Differential lock inop

[dhirocz]

So the other day I was getting loaded at a shipper and had to use a loading rack I was unfamiliar with. As I backed in, the trailer tilted just enough that it pulled up the drives on the passenger side of the truck.

According to them, this is a common problem which is why they don't use that rack often.

In any case, with both pairs on the passenger side spinning an inch in the air, I stopped it and turned on the diff lock. It made no difference. I couldn't move even though the driver's side was on the ground...ended up throwing a chock block under the passenger side tires to move the truck.

Correct me if I'm mistaken, but the diff lock is supposed to lock the drive axle(s) together to share torque out of both axle shafts in an axle. Inter axle lock is supposed to lock the drive axles together (but my truck isn't equipped with that). I'm assuming with one diff lock switch that the lock is for the front drive axle.

I definitely have air to the switch...haven't gotten the truck home yet to investigate much...I'm assuming there is a valve or solenoid that I need to look for that controls this under the truck in the vicinity of the axle?

I want to get this issue fixed. I've not a dedicated local deal going that pays me really well to the truck...and I hardly burn fuel. I don't wanna be that guy who has to call for a tow truck at the shipper, stuck at an angle in front of the scale, that would suck!!!

[iceman]

I am not exactly sure how other trucks are but on mine, the interaxle diff (which is the one most trucks come with and always the one you lock before any other lockers) will lock one of the front to the opposite corner in the rear.(think of it as and X) As traction allows it will switch, but only two wheels will always spin. So technically one tire on the drivers side should have turned. But, if both of them on your passenger side were spinning it might be a different setup(i think Meritor does it different) in which case if you did engage your switch it should have turned the tires on the other side. Were they both spinning before or after you engaged the diff lock switch?

[Rawze]

On most trucks, the diff lock only enforces the drive-shaft to spin from the front diff to the rear diff. Has nothing to do with forcing both tires to spin on the same axle. With it off, only one tire spinning will make you get stuck. with it on, it takes one tire at each of the axles to make you get stuck. They are typically referred to as a "inter-axle" lock.

They do make diff locks that enforce both tires to spin on the same axle, but most highway trucks do not have this option. They are typically referred to as an actual "differential" lock, "double", or Positive traction" lock.

[imalumberjack]

(07-11-2018 )Rawze Wrote:  On most trucks, the diff lock only enforces the drive-shaft to spin from the front diff to the rear diff. Has nothing to do with forcing both tires to spin on the same axle. With it off, only one tire spinning will make you get stuck. with it on, it takes one tire at each of the axles to make you get stuck. They are typically referred to as a "inter-axle" lock.

They do make diff locks that enforce both tires to spin on the same axle, but most highway trucks do not have this option. They are typically referred to as an actual "differential" lock, "double", or Positive traction" lock.

Rawze is correct its like locking in 4X4, in general most trucks in normal driving send power to back axle and it will go to side with least traction, engage the inter=lock and it sends power to both axles but only to tires with least traction (not side dependant) if you have the double diff lock this locks all 8 tires and some trucks you can separate (front axle is locked-rear axle is locked or both) just a note in general you can not turn with all axles locked, I use it in extreme conditions (hopefully before i'm stuck) and release the locker as soon as possible but leave in the interlock until I'm sure I'm not stuck. Sometimes you can dump the air valve on suspension and it changes where the axles are allowing the truck to touch one of the tires to the ground in order to move forward or back.

[kryten]

The way it was explained to me years ago was in normal conditions each wheel will put down 25% of the load. If in this configuration 1 wheel looses traction 100% of the power will go to that wheel. Engage the power divider and each diff will receive 50%. If one wheel now looses traction all the power of that diff will go to that wheel. But you still have 50% of the trucks power still going to the other axle, 25% per wheel. If the loss of traction is bad enough you can have 1 wheel spinning on each axle.

Now to get into the diff locks. Most trucks that run the mountains will have a diff lock of some kind. I have what I call a "3 way" diff lock. Only 1 axle on my truck locks the wheels together so if I get into trouble only one wheel will let loose and as long as one of the other 3 wheel has traction I keep moving. With my setup I can still turn with it engaged. I would think most train trucks run a "4 way" locker. Both axles will lock giving maximum traction. With this set up you can't turn, all that will happen is you push the front end in whatever direction you're pointed.

[Unilevers]

power dividers or inter axle locks put power out of one diff into another diff - both differentials still function as normal just that 2 of the pinions have input power now instead of just one. You can still get stuck if its tilted as only one side of now both front and rears diffs will transmit power.

Differential locks or Lockers Lock the axle shafts on one differential assembly together. It removes the "Differential" part of a diff and both sides transmit power 50%. They are physical splined collars that fit into the end gears of the diff and the splines of the axle to lock them together. If you shift these in while the diff is being a Differential then it all goes bad.

Now if you have a inter axle and a diff lock you can force power to both diff's and lock both sides of each diff to drive 50%.

Now up here in the oilfield alot of our units are tri drives and they have inter axles and diff locks. So the front 2 diffs have power dividers and all 3 diffs have Lockers. Ever been stuck because you can go only forward and back and cant turn? thats what happens when everything is all locked up on a tri drive.

ever wonder why the power divider always breaks first on a tri drive? It takes 50% of the power input while the other 2 diffs get 25% food for thought!