Yukon Gear Master Overhaul Kit For GM 8.5in Front Diff

A K5 Blazer, Jimmy, Suburban or square-body K10 and K20 pickup that howls in four-wheel drive, drips gear oil from the front pinion or clunks when the hubs are locked is telling you the front ten-bolt needs attention. The Yukon Gear and Axle YK GM8.5-F is the master overhaul kit for the GM 8.5 in. front differential, with Timken bearings and races, axle seals and all the setup hardware to rebuild the solid front axle these trucks are known for.

What the master kit does in a GM 8.5 front axle

The GM ten-bolt front is an iron-beam, leaf-sprung drive axle with pressed-in ball joints, built around an 8.5 in. ring gear. Like the rear axles it shares a name with, the pinion turns on two tapered bearings set with a crush sleeve, and the carrier rides on side bearings with shims that control backlash and preload. A front axle has a harder life than most rears: it sits idle in two-wheel drive, then takes sudden shock loads in four-wheel drive, and water crossings get past tired seals. Worn bearings let the gears move, the pattern wanders, and the axle gets loud under load.

The YK GM8.5-F includes Timken carrier bearings and races, Timken pinion bearings and races, a pinion seal, axle seals, a complete shim kit, ring gear bolts, a pinion nut, a crush sleeve, thread locker, marking compound with a brush and the cover gasket. The axle seals are what set this front kit apart from Yukon's rear 8.5 kits, so the axle comes back together dry.

Symptoms of a worn front ten-bolt

• Whine or howl from the front only when four-wheel drive is engaged
• Growl that changes with speed in 4WD, typical of carrier or pinion bearing wear
• Clunk when engaging 4WD or getting on and off the throttle with the hubs locked
• Gear oil around the pinion seal, the axle tube ends or the cover
• Milky gear oil after water crossings, a sign that seals are letting water in

How to confirm it is the front differential

Drive the truck in two-wheel drive with the hubs unlocked, then lock the hubs and repeat in 4WD on a loose surface. A noise that only appears in 4WD and changes between throttle and coast points to the front gears or bearings. With the front on stands, rock the front pinion yoke to check for play, and pull the fill plug to look for water or metal. Measure backlash with a dial indicator and magnetic base before teardown so you know where the axle started. Worn hubs can mimic axle noise, so spin each locked hub by hand and check the locking hubs while the truck is up.

Fitment

This kit is listed for the GM 8.5 in. ten-bolt front differential. Torque King's usage chart puts that axle under most 1977.5-1980 Chevy and GMC half-ton and three-quarter-ton 4x4 trucks and SUVs (a Dana 44 was also used in those years), all of them from 1981-1987, and the Blazer, Jimmy and Suburban from 1988-1991. Identify it by the oval ten-bolt cover, about 11 in. tall by 10-1/4 in. wide, with no flat sides; a Dana 44 cover has flat edges. It does not fit the independent front axles on 1988-and-later pickups. Send us your year and VIN and we will confirm fitment, or browse the full lineup on the rebuild kits page.

Install notes

• The front axle shafts have to come out before the carrier can: remove the hubs, spindle nuts and spindles, then slide the shafts out. Inspect the spindles and their bearings while they are off.
• Install the new axle seals before the shafts go back in, and guide the splines through so they do not cut the seal lips.
• Record the factory shim stacks; they are the starting point if you reuse the gears.
• Press races fully home with a proper driver, such as our 43-piece bearing race and seal driver set.
• Set pinion preload slowly against the new crush sleeve and check rotating torque often.
• Use thread locker on the ring gear bolts and confirm the pattern with the marking compound.
• If you regear the rear, the front must match the same ratio.
• Fill with 75W-90 gear oil to the bottom of the fill hole.

Which trucks have the GM 8.5 front ten-bolt?

Per Torque King's usage chart: most 1977.5-1980 Chevy and GMC half-ton and three-quarter-ton 4x4 trucks and SUVs (some got a Dana 44), all of them from 1981-1987, and the Blazer, Jimmy and Suburban from 1988-1991.

Is this the same as the GM 8.5 rear kit?

No. This kit is built for the front axle and adds axle seals, which the rear 8.5 kits do not include. Order the rear kit separately if you are doing both axles.

Will it fit my 1995 Silverado 4x4?

No. Chevy and GMC pickups moved to independent front suspension for 1988, and those independent front differentials need a different kit.

What is included?

Timken carrier bearings and races, Timken pinion bearings and races, a pinion seal, axle seals, a complete shim kit, ring gear bolts, a pinion nut, a crush sleeve, thread locker, marking compound with a brush and a gasket.

What fluid does the front axle take?

75W-90 gear oil, filled to the bottom of the fill plug hole. Change it after any deep water crossing if it looks milky.