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How to tell if limited slip works?

Discussion in 'Ford Trucks' started by BKFC255, Jan 15, 2009.

  1. BKFC255

    BKFC255 Senior Member
    Messages: 140

    I have a 06 F 150 with 3.73 LS. Not sure how it works it. Most of the time when on a icey drive or in some amount of snow it appears only one rear wheel spins. not helping me much when plowing. I checked for the code on the door and it is the code for 3.73 ls. any answers on how to tell if it works when it will kick in. Because it does not work like a locker and i thougt it was almost the same idea.
  2. fortydegnorth

    fortydegnorth Senior Member
    Messages: 219

    Limited slip is much different than a locker. Limited slip often doesn't work as well as you hope it will. Lockers are more mechanical almost like a ratchet. Limited slip used more of a clutch. Changing the fluid and having it checked is about the only way to know if its working up to spec. Ford is not known to have great limited slip differentials. Granted they are strong but they don't lock up very good.
  3. BKFC255

    BKFC255 Senior Member
    Messages: 140

    Mine only has 30000 on it. I heard it you knoow it works if you are backing up and you start to slide side ways. I dont know how true that is I figured it was from just slideing around on ice or snow. So you just dont know when you can count on it, more or less hit and miss.
    Last edited: Jan 15, 2009
  4. linckeil

    linckeil PlowSite.com Addict
    from CT
    Messages: 1,272

    i had the stock ford limited slip unit in my ford 10.25" rear axle. but a limited slip/posi will fail you when you really need it. get one rear tire on ice and one on pavement and all power will be put to the tire on the ice and you will not go anywhere. the limited slip/posi will behave just like an open differential when you need it most, which will just contribute to faster clutch wear in the limited slip, thus decreasing its efficiency even more so.

    a locker will do just that, lock both rear wheels together. the one tire on ice on the one tire on pavement will get an equal amount of torque and you will drive out of it. i upgraded to a locker in my ford 10.25" rear from the limited slip and noticed a gain in traction. just stay out of the gas on wet roads as a fish tale is much more likely with a locker. and when plowing, always do it in 4wd to help prevent a fish tale while plowing in the event you hit the gas a bit too hard.
  5. dmontgomery

    dmontgomery PlowSite.com Addict
    Messages: 1,238

    I had a Detroit Tru Trac LS put in my Ram and now seldom need to plow in 4wd.........
    Last edited: Jan 15, 2009
  6. tjctransport

    tjctransport PlowSite.com Addict
    Messages: 1,390

    if you encounter slippage in a vehicle with a limited slip rear diff, gently apply the brakes as you gently apply the throttle. this will help with the LS engagement.
    it is basically the same thing as the GM traction control. only you determine how much braking is applied as compared to the computer doing it in the GM.
  7. Dissociative

    Dissociative 2000 Club Member
    Messages: 2,066

    that does work but only to a point....

    stock LS in a ford are junk..plain and simple ....upgrade it
  8. Ggg6

    Ggg6 Senior Member
    from IL
    Messages: 521

    Come on George you personally know two guys with the factory Ford LSD and they work great. In fact one of them acts very similar to a locker it is so tight. Mine works really nice and smooth, without the need to apply the brakes to get it to work.
    The Ford LSD is a very good strong unit when set up correctly. This correct setup is rarely achieved from the factory, why I don't know. But I have heard stories about wrong clutch/steel stacking, wrong shimming, etc. This fall I installed new clutches and steels and experimented with the amount of shims till I got a good working LSD. BTW I am not running any friction modifier.
    So when set up correctly the Ford LSD works very good. It is not junk by any means. Now having said that it's no Detroit locker either.
    BKFC255- That deal with driving backwards I think is BS but I may be wrong.
    Last edited: Jan 19, 2009
  9. snow game

    snow game Senior Member
    from RI
    Messages: 255

    I'm glad I found this post and don't want to ijack it, but. I have a brand new 08, at times going from hitting the pile into reverse I have a "slipping kind of grinding feeling" I have been plowing for more than half my life. It's not "me and old habbits", my 06 diesel or any other Ford I had never did this unless my timing was off, this has happened more times in the past three weeks than all my years of plowing. Is the the LS kicking in or is something wrong?
  10. Dissociative

    Dissociative 2000 Club Member
    Messages: 2,066

    ummm...no i know two guys who re-did their factory LS and jazzed up the shims to make em dig harder....definitely NOT factory sponsored action...and definitely NOT something i would recommend ANYBODY try without first finding someone who knows how to do it correctly. it works yes...but you can;t go into a shop and ask for that unless you have a really good diff. shop around you...99% look at you like you're crazy..

    for most it's better to just upgrade.....for us grease hands it may be different.
  11. Ggg6

    Ggg6 Senior Member
    from IL
    Messages: 521

    Tony and I both changed the shims in our LSD's to increase the preload, truly it is not rocket science. What you imply by "jazzed up the shims" I have no idea, but nothing special or secret was done. We added shims to his, and mine required new clutches so a new fricion/steel set was installed when the additional shims were added to mine. I never said our LSD's were the factory set up, just that we are using the Ford LSD not an aftermarket one. I specifically said that a good working set up is rarely achieved from the factory. IMO this is due to poor assembly quality, but this can be corrected easily by rearranging the order making sure to alternate steel, friction, steel, etc.
    BTW Toni and I are just too busy right now to rebuild your LSD. We don't want to say "yeah bring it over" and then have your truck tied up when you could be making money with it. When things slow down we would be happy to do the work.
    Last edited: Jan 21, 2009
  12. Ggg6

    Ggg6 Senior Member
    from IL
    Messages: 521

    snow game- It is really hard to diagnose symptoms like you described over the internet. I really would only be making a guess. If you drive forward in a tight circle on dry pavement do you hear the same noise?
  13. Dissociative

    Dissociative 2000 Club Member
    Messages: 2,066

    ford never sets them up tight from the factory because too many people whine about it when on dry pavement...too many complaints about hopping or sliding out around corners....they are made to slip when you lean the truck over to one side so you DON'T fishtail like a mustang...again simply done that way to please the 99% of most drivers situations.

    the average person doesn't want a tight LS, they want smooth, quite, action with no noticeable effects. Thats why they are set the way they are. They work fine on boat ramps and other level surfaces.

    now you guys go jazzing with the factory set up by adding shims (as good as it works) and making it grab harder is effective for you...great...hopefully me too

    i still stand behind the fact that 9 out of 10 people (even shops) i have asked to do this for me flat out refuse...they just rather install a properly set up after market unit that was designed for such features than to take on the responsibility of modifying the stock unit to do so..(again as good as it may work)

    i like the idea....and i want to try it...but just letting out my experience with the whole mess.

    i also hear stock is stacked (steel--steel-steel-friction-steel-steel-steel-friction) and if you restack them (steel-friction-steel-friction-steel-friction) it works much better too
    Last edited: Jan 21, 2009