2nd Gen Non-Engine/Transmission Help: Confused about friction modifier

[Kyle]

I've got limited slip in my Dana-80.



I just changed the rear fluid (I use LE 90-wgt) and did NOT add modifier. I did a dozen lock-to-lock figure-eights on asfault and the rear tires never barked. Jacked up one side in neutral, brake off and I can turn one rear wheel with my hands, but there's definately some resistance -- it won't "spin" by hand.



The guy at the parts counter told me the tires would bark with no modifier and to put in just enough to stop it. He said the more you add, the slipperier the limited-slip clutches get.



What gives? I expected more bite. Are the clutches starting to wear out after 69,000 miles?

 

[jponder]

Excellent POST. I have wondered about this also. I have seen it explained as you said KYLE ie add friction modifier till the chattering stops. What gives?

 

[Deezul1]

My experience has been the opposite of what was posted above. I changed my diff oil out and installed a synthetic and assumed that no friction modifier was needed. When turning slow speed corners with windows down I could hear a little tire slippage and was wearing back tires out pretty fast (no burnouts either) so added friction modifier and problem solved. I was under the impression that the modifier was to allow the clutches to slip some when turning which they wouldnt do without it.

 

[CFast]

Are the LS's in these trucks the clutch type like the Sure Grips chrysler used back in the 60's? I have one of those in my duster, with just oil it grips so hard in a turn that the car actually hops. Added friction modifer, now it works GREAT! Dual black marks for miles and miles, and turns a corner with no hop. I've only had my RAM a month so I haven't pulled the diff cover to see what the LS is. Hopefully it's the clutch type.

 

[Gary - K7GLD]

WELL, it's good we got THAT all cleared up, and the confusion thoroughly eliminated...



(EDIT - my post further above was off base, and I decided to delete it to avoid further confusion)



And yup, i got tangled up on the FM use in cases where the LS does NOT function (just slips) with the new lube - went thru the same thing when I tried a well known synthetic in my own LS differential - ended up having to drain it and go to a synthetic blend to get a proper mix of synthetic protection, while still getting proper LS operation...



BUT, I've never heard of using the FM successfully in cases such as I experienced, where from all appearances, the lube was ALREADY too slick...



But as is evident, LS units vary greatly, and it's always a good idea to check for proper LS operation after switching lubes - if proper LS operation is important to you!

 

[SnoKing]

I had to add a half bottle of FM after going to synthetic in my truck, was grabbing on corners. SNOKING

 

[Straight6Jeff]

I talked with Rob from Drivetrain Specialists on Monday regarding my D80 restack and the spool like performance. He recommended dumpin ghte fluid, adding a quiality semi-synthetic, and using 3-4 bottles of the For motorsports performance friction modifier. he was adament about it being the ford performance, as the parts-store brands are useless. Gonna give it a try this weekend. Hopefully it works, or I will be restacking to loosen it up a bit.

 

[willyslover]

no way would I add 3 or 4 bottles at once guys... . [no flame Jeff]



Add the stuff a ounce or two at a time then do the fig 8's until the clutches release... adding all at once may over modify as all assemblies are not the same from the factory, and all are not worn the same at the time of oil change... over modification WILL render the unit usless

 

[Straight6Jeff]

Good point Willys. It's been four thousand miles since I did the restack, and the LSD hasn't slipped at all. Valve stems are in the exact same place with respect to each other. Rob sounded like he was speaking from experience, as he inquired as to wheather I had an aftermarket cover wit increased capacity. He said that with eight quarts of total capacity, it would probably take the heavy part of four bottles of the Ford Modifier. I will start with two and add some if needed. The nice thing with the mag-hytec is the ability to drain and tweak the final concentration of dif fluid/modifier. It seems that the Ford midifier will forma "tacky" when heated via the slipping of the clutches, thus promoting LSD.



This weekend will see a lot of fluid experiments.

 

[RowJ]

Great discussion!



Dan, Excellent comments-save one point. Synthetics are no more slippery than regular oil. (this misconception has been around for years due to dyno results from racers). They tend to produce more HP due to higher quality additives.

However, Higher quality gearlube manufactures, which includes many synthetics, tend to add the friction modifier to all their rear end products.



Kyle, I believe L. E. is one of these companys (includes FM in their gearlubes). Calling their 800 # would easily confirm this.



In either caes. if you are not "draging" around corners, what you have is working and I would not add to it.



Rowland

 

[willyslover]

I run a synthetic and have since 10K [at 95k now]. . and need no modifier at all... my unit works great ... . however I can feel some wear when in snow as I'm starting to drop a bit of traction at a wheel. . also I have a Mag Hytec cover

but there have been posters who from the factory went to systhetics and need some modifier do to factory settings being a bit tighter. .

IMHO . . I would not ad more that a very few ounces and test, then add to needs but at 1 or 2 ounces at a time with figure 8's in between

 

[Gary - K7GLD]

"In either caes. if you are not "draging" around corners, what you have is working and I would not add to it. "



ACTUALLY, what Kyle said was:



"I can turn one rear wheel with my hands, but there's definately some resistance -- it won't "spin" by hand. "



I suppose it depends on a fellas interpretation ow what "some resistance" is - but I, personally, think that's WAY too little LS action to be of practical value in real life situations - as I recall, the spec for measured resistance in a test like the above was quoted as being somewhere in the vicinity of about 95 ft. lbs of torque to cause the LS clutches to start slipping - considerably more than just a little...

 

[Sixpack]

Originally posted by Dl5treez

The techinical name for what is in the Dodge truck is a Dana Trac-Lok, although some have found a Powr-Lok much to their happiness upon pulling the cover.



Dan-

How does one tell the difference with the cover off? What do you look for?

 

[Kyle]

"some" resistance

Gary's captured my concern correctly. I'm concerned that there isn't enough "limit" to the limited slip. I'm thinking the clutches slip too easily - especially since I didn't add any modifier.



The shop manual says if it slips at less than 30 ft-lbs or more than 200 ft-lbs then it "should be serviced. " That's a pretty big range but that's kinda how the manual is on a lot of things.



I didn't put a torque wrench on it so I can't say for sure. I do have 35" tires which gives me more leverage. It took both hands, but I didn't get red-faced making it slip. In any case it sure seems, as Gary put it, "WAY too little LS action to be of practical value in real life situations. "



I presume my initial thought was right -- adding modifier, if anything, would only make it slip easier.



As it stands now, it's not hopping on the corners so I'm not going to add any friction modifier. I'll put that money into my air-locker fund.

 

[Gary - K7GLD]

Kyle, I was very interested in reading your reference to a tech manual spec of 200 ft. lbs. for LS clutch slippage - other estimates so far have been sorta vague, glad to see something a bit more authoritative!



What *I* ended up doing in the same situation you are now in, was going to Valvoline 90/140 "synthetic blend" lube - I wanted something better suited to towing in summer temps, but really wanted the full effectiveness of the LSD for RVing situations where traction is poor. In my case, that blend was perfect right out of the bottle - but there's so much variation from one LSD unit to another, it can be nearly impossible to claim it would work for someone else.



With even STOCK trucks providing around 1200+ ft. lbs. of torque at the rear wheels, 200 ft. lbs. effective LS action certainly isn't TOO much!

 

[CFast]

So what brand of FM do you guys use? I bought a bottle at napa for my clutch type sure grip that works great. will it work with these LSD'S?

 

[Straight6Jeff]

I did not get to try the Fordmotorsports performance friction modifier... as the parts place forgot to order it. I will hopefully be able to get it in the next few days. If the FM doesn't loosen mine up a bit, I'll be retacking to 4 or 5 active plates, instead of 6