Gear Lube?

[JayJay]

I know this question has been debated, but...

I'm installing a Mitchell overdrive and Mitchell requires 85/140 petroleum-based (not synthetic) gear lube. I currently use 600W (from the vendors, don't recall where I got mine) in my transmission, differential and steering box. It would be convenient, but by no means deal-breaker, at the next fluid change (coming up before I head to Ruidoso in June for the MAFCA convention) to switch everything to 85-140 so I would need to carry only one gear lube. I have no particular complaints about how things work with the 600W, other than the tranny does shift very stiff and grinds a lot when cold.

Does anyone see any huge negatives to this plan?

I have no idea what fluid is in the shocks. 85-140 for there too, or is that too thick?

Thanks.

[Brentwood Bob]

Your shocks were 85-140.

[JayJay]

Thanks, Bob. I was speaking about the ones in my '31, not the ones for the '30 that you rebuilt for me. Those are still on the shelf waiting for the frame.

JayJay

[nkaminar]

The 600W oil was good in 1930. (600W does not mean that it is SAE 600 weight.) But that was 90 years ago. The modern gear lube oil has additives that will extend the life of your gearbox, over drive, rear end, and steering box. The multi grade means that it will act like SAE 85 when it is cold and SAE 140 when it is warm. So you shouldn't have the problem with stiff shifting when cold.

There are two versions of the 85W-140 gear lube, G4 and G5. Mitchell recommends using the G5 which has twice the additive than the G4. However there have been some problems with the G5 in synchronized transmissions because when the additive wears off the synchro rings, which it is designed to do, it takes a little bit of the brass with it. It sticks a little too much. I have recently switched from G5 to G4 in my Mitchell overdrive and Mitchell synchronized transmission. (The additive wears off in preference to the metal underneath and then more gets deposited.)

[JayJay]

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Originally Posted by nkaminar

The 600W oil was good in 1930. (600W does not mean that it is SAE 600 weight.) But that was 90 years ago. The modern gear lube oil has additives that will extend the life of your gearbox, over drive, rear end, and steering box. The multi grade means that it will act like SAE 85 when it is cold and SAE 140 when it is warm. So you shouldn't have the problem with stiff shifting when cold.

There are two versions of the 85W-140 gear lube, G4 and G5. Mitchell recommends using the G5 which has twice the additive than the G4. However there have been some problems with the G5 in synchronized transmissions because when the additive wears off the synchro rings, which it is designed to do, it takes a little bit of the brass with it. It sticks a little too much. I have recently switched from G5 to G4 in my Mitchell overdrive and Mitchell synchronized transmission. (The additive wears off in preference to the metal underneath and then more gets deposited.)

nk - thanks, very helpful discussion (and I know 600W is not SAE 600, but good to reiterate). I think I will switch tranny and differential over to 85-140, but hold with the GL5 at least as long as the Mitchell is within warranty since that's what they require (no brass synchro rings in either).