I have a 2000 F-150 4x2 with the 3.55 ratio regular axle. As I understood it the axle is a limited slip diff, but yesterday I had one wheel spinning on ice while the other sat still on solid ground. I called the dealer and he said that I probably need to add friction modifier. ??? isn't that a lubricant? isn't the limited slip a mechanical operation? What exactly is going on here?

Am I wrong in thinking I have a limited slip?

Is there something majorly wrong?

Or will the simple addition of some friction modifier fix my problem?

 

Chris

I can't agree more. I have a 2000 F-150 4x4 and I recently developed "shuttering" in the rear end. The recommendation by several on this site was to use "friction modifier". I went to my local parts store and asked for that product. The guy gave me a high end lubricant. "Friction modifier" means to me a friction enhancer, not friction reducer. I am as confused as you are.

DaWG

 

Hey guys, I was as confused as you until about a week ago, I finally got tired of the shudder and decided to figure out what different weights of lube were exactly and why using the friction modifier to make things slippery worked... The best info I found was on how stuff works. Notice that you don't notice the shudder if the truck is cold. That is because the multi-viscosity oil flows easier. http://auto.howstuffworks.com/question164.htm This allows the clutches in your limited slip to slip easier and not lock up http://auto.howstuffworks.com/differential6.htm

When the polymer chains in the multi-viscosity oil are warm, they are long, this causes the clutches to stick, the modifier allows the long polymer chains to slip past eachother, allowing the limited slip differential to slip internally and transfer torque to the wheel that needs it. That is the sense I made out of all the tons of info on the web. Howstuffworks.com is an awesome source of nerd info, at least I think so.

Another web site that I found is here: http://www.1st-in-synthetics.com/slip_lock.htm
I know that one is biased though, but it is still pretty good info on why the stuff works! Anyway, I hope you guys find this stuff as interesting as I did.

 

John

You have told in a way that I understand it. Now I will head back and buy the lubricant at the auto parts store. Thanks for taking the time to explain.

DaWG

 

hmmm...

I don't have a shudder problem, I have a one wheel spinning, one wheel not problem. so I'm not sure that I am on the same page about the need for the friction modifier. I called two other dealers in town and they basiclly said I don't have a limited slip, sorta.

It was explained to me that the limited slip works when the truck is in motion and there is pressure on one of the wheels (as in when you are in a turn there is pressure on the outside wheel) but when the truck is not in motion the wheels will work as if it was a full slip (such as when one wheel is on ice)

I am not sure I get it still (how does the diff know if the truck is in motion or not? if the gears are turning doesn't it think the truck is in motion? why in the world would they do it that way?) but two dealers said that that is the way it is, and that there is nothing wrong with my truck, for what that is worth.

any further info, explanation or clarification on this would be read eagerly

 

Sometimes a slight application of the parking brake will assist the limited slip so that the wheel not spinning will get some more torque. Someone posted that this was even mentioned in their owners manual.

 

sounds crazy... but it just might work!

I will have to remember that next time I have the one spinning wheel problem.

Also I will have to look in the manual about that, I love when ghetto fixes are "officially sanctioned."

 

 

Ah Ha!

I have the 3.55 open.

I knew I had the 3.55, but I did not know it was an open diff. Now I know. I guess I was just lucky for the last four years to have never had the one wheel spinning problem before.

This makes me feel better to know that it isn't broken... but now I want the limited slip.