I read my FSM and it said to refill the model 60 and model 70 rear axle with 7 pints of SAE 75W-90 gear lube. I used Castrol Syntec full synthetic 75W-90. Now I read in the Owner's Manual that the 75W-90 is only recommended for temperature ranges below -10*F (ain't happenin' here in Oklahoma any time soon) and that an 80W-140 or 85W140 is recommended. Why the discrepancy and what are you guys using? Did I go too thin? I hate to drain and loose $30 of synthetic gear lube but I'd hate even worse to toast the gears and bearings and I'm making a 500 mile trip on Monday so I've got to get it right.

 

My FSM has a chart that shows what weights are acceptable for 3 different temperature ranges: over 90 F, -10 F to 90 F, and under -10 F.

I think you went too thin. The only time my FSM says that 75W-90 is acceptable is in extreme cold weather. I know you tow, so I'd recommend the 80W-140 or the 85W-140. I don't tow, so I'm running 80W-90 for better flowing lube at the temps the gears are seeing.

Beats me why Dodge screwed up. At least you caught it before the pinion welded itself to the ring gear.

 

It you have a limited slip make sure you add the modifier to it.

 

I put mobil 1 in mine about 25000 miles ago. I don't tow but haul a camper all the time. I used the 75-85 or something like that. It was the only one mobil made at the time. I could have sworn my fsm said to use the 75-90 or so. I'm not even sure they had the 75-140 in 1993. Anyway for towing dodge recomends the one with the 140, not sure if its 75-14- or 85-140. Unless you're towing something huge I wouldn't worry about a 500 mile trip. Mobil one comes with the modifier in it.

 

Thanks guys. Mine's just a 1-wheel drive so no modifier needed and since I'm running empty this week, I'm going to leave the 75W-90 in it and take it easy on it. I'll try to find some synthetic 85W-140 to change it to before I pull trailer any significant distance.

Anybody found a synthetic 85W-140 that they can recommend? Lots on dino 85W-140 to be found and Valvoline makes a partial synthetic in that weight but the only full synthetic that I've found is Walmart's Tech 2000 brand, Coastal, and Lubrimatic and I don't know anything about any of them. Was hoping to find it in Castrol or Mobil 1 but neither appears to make it in that weight. Suggestions?

 

Valvoline now makes full synthetic 85-140, I have it in mine, got it from NAPA.

 

Mobil 1 Came out wirh it recently