Rear Diff Identifier

Identify Toyota, Ford, GM and Dodge/Mopar rear differentials by cover shape, bolt count and ring-gear size — with common ratios.

Eskimo Auto & Truck Parts — Rear Diff Identifier

https://www.eskimoautoandtruckparts.com/tools/rear-diff-id · (780) 473-2424

Reference only — verify against your owner's manual or factory service information before performing any work. Full terms: https://www.eskimoautoandtruckparts.com/tools/terms

GM/Chevrolet axles

GM 7.5" / 7.625" 10-Bolt (rear)

7.5 in. (enlarged to 7.625 in. from ~1986; the two interchange and are treated as one family) ring gear

10-bolt oval cover

Cover / bolts: 10-bolt oval cover, approx. 8-5/16 in. x 10-9/16 in.; distance from the bottom-center bolt to the adjacent bolts is 3-1/4 in.
Common vehicles: 1975-2005: Camaro/Firebird (F-body), Monte Carlo/Regal/Grand National/Cutlass (G-body), full-size B-body cars, S-10/S-15 Sonoma pickups and Blazer/Jimmy, Astro/Safari vans
How to identify: Small oval cover with two small cast-in lugs on the housing near the lower cover bolts (roughly 5 and 7 o'clock); 1.438 in. pinion; C-clip axles; ratio/plant/date code stamped on the axle tube. The 3-1/4 in. lower-bolt spacing separates it from an 8.5, which measures 3-3/4 in. The later 7.625 version is visually near-identical - treat as the same axle for ID purposes.
Common ratios: 2.73, 3.08, 3.23, 3.42, 3.73, 4.10

GM 8.2" 10-Bolt (classic Chevy)

8.2 in. ring gear

Cover / bolts: 10-bolt cover; two factory styles - an ~11 in. smooth cover, or a 10-3/4 in. cover with a hooded/diagonal ridge at the top
Common vehicles: 1964-72 Chevelle/El Camino, 1967-69 Camaro, Nova (into the early '70s), and 1960s-early-'70s full-size Chevrolets
How to identify: Lower half of the center casting is smooth and rounded with NO cast lugs at the bottom - the quickest tell vs. an 8.5. Ring-gear bolts are 3/8-24 left-hand thread with 9/16 in. heads (an 8.5 uses 7/16 in. bolts with 3/4 in. heads); 1.438 in. / 25-spline pinion; C-clip axles on Chevy versions, while Buick/Olds/Pontiac variants use bolt-in axles with retainer plates; ratio/date/plant code stamped on the axle tube.
Common ratios: 2.56, 2.73 (high-ratio carrier); 3.08, 3.36, 3.55, 3.70 (low-ratio carrier, split at 3.08)

GM 8.5" / 8.6" 10-Bolt

8.5 in. (8.625 in. "8.6" version in 1999-and-up trucks) ring gear

Cover / bolts: 10-bolt cover; most common is an ~11 in. round cover with a bulge on the driver side, though some truck versions use a 10-5/8 in. irregular cover; distance from the bottom-center bolt to the adjacent bolts is 3-3/4 in.
Common vehicles: 1970-81 Camaro/Firebird; 1971+ A/B/G-body cars (Chevelle from late 1972); 1/2-ton trucks, SUVs and vans through 1998; 8.6 version in 1999-2013 Silverado/Sierra 1500 (GMT800 + GMT900; 2014+ moved to 9.5/9.76); also served as the solid FRONT axle on 1977-91 4x4 K10/K20/Blazer/Suburban
How to identify: Two large squared-off cast lugs with vertical sides at the 5 and 7 o'clock positions on the bottom of the case, plus flat cast webs on the front of the housing (8.5-only feature). 1.625 in. pinion with 28 or 30 splines; ring-gear bolts 7/16-20 left-hand with 3/4 in. heads; C-clip axles (rare 1971-72 BOP bolt-in variant exists). The 8.6 (1999+) is visually near-identical, with 30-spline axles and disc or drum rear brakes depending on year/package (discs 1999-2004; drums standard on most 2005-2013 1500s). Lower-bolt spacing of 3-3/4 in. vs 3-1/4 in. distinguishes it from a 7.5.
Common ratios: 2.41-4.10 factory range; commonly 2.73, 3.08, 3.23, 3.42, 3.73, 4.10

GM 8.875" 12-Bolt (car & truck)

8.875 in. ring gear

Cover / bolts: 12-bolt cover; car cover is oval, approx. 10-15/16 in. wide x 10-5/8 in. tall; truck cover is an irregular (non-oval) shape with a raised area over the ring gear
Common vehicles: Cars 1964-72 (Chevelle, El Camino, Camaro, Nova, Impala, Monte Carlo); trucks 1965-87 (C-series pickups, G-vans, Blazer)
How to identify: Car and truck versions share the 8.875 in. ring gear but do NOT interchange: car pinion is 1.625 in.; truck pinion is 1.438 in. with a narrower carrier (early truck axles use 12 coarse splines). Oval cover = car, irregular cover = truck. Ratio/date/plant/Positraction code is stamped on the passenger-side axle tube; C-clip axle retention; factory Positraction units use 30-spline axles.
Common ratios: Car: commonly 3.07, 3.31, 3.55, 3.73, 4.10 (carriers: Type-2 to 2.73, Type-3 3.08-3.73, Type-4 3.90+)

GM 9.5" 14-Bolt Semi-Float

9.5 in. ring gear

Cover / bolts: 14-bolt cover (same bolt count as the 10.5 in. full-float - check the wheel hubs to tell them apart)
Common vehicles: 1981-99 Chevy/GMC light-duty C/K2500 pickups and Suburbans, some heavy-half 1500s (454SS, diesel), Tahoe/Yukon; G30 and Express/Savana vans into the 2000s
How to identify: Semi-floating: axle shaft ends are flush with the wheel face - no hub protruding through the wheel center (comes in 6- or 8-lug). If it has 8 lugs but no visible axle end, it is the 9.5 SF, not the 10.5 FF. 33-spline C-clip axles, 1.876 in. pinion, ~3.25 in. axle tubes.
Common ratios: 3.42, 3.73, 4.10

GM 10.5" 14-Bolt Full-Float

10.5 in. ring gear

Cover / bolts: 14-bolt cover; large, roughly octagonal shape
Common vehicles: 1973-2000 Chevy/GMC 3/4- and 1-ton pickups, Suburbans and vans; continued in Express/Savana 2500/3500 vans, and 2001-2010 Silverado/Sierra 2500HD with the 6.0L gas engine kept an updated AAM 10.5 14-bolt (removable 6-bolt pinion support); 3500s and Duramax/8.1L 2500HDs moved to the AAM 11.5
How to identify: Full-floating design: 8-lug hubs protrude roughly 2-4 in. beyond the wheel mounting surface with a visible bolted axle flange at the center - the classic tell vs. the 9.5 semi-float. 30-spline full-float axles; ring gear mounts with 12 bolts; no C-clips. Widths approx. 67.5 in. (SRW), 72 in. (DRW), 63.5 in. (cab & chassis). Carrier break between 4.11 and 4.56.
Common ratios: 3.21-5.38 factory range; commonly 3.73, 4.10, 4.56 (also 4.88, 5.13)

AAM 11.5" 14-Bolt

11.5 in. ring gear

Cover / bolts: 14-bolt cover on a cast-iron center section
Common vehicles: 2001–2019 Chevy Silverado / GMC Sierra 2500HD and 3500; 2003–2018 Ram 2500 and 3500 — Ram 3500 moved to the AAM 11.8 partway through 2013, so check the build sticker
How to identify: Looks like an oversized 14-bolt: full-floating, 14 cover bolts, but with an 11.5 in. ring gear (12 ring-gear bolts) and roughly 10,000 lb GAWR - about 1,500 lb more than the 10.5 it replaced. GM and Ram versions do not interchange (different axle tubes, hubs and brackets) even though both use 30-spline shafts; GM tubes measure ~4.0 in. at the spindle vs ~3.5 in. on Ram.
Common ratios: GM: 3.73, 4.10; Ram: 3.42, 3.73, 4.10

GM/AAM 9.25" IFS (front)

9.25 in. ring gear

Cover / bolts: 1988-2010: two-piece aluminum clamshell case with no conventional rear cover; 2011+: one-piece Salisbury-style case with a removable service cover
Common vehicles: 1988-2010 K2500/K3500 and Silverado/Sierra 2500HD/3500 4x4 (clamshell style); 2011+ Silverado/Sierra 2500HD/3500HD 4x4 (Salisbury style)
How to identify: Lightweight cast-aluminum center section mounted to the IFS crossmember, driving CV axle shafts - found under 8-lug 3/4- and 1-ton 4x4s. 33-spline axle shafts. Pre-2011 clamshell cases split in two to service; 2011+ AAM Salisbury cases have a removable cover instead. Distinguish from the half-ton 8.25 IFS by truck rating and its larger 33-spline (vs 28-spline) shafts.
Common ratios: 3.42-4.56 factory range; commonly 3.73, 4.10

GM/AAM 8.25" IFS (front)

8.25 in. ring gear

Cover / bolts: Two-piece aluminum clamshell case; no conventional rear cover
Common vehicles: 1988 through late-2010s Chevy/GMC 1500 4x4 pickups and SUVs - GMT400/800/900 Silverado/Sierra 1500, Tahoe, Yukon, Suburban 1500
How to identify: The half-ton IFS front: aluminum clamshell center section with 28-spline axle shafts (the HD trucks' 9.25 IFS uses 33-spline). Case style evolved across GMT400/800/900 generations but remained a clamshell. Ratio is easiest to confirm from the glovebox RPO sticker: GU4 = 3.08, GU6 = 3.42, GT4 = 3.73, GT5 = 4.10.
Common ratios: 3.08, 3.42, 3.73, 4.10

Cover silhouettes are schematic — for identification only, not to scale, and shown only where the shape and bolt count are well documented. Quick method: count the cover bolts and measure across the ring gear, then call us with the axle + ratio and we'll pull a match from the yard, complete and ready to swap.

Once you know your axle, check your ratio with the gear ratio calculator — or skip the math and request a complete differential from our yard.

Reference information only, provided "as is" without warranty. Specs vary by exact vehicle, trim, and production date — always verify torque figures, capacities, and fitment against your owner's manual or factory service information before performing any work. Tool Terms of Use.

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