How do I unlock the center diff?

Discussion in '80-Series Tech' started by sodajerk, Jul 6, 2005.

  1. sodajerk

    sodajerk

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    This is on a 1997 lx 450


    I think my center diff is locked even though the light is off.

    Question #1 how do I tell for sure.

    Question #2 how do I get it to unlock?

    Russell
     
  2. elmariachi

    elmariachi

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    Why do you think it is locked?
     
  3. sodajerk

    sodajerk

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    Tried all the test I know,

    jacked front driver up put in neutral and I could not rotate the tire.

    also ( in same position) I put it in gear and it would not spin)
     
  4. elmariachi

    elmariachi

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    Jacked up, the driver front should turn by hand ...and will cause the truck to head backward if front is turned backward. In gear it should spin.

    Do you have a center diff lock switch? How many miles are on the truck? How long have you had it? Have you ever seen the orange indicator light on? If you pull it into low, does the orange light come on?
     
  5. sodajerk

    sodajerk

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    it has 90k on the clock, no center diff switch, I have had it about 6,000 miles and it has always had a serious front tire scrub but I thought that was normal. I think maybe now I was mistaken. The indicator light seem to function correctly, when the t-case is in low the light comes on and it goes off when shifted to high.
     
  6. elmariachi

    elmariachi

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    I know what it feels like when its locked, but maybe someone else might not. My advice is this. Go to a parking lot and pull it into low range. Then drive forward and start to turn a little more as you go. You will "feel" the driveline start to bind. Then put it back in High and do it again with the transmission in Low 1. See if you can get it to feel the same way. My guess is its staying locked especially if you think the tires are scrubbing. But on the ones I have owned, it has been easy to tell if I am on dry road and turning with my center diff lock switch on.

    Anyone care to jump in?
     
  7. Rookie2

    Rookie2

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    I think most would suggest doing it on gravel. Run it in Low with the center locked and do a fairly tight slow donut. If you're doing a left hand donut, you'll hear the left side bark/skid as it's trying to maintain the same wheel turn as the right side. With the rig in normal drive mode, this bark/skid should not occur.

    :beer:
    Rookie2
     
  8. elmariachi

    elmariachi

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    Agreed, but he thinks he's already been running like this on pavement so I was thinking that doing it on pavement might help him better recognize the bark/bite.
     
  9. sodajerk

    sodajerk

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    I am pulling the front drive shaft, that should answer it.
     
  10. Rookie2

    Rookie2

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    Hehe... I love it! He's already been F'ing it up, so lets "F" it up some more :D

    Joking of course.
     
  11. elmariachi

    elmariachi

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    BAAAAHAAAHHAAAAA.....I thought of that after I posted it. ;p

    Its :flipoff2: with the newbie night. :D
     
  12. sodajerk

    sodajerk

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    Pulled the front drive shaft and it drives alot different (smooth). Am i right that it should not drive if the center diff is unlocked and the front drive shaft is off? Cruised AT 70 tight circle forward and reverse.
     
  13. elmariachi

    elmariachi

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    It sounds to me as if it is in fact staying locked in Hi range. Surely the FSM has a process for diagnosing it...that's where I would start. If you are sure it is staying locked, I would suppose it would be better to leave the shaft out until you get it fixed.

    EDIT>>>Yep, section TR-24 of the FSM details a simple process for troubleshooting the CDL motor shift control system. I would start there but I would also check the wiring harness connections at the transfer case as well as the fluid level.
     
    Last edited: Jul 6, 2005
  14. TX_TLC

    TX_TLC

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    Russell...

    Give me a call..I can come by and we can compare...lock mine and you drive it...then unlock see if it is the same as yours with the drive shaft out.


    This might also answer your clicking post birf.... :idea: maybe?

    David
     
  15. elmariachi

    elmariachi

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    All the more reason to put your location in your sigline. Had I know you were in Abilene, I would have already suggested you go see David.
     
  16. sleeoffroad

    sleeoffroad Supporting Vendor

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    Most probably a failed viscous coupling: Makes the truck act if the center diff is locked:
     
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