Diff rebuild by "pro" not going well

alcyon

Active Member
Jun 15, 2017
174
42
28
Kuala Lumpur
I finished rebuilding my original diff. Setting is as follows, original pinion depth shim 1.94mm. Pinion preload 1.3Nm or 11.5inlb. It feels much more tighter than before. I plan to swap the diff in another 2 weeks. In the meantime, I put in half the amount of gear oil and breaking in the pinion bearings everyday by turning the handcrank for 10 minutes. The last rebuild on this diff netted me a 7inlb preload, and when I pulled it off after 2 months and 1000km, the preload was 2.5inlb, which is a loss of 4.5inlb. i suspect the whine at 60 to 70kmh is the "loose" pinion preload. Lets see if the high initlal preload will solve the whine. Even with a preload loss of 5inlb, i should have 7inlb for a very long time.
The backlash remains at 0.18mm average.
Now for the auction diff which is still in my car. I drove around these past weekend, and went up to speeds up to 145kmh. It is smooth at higher speeds, and the vibration at such speeds I had before are now gone, the auction prop shaft solved this problem. Now for the not good, the whine at 60 to 70kmh is there, especially when the oil is hot. It is the diff, as there is a difference in the sound intensity vs my original diff. There is also a whine hum at 35kmh while accelerating.
I suspect maybe the bearings are too old or pinion preload isnt enough. Anyway, i am planning to change the bearings in the auction diff by the coming month to a low mileage used bearing set, and increasing the pinion preload to the same preload I have on my original diff, this will depend on the sound that the original diff makes after testing it. Hope this will finally solve my issues. Will report back at the end of the month.
 
Last edited:

alcyon

Active Member
Jun 15, 2017
174
42
28
Kuala Lumpur
I installed the original diff last week. It has so far the tightest pinion preload. I break in the diff with speeds under 60kmh, with three 5 km trips and 1hr cooldown. It is silent and no grinding or whining sounds under 60kmh.
Today I finally drove a further distance and went up to 80 kmh. At 59 to 75kmh, there is still a slight noticable whine. Looks like the high pinion preload did not solve the issue. However, considering that as soon as I let off and coast, it is the quietest it has ever been in a very long time.Under hard accelration also it is silent, but light accelration or crusing at 59 to 75kmh, it whines. I think this noise is some kind of resonance that is amplified by the poly subframe bushings. There is nothing else I can do on this diff, and I will drive it many more miles and make a decision. But I think I am done with this and there is noting else I can do. I will try again if the sound gets worse, but with this high pinion preload I dont think it will get worse. I plan to swap out the diff oil to MOBIL SHC 75W90 after break in period. I will break in for a 1000km this time. I also plan to make rubber pads 3mm thick, hardness 40 Shore A and place them above each poly bushing as extra insulation / isolation. Perhaps this will cut the resonance being transmitted.
I will still rebuild the auction diff with low mileage used bearings, but just gonna keep the diff as spare.