Gearbox oil

I love oil threads. Until they gets so many answers that I gets bored. Just like asking what Scotch Whisky is best.
The AMC gearbox was originally meant to use SAE 50 motor oil. About same viscosity as 75/90 gearbox oil.
Most of us don't use our bikes for frequent long distance high speed travelling. So not much wear.
My guess is that any gearbox oil will be good enough. As long as it is yellow metal friendly. Some GL-5 oils are not yellow metal friendly.
Though TTI says don't use shock proof oil in there gearboxes. Might be the same with AMC boxes.
If your gearshifting gets harder it might be the wrong oil.
The benefit of changing to another oil is that you gets fresh oil in the box.
 
Modern gearbox and motor oils are vastly superior to the oils these machines originally used .
The real issue is running contaminated oil without noticing it in time , water ingress contamination and metal particles come to mind .
 
I have always used what was recommended in my workshop manual and measure the right amount that goes into my GB with a measuring cup, has worked for me for the last 48+ years, been so long since I been in my GB, since replacing the worn kick start gear, pawl and a broken kickstart shaft where the pawl was connected to the shaft, caused from the worn gear, haven't had had any problems since, that was well over 20 years ago, the layshaft bearing blew back in 1978 with 12k miles on the clock.
Hypoid GB oil 90w is what I have always used and only replace the oil when I go inside my GB.

Ashley
 
I am using the redline MT-90 since I went over to the dark side and bought a XK150 Jag. The redline is probably the preferred gearbox oil in vintage Jags and is specifically yellow metal friendly. I thought it definitely improved the shifting of the gearbox in my Combat but that also could be my imagination. I will continue to use it and am using it whenever there are yellow metals in the gearbox. Plan to put it in the rapide I am building now.
 
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