USA Standard Gear Spider Gear Kit For GM 12 Bolt Car and Truck
A Chevelle, Camaro, Nova or Impala with a 12-bolt that clunks when you turn into a driveway, or a C10, K10, Blazer or Suburban that clicks from the rear in tight turns, very often has worn spider gears in its open differential. The USA Standard Gear ZIKGM12-S-30 is a replacement spider gear set for the GM 8.875-inch 12-bolt, car and truck, with 30-spline side gears. It lets you fix the open carrier you already have instead of buying a new one.
Both the car and truck 12-bolt use an 8.875-inch ring gear and a 12-bolt cover, and both use C-clips to hold the axle shafts in. Inside the open carrier, two 30-spline side gears ride on the axle shaft splines and two spider gears turn on a cross shaft between them. The cross shaft is held by a single lock bolt. Driving straight, the gears stay locked together. In a turn the spiders spin on the shaft so the outer wheel can turn faster. On a 12-bolt the cross shaft has a second job: the inner ends of the axles butt against it, which is what keeps the C-clips seated. A worn shaft or chewed thrust washers let the axles move in and out, and that slop shows up as clunks and as chipped teeth on the spider gears.
The kit includes two side gears, two spider gears, the thrust washers, the cross shaft pin and the cross shaft pin bolt. It is for open carriers only.
Pull the cover and drain the gear oil into a clean pan. Turn one rear wheel by hand with the other held and watch the spider gears for chips, cracks or a rough feel. Check the cross shaft for a stepped wear groove and look at the thrust washers for scoring. A rising whine at highway speed points more to the ring and pinion or carrier bearings. If that is your noise, a car axle rebuild with the GM 12-bolt car master bearing kit or the GM 12-bolt truck master bearing kit is the right repair.
This kit fits GM 8.875-inch 12-bolt open carriers with 30-spline axles, car and truck. USA Standard's catalog lists 1964-1972 Chevelle, El Camino, Impala, Bel Air and Biscayne, 1967-1972 Camaro, 1969-1972 Nova and Firebird, 1970-1972 Monte Carlo and GTO, and GM light trucks: 1963-1987 C10, K10 and Suburban, 1969-1987 Blazer and K5 Blazer, R10 and V10, plus GMC C15, K15, C1500 and K1500 trucks, and G10 and G1500 vans. Most of these vehicles were also built with other GM axles, such as the 10-bolt. Count the cover bolts (12 on this axle) and check for the 30-spline count. If your 12-bolt has a factory Positraction or an aftermarket locker, this open kit does not apply. If you upgrade instead, see the Dura Grip Positraction for the 12-bolt, 30-spline. Send us the year and VIN when in doubt, and browse more kits in our rebuild kits section.
| Brand | Yukon Gear & Axle |
| Part number | ZIKGM12-S-30 |
| Fits | USA Standard Gear Spider Gear Kit For GM 12 Bolt Car and Truck |
| Type | Differential Spider Gears |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Yes. It is listed for GM 8.875-inch 12-bolt car and truck axles with open carriers and 30-spline axle shafts.
Two side gears, two spider gears, thrust washers, the cross shaft pin and the cross shaft pin bolt.
Yes. The spider gears come out through the carrier window, so the carrier stays in the housing and backlash and bearing preload are not affected.
No. This set is for open carriers only. A Positraction or limited slip unit uses different internals and clutch packs.
Count the cover bolts. The 12-bolt has 12 and an 8.875-inch ring gear. GM's 10-bolt axles have 10. Check the spline count on an axle shaft while it is out, too.
Quality 75W-90 GL-5 gear oil is typical for an open 12-bolt. Check the shop manual for your year for the exact grade and fill level.
