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Have you ever noticed that there's a whole lot of discussion over what fluids to use in a truck that's over 50 years old? Somebody asks: "What sort of brake fluid should I use?" and there's an immediate answer of "Use this type." but then somebody chimes in "You can use that kind, but..."

I don't know if that's because different types of fluids are used because one truck is fully stock, just like back in '52, and another truck has been modernized, and can use a different type of fluid...

Problem is, all the answers are right, as it relates to the multitude of variations that can be found in our beloved M-37 series beasties...

So here's my question, and the caveat is simple: Assume that I can start from square one, and rebuild the truck's system around fluids that will be available on the market now and in the near future...

That having been said, allow me to tap into this vast storehouse of information. What fluids do I put in my truck?

Brake fluid.
Engine oil (stock 213 in-line milspec six cylinder).
Transmission (stock four speed).
Gear oil.
Bearing grease.
Axle grease.
and, of course, the stuff that goes into the LU-2 winch.

Second question:

I'm going to change out all of the rubber lines on the truck, but should I replace all of the steel lines, or would that depend on the condition of each line?

I'm putting together a definitive list, upon which I am making my budget, so I beg your indulgence!

Thanks much!

Bill

Brake fluid. - DOT 4 (but use a lot of 3, as they are compatible)
Engine oil (stock 213 in-line milspec six cylinder). - Had used straight 30W, but trying Valvoline MaxLife 10W-30
Transmission (stock four speed). - Used JD GL5 85-90, but should have used 50W I believe
Gear oil. - JD GL5 85-90
Bearing grease. - High Temp Disc Brake Wheel Bearing grease
Axle grease. - JD GL5 85-90

Unless you actually re-engineer a system in the truck the original spec lubricant's and fluids will work just fine.

Brake fluid confusion comes from the Army. They switched to DOT 5 silicon based fluid which is not compatible with Dot 3 or 4. The confusion occurs after they leave the Army and different fluids are accidentally introduced. If you still have the stock brake system then you must use what has been in there or you must completely replace all parts , hoses and lines to make a switch to either of the other two fluid types. No matter how hard you try to flush silicon from the system there will always be traces left in several places.

The same Hypoid gear oil used during the 50's and 60's will still do a more than adequate job for you today.

Modern engine oils are designed for use in modern engines which have much tighter bearing clearances and operate at much higher internal temps. Therefor the best choices are still straight weight detergents basing weight on season. The multigrades are not a good choice but the stock engine can survive on them but stay with 10w?? as a minimum. 5W?? is just too thin when cold and hot.