Brian and I recently welded our 8.5” 10-bolt GM axle tubes
to our differential housing per the popular recommendation. Since the differential housing is Nodular Cast Iron and the axle tubes
are steel, the welding
is not particularly straightforward. We did some research beforehand to ensure we did the job correctly. The result of this research yielded the following weld schedule, which was what we used:
Weld process : TIG (Gas Tungsten Arc Weld)
Weld Current: 165A (this was a measurement taken during the weld)
Shield Gas: Pure Argon (approx 25 CFH)
Electrode diam: 3/32”
Preheat Temp: 400-600degF
Interpass Temp: 400-600degF
Preheat Method: Rosebud tip on Oxy-Acetylene torch (Victor 315C torch handle)
Filler Material: FM-99, (meaning 99% Nickel)
Filler Rod diam: 3/32”
Filler Data: 71,000 psi ultimate tensile Strength and 12% Elongation See here
Post weld treatment: Mechanical peening and slow cool (recommend 100 degF/hr but we were only able to achieve 200 degF/hr using insulation blankets)
Step 1) The differential was stripped of all its parts (including bearing races and seals). I don't know if this is mandatory, but we did it anyway.
Step 2) Grind all the rust and casting scale off the differential housing and the axle tubes
. Make sure to grind right down to clean material leaving no corrosion pits or casting pores. Notice in the illustration below that the differential housing had to be ground concave in order to get right down to the intersection of the axle
tube and the housing since the grinding wheel usually has a rounded edge.
This is a picture of the ground area:
This picture shows how clean the surfaces needs to be.
Step 3) Since the differential housing required pre-heating and interpass temperature control, we wrapped the differential housing in ordinary fiberglass house insulation (with paper batting removed). The housing stayed wrapped the entire time, from before pre-heat until after cool-down.
Step 4) Preheat the cast iron differential housing using a broad flame a few inches inboard of the steel axle tubes
. This is best done with a “rosebud” tip as shown in the picture below. The axle tubes
did not end up requiring direct heating with the torch since they were in such good contact with the housing. The proper pre-heat temperature was measured by special temperature indicating crayons. The crayon is wiped on the surface to be measured and it melts if that surface is above the crayon’s indicated temp. One well known manufacturer in the welding
industry has a product called Tempilstiks. See here
Here is a picture of the preheat temperature measurement:
Step 5) The first welds were made in three places, about one inch long and evenly spaced around the axle
tube. Then, these segments were joined to form a complete weld pass followed immediately by mechanical peening. The peening was accomplished using a three pound sledge and a piece of steel with a rounded nose as seen in the picture below. This is done to place the weld fillet into compression, reducing the risk of cracking during cooling. The second pass completed the weld and was also peened immediately.
Here is the tool used to peen the weld:
Step 6) The differential housing was heated again to the maximum pre-heat temperature. Immediately after heating, the entire rear end was wrapped in fiberglass insulation and allowed to stand for four hours.
Time to pull some wheelies!