dramatically compared with a TH400 or 4L80E, while overdrive determines cruise rpm. Use the calculators before buying a ring-and-pinion.
| Question | Check Before Buying | Why |
|---|---|---|
| What axle is it? | Housing/cover, ring-gear family, donor year/model, spline count, brakes | “10-bolt” and “14-bolt” are not precise enough for parts ordering. |
| Will it fit? | Wheel-mounting width, spring/link mounts, pinion location, bolt pattern | A strong axle that does not match chassis geometry creates fabrication work. |
| Will the driveshaft connect? | Yoke/flange type, U-joint series, pinion position, transmission length | Transmission or axle swaps often change driveshaft length and joint requirements. |
| What ratio? | Tire diameter, transmission ratios, desired cruise RPM, powerband | Axle ratio cannot be chosen intelligently in isolation. |
| Open, LSD or locker? | Street use, towing, drag use, tire size, differential compatibility | Traction behavior and service needs differ substantially. |
Gear Setup Is Precision Work
Ring-and-pinion work is not just bolt-on assembly. Pinion depth, bearing preload, backlash and tooth-contact pattern must be established correctly. Chevrolet Performance's own gear-kit instructions point installers back to the vehicle service manual for detailed procedures and specifications.