Who can tell me how this works? Thanks

From the Eaton Service Manual

 

You can engage it while moving. Just don't do it if you spinning...

 

I don't know if were all on the same page or not or if we all have different spec'd trucks but this is how almost all of the trucks I've driven are set up. On most of the trucks I've had, all the tires will spin regardless if the interaxle switch in engaged or not. On almost all the trucks I've driven the divider is nothing more then another differential that allows the front and rear axle to spin indepentently while still providing power to both. When the interaxle switch is engaged it locks that differential/divider so both front and rear axle have 50/50 power going to them. That still doesn't lock your other two differentials into posi trac, unless you have additional locks for them, which in every truck I've driven that has full lockers will have three lock switches total. One for the divider and one for each axle.

Also I've engaged and disengaged my axles on the move hundreds of times and never had an issue, although I do it below 30mph when none of them are slipping and I let off the throttle, as somebody had mentioned.

 

100% correct, Thanks

 

You would have a dif failure because they are working against each other

The only one i know of that does/did that is the mack with the cam system they have, not sure of old old ones but as of know only ones i know that automatically kick in when it is losing traction

You can shift them in AS LONG AS NO WHEELS ARE SPINNING (LOOSING TRACTION) But driving down the road you could, no reason to but wouldnt hurt it

 

Not trying to pick your post apart and maybe I'm just reading into your reply wrong but, waiting to start spinning or waiting until you get stuck before engaging your divider/lockers/4 wheel drive system on whatever your driving is a common mistake people make both in big trucks and 4 wheelers assuming your system allows on the fly engagement. Once you start spinning, or wait to get stuck before engaging your added traction device, your pretty much back to where you started, since the first set of tires that lost traction are almost useless at that point. Whether climbing a snow covered road or mountain pass, or going thru a muddy field, engage your system and keep your momentum up. Keep in mind that your steering is reduced and that can present other issues, otherwise that's what it's there for.

For what it's worth here is some of my experience. On one old truck, I drove from Liberal, Ks to El Paso with my inter-lock on going 35 mph the whole way during a bad winter snow/ice storm where I was fighting for every ounce of traction the entire trip. Not to mention countless trips across Colorado during winter storms. That truck never had to have it's axles or divider rebuilt and it had over a million miles on it. I've gone thru countless muddy fields both in semi trucks and 4 wheel drive bucket trucks doing tree work and never have had axle failures or transfer case issues. My pick up truck is 13 years old and I've driven in 4hi for hundreds of miles thru snow storms when going on winter vacations to the Dakota's or to Colorado (not going over 50mph) and it has it's original transfer case and axles. Again, that's just my experience with however my equipment has been spec'd. Also, keep in mind that I don't slam things around or drive fast while engaging any added traction devices.

 

Never drove a Mack, but I spent a lot of time driving trucks "off road" and I could see both drives churning even when the interlock was in the off position.

 

Don't know what kind you had but on my SQHD's its the right rear that does all the driving but the left front will spin also. Alot of times the tires will spin making you think they are working but they are only spinning cause they have no resistance.

The only thing I know about Mack rears... they are probably one of the toughest built. I also think they are always locked in. I know the one I drove I very rarely got stuck. ANd I burried that sucker up to the housings a time or two!

 

Ok Iv read all the post on hear so far and some are right most are wrong. All 4 corners get the same amount of power all the time going down the road on ALL tandem axle trucks. All tandem axle trucks have 3 differentials. One in each diff and the power divider diff in front of the front rearend. Any one wheel on any truck can spin out seperate of the others if it loses traction. They dont just drive the rear axle only. The reason the rear seems to be the one that spins out more frequently is because is has less weight on it especialy when empty or bob tailing. If you drop one front wheel in a hole it will be the one that spins out. When you engauge the power divider its differential will lock sending power to both front and rear diffs equally no matter how much traction the wheels have. If you still spin out you will notice at least one wheel on the front and one on the rear will spin. It could be both right or both left or one on either side but one on each axle assembly will drive. With out the divider locked any one of the 4 corners can spin independand of the other 3. Many trucks today also have a lockable diffs in the rears them selfs. Some in only one (3/4 lock) usually in the rear rear. Others in both. (Full Lock).With 3/4 lock you can lock the power divider and the rear rear and at least 3 wheels will drive no matter how much tracrion you have.Both rear wheels and atleast one front will spin even in a spin out. It could still be either the left or right front that spins depending on what wheel has the least traction. Full lock engauges all 4 corners equal. If one slips they all slip. 3/4 and full lock should only be used with low traction straight line driving. If you try to turn with a heavy load the drive line will bind up and may cause the axles or differentials to break. This is why we have differential in the first place. When you turn you wheels need to rotate a different speeds. If they were locked together they couldn't do this.
Back to the power divider. The reason trucks have them is because of tire where. ALL tandem axle trucks where the rear drive axle tires faster. Why? When you turn a truck pivots on the front drive axle and the rear axle drags side ways ever so slightly whereing the tires faster than the front drive axles. If the tires arnt the same exact size they will not turn the same amount of revolutions per mile. If this were to happen and every thing were locked together the axles, ring and pinion gears, u joints and drive shafts would all bind up and destroy them selfs. Problem is the differential that keeps this from happining also alows power to go to the wheel with the least traction.
As far as locking the power divider while moving it wont hurt any thing at all but if your spining and you lock it all hell will break lose. It will tear the locking teath off an most likly destroy the whole front diff asembly. Some might ask why would you ever lock it while moving? Well how about if you are about to climb a snow or ice covered hill. If you pull in to a muddy or snowy parking lot. How about a parking lot full of deep pot holes. As long as the wheels are rolling and not spining lock it in it will do no harm at all. If you think your going to spin lock it in before you do and you might not spin at all. If you still spin you will have at least 2X the traction to help keep you moving.
As far as Mack rear ends go they have to different power dividers. One works just like all the others. Flip the switch on the dash and it locks. The other has no swithch and is automatic. Well they call it auto but they dont work real well. If you completly drop a wheel in a whole you all done. Applying break presure when spining can some times fool it by slowing down the spining wheel and putting some power to the wheel with traction but with many years of offroad driving I think they suck. Give me the switch on the dash any day.
As far as different gears in the same truck its a bad idea but it wont cause the rearend to break in a few miles or where tires out as long as the power divider is un locked. Remember thats what the power divider dose is let thing turn at different speeds and not bind up. How ever with that being said if you were to lock the divider things would bind up very fast. Tires would start to skid and bind up in only a couple feet and and rearends and other driveline components would break in a short distance. Shifting would be almost impossiable because the driveline would bind up so tight the truck would just stop. Different gearing would also where out the power divider very fast. Even when not locked their is little movement in the power divider differential. If gearing were different their would be alot and it would where out fast.
Just think of the power divider as 4 wheel drive. Use it when you would use 4 wheel drive. You can run down the road in a snow storm with it locked and you will do no damage at all. You can leave it locked for hunderds of mile if the road is snow or ice covered. You can lock it at any speed as long as your not spinning. Even on hard ground at slow speed and short distances (a truck stop or parking lot with deep pot holes ) it wont hurt anything to lock it in.Its their to help you. Its your friend. Learn how to use it and be stuck a lot less. OTR drivers may only use it in snow or ice but dump trucks, concrete mixers, log trucks, oil field trucks and other off road trucks might use it daily. Some OTR company trucks dont have a lock switch at all.(US Express) They made their trucks dummy proof. You cant break a power divider by engaugeing it during a spin out if you cant lock it.
If I didn't explain it good enough ask me more questions and Ill try to explain better.

 

Question about the Mack rears? Did they make ones that were always engaged? The reason I ask is I never had the problem your describing and the truck I drove never had a switch. SO I'm confused?