Yukon Gear High Performance Gear Set For GM 12 Bolt Truck in a 3.73 Ratio
Many Chevy and GMC square-body and earlier half-ton trucks left the factory with tall, highway-friendly gears in the 12-bolt rear. Put a bigger tire under a C10, K10, K5 Blazer or Suburban, swap in a TH400 or an overdrive transmission, or just rack up enough miles for the old set to howl, and a 3.73 is the ratio most owners land on. The Yukon Gear & Axle YG GM12T-373 is a new 3.73 ring and pinion built for the truck version of the GM 12-bolt.
Yukon lists this set with an 8.875 in. ring gear, a 30-spline pinion and 12 ring gear bolts. The pinion rides on two tapered bearings held in preload by a crush sleeve and drives the ring gear on the carrier, so every turn of the driveshaft becomes 1/3.73 of a turn at the wheels. Moving to 3.73 from a 3.07 gives about 21 percent more torque at the tires, and from a 3.42 about 9 percent. In a truck with a three-speed automatic that means a stronger pull off the line and fewer kickdowns on grades. With an overdrive swap, 3.73 also keeps the converter and engine in a usable rpm range at highway speed. Keep in mind the truck 12-bolt is not the Chevelle and Camaro rear with a different badge: the carrier, ring gear offset and inner pinion bearing are all different, so car parts do not interchange.
Count the cover bolts and look at the cover shape; the truck 12-bolt has an irregular cover, while the car 12-bolt cover is a smoother oval. Find the current ratio from the axle code or by turning a rear tire once and counting driveshaft turns, using our axle ratio and code guide. If you are unsure whether the noise is in the axle at all, the TH350 gear ratios and specs page shows the transmission side of the gearing, and our differential whine diagnosis guide helps you separate gear noise from bearing noise.
Yukon lists this set for the GM 12-bolt truck rear in 1963-1986 Chevrolet C10 and K10 pickups and Suburbans, 1967-1986 G10 vans, 1969-1974 Blazer and 1975-1986 K5 Blazer, the 1987 R10 and V10, and matching GMC C15/C1500, K15/K1500, G15/G1500, G25/G2500 and Suburban models, plus the 1987 R1500 and V1500. Not every truck in those years has a 12-bolt; many have a 10-bolt or a 14-bolt instead, so count the bolts before ordering. This set fits the 4-series carrier for 3.73 and numerically higher ratios. A truck that came with lower gears may have a carrier that will not position the new ring gear correctly, so check your carrier, or send us your year and VIN. If you only need the pinion side refreshed, the GM 12-bolt truck ring and pinion installation kit is built for this axle.
Do not reuse old bearings with new gears. The Yukon YK GM12T master overhaul kit or the GM 12-bolt truck Timken master bearing kit covers the pinion and carrier bearings, races, shims, seal and crush sleeve. Yukon's setup chart gives the 12-bolt truck a starting pinion shim of 0.030 in., 13-15 in-lb of preload on new pinion bearings, 55 ft-lb on the ring gear bolts and 60 ft-lb on the bearing caps. Pull the C-clips by removing the cross-pin first, keep the side bearing caps on their own sides, and read the pattern on drive and coast with marking compound. Fill with 75W-90 gear oil, adding friction modifier for a limited-slip carrier. Break the gears in gently: light driving for the first 15 to 20 miles with a cool-down, no hard acceleration for 100 miles, no towing for at least 500 miles, then change the oil.
| Brand | Yukon Gear & Axle |
| Part number | YG GM12T-373 |
| Fits | Yukon Gear High Performance Gear Set For GM 12 Bolt Truck in a 3.73 Ratio |
| Type | Final Drive 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.
No. This is the truck 12-bolt set. Passenger car 12-bolt rears use a different carrier, ring gear offset and pinion bearing, so they need car-specific gears.
Yukon lists this set for the 4-series carrier used with 3.73 and numerically higher ratios. Lower-ratio trucks may have a different carrier series, so check yours before ordering or send us your year and VIN.
For a half-ton truck with a three-speed automatic, 3.73 is a common choice for tires around 31-33 in. Larger tires or heavy towing often call for a deeper ratio such as 4.11.
Pinion and carrier bearings and races, the pinion seal, shims, a new crush sleeve and ring gear bolts. A master overhaul kit or master bearing kit covers these parts.
75W-90 gear oil is the usual fill. Add friction modifier if the truck has a limited-slip or Positraction carrier, and change the oil after the break-in miles.
