Transmission lubricant

[DJ]

There was a discussion on the M37 site about trans lube. One side says 90w gear lube has additives in it that are harmful to the brass parts in the tranny,and 50w motor oil should be used. The other side says 90w gear lube is the lube of choice. I searched the old posts ,but couldn't find a answer.What is the opinion here as to what should be used?


Thanks DJ

[C15TA]

I will try this again as my first post didn't show up.
Most modern lubricants are technically better and do more but are not as good for older vehicles. I use 50W motor oil in all my vehicles trannys and my customers older stuff. It is the same viscosity as 90 gear oil. You do not need EP additives in a trans, unlike a differential.

The new engine oils lack zinc and it is necessary for flat tappet engines, so when doing an engine oil change put in a can of EOS. It is worth the extra $$$. An alternative is one of the long life motor oils for high mileage cars. I know Valvoline is one supplier. These usually have zinc or a zinc alternative.

I have spent hours on the phone driving every refinery and lubricant laboratory in the US and Canada crazy. These people have been more than forthcoming with helpful info.
Cheers,
Barry

[TomM]

A 90w with a GL5 MT-1 rate will not harm your yellow metal parts in the trans. Be sure you see the MT-1 rateing.

another choice is to get a strat 90w mineral oil. I picked up a 5 gallon bucket from a local oil wholesaler and it is very thick. It is probably so thick that it is difficlut to get flowing in cold weather so I stick with the GL5 MT-1 in most transmissions.

Tom