Differential Oil Replacement - 3.21 LSD

[The Critic]

Traditionally, differentials produce a significant amount of break-in debris during the first 5,000 miles of operation. For this reason, I completed my first rear differential oil change at 5,740 miles.

The fluid I drained was "yellow/orange" with a slightly milky appearance. The truck has never been exposed to any water since it was purchased in June so I am not sure why the fluid was slightly milky. However, I found it interesting that the drain plug did not have any debris on it at all. My truck is a 2020 1500 5.7 eTorque 2wd with the 3.21 anti-spin rear differential.

FCA has updated the gear oil recommendation from the information printed in the owner's manual, but only for 3.21/3.55 rear axles. Previously, there was a special gear oil (MS-A0160) for the 3.21/3.55 C235 rear axles on 2017+ Rams which was part #68340460AA. The FCA Tech Authority site now lists part #68218655AC for the 3.21/3.55 rear axles plus 5 oz of friction modifier. Part #68218655AC is FCA's universal 75W-90 gear oil which is "For use in all FCA US LLC corporate axles" and is spec MS-9763.

The FCA Tech Authority site lists oil capacity as 5.68 pints plus 5 oz of friction modifier for 3.21/3.55 differentials equipped with a mechanical LSD. By volume, this is 5.5% of friction modifier.

I contacted Redline's Tech Dept and was advised that their 75W-90 contains 5% of friction modifier by volume. Amsoil and Mobil 1 declined to provide any specific information on the quantity of friction modifier in their gear oils. Redline's 75W-90 is suitable for use in applications requiring a FCA MS-9763 spec gear oil.

I used approx 2.5 qt of Redline 75W-90 for the refill. I drained about 2.2 qt from the rear differential. So far, I have not felt any chatter on turns after 60 miles of driving, but I will update the thread if I do.

Also, the drain plug is a 14mm hex and the fill plug is a 8mm hex. I used the stubby ones.

Hope this helps.

Amount of oil drained:

New oil used and amount remaining:

FCA Tech Authority Service Information:

 

[jdefoe0424]

Amsoil packages their own friction modifier, Slip-Lock, to be used in applications with limited slip differentials. However, if you look up our trucks they specify using the Mopar limited slip additive.
I'm at about 16k but aim to change my diff fluid to synthetic soon, mostly for a mileage gain in the winter.

 

[The Critic]

Amsoil packages their own friction modifier, Slip-Lock, to be used in applications with limited slip differentials. However, if you look up our trucks they specify using the Mopar limited slip additive.
I'm at about 16k but aim to change my diff fluid to synthetic soon, mostly for a mileage gain in the winter.

This is what the Amsoil website shows for their SVG 75W-90 product:

"AMSOIL SEVERE GEAR is compatible with most limited-slip differentials. For applications that require additional limited-slip friction modifier, add AMSOIL Slip Lock®."

Amsoil Tech Services informed me that their oil usually does not require additional friction modifier, but recommended adding their Slip Lock if I experience chatter. But without knowing how much additive is already mixed into their fluid, it makes the situation a bit more challenging.

 

[Ram2020ecodiesel]

Traditionally, differentials produce a significant amount of break-in debris during the first 5,000 miles of operation. For this reason, I completed my first rear differential oil change at 5,740 miles.

The fluid I drained was "yellow/orange" with a slightly milky appearance. The truck has never been exposed to any water since it was purchased in June so I am not sure why the fluid was slightly milky. However, I found it interesting that the drain plug did not have any debris on it at all. My truck is a 2020 1500 5.7 eTorque 2wd with the 3.21 anti-spin rear differential.

FCA has updated the gear oil recommendation from the information printed in the owner's manual, but only for 3.21/3.55 rear axles. Previously, there was a special gear oil (MS-A0160) for the 3.21/3.55 C235 rear axles on 2017+ Rams which was part #68340460AA. The FCA Tech Authority site now lists part #68218655AC for the 3.21/3.55 rear axles plus 5 oz of friction modifier. Part #68218655AC is FCA's universal 75W-90 gear oil which is "For use in all FCA US LLC corporate axles" and is spec MS-9763.

The FCA Tech Authority site lists oil capacity as 5.68 pints plus 5 oz of friction modifier for 3.21/3.55 differentials equipped with a mechanical LSD. By volume, this is 5.5% of friction modifier.

I contacted Redline's Tech Dept and was advised that their 75W-90 contains 5% of friction modifier by volume. Amsoil and Mobil 1 declined to provide any specific information on the quantity of friction modifier in their gear oils. Redline's 75W-90 is suitable for use in applications requiring a FCA MS-9763 spec gear oil.

I used approx 2.5 qt of Redline 75W-90 for the refill. I drained about 2.2 qt from the rear differential. So far, I have not felt any chatter on turns after 60 miles of driving, but I will update the thread if I do.

Also, the drain plug is a 14mm hex and the fill plug is a 8mm hex. I used the stubby ones.

Hope this helps.

Amount of oil drained:

New oil used and amount remaining:

FCA Tech Authority Service Information:

Hey when you did the drain and fill was it on level ground or did you have to do something speacial like raise front to fill differentials and visa versa for front differential. Fcca like to make it difficult

 

[The Critic]

Hey when you did the drain and fill was it on level ground or did you have to do something speacial like raise front to fill differentials and visa versa for front differential. Fcca like to make it difficult

It was doable on the ground.

 

[c3k]

Perfect timing on bringing this thread back up top.

I'm a firm believer in an early first oil change for all the oils. If the gears are new, they're gonna break in and produce swarf and whatnot in the first couple of thousand miles. I like getting rid of that debris as soon as possible, rather than have it circulate for a "standard" change interval.

Just to clarify, the rear differential drain plug IS magnetic? (I'd like to think so...but that's an assumption.)

Your sig shows a 4x2. I'll be getting a 4x4, so I'll be doing the front diff as well.

Thanks.

 

[The Critic]

Perfect timing on bringing this thread back up top.

I'm a firm believer in an early first oil change for all the oils. If the gears are new, they're gonna break in and produce swarf and whatnot in the first couple of thousand miles. I like getting rid of that debris as soon as possible, rather than have it circulate for a "standard" change interval.

Just to clarify, the rear differential drain plug IS magnetic? (I'd like to think so...but that's an assumption.)

Your sig shows a 4x2. I'll be getting a 4x4, so I'll be doing the front diff as well.

Thanks.

I do not recall. However, the fluid was very clean and there was no debris on the plug.

 

[kdoublep]

Good to know it was clean and debris free. At least you know. Thanks for all the info.

 

[Lit_AF]

Perfect timing on bringing this thread back up top.

I'm a firm believer in an early first oil change for all the oils. If the gears are new, they're gonna break in and produce swarf and whatnot in the first couple of thousand miles. I like getting rid of that debris as soon as possible, rather than have it circulate for a "standard" change interval.

Just to clarify, the rear differential drain plug IS magnetic? (I'd like to think so...but that's an assumption.)

Your sig shows a 4x2. I'll be getting a 4x4, so I'll be doing the front diff as well.

Thanks.

I strongly believe the front differential oil weight is different too correct?

 

[IvoryHemi]

I strongly believe the front differential oil weight is different too correct?

 

[WXman]

You didn't take the inspection cover off? Then of course you didn't find the metal shavings. The magnet is only accessable when you take the inspection cover off.

I just did mine at 16,000 miles and the magnet was covered in metal sludge.

Also, the Valvoline full synthetic sold at Walmart comes in the easy pour bags AND has friction modifier in it already.

 

[The Critic]

You didn't take the inspection cover off? Then of course you didn't find the metal shavings. The magnet is only accessable when you take the inspection cover off.

I just did mine at 16,000 miles and the magnet was covered in metal sludge.

Also, the Valvoline full synthetic sold at Walmart comes in the easy pour bags AND has friction modifier in it already.

I was expecting for a magnetic drain plug, but I guess FCA is different than the Asian imports I am used to working on.

I plan to remove the diff cover at my next oil change.

 

[Malodave]

Any one have the Gasket Part Numbers for a 4X4 Ecodiesel with 3.21 Gears?

Thanks,

Malodave

 

[The Critic]

Any one have the Gasket Part Numbers for a 4X4 Ecodiesel with 3.21 Gears?

Thanks,

Malodave

It uses RTV for the cover. You must use a special RTV for differentials because the friction modifier will attack most RTV’s.

Use either the Mopar stuff:

Or this permatex product:

Permatex 81182 Gear Oil RTV Gasket Maker, 3 oz. https://www.amazon.com/dp/B0023GM2KK/ref=cm_sw_r_cp_api_glt_fabc_ZZ1F8YBKGN4J3BB5SSM7

 

[WXman]

If you can find that special gasket maker, use it ^^^^

If not, I've been using the Permatex black for the past 25 years and I've never had a single leak or issue.

 

[BowDown]

If you can find that special gasket maker, use it ^^^^

If not, I've been using the Permatex black for the past 25 years and I've never had a single leak or issue.

Same here, used permatex black or the ultra blue on my diff many times