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Servicing Yokes & Seals

Posted in How To: Transmission Drivetrain on September 20, 2017
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Transmissions and transfer cases are connected to axles using driveshafts, and those connections use U-joints and yokes. While the typical wear item in these links are the U-joints, there are times when yokes can give you problems as well. You may need to swap a yoke to one that supports a different-sized U-joint or when excessive U-joint angles are in play yokes may wear or become damaged. Transfer case or pinion yoke seals can start to leak over time and warrant replacement.

Yokes on the transfer case can usually be easily removed and replaced, retorquing the nut to factory specs. However, when it comes to axle pinion yokes, life can get a bit more complicated. The pinion gear spins on a pair of tapered roller bearings in the axlehousing or in the third member of an axle. During initial installation of the pinion with new bearings the installer preloads the bearing stack with a bit of tension. As the new bearings break in, that slight preload will diminish and leave the bearings free to spin but with no end-to-end play in the stack. If no preload were used, the bearings would end up with slight play in the assembly.

When installing the pinion, there are two ways to set the bearing preload. In one instance, a nonreusable crush sleeve is collapsed between the bearings when the assembly is tightened by the pinion nut, and this sleeve provides the bearing preload tension. The second method uses a solid cast-iron spacer, which does not collapse, so shims next to the spacer are added and subtracted to accurately set the bearing preload.

To remove and replace a pinion yoke and/or seal on an axle with a solid spacer, you can simply remove the pinion nut and then reinstall everything with a new pinion nut, tightening it to the proper torque spec. However, you can't really do this on an axle that uses a crush sleeve in the pinion bearings as you cannot reliably gauge the pinion bearing preload with a new yoke or nut.

We have seen cases where the pinion nut and yoke were removed to replace a pinion seal on an axle with a crush sleeve. The same yoke was then reinstalled and the same pinion nut reused, and tightened back to its exact original position. In these cases, the pinion nut was tack-welded to the end of the pinion to reliably retain it. This can be used when you'd really like to avoid tearing into the axle and you'll risk a quicker, cheaper fix.

When removing and installing yokes you'll need some way to hold the yoke while you tighten its nut. You can purchase tools designed to bolt to the yoke. This is a homemade tool that was made from part of a salvaged Toyota driveshaft flange with a metal rod welded to it.
You can see where the driveshaft yoke was contacting this pinion yoke due to excessive joint angle. It eventually led to worn yoke splines and damaged U-joint components. It was time to replace this yoke. Once the yoke is slid off the splined pinion or shaft, the seal can be easily pried free.
As mentioned, some axle pinions are set up with crush sleeves and need to be reassembled with a fresh crush sleeve. In that case, removal of the differential carrier is needed to get the proper pinion bearing preload. If dealing with a solid spacer setup, you'll probably find a stack of preload shims sitting behind the outer pinion bearing when you remove the bearing for inspection.
New seals can usually be carefully tapped into the axle or transfer case housing using a seal driver or small block of wood. When replacing seals that mate to a yoke, ensure the yoke seal surface is smooth and not pitted or badly scarred. It's generally a good idea to add a little silicone sealer to the mating splines to stop any oil creep there.
Note that the area where the yoke nut resides in some yokes can be tight. Many impact and some standard sockets may not offer good engagement on the hex nut. Specialty thin-wall sockets are available. However, for occasional use, we've taken cheap sockets and ground down the outer diameter near the end to fit in the depth of the yoke.
There are two methods of U-joint retention commonly used. U-bolts (left) go around the U-joint cap and through the yoke to be secured with nuts. Stamped straps (right) are secured to the yoke with small bolts. The U-bolt style is the stronger and more reliable option of the two.

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