Dana 70 Companion Flange 29 Spline Spicer 2010948

If the pinion seal on your Dana 70 keeps weeping gear oil no matter how many seals you put in, or the flange clunks and rocks on worn splines, the flange itself is usually the problem. This is Spicer 2010948, the genuine Dana-made round companion flange for a 29-spline Dana 70 pinion. Owners of older GM C20, C30, G30 and Express or Savana heavy vans, plus anyone rebuilding a Dana 70 or building a custom axle, search for exactly this part when the seal surface is grooved or the driveshaft end has been damaged.

What the companion flange does on a Dana 70

The companion flange slides onto the splined end of the pinion gear and is clamped there by the pinion nut. The driveshaft bolts to its face, so every bit of engine torque headed for the ring gear passes through these 29 splines. The hub of the flange also does a second job: its ground outer diameter is the running surface for the pinion seal lip. On 2010948 that hub is 1.875 in. and is machined smooth, which is why a scored or rusted flange will chew through a brand-new seal in a few thousand miles.

This is the round style rather than a U-bolt or strap yoke. The face has eight threaded M12-1.75 holes on a 4.25 in. bolt circle with a 2.000 in. male pilot, and it is rated for the 1350 series driveline. Because the flange stays on the axle, you can pull or swap a driveshaft without disturbing the pinion nut or the seal.

Symptoms that point to the flange

• Gear oil sling on the underside of the cab or the driveshaft, coming from the front of the axle, that returns after a new pinion seal.
• A visible groove or pitting on the seal surface of the old flange where the lip rides.
• A clunk on take-off or when shifting into drive, with play you can feel by rocking the flange by hand.
• Fretting, rust dust or twisted splines on the pinion end after the old flange comes off.
• Damaged threads or elongated holes after a driveshaft came loose or a U-joint failed.

How to confirm before you buy

Grab the flange and try to rock it up and down and side to side. Movement there means worn pinion bearings or a loose nut, not only a flange problem, and it needs to be fixed during the same job. Clean the seal area and look at it in good light; a groove you can catch with a fingernail means the flange should be replaced along with the seal. Our Dana 70 rear axle problems and rebuild cost guide walks through bearing noise, leaks and what a full rebuild involves, and the carrier bearing noise guide helps you tell a bearing growl from a driveline vibration.

Fitment

Spicer catalogs 2010948 for a 29-spline pinion in 1350 series service. It is listed for Dana 70 rear axles in GM trucks and vans, including Chevrolet C10 and C20 pickups and Suburbans from the 1960s and early 1970s, 1968-1972 G10 vans, 1975-1991 G30 vans, 1984-1986 C30, 1988-1990 C3500 and Express 2500 and 3500 vans. Those trucks were built with more than one rear axle, so look for the Dana tag or casting on the housing and count the pinion splines before ordering. Your driveshaft must also have a matching round flange on the 4.25 in. bolt circle; a truck that came with a U-joint yoke on the pinion will need the driveshaft end changed. If you would rather stay with a yoke, the Yukon 1350 yoke for Dana 60 and 70 uses the same 29-spline pinion. Not sure? Send us the year, VIN and a photo of the axle tag, or browse more axle hard parts.

Install notes

• Mark the driveshaft to the flange so it goes back in phase, then unbolt it.
• Check pinion bearing preload with an inch-pound torque wrench before you loosen the nut, and count the turns as it comes off.
• Use a two-jaw or flange puller; do not hammer the flange off the pinion.
• Install a new pinion seal, coat the seal hub and splines with gear oil, and draw the new flange on with the nut rather than driving it.
• Many Dana 60 and 70 pinions set preload with shims, not a crush sleeve. Torque the nut to the spec for your axle and recheck preload.
• Refill with the gear oil your axle calls for, typically 75W-90 or 75W-140, and add friction modifier if it has a limited slip.

If the bearings are already noisy, do the job once with the Dana 60/61 rear master overhaul kit or the Timken Dana 60 master bearing kit; check the pinion bearing numbers against your Dana 70 before ordering either.

Will Spicer 2010948 fit my Dana 70?

It fits a Dana 70 pinion with 29 splines when you want a round 1350 series flange. Count the pinion splines and confirm the axle tag before ordering, and make sure your driveshaft has a matching round flange with an 8-hole, 4.25 in. bolt circle.

What are the flange dimensions?

Spicer lists a 4.25 in. bolt circle with eight M12-1.75 threaded holes, a 2.000 in. male pilot, a 1.875 in. ground seal hub, 1.325 in. spline major diameter and 1.5 in. through-hole length, rated for 1350 series.

Should I replace the pinion seal at the same time?

Yes. The old seal lip has already worn to the old flange surface, so it will not seal reliably on a new one. Install a new pinion seal every time the flange comes off.

Does it come with a pinion nut or seal?

No. This is the flange only. Plan on a new pinion seal, and a new pinion nut is cheap insurance when the old one has been off before.

Why does my new pinion seal keep leaking?

The most common reason is a grooved or pitted seal surface on the flange hub. A worn pinion bearing that lets the flange move, or a vent that is plugged, can also push oil past the seal.

What gear oil goes in a Dana 70?

Use the grade your vehicle manual lists, typically 75W-90 or 75W-140 gear oil, plus friction modifier if the axle has a clutch-type limited slip.