Return to 410 Gear Pattern Setting
Both axle shafts showed wear like below. I swapped out the axles and also changed out the axle bearings and seals.
Pry the axle seals out of the ends of the axle tubes. This can be done with any number of tools. You will destroy the seal in the process. This slide hammer was used to pull the axle bearings out. I could not get my bearings to budge at first. I pried the bearing cage out and extracted all of the rollers. Then I was able to get the slide hammer to tug directly on the bearing race. At that point it was fairly easy to yank it out of the tube.
After you drive in the new bearing, oil it because it normally depends on differential oil sloshing while you drive. Drive the seal in flat being careful to not warp it. Oil the lip so it won't burn up on the new axle from being dry.
I had to install new lugs on the new axles before using them. I was really surprised at how much force I needed to put them in place. I used a 2 lb hammer to pound them in after supporting the axle flange over a large socket.
Make sure you reinstall your C-clips properly. Install the paddle and torque its bolt as best you can. Use some Loctite on it to make sure it stays put.
I used the supplied paper cover gasket that came in my rebuild kit. I have never had a problem with leaks using this kind of gasket. As long as you are careful not to bend the rear cover it should work fine.
Fill the axle until the fluid is level with the fill hole. I break the gears in on non-synthetic oil for about 500 km. I also found that despite the stories out there, my Torsen made odd noises when I turned until I put the GM differential additive into the fluid.
Everybody has an opinion on this. All I can tell you is to put your hand on an axle housing after driving your car for a while with new gears and compare it to a car with 1000's of miles on it. The broken in axle is warm but not hot. After 40 km of careful driving on a new axle, it is pretty hard to leave your hand on the center section, it is really hot. After my 3'rd easy drive which brought me to a total of 200 km the center of the differential case was 190oF.
When I was breaking in my 373s I noticed the hum got louder as the axle heated up and the oil viscosity went down. This tendency got much better as the gears broke in and produced less heat. This was even more true when I switched to synthetic since the viscosity changes less at elevated tempatures.
With the new 410 gears, I drove it carefully up to speed to see how good a job I did. They were essentially silent at all speeds. Between 95-110 kph there was a hint of a sound and only once the oil was warmed up. The next day the same thing happened, quiet at first and only slightly noticeable once warm. From last year's experience this will be a non-issue once it is broken in and the oil is switched over to synthetic.
I also noticed that even after my first test drive when the axle was at its hottest the axle was not as bad as when I did the 373s. I believe this is likely due to having the pattern meshed well from the get-go.
Overall I am really happy that this is now done and I am happy that I now understand gear meshing well enough to fix the original factory noise level. I suspect my housing really is at the edge of the acceptable spec for hypoid distance and this makes the patterns that much harder to read and find a workable solution.
The following are examples of gear pattern changes with back lash changes on both the drive side and coast side of the gear.
The 2001 manuals for my Camaro have some really poor schematic drawings of what happens to your pattern under different conditions. These photos were taken from a 1971 Pontiac service manual, click on the pictures to see them full size. That old manual had far superior diagrams for pattern and bearing wear. (Click to see full size).
