Old Differential Disassembly


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The Chevrolet Differential

My truck has a Chevrolet 15,000# vacuum actuated 2-speed rear axle. During my initial test drive, I discovered a problem that I believed was related to the 2-speed rear axle. Rear axle operation was normal when in "Low"; however, when shifted to "High", it felt and sounded like the truck was popping out of gear. Shift it back to "Low" and everything worked fine. It should be noted that the original differential was replaced by the previous owner (or owner before him) for some undisclosed reason. The original differential was, however, included with the purchase of the truck.

I decided to take the original differential apart in an attempt to figure out why it needed to be replaced. This merely involved taking the differential apart, cleaning the pieces and looking for obvious signs of failure such as broken components, excessive wear and tear, thermal damage, etc.

The removal of all the components was fairly straightforward, though I sure am glad I bought that 24 piece 3/4" socket set...everything is big on a C60. Each piece was cleaned in my parts tank as it came off. I found the major components (yoke, drive pinion gear, ring gear, shifter sleeve and yoke, bearings and races) to actually be in great shape given their age and the fact that it's a 2 ton truck.

Next I unbolted the ring gear from the Differential and Planet Support Case and Ring Gear and split open the case to reveal the sun and planetary gears.

The first sign of trouble came in the form of thermal damage to the Differential and Planet Support Case and Ring Gear. Note the bluish thermally induced discoloration on the inside walls of the case. Additional thermal damage was found on the top and base area of each of the four differential pinion gear posts, again evidenced by the bluish thermally induced discoloration.

The differential was then disassembled piece by piece and each component was cleaned and inspected. The thumbnails below detail the piece by piece disassembly of the differential.

wpe1.jpg (48388 bytes)   wpe3.jpg (50469 bytes)   wpe5.jpg (46180 bytes)   wpe7.jpg (47231 bytes)   wpe9.jpg (51801 bytes)   wpeB.jpg (55087 bytes)

Excessive scoring was noted on the inside of the 2 halves of the Differential and Planet Support Covers. Further inspection revealed scoring and galling of the spider shafts and differential pinion thrust washers.

This truck has a 22,000 lb. GVWR. Inspection of the frame and undercarriage prior to purchase revealed no obvious signs of abuse (cracks in the frame of leaf spring hangers, sagging springs due to fatigue, frame twist, etc.). Therefore, the thermal stresses must have been caused either by using an improperly rated lubricant or by an insufficient quantity of lubricant rather than severe overloading. In addition to the obvious property of lubricity, gear oil also dissipates heat from the metal components. The damage observed here suggests that there was an inadequate quantity of gear oil in the differential case, thus leading to the thermal damage on the inside of the differential.

Aside from the damage to the inside of the differential, the rest of the 2 speed components are actually in great shape. It's unfortunate that improper maintenance most likely led to the failure of this differential. 



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