driving with differential locked

Why would you ever need to do that?

 

Try it, see what happens, and let us know. Personally I would not do it. There's not one single reason too run with diffs locked at 50mph.

 

We had a driver do that and grinded the gears down severely and had to take it to freightliner. But he drove at 65 mph for 150 miles.
Shop told us 35 max. He said after that damage starts to take place. The drier the pavement the wise it can be. Which was our drivers case. Started in snow but forgot about the switch.

 

Many newer trucks automatically disengage above 25 mph or so or on top side of tranny .. I think the main reason is excessive heat which leads to wear is what most say

 

Do you mean the actual differential or the switch that say inter axle lock? They are similar, but do different things. I heard Kevin Rutherford explain this once. Basicly, with the inter axle unlocked, the power from the drive shaft is transferred between the axles as needed. On flat level dry road, the division is 50/50. That can change lots of times depending on any number of factors such as weight, road conditions, etc. Just like a differential that will send all the power to the on wheel that is in the air (less traction) instead of the on the ground, the inter axle lock will do the same the thing with the axles. Which why when stuck in mud or on ice, you will see one axle spin. Locking in the inter axle lock will lock the axles together and power will be sent 50/50 to each axle no matter what. As most company speced truck do not have a differential lock, even with the axles lock in, it is still possible to be stuck and both tires on the same side will spin in the mud. According to Kevin Rutherford, running with the inter axle lock on will not hurt anything except fuel economy.

So, the inter axle lock will lock the axle together to each for 50% power to each axle not matter what. Differentials will only lock in the tires on the axle to each get 50% of the power sent to the axle. With them both of them on, you can pretty much get yourself out most situations. Running with the differentials lock in will affect tire wear. When the truck turns, the outside wheel needs to move faster as it has further to travel during the turn. The differential allows that tire to move faster. When it is lock in, the outside tire cannot mover faster like it needs to during the turn. Therefore, the tire will scrub and jump around causing excess wear.

So, in order to maximize tire wear and mpg, it is best to run down the road with both inter axle and differential locks (if equiped) disengaged.

 

if both sets of duels on the axle are the exact same size and you drive in a perfectly straight line then in theory you could drive with the differential locked, but having those perfect conditions is near impossible. I don't even know if I'd drive with the inter axle locked because differences between the size of the front and rear tires will cause problems on a high traction surface.

 

As suggested above I would leave the inter-axle and differential locks off if on the highway and above 35 mph. Going up or down a hill in adverse conditions I'd lock them up as needed. If you're off road I'd leave the inter-axle locked up since you're on dirt, likely moving slowly, and you have less chance of spinning out if you happen to lift a wheel off the ground at slow speeds.

 

The new ones disengage after a certain mph as to not damage anything. It's a safety feature of sorts. The computer catches it and disengages the differential lock.

 

I broke an axle on a 2007 386. I had to lock the rears in and limped it about 80 mi to the nearest Pete shop in Bangor. Never hurt anything and I was scaled at 80k with a load of lumber and ran pretty much the speed limit (65 - 70 mph) the whole way.

I called the carrier for a tow truck,.. he said to limp it to the Pete dealer. I did as I was told. I had heard it was not good,.. he sad he had gone over 300 mi with a broken axle in another truck with no problems. So I rolled with it.

That was 2 1/2 years ago and other than that axle,.. its had no other rear end problems. Carrier still owns the truck.