I just bought some 75w-140 full synthetic gear oil for my 10.5" AAM. I pulled the same 5th wheel with my '03 Cummins powered Ram and it's 10.5" AAM sounded like it had 144k miles on it when I traded it with 44k miles using 75w-90 full synthetic. The vibe may have been the cause of the early worn out sound but I'm thinking with the weight we tow and the Florida heat, 75w-140 would be better. Of course Chrysler is going to say 75w-90. They have to push the lighter oil to keep the feds off their backs with CAFE requirements. So who's running 75w-140 and has it done good in the AAM?

 

I running Royal Purple 75w-140. 5k miles on it so far. Did make the rear whine a little quieter.

MikeyB

 

the 75w140 is now recomemded in the aam 11.5" rears when heavy towing or hot weather is a factor... i am running 75w90 in both of my diff's as i don't tow anything and we don't get too much hot weather here in the toronto area [although 2 weeks back was nasty hot/humid]

 

I have also heard that DC now recommends the 75w140 for the 11.5 I had already bought a 5 gallon can of 75w90 before they ever came out with this recommendation. I guess I'll use it up and then go to the 75w140.

 

I was going to do the 80w90 until I read the TSB....so I used the 80w90 in my 97 Cougar and am going to buy Royal Purple 75w140 for the Ram.

 

I am using 75W-140 in my 10.5" AAM. Have 48,000 miles on it so far. No problems.

 

Thanks for the replies! Are you filling to the fill hole on the 10.5" or doing the 1" below method? My dad's long retired GM mechanic friend thinks they're doing that mostly for cost savings and CAFE numbers. AAM said it won't hurt to fill to the fill hole. It might lower mpg just a little. The manual says overfilling can cause foaming and overheating as a result so I was thinking of just going with 2.5qt instead of the specified 2.38qt. That way it'll still be below the fill hole and I'll have .5 qt already for next time. At $14.~ a quart, every little bit helps.

 

fill till it runs out the hole... that is not overfull... if you think it is, feel free to fill it to 1" low as the manual states 1/2" below ±1/2" [or was it 1/4" below ±1/4"???]

 

Do you have the same issues as the Dana's did with wheel seal's leaking when overfull?

 

My original gears went south using the DC recommend (and expensive) stuff. When they put the new gears in, the tech put in Redline 75W140 at my request and he agreed it was a better way to go. Also an AMM engineer advise me that "there are certain benefits to the heavier oil" but stopped short of saying DC was wrong. As he said, these axles are used from Mexico to Alaska and I guess DC wanted a "fits all" oil. I have not had a problem with the heavier oil and I tow heavy. Too bad it took DC three years to figure it out.

Casey

 

I've been running 75W-140 in my 11.5 AAM, filled to the hole. The heavier stuff has not had any affect on my fuel mileage.

I'm still running 75W-90 up front.

 

I fill mine until it runs out the fill hole.