Limited Slip Fix
Fleet Mechanic
Joined: Feb 2007
Posts: 1,852
Likes: 39
Well, since this thread is about limitied slips, let me toss this out there and you guys can let me know what you think.
It's my understanding that a limited slip works like this:
The clutches are between the side gears and the carrier. A spring sets up a preload, so that there is always some drag on the clutches. Then, when a large amount of torque is applied through the driveline, the cut of the spider gears and the side gears forces the side gears laterally, so that they exert even MORE pressure on the clutches.
Does this sound correct? I seem to recall this description from one of the diff patent documents I have read. I only bring this up because there has been some mention of using limited slips/posi's in racing applications, and it seems to me that the amount of "lockup" (for lack of a better word) that you'd get from the preload alone would be pretty worthless in such an application. I think the spring preload is just to keep grandma from getting stuck in the snow, and also to provide enough drag to initiate the "lockup" in higher-torque applications.
What do you guys think?
It's my understanding that a limited slip works like this:
The clutches are between the side gears and the carrier. A spring sets up a preload, so that there is always some drag on the clutches. Then, when a large amount of torque is applied through the driveline, the cut of the spider gears and the side gears forces the side gears laterally, so that they exert even MORE pressure on the clutches.
Does this sound correct? I seem to recall this description from one of the diff patent documents I have read. I only bring this up because there has been some mention of using limited slips/posi's in racing applications, and it seems to me that the amount of "lockup" (for lack of a better word) that you'd get from the preload alone would be pretty worthless in such an application. I think the spring preload is just to keep grandma from getting stuck in the snow, and also to provide enough drag to initiate the "lockup" in higher-torque applications.
What do you guys think?
Senior User
Joined: Feb 2007
Posts: 239
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From: sticksville (Walsh AB. CA
Originally Posted by SonicBlueF350
Just changed the fluid in my rear axle and left out the friction modifier. Isn't this supposed to help with making the limited slip clutches grab better? Well after changing the oil, I installed a SCT custom tune(street/economy) and now the right rear tire is spinning a lot more. I have a lot more power than when I was running a Predator in the performance/economy mode. I only have 17K mi on the truck. Do I need an aftermarket locker/limited slip?
Thanks
Thanks
Senior User
Joined: Nov 2006
Posts: 476
Likes: 0
A month ago I asked a friend of mine that is a Ford dealer mechanic about this and other stuff about my truck. Basically he said in the optional LS (Limited Slip) axles that Ford adds/recommends too much (8oz) of FM (Friction Modifier) that renders the LS useless. He thinks Ford does this for increased life but not caring about performance. He said the LESS FM you add, the MORE grip the LS axle will have on the road. He said in the Super Duty LS usually 4oz of FM works the best. Adding no FM will result in axle binding when taking sharp turns or a U-turn.
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Senior User
Joined: Jun 2003
Posts: 100
Likes: 0
Originally Posted by Randy Pederson
What type of oil did you use some have FM already installed.
Laughing Gas
Joined: Aug 2005
Posts: 1,156
Likes: 10
From: Drain Oregon and Sacramen
Originally Posted by SonicBlueF350
Just changed the fluid in my rear axle and left out the friction modifier. Isn't this supposed to help with making the limited slip clutches grab better? Well after changing the oil, I installed a SCT custom tune(street/economy) and now the right rear tire is spinning a lot more. I have a lot more power than when I was running a Predator in the performance/economy mode. I only have 17K mi on the truck. Do I need an aftermarket locker/limited slip?
Thanks
Thanks
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