rtkjmk wrote:I plan on draining and refilling all the gear lube on my M37, trans,transfer and both diffs , my question is can I use a GL5 gear lube or should I be looking for some GL4 gear lube ? Finding a GL4 in my area has been a little difficult . It seems that GL5 is the replacement gear lube now .
Actually gear lube oils that you mentioned should only be used in the differentials. GL5 in an 80-90 grade is good there, however there are premium grade oils that are MUCH better than the over the counter stuff at Wal-Mart. Royal Purple is top of the line, their product is called Max Gear.
The transmission and transfer case will be much better served by using a 30,40,or 50 weight straight grade engine oil. This is in accordance with the ambient temp at your location, the 30 weight in cold climates, 40 in moderate climates, and 50 in warmer climates. Most of ours get either 40 or 50 weight. Again my top recommendation would be Royal Purple engine oil in the appropriate weight grade. You will immediately enjoy better shifting and better lubrication of your components, especially in cold weather. Oil is very different these days than it was when the manuals for the M37 were printed. Technology has come a LONG WAY since then.
Keep this in mind when searching for lubricant sources, the old line "you get what you pay for" has never been more true than it is today. Cheaper oils of today are extremely poor quality products, the old names you've heard for years are nothing more than a name these days. Good quality lubricants are expensive, cheap stuff is too, in more ways than one.
Pouring top $$ oil in a component that is worn out or has issues is not a miracle fluid. FIX ANY ISSUES up front. Pouring top quality oil in a component that is in top notch condition will save you money all day long. You will enjoy a much longer trouble free life from your components as a result of using good lubricants.