The differential pinions ride on pins, and the three pins are supported in the square center block. The three roll pins not only prevent the differential pinions from coming out, but also serve a secondary purpose of preventing the pins from rotating inside the differential housing.
With all of the parts clean and inventoried, the first order of business is to pre-lube all washers and gears using standard Type 2 grease. The grease serves a couple of purposes. It provides the much needed lubrication before the axle starts rotating and oils itself from splash.
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The grease also serves as an assembly helper to hold the washers in place. Use a standard acid brush to spread the lithium-based assembly grease in place. Acid brushes typically have a tin or metal handle and are about 6 inches long. These are perfect for grease and other petroleumbased products because the handles do not become saturated as do typical wooden handles. Some plastichandled brushes deteriorate over time when exposed to grease. Inexpensive acid brushes are found in your local hardware store’s plumbing section as they are used for spreading flux prior to soldering copper plumbing.
Step-1: Grease Pinion Surfaces
Use a standard acid brush to spread the lithium-based assembly grease on the pinion surfaces.
Step-2: Grease Side Gears
Evenly spread a small dab of grease on the back surface of the side gears. This grease serves two purposes: to provide lubrication at initial running and to act as an assembly aid to hold the parts in place.
Step-3: Install Pinion Washers
Apply a small amount of grease to the gears. Set the washers in place on the pinions. A grade 2 lithium-based grease with extreme pressure additives works perfectly for this and is readily available. Even Wal-Mart has it; just look for the National Lubrication Grease Institute (NLGI) grade 2 label on the tube.
Step-4: Lay Down Washers
Put the side-gear washers in place. They are non-direction sensitive, so either side up is fine. Just make certain that all of the washers are installed and do not fall out during assembly.
Step-5: Grease Top of Washers
Add a thin layer of grease on top of each washer.
Step-6: Secure Differential
You can fabricate simple and helpful tools to hold components for the differential assembly. Here, the end of an old axle shaft has been cut off and welded to a chunk of steel plate. This is an 8.8-inch part, but the same can be made for a 9-inch.
Place the empty differential housing on the old axle shaft end and then into a vise. The 9-inch uses a two-piece differential (as compared to the single piece of the 8.8-inch differential), so you assemble the internal portion into the larger portion and then install the cover.
Step-7: Install Side Gears
The first part to be installed is one of the side gears. Make sure that the washer is still in place on the back face so the gear and washer can be set in place in the bottom of the differential case.
Fully seat the gear all the way into the differential housing. Make sure to correctly line up the spline teeth.
Step-8: Install Pinion Gears (Important!)
First, slide the long pin in by hand and only deep enough to hold it in place. Note that there are only three rollpin holes in the differential case. These are spaced at 90 degrees and line up with the differential pin through the holes. The long pin goes in the middle of the three. Make sure to put the solid end in first. Ensure the differential pin stays below the differential case’s inside diameter, so you can get the gear in place. Also, orient the pin so that the hole in the end lines up with the roll-pin hole in the differential housing. It will be vertical, as shown here.
Perform the same procedure for the two small pins. Have the long pin at the 6 o’clock position with the two smaller pins at 3 o’clock and 9 o’clock. Again, pay attention to the orientation of the roll-pin holes.
Install the differential pinion gears one at a time. Install the first gear on the long shaft. Make sure that the washer in still in place. Set the pinion in mesh with the side gear teeth and align it with the long pin shaft.
Step-8: Install Pinion Gears (Continued)
To hold the pinion gear in place, partially push the pin in (shown). Double-check that the washer is in place. Take care not to rotate the roll pin retention hole out of place. This is just a good practice to keep things aligned.
As always, check to make sure the pinion washers are in place. As before, ensure that the pinion teeth mesh with the side gear and partially install the pin to hold the pinion in place.
Step-9: Install Rest of Pinions
Here is what the differential should look like with two of the pinions in place. The third and fourth pinions follow the same steps as above. The only unique part is that the third pinion temporarily rests in place without a shaft to support it.
Step-10: Install Support Block
Once all four of the pinions are in place, the differential pins should support and hold three of them. Now install the differential gear and pin support block. Just set it in place on top of the side gear and align with the differential pinion shafts.
Step-11: Make Sure Washers are Installed
Once installed, the support block should appear as shown. This is another good opportunity to look over all the pinions and make sure that the washers are in place. I have mentioned checking for the correct placement of the washers many times. Make sure they are installed. They are crucial for the correct operation and longevity of the unit.
Step-12: Install Differential Pins
Make sure that the roll-pin hole is still positioned correctly and slide the long pin in place.
Slide the two short pins in place. Just as with the long pin, make sure to align the roll pins with the holes in the differential case.
To install the pins I use this modified center punch, but any standard punch or even a nail of the correct diameter works. Make sure that the differential pins are correctly lined up before you press in the roll pins. The roll pins can be a little tricky to remove if things aren’t lined up, so take the extra time to be certain they are lined up. If the roll pin is not aligned correctly and the pin is partially driven in, it hits the differential pin and jams in place. Then pliers or some other means need to be used to remove the pin; typically this destroys the pin.
Step-13: Install Roll Pins
The roll pins are an interference fi t so they require some persuasion to get started and installed. They have a slight radius on the ends to help them compress into the holes. Begin to lightly tap the roll pins into place.
Continue to lightly tap the roll pins into place. Don’t be too aggressive as you don’t want to peen over the ends. Be careful to tap them straight down so they don’t bend. Repeat this for all three pins. Do not drive them all the way down just yet. Note some gear oil in the differential case window (arrow). I use a combination of grease and a light coat of gear oil to hold the washer in place during assembly.
Step-14: Make Pins Flush with Top Surface
Use your center punch to drive the pins. Proceed with light taps until all three pins are flush with the top surface.
Step-15: Drive Pins into Place
Drive all three pins just a little below the top surface. This makes sure that they do not interfere with the mating cover.
Step-16: Verify all Pins are in Place
Shown is a close-up of the roll pin just below the top surface. Also notice the pilot diameter has a slight chamfer to help you install the opposite case half.
Step-17: Apply Grease to Pinions
Before installing the side gear, place a dab of assembly grease on all of the pinions.
Step-18: Rotate Side and Pinion Gears
Give them a little roll as well to distribute some of the grease. I want to feel a smooth rolling motion and not a bumpy motion. Make sure that the washer is in place and apply assembly grease to the face of the washer.
Step-19: Install Side Gears
Set the other side gear in place. Since the pinions are aligned correctly from the bottom side gear, the second side gear just drops right in. It lines right up with the gear teeth of the four pinions.
Step-20: Double-Check Washers
Make sure that the washer is in place and apply assembly grease to the face of the washer.
Step-21: Close Case Halves
Carefully line up the differential case with the pilot diameter. Be sure the ring gear bolt holes line up at the same time. You may even want to use some ring gear bolts or pins to guide the two case halves together. Once you have done many of these, you will be able to do it by sight.
Step-22: Install Side Cover
Once in place, lightly tap the center of the differential. You can use a dead-blow or plastic mallet (shown). You can also use a block of wood to protect the differential cover. Be careful to not dent or ding the bearing surface.
Here, the two halves are properly aligned and pressed completely together. There should be virtually no gap all the way around and even on the case split line as shown.
Written by Joe Palazzolo and Republished with Permission of CarTech Inc