Fluid types

[Salteen]

I have misplaced my owners manual... does anyone know the recommended gear oil for the front and rear diff, and transfer case? Also whats the best for the trans? I put in 80W90 Lucas but it seems as though that doesn't do to good. I read amsoil is pretty good.

Recommended oil brands???

Thanks yall! -Paul

[SubGothius]

According to my '87 owner's manual:

• Manual Trans and Transfer Case: GL-4 gear oil SAE 80W or 75W85
• Front and Rear Axles: GL-4 gear oil SAE 90 or 80W

As you might expect, go with the lower-weight W specs if you're anywhere it regularly drops below freezing, or the higher-weight specs if you're in a hot climate (e.g. far south/southwestern US).

Although it does technically say "GL-4 or higher", that was before GL-5 was developed, which really doesn't play nice with many gears that spec GL-1 thru GL-4. The general rule now is to only use GL-5 for gears that specify it, and only GL-4 for gears that specify that, but gears spec'd for GL-1 through GL-3 can safely update to GL-4.

AMSOil, Redline, and Royal Purple are all well-regarded top-notch synthetics that will probably outlast your truck and you on a single fill (at least for gears).

[Salteen]

This was very helpful SubGothius. Just picked up 4 quarts of gear oil for the trans/transfer case and 4 for the differentials.

[B-Line]

Only gl-4 in the trans. They have soft metals synchros that require it.