Junkyard 10-bolt now or save for a 9-inch?
If it's an 8.5/8.6, a junkyard 10-bolt can be a real option — it's the one high-performance 10-bolt. The 7.5 and 8.2 are much more limited:
Last updated
| GM 10-bolt | Stock capacity | Notes |
|---|---|---|
| 8.5 / 8.6 | The only high-performance 10-bolt; can hold about 1,000 hp built properly | Large square lugs at 5 and 7 o'clock; flat webs on the front; 28- or 30-spline |
| 8.2 (1964–72) | About 400 hp on street tires, 350 on drag radials, 300 on slicks | Built for racing: about 500 hp on street tires, 400–450 on slicks |
| 7.5 / 7.625 | About 350 hp on street tires | Maxes out around 500 hp with maximum effort and expense; 28-spline only, no 30-spline upgrade |
When to save for a 9-inch: Most Ford 9-inch units handle 600 hp or more, and reinforced ones over 1,000. Direct bolt-in 9-inch housings exist for several GM applications, including muscle cars and C/K pickups. At 600 hp and up, especially with boost and slicks, put the money into a stronger rear rather than building a 10-bolt.
Telling them apart: measure from the lower center cover bolt to its neighbors — about 3-1/4 in on a 7.5, 3-3/4 in on an 8.5/8.6. The 8.5 has large square lugs at 5 and 7 o'clock; the 7.5's are small. Confirm with the codes stamped on the axle tube.
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Check before ordering a differential and bearings
The 8.5/8.6 uses a 1-1/4 in pinion nut, left-hand-threaded 7/16-20 ring gear bolts, and a 1.625 in pinion shaft with 28 or 30 splines. Most use C-clip axles. The 8.5 and 8.6 share the same basic design; verify the actual axle and spline count before ordering parts.