What kind of fluid is good in the rear diff??

[C. Harlan]

I am going to be doing a fluid change here in a week or so. . I would like some input on this. ALSO, do I need friction modifier??



-Chris-

 

[TomGolden]

You of course have the age old choice - Dino or Synthetic?

Then you chose the weight of the oil. If you will tow regularly, a heavier weight oil is recommended, and many would say go synthetic for sure if towing a lot.



I personally switched to Amsoil Series 2000 75W-90 in both differentials. They also have a heavier weight at 75W-140.



Royal Purple and Redline also make well respected synthetic oils & lubes, not sure of their precise weight offerings though.



Whoops - forgot the final question you asked. Most people have posted that if you go with a synthetic lube, you likely won't need friction modifier. I don't use any in mine. I have seen a couple poeple post that even when using synthetics, they needed a friction modifier... . I would say if you go synthetic, do not add any modifier at first, drive the truck a bit and listen/feel for chatter from the rear diff, and then add modifier if needed.



Tom

 

[John Berger]

I'm running 8 quarts of Amsoil Series 2000 75W-140, plus 8 ounces of Mopar friction modifier.

 

[stevek]

I'm partial to Mobil 1 75w90

 

[RustyJC]

Royal Purple offers a 75W-90 synthetic and an 85W-140 synthetic. Since we tow heavy (10,380 GVW versus 10,500 GVWR, 21,180 GCW versus 21,500 GCWR), we're using the 85W-140. It has the friction modifier built into its formulation, so we did not have to add any supplemental Mopar friction modifer to keep our Dana 80 limited slip happy. I got it at my local NAPA.



Rusty

 

[paccool]

Like Rusty, I'm running the 85-140 RP. I tried it without modifier but it chattered so I put in one bottle of modifier and all was well. I had just had the rear end rebuilt about 2500 miles before and wanted to let it lap in with dino before switching over. All the limited slip clutches were replaced and everything was pretty tight so that may have been part of the reason for the modifier.

 

[Hohn]

I used Mobil 1. I should have checked it out before dumping friction mod in. It slips too much now.



Redline make a great gear oil that doesn't need friction modifier. They also make "shockproof" gear oil that a lot of drag racers swear by.



I would say a synthetic is a better deal in gear oil than engine oil-- you can TRULY run extended drains, and the temp decrease can be substantial. .



Hohn

 

[mhenon]

differential fluid

I just changed mine out and read a lot of post before doing it. As I tow a trailer part time, and the manual "strongly" recommended a 85w/140 lube, I went with Valvoline synthetic blend.

It didn't require any friction modifier and the limited slip worked perfect. It seems other TDR members have used this lube with good results.



Mike

 

[Okie-Go]

Amsoil 75-140. Why go get it? They just deliver to your door.

 

[BV]

Royal Purple 85/140 in back and 75/90 in the front. No added friction modifier.



BTW - You only need the modifier if you have the LSD (Limited Slip Differential).

 

[Gary - K7GLD]

Like Mike up above, I use the Valvoline synthetic blend 85/140 - I tow in the Sierra quite a bit, so far the LS is working fine, no modifier needed...

 

[Texas Diesel]

I use Mobil 1 75W-90 and have had some trouble with figuring out how much modifier to use, didnt have enough then added 2 onces more and it's too much. I will try Royal Purple next time. I put RP in the transmission and saw a drop of 10-15F, and you can get RP from JCWhitey.

 

[C. Harlan]

Well, I got some Royal Purple 75-140 for the rear end... now its just a waiting game for the clutch to get to Peter, and get a new hub on it to accomodate the NV5600. . Hopefully it will not need any friction modifier.



-Chris-