HD rear locking diff.

regcab02HD · April 15, 2002

I went to check my hog traps today and had to go through a ditch to get to them. The ditch had alittle mud and water in it. I made it through ok but decided to see how long it took for the rear locking diff. to kick in. So I backed up so the rear wheels were in the mud.

I then put it in first and let off of the clutch. One tire started spinning and then the other. I pushed the gas alittle more and one of the wheels seemed to slow down and then turn faster. Then slow down and speed up. I looked in the mirror at the other wheel and it did the same thing. I then started to hear a thumping from the rearend. It wasnt' just one thump, it was like thump, then a pause, then thump, then another pause, then thump. There was maybe a second in between the thumps.

I figured I would hear one thump from when the locker kicked in, but it kept on making a thumping sound. The only thing I could figure out is the the locker was locking, then unlocking, the locking again.

Does anyone know what could be wrong? Has anyone ever had this problem?

To get out of the ditch I put it in 4 High and let off the clutch. The pickup didn't move. So I stepped on the clutch and let out again, then it moved. I guess since I wasn't moving the transfer case didn't engage. Has anyone had this happen to them? I have put it in fwd many times before and never had a problem, just this time.

YANKEES · April 16, 2002

Haven't we heard the three thump theory somewhere before? Sounds like a case of O.J. Simpson..three thumps and a house guess (Kato Kalin)...Quick fix..stopping giving O.J. a ride

Just kidding..sorry, don't know the answer to your problem, but, could not resist alittle humor.

Colorado Kid · April 17, 2002

I haven't noticed it in this truck yet, but in the ancient '82 with 250 I-6 I observed exactly what you're talking about. If both wheels werre in very low traction conditions it seemed to only lock for a split second, evidently the bump ("thump") when it locked kicked the "Slow" wheel hard enough that it then exceeded the speed of the "fast" wheel for just long enough to release the latch. Also when the traction is switching from one side to the other you get repeated "thumps":

Starting from a dead stop , one wheel (Low traction) begins to slip, after part of a revolution the diff "locks" (thump)applying torque to the higher traction wheel. The "lock" is held by a reaction to the torque being transmitted to the "high traction" wheel. If that wheel crosses a patch of ice and slips the diff unlocks, if it slips enough the diff relocks sending torque to the "other" wheel (thump). Each time there is a partial revolution of wheel spin before the next thump.

Perfectly clear, right? ???

pullinpower · April 17, 2002

regcabhd02 what is happening I think is the rearend "dug"in up to the chunk and was freewheeling with no weight on the wheels.There is nothing wrong,mine has done it also when I got hung up.

regcab02HD · April 18, 2002

Hey pullinpower, I think that's what happend. The wheel started freewheeling and then locked back in.

Can you explain the front wheels not pulling when I put it in FWD. But when I stepped on the clutch and let off it started pulling. It's still puzzling me.