The best rear differential spider gears are the ones matched to your axle, carrier, spline count, and differential type. The USA Standard Gear GM 8.6-inch set is a targeted option for specified 2000–2006 carriers; its AMC Model 35, GM 12-bolt, and Ford 8.8-inch sets serve other distinct applications. A separate Ford 8.8-inch kit listing describes a 31-spline application and limited-slip performance. Confirm the exact differential before ordering: these parts are not interchangeable simply because they are all spider gear sets.
| Product | Best for | Key fitment detail |
|---|---|---|
| USA Standard Gear GM 8.6-inch | Specified GM 8.6 carriers | 2000–2006; carrier design and casting numbers matter |
| USA Standard Gear AMC Model 35 | AMC Model 35 owners | 1.560-inch side gear bore |
| DOFOCH Ford 8.8-inch kit | Buyers checking a listed 31-spline kit | Listing specifies 1986–2013 applications |
| USA Standard Gear GM 12-bolt | GM 12-bolt car or truck owners | 30 spline |
| USA Standard Gear Ford 8.8-inch | Ford 8.8 open differentials | 31 spline; not for limited-slip units |
USA Standard Gear GM 8.6-Inch Spider Gear Set
Best for: Buyers repairing a compatible GM 8.6-inch open differential with the specified V2 carrier design. The fitment information identifies 2000–2006 applications and carriers with one large and one small opening, casting number 7875 or 1073.
The set includes two side gears, two pinion gears, a cross pin shaft, cross pin bolt, and spider gear thrust washers. That makes it a clearly specified replacement set for the listed carrier configuration.
Check before buying: Do not rely on axle diameter or vehicle year alone. The carrier design and casting number are important, and this set is not described as a universal GM 8.6 replacement.
USA Standard Gear AMC Model 35 Set
Best for: AMC Model 35 owners whose differential uses a 1.560-inch side gear bore. This application-specific sizing makes it a better choice than a generic set when the axle and bore match.
USA Standard Gear describes it as an OEM replacement-quality set. Included parts are two side gears, two pinion gears, a cross pin shaft, cross pin bolt, and spider gear thrust washers.
Check before buying: The listing’s Model 35 designation does not eliminate the need to verify the side gear bore. Avoid choosing it if that dimension or the axle identification is uncertain.
DOFOCH Ford 8.8-Inch 31-Spline Kit
Best for: Buyers investigating a replacement kit for a Ford 8.8-inch rear axle who can confirm that the listed 31-spline application and part references match their differential. The product description names 1986–2013 Ford 8.8-inch rear axles and lists several replacement identifiers.
The seller describes a 31-tooth spiral gear design and claims improved torque distribution and traction. Treat those as listing claims, and verify what components are actually included before purchase, especially because the product name also refers to a clutch kit.
Check before buying: Confirm axle year, spline count, differential configuration, and part number with the seller or a parts professional. The description alone does not establish fitment for every Ford 8.8 axle.
USA Standard Gear GM 12-Bolt 30-Spline Set
Best for: GM 12-bolt car and truck differential owners who need a 30-spline standard spider gear set. The listed axle family and spline count provide useful fitment checks before ordering.
The package includes two side gears, two pinion gears, the cross pin shaft, cross pin bolt, and spider gear thrust washers. USA Standard Gear identifies the set as OEM replacement quality.
Check before buying: This is not identified as a fit for every GM rear axle. Verify that the differential is a 12-bolt unit and that the 30-spline specification matches.
USA Standard Gear Ford 8.8-Inch 31-Spline Set
Best for: Ford 8.8-inch owners with a standard open differential and 31-spline application. The set is identified as steel and uses a 7/8-inch cross pin shaft.
The key advantage is the explicit restriction: the listing says it does not work with 28-spline applications or positraction/limited-slip differentials. That makes this option easier to screen when the axle configuration is known.
Check before buying: Avoid this set if the differential is limited-slip or the axle uses 28 splines. Confirm the open differential type and spline count before selecting it.
Buying Guide: How To Choose Rear Differential Spider Gears
What axle and carrier do you have?
Start with the differential family, such as GM 8.6, AMC Model 35, GM 12-bolt, or Ford 8.8. Then check carrier details, casting numbers, model year, and any measurements specified by the product. A matching vehicle make is not enough to establish fitment.
How important is spline count?
Spline count identifies how the side gear connects to the axle shaft. Compare the actual application with the listing: the products here include 30-spline GM 12-bolt and 31-spline Ford 8.8 options. Do not assume that two sets for the same axle family share the same spline count.
Is the differential open or limited-slip?
Spider gear sets are configuration-specific. The USA Standard Gear Ford 8.8-inch 31-spline set is expressly for an open differential and excludes positraction or limited-slip units. If the differential type is unknown, identify it before ordering rather than relying on the product title.
What should the kit include?
Compare the included parts with the repair need. Several USA Standard Gear sets list two side gears, two pinion gears, a cross pin shaft, bolt, and thrust washers. For other listings, confirm the full contents directly; a product title alone may not describe every component.
Frequently Asked Questions
Are rear differential spider gears interchangeable?
No. Fit depends on axle family, carrier design, spline count, and differential type. Check the specifications for the exact unit.
Can I use open-differential gears in a limited-slip differential?
Not automatically. The Ford 8.8-inch 31-spline set listed here specifically excludes positraction and limited-slip differentials.
What does a side gear bore measurement tell me?
It is a fitment dimension for the side gear. The AMC Model 35 set requires a 1.560-inch bore, so verify that measurement before purchase.
Which set is for a GM 12-bolt?
The USA Standard Gear GM 12-bolt set is listed for 30-spline car and truck differentials.
What should I do if I cannot identify my differential?
Use axle or carrier identification information and consult a qualified parts professional. Confirm the part number and specifications before ordering.