M40/41 oil

[spock345]

I've got two gearboxes to fill. I've currently got a bunch of bottles of Redline MT90 and MTL that I forgot I had.

I know the MT90 will probably work well in the M40, given that the original spec is a 90W gear oil.

Anyone tried running Redline oil in their J type M41?

To be honest I am probably overthinking it.

 

[hiperfauto]

It might be too viscous for the overdrive. The greenbook calls for 30W in M41 transmissions and ATF in M46 transmissions.

 

[spock345]

It might be too viscous for the overdrive. The greenbook calls for 30W in M41 transmissions and ATF in M46 transmissions.

Yeah, that is my worry with MT90. Seems like it would want something between MT90 and MTL given that MTL is analogous to ATF (I think, multigrade still messes with my perception of viscosity and no one publishes charts of this stuff).

Oh well, I've also got a bunch of 30w.

 

[dl242gt]

FYI I've used 75-80w gear oil in my M47 and it worked well. It was synthetic Lucas and seemed to make the gearbox happy.

 

[Khrrck]

FYI I've used 75-80w gear oil in my M47 and it worked well. It was synthetic Lucas and seemed to make the gearbox happy.

The cars with separate overdrives need a lighter oil due to the way the overdrive mechanism works unfortunately.

 

[spock345]

The cars with separate overdrives need a lighter oil due to the way the overdrive mechanism works unfortunately.

75w80 gear oil is approximately the same viscosity range as an SAE 30 engine oil at operating temperature (assuming that common 100 celsius measurement). I think the key point there is operating temperature. SAE 30 should be a decent amount thicker than 75w80 gear oil at room temp. I feel like I need to start drawing up a chart to keep all the numbers straight in my head.

I've read of people using SAE 30, 15w40, 20w50, 75w90 GL-4, and MTL (75w80) in an M41. Factory options in my '73 144 manual for an M41 with a J type was either an SAE 30 or 20w40 (afaik 15w40 or 20w50 is the closest available equivalent).

 

[c1800]

Mtl is fine, actually better than 30W or others in an M41. Smoother shifting. 4 years on.

 

[spock345]

Mtl is fine, actually better than 30W or others in an M41. Smoother shifting. 4 years on.

I ended up putting some of the MT85 I had on hand in the M41. Shifts quite nicely. Pretty much a mid point between MTL and MT-90. Probably fits where I live because of mild winters and quite hot summers (high 80s into the 90s are the norm). I'm going to put my bottle and a half of MT-90 in the M40 once it goes into the car. Currently have a bit of cheap napa 30 weight in it so it doesn't sit entirely dry until the car is ready.