A recent post discussing multiple premature rear axle failures, prompted me to put this post together. Does your shop take axle repairs seriously enough to provide the necessary tooling to achieve accurate pinion depth setting without trial and error or guess and by golly methods? Do you have to make do? Do you have alternate pinion shim selection tools that you are willing to demonstrate or share here? I have seen and used others, some good, some not so good. Gauge tools come in various shapes and sizes.

There are several methods to achieving successful pinion depth, given the work place circumstances. If the same axle housing is being used on an integral style axle housing, technicians will often get away with re-using the original shim.

What happens when your parts department hands you a brand new or used axle housing for you to build? Yes, I am well aware that there's a general starting shim depending on axle ratios, but why not blow the dust off that pinion depth gauging kit and give it a whirl?

This post will outline some of the tools and processes to achieve the pinion depth setting for a GM American Axle Manufacturing (AAM) 8.625" rear axle as used in many light duty GM pickup trucks. Set up is similar for other integral housing GM corporate and AAM axles. 10.5" corporate axles use a removable pinion carrier which is shimmed between the housing to achieve pinion depth. That will not be covered here.

Danas are also a different beast which require a slightly different location for shimming and use shims rather than collapsible spacers to achieve pinion rotational torque, so they will not be referenced in this post. GM uses nominal pinions, no +/- numbers to incorporate as in Danas of the past and other brands.

Along the way, some of the tools as used in GM dealerships will be depicted. You will likely have alternate tools and methods and that's fine by me. The object isn't to proclaim that the OEM tools and methods are the only way, it's simply to share effective information with interested parties who may benefit from discussion.

During axle disassembly the time will come to remove the companion flange (yoke) from the drive pinion. This tool [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] makes light work of holding the flange still while removing the pinion nut and washer. The forcing screw is then installed and the flange can be drawn from the pinion with a 1" socket and driving method of your choice. Here's the tool assembled on the flange following removal from the pinion [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo].

A driver handle threads onto the drive pinion and the pinion is removed from the bearings and the collapsible spacer and rear pinion bearing removed. Shown is the rear pinion bearing removal tool for later AAM axles. [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] This can then be mounted in a bearing splitter and pressed from the drive pinion.

The later design bearing cannot be removed using a bearing splitter alone as in previous designs. Both the early and later dsign bearings will physically fit into the axle housing and onto the drive pinion, but cup and cones are not interchangeable due to different internal dimensions between the cup and cone.

To save knuckles and minimize the chance of damage to the housing, I use this [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] MAC Tools PB37L driver to remove front and rear pinion bearing cups from the housing. It is approximately 18" overall length and does the job very well. Contrary to popular belief, the words "brass" and "bearings" should not be used in the same sentence. Brass can easily chip or transfer and embed in the surface of other components.

Always thoroughly clean and inspect the pinion bearing bores and shoulders for nicks and burrs after bearing removal. Use the end of a file or gasket scraper to remove any burrs, otherwise the replacement bearing cup may not fully seat in the bore.

Lubricate the bearing bores and outside of the pinion bearing cups, then install using the appropriate bearing drivers. Ensure the cups are fully seated. If the rear bearing is not fully seated, you might as well guess the required pinion shim! In these axles the shim fits between the drive pinion head and rear bearing.

Here's the GM spec pinion depth gauging kit, which has adaptors and two arbors which fit the needs of 6.5" - 9.5" GM axles. [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] and instructions/application guide [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo]. Here's a better view of some of the adaptors and gauge plates [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] and [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo]. Here is how the selected adaptors and gauge plate will fit in place of the drive pinion [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo].

With the gauge plate assembled in the housing in lubricated bearings and the specified rotational torque achieved [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo], the 8.5" gauge block will be utilized in this instance. 8.5" ring diameters were updated to 8.625" many years ago, as were 7.5" to 7.625" ring gears, but the gauge plates are the same. [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] shows the gauge arbor, discs and dial indicator assembled in the axle housing. With the side bearing caps installed and torqued to specs, the arbor should rotate freely. A misaligned bearing bore can quickly be identified using the arbor.

This is my well-used personal kit for axle set up with a few extras. [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo]

With the dial indicator in alignment with the head of the spring loaded arbor plunger and the plunge tip placed on the gauge plate, slide the dial indicator down the pillar until approximately 3/4 revolution of gauge travel is noted after the indicator contacts the arbor plunger.

Rotate the arbor, while maintaining plunger contact with the gauge plate and note the location of highest upward deflection of the arbor plunger. Zero the dial indicator at this point [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo]. Recheck and make any re-adjustment to ensure that maximum upwards movement indicates zero."

Rotate the arbor until the plunger moves completely off the gauge plate surface. Read the measurement on the dial indicator. [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] In this case the original shim actually measured 0.0375" with a micrometer and is very close to the gauged shim value on the dial indicator.

With the shim and drive pinion rear bearing lubricated and installed, assemble the pinion into the axle housing, install a new collapsible spacer (crush sleeve) lubricated front pinion bearing, pinion seal and companion flange with sealant on flange splines. Install washer, a new pinion nut and tighten nut to achieved specified rotational torque. Rotating the pinion and a light "love tap" will seat the pinion bearing rollers which have a tendency to skew slightly during the tightening process. Use your preference of brute force or torque multiplier [2007 Chevrolet Silverado 1500 Classic LT, Not Applicable photo] to collapse the spacer. Be very careful to advance slowly in small increments when close to achieving spec torque which noted during rotation of the pinion.

With the pinion shim selected and installed, all that remains is to reassemble the gear case into the housing, set backlash and side bearing preload, then take a contact pattern. There's nothing to that part of the process, or is there??? How is shim selection achieved to obtain backlash and side bearing preload measured? Maybe next time.

For those who have never experienced set up of rear axles, I hope you found this process interesting. Other methods and tools will differ. Feel to share your methods.

Regards.

Martin from British Columbia

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