Ram ZF Differential and Amsoil Severe Gear

[2021QCBH]

I purchased my 2021 Ram 1500 new in the fall of 21. I ran the factory fill until 50k and changed out to Amsoil Severe gear 75-90. This truck is a 3.21 and calls for that (the 3.92 gear calls for a 75-140).

Since around 50k its had a very light “howl” on light deceleration around 62 mph. Only shows up once the fluid is good and hot but the last 3k miles its got a little louder and more broad (60-65). I’m right at 99k as of this week. Had it on a long trip this weekend 3.5 hours unloaded and 2 hours towing. Once it was good and hot I could hear it more than usual.

When I dumped the factory fill it still looked pretty light and honey colored. The Amsoil came out yesterday not looking so great (see photos below). Understand it may be a symptom of the rear end noise. Most inter webs point to pinion gear wear/end play. Under it messing around last night the back lash feels normal/like it always has and there was no end play in the pinion I could detect at all by hand. Maybe it just has some odd gear wear/pattern. I always measure temps on long highway trips when towing and I’ve never seen over 190 on the diff cover. Pinion seal is still bone dry. The other photo is what I was able to scrape off the magnet with my finger (conveniently located just inside the big drain hole so you can access with a finger easily).I stayed with the 75-90 to keep the excellent fuel economy this 5.7 happens to get (not all do). This time around I figured if it only really surfaces when the fluid is hot something thicker would keep it quieter. I already had some severe gear 75-110 but I picked up some O’Reilly/master pro 75-140 cheaper synthetic in case I need to dump it soon so I’m not wasting the more expensive stuff.

Hopefully I can prolong the life of the unit with thicker lube but I’m more concerned about failure while I’m on a long trip. I tow frequently locally as well as 500-1000 miles from home. Nowhere near the rated capacity of the truck but usually around 4500 lbs trailer with near max payload in the truck. Maybe I’m just doing more than a normal 1/2 ton can handle or I need to be on a 25k service interval for the rear diff. Not real excited about a diff rebuild but I do need to add a limited slip to this one. Settled for non because the deal was too good to pass up in 2021.

Not super impressed with the looks of the Amsoil. May end up sending it in for analysis and if it comes back shining I guess it just makes some noise…​

 

[snj1013]

Just changed the differential fluid in my 2019 with 3.21 rear end at 123k for the first time. I don't tow much, and had no issues. I used Valvoline 75-90w synthetic lube and think anything else is overkill View attachment 12507273_vlv_889785_pri_larg.webp