Friction Modifier Question

[Harry5150]

What would happen if friction modifier wasn't put in with an oil change on a LS 3.73 differential?

I did a gear oil change with Valvoline Durablend synthetic gear oil and didn't put friction modifier in. I assumed that it was in "synthetic" fluid when I did it.

What does friction modifier do? Increase friction or decrease it?

Have I cooked the clutches? I've only driven on the road since the fluid change.

 

[aldive]

I use Mobile 1 in my rear end w/o adding any friction modifiers. No problems ever. Its a LS 3.83.

Read this thread for more info.... http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=16;t=000131

 

[DesertSpive]

Originally posted by Harry5150
What would happen if friction modifier wasn't put in with an oil change on a LS 3.73 differential?

Most high quality synthetic gear oils do not require friction modifier (Amsoil and Ford to name a couple). I would say you are okay, but you can always add it if you want. Just read the label, usually they will say on the bottle if it is required or not. Also, was it synthetic? I think it is a blend.

--Sean

 

[Alec]

If you don't know if you need it or not, add some. If you do need it and don't have any, your LS will want to lock up more.

 

[MrShorty]

Like Alec said, the friction modifier helps keep the clutches from binding/chattering in corners and such.
At that age (I'm guessing 50K-60K miles), the clutches are possibly worn out and it may not matter anyway. Most opinions I've read give those clutches about a 50K mile lifespan.

 

[Harry5150]

DesertSpive - It is actually the synth blend.

I dont have any chatter but I think my clutches are toast anyway.

Alec - So you're saying if I don't put the FM in, I have a liquid locker?

 

[MrShorty]

When I rebuilt the LSD in my BII, for the first little bit (10-20 mi), it was quite aggressive -- I was impressed. I have since wondered what would happen on a newly rebuilt unit if you left the friction modifier out? consistently more aggressive? road manners? life span/durability?

 

[Alec]

With an LS that needs the modifier and if you're running fluid without that property:

The LS would wear really fast, misbehave on corners and under accel, make noise, and drive you nuts!

EDIT: I know, my mechanic forgot once to put it in and I was going crazy!

 

[MrShorty]

Originally posted by Alec
With an LS that needs the modifier and if you're running fluid without that property:

The LS would wear really fast, misbehave on corners and under accel, make noise, and drive you nuts!

EDIT: I know, my mechanic forgot once to put it in and I was going crazy!

It seems to me that those "properties" (with the exception of wearing out) of an LS w/o friction modifier are the same kinds of "complaints" that are associated with lockers, aren't they?
It's interesting that you've experienced the Trac-lok w/o the modifier. How would you compare it's behavior then to a true locker? I've never driven a truck with a locker in it, so I don't have a reference.
As far as durability, I wonder how long they would last...5000 miles? 10000? At that point, if that's the kind of performance you're after would one be better served just buying a locker? probably.

 

[Alec]

My experience was with my Eaton LS. It didn't behave like a locker without the FM, it just behaved badly.

I have heard the stock Ford LS will behave much more like a locker without the FM, but will wear out very quickly and not be fun to drive.

 

[TPLYNCH]

Just for my own personal info, isn't the friction modifier added to assist the clutches "grabbing" and maintain the traction to both wheels??

 

[MrShorty]

check out the link in aldive's post above. According to them the friction modifier is there to allow for more slippage, so the clutches don't bind in corners.
One interesting note I saw there, is that one can reduce the amount of friction modifier (say 2 ozs instead of 4) and get a little more grab from the limited slip.
I wonder how well it would work to have two formulas for the differential fluid. One that's in there most of the time for the daily routine with friction modifier in it. But drain it out and put in lube with no FM in it for trail rides and such? A little inconvenient, yes. but doable. may have to try it sometime.