Friction Modifier

[SlyBones]

Changed the front and rear diff fluids. Had Amsoil Series 2000, 75w-90 installed in both. Have not added any friction modifier to the rear yet. From different threads around here in the past, I see some never add any, some add 1/2 as much, etc.



So what the best way to determine if or how much to add?



Currently seems smooth going around corners, and dont hear any noise. As long I dont apply too much power. Add a little power to the turn and you can feel its kinda rough or jerky around the turn.

 

[CumminsPuller]

Try doing figure eights.....

Slybones..... i aswell changed to the amsoil 75w-90 a few months ago, and had a bit of chatter in the rearend when i did slight turns..... it was recommended to my to do several figure eights in a large open area... ..... that should work the lube back out in the axles... . getting everyhting nice a lubed..... it worked for me... . if not then add a bit of modifier... . until it sounds and feels ok.....



-Jason

 

[Spooled-up]

I too just switched to Amsoil 75W-90. Right after the switch I had a rumbling that I guess was the chatter that everyone talks about. I just put in 8 oz. of the Mopar friction modifier and it no longer "rumbles" around the corners. Some guys have had to use the modifier with the Amsoil. I guess it depends on the truck.

 

[John]

Hey There SlyBones!

The reason it is suggested to do several figure eights after a gear oil change is to properly slip the LSD clutch plates, allowing the new gear oil to penetrate same. After said ritual, you should then assess the LSD characteristics. Some of the Dana LSDs are setup tighter than others. A Red Line tech. once told me that Dana LSDs typically took from 6-8% friction modifier to tune properly (Amsoil Series 75W-90 and Series 2000 75W-140 have 5% friction modifier). By properly tune I mean, if you make a sharp 90 degree turn under slight throttle, you should just have the LSD clutch plates slip enough to eliminate shuddering... but no more or you will reduce the effectiveness of the LSD. That said, you can seemingly have the LSD characteristics properly tuned and still experience shuddering several months to a year later. Additional friction modifier can be added as required/desired. I would add only enough to properly tune the LSD... 1-2 onces at a time.



Just for comparison, I had to add several onces of Mopar friction modifier to my Amsoil Series 2000 75W-90 gear oil however, when I semi-recently changed my gear oil again (this time I went with Amsoil Series 2000 75W-140), I didn't have to add any friction modifier... at least not yet.



BTW, even with the LSD properly tuned, if you apply a large amount of throttle while taking a sharp turn (on pavement) you will still experience the shuddering... the LSD is simply functioning as intended. Remember your old hot rod days... you would apply the brakes, give it a fair amount of throttle (ok, a lot ) and leave two *****in stripes on the pavement. Yeehaw! Same deal here.

 

[forr]

Three months and @4k miles ago I changed out my diff fluid for the 75w90 Amsoil. I was tempted to leave out the friction modifyer altogether but decided to add 1/2 the dealer recommended volume. Figured I'd drain it out if clutches didn't engage/disengage right. Now the rear limited-slip works better than it did from day one with factory gear oil. No clicking, no banging, and the limited slip works every time under no to light throttle (As I understand it the Dana 80 limited slip in our trucks and the old trac-loks are not designed to work under heavy throttle).



This worked for me.

 

[John]

OOPS! I spoke too soon!

Originally posted by John

... when I semi-recently changed my gear oil again (this time I went with Amsoil Series 2000 75W-140), I didn't have to add any friction modifier... at least not yet.

After scrutinizing my LSD performance yesterday I found I needed to add some friction modifier after all. I added about 1. 5 oz. which restored the LSD characteristics to the condition I prefer.