I've found that if you use a normal gearbox oil in a grey box it can cause difficult shifting. Typically an oil much closer in viscosity to engine oil gave better results. The strange thing was that it was inconsistent across different gearboxes.
Harv, if you're reading, Did you find any issues like this in your gearbox analysis?
Ken
The workshop and owners manuals indicate that the grey motor crashie should run S.A.E 90 straight-run mineral gear oil (943mL, plus 170mL into the rear compartment during rebuild). The various oil companies recommend Shell Spirax S2A80W90, Caltex Torque Fluid 454, Valvoline Premium Mono 50, Castrol Edge Sport 25W-50 or Castrol Edge 25W-50, or BP Hypogear 80W90.
Interesting that the Castrol boys recommend an engine oil… perhaps in error. However, when you look at a typical engine oil, it is not too far different from the gear oils recommended. For example, comparing Shell’s HX3 20W50 engine oil to the Spirax variant above shows only
a) a 1% difference in density
b) only 7% difference in viscocity at 40ºC (ie the oils will bevave very similarly when the vehicle is cold/lightly loaded)
c) 20% difference in viscosity at 100ºC (the gear all is thicker than engine oil). Note though that both oils are 90% thinner than when they were at 40ºC… this 20% is really little difference.
My guess is that engine oil will do in a pinch, and will behave similarly. Different gearboxes with differences in wear, thrust and adjustment probably make for different behaviour.
Cheers,
Harv
