2nd Gen Non-Engine/Transmission friction modifier help

[Mike Cureton]

I am writing this from the aircraft carrier HARRY S TRUMAN on deployment in the Med. So it will be awhile until I get to drive my baby.



A few months ago I installed a Mag Hytec rear diff. cover and filled the axle with AMSoil 75-90.

Do I have to add friction modifier? I have a limited slip rear end, does it matter? What purpose does friction modifier serve?

If so, what is the best type to use and where can I get it?



Thanks in advance for your help.

 

[LSMITH]

Hey Mike, sorry to hear about the deployment, been there and done that!!



When you get back drive the truck for a while, if you get chatter in the rear when turning you will want to add Mopar friction modifier 2 ounces at a time. Drive a couple of tight figure 8's, then give it a couple days of driving. Keep adding until the chatter goes away or is VERY slight. Don't add it as a matter of course.

 

[Gary - K7GLD]

It's my understanding that the sole function of friction modifier is to INCREASE the slipperyness of differential lube to prevent limited slip clutch chatter that often occurs with many differential lubes. It would seem reasonable that the best place to buy the modifier, is at the place that sells/services the differentials - a local Dodge dealership - there's precious little monetary incentive to run around looking for something cheaper... Since the Dana differential is also used in Ford trucks, it's possible the Ford brand would work well too...



It's a good idea to make sure you actually NEED the modifier - if your LS isn't showing any symptoms of chattering, you probably don't need any - on the other hand, if the Amsoil in your differential happens to perform the same way the 75/140 Amsoil did in MY differential, your LS function MIGHT not be working at all any more due to the wide variations apparent in the clutch packs in the Dana LS units, and the slipperyness of the Amsoil lube - I ended up having to drain my differential, and refilled with Valvoline synthetic blend 85/140 to restore my LSD to proper operation...



YMMV...

 

[Loren]

Mike,



Thanks for serving our country when we need it. For what it's worth, I'm a centurion (100 landings) on the Independence. I got most of those traps in the Med. It was a few years ago, as the Indy is now a west-coast ship, I think. (Okay, okay. It was more than a few years ago. It was 1977. )



The friction modifier is used to make the differential oil more slippery. It is required only in limited-slip differentials like yours.



Synthetic oils are already more slippery than petroleum oils, so in some trucks the friction modifier isn't required if a synthetic is used. This seems to be variable from truck to truck. My truck has Amsoil 75W-90 oil, and doesn't require the modifier, but I have read of other owners who had to put it into their rear-ends (maybe "differential" would be a better word) to prevent chatter.



The way you know whether or not you will need it is to drive the truck in tight turns. If the differential oil is not slippery enough, the rear tires will skid and slip excessively, indicating that the differential is "locking up" and preventing the wheels from turning at different speeds. If this happens, you will need to add friction modifier to make the oil more slippery. You are the one who will determine whether the skidding and slipping is "excessive" or not.



If the tires do not skid or slip at all, the differential oil may be a bit too slippery already. No friction modifier is necessary, and your limited-slip differential may not prevent tire slippage as well as it was designed to do. The only cure for this is to change the differential oil to one that is less slippery.



There is a standard amount of friction modifier that is recommended for the differential, but since each truck seems to be different in this regard, most experienced people recommend trial and error for determining how much you need.



If friction modifier is required, add just one bottle to the differential. Drive the truck for a while to mix it in. Many drivers recommend driving a few figure-eights to lubricate the clutches. Then see how the differential behaves in tight turns. Again, you will determine if the tire slippage is enough or excessive. If the tires still slip and skid too much for you, add another half bottle of modifier and do the whole thing all over again. Keep this up until you are happy with the result.



The friction modifier can be purchased in small (about 4 ounce) bottles at the dealer for a reasonable cost. I don't know if you can find it elsewhere.



My experience with the Amsoil leads me to believe that you won't need to use any of it at all.



Enjoy the truck when you get home. Stay safe out there.



Loren

 

[dan_gilson]

1st Thanks!



You might want to talk with Roy at Mag-Hytec. He even recomended the friction modifier when using the LE synethic that he sells. Also, because you have increased the capacity of the differential you may need more friction modifier than normal. He recommended 3 bottles for me. It is quieter now than new and still working fine. I have had it up on stands to verify that the differential has not opened up.



For the price of the friction modifier I just can understand why people would want ot risk their clutch packs. A few $$ in cheap insurance versus a high ticket item of the clutch packs.

 

[Mike Cureton]

Thanks for all your help.

Reading the forum makes me homesick, I can't wait to get this cruise over with. My RAM needs a good bombing!!!

 

[Gary - K7GLD]

Dan sez:



"I have had it up on stands to verify that the differential has not opened up. "



Out of curiosity Dan, exactly HOW did you physically test your LS for proper operation? This question has come up before, and there IS apparently a test procedure for accurately testing the LS clutches for proper condition and operation - how did you do it?



I know that after installing Amsoil in my differential, I could jack up one rear wheel on my truck and not even begin to spin it manually against the clutches - yet when actually operating the truck with one wheel on a slippery surface, it spun freely while the other provided NO traction - obviously, a mere visual or casual "test" won't necessarily reveal poor LSD opertion.

 

[dan_gilson]

I confess, I did not look through the manual to see what test(s) could be done.



I just jacked it up and threw it into gear and both wheels were spinning in the "right" direction. I could not stop either. Also with the it out of gear and engine off I could hand spin each and the other turned in the same direction.



If I get time tonight I will see what the Dodge service manual says.



Anyone else have suggestions for a test?

 

[rgreen]

Also have the Amsoil 75-90 in my differentail, 4w limited slip. 1996. Have not noticed any kerchunks in the turns, have not added any additive. I do notice kerchanking when in 4 wheel drive from the front on turns. Do not know wether to turn to the friction modifier for that or wether it is not related.