Power Divider Question

[niceguypmp3]

On my early 80's Mack I have a question about the rear end power divider. I had always wondered why it seemed quite hard to even spin the tires on the back of this thing when on a soft surface until the other day. I had the roll off tub lifted clear up in the air and I was going to back up, but didnt realize it was up so high and it had both sets of duals on the right side just a smidge off the ground. When I went to back up, i noticed the truck didnt move of course and both axles on the right were turning at the same time. I thought, maybe the power divider was locked in, so I flipped the switch and the buzzer went off, I had just engaged it, it had already been off, so i flipped it back off and of course the air switch hissed air. I tried to move again and the same thing. Both sets of tires on the right would spin at the same time and the same speed. Is there something wrong? We've had the truck almost a year and have put several thousand miles on it and have never engaged the power divider. How does it work on this truck? Does it always use power to both rears and the power divider's purpose is to lock in the rear ends as posi? I hope this isnt in the wrong area of the forum. Excuse me if it is. Thanks everyone!

[Firemack]

Niceguypmp3-

The power divider should engage your your rear (rear) axle. The power is normally applied to front rear axle in tandem axle trucks. If you had both right side wheels off the ground switching to the rear (rear) axle would not help if you don't have posi rears on your truck. If you had posi rears, either rear should have moved the truck. Normally you would use the power divider is if your raised the front (rear) axle off the ground and the (rear) rear axle still was in contact with the ground such as going over a curb etc. Hope that helps, if you have the owners manual you can read up on the use of the power divider.

Firemack

[fjh]

On my early 80's Mack I have a question about the rear end power divider. I had always wondered why it seemed quite hard to even spin the tires on the back of this thing when on a soft surface until the other day. I had the roll off tub lifted clear up in the air and I was going to back up, but didnt realize it was up so high and it had both sets of duals on the right side just a smidge off the ground. When I went to back up, i noticed the truck didnt move of course and both axles on the right were turning at the same time. I thought, maybe the power divider was locked in, so I flipped the switch and the buzzer went off, I had just engaged it, it had already been off, so i flipped it back off and of course the air switch hissed air. I tried to move again and the same thing. Both sets of tires on the right would spin at the same time and the same speed. Is there something wrong? We've had the truck almost a year and have put several thousand miles on it and have never engaged the power divider. How does it work on this truck? Does it always use power to both rears and the power divider's purpose is to lock in the rear ends as posi? I hope this isnt in the wrong area of the forum. Excuse me if it is. Thanks everyone!

The Mack power divider is a diffrent animal!It is is a series of piston like wedges with an inner and outer cam as one piston or wedge is forced out when wheels speeds are diffrent one is on its way in the iiner cam is offset it acts as a ratchet or limited slip only between axles.Is a very diffrent thing to try an discribe with out you actually seeing it!Bottom line think of it as a limited slip!

[niceguypmp3]

Fjh, so what you are saying is that with the right side of both rear axles off of the ground and the power divider supposedly "out" according to the writing, then both right sets of tires will spin if off the ground? And if i lock it "in" then it makes the axles work like limited slip rearends? I hope that is what it is supposed to do, because we've been driving it this way. Surely if it was wrong, then it wouldnt still be driving after all this time like this.

[theakerstwo]

fjh is right it is hard to explain but again the air lock maybe engaged all time so to check take the shifter cyl off and check to see if it is engaged all time . Also to decribe what it is for is it locks the front to the rear and makes them pull together instead of letting the power flow thru the front as well as the rear as each has traction and then it loses all power when one slips.The air locker has the ability to lock sloid were the power devider that does not have air lock is a spring loaded limit slip.

[fjh]

The Mack power divider is a diffrent animal!It is is a series of piston like wedges with an inner and outer cam as one piston or wedge is forced out when wheels speeds are diffrent one is on its way in the iiner cam is offset it acts as a ratchet or limited slip only between axles.Is a very diffrent thing to try an discribe with out you actually seeing it!Bottom line think of it as a limited slip!

It makes the power divider limited slip not the diffs!But Mack also made a differenial with the same set up contained in it!

[Greg Rider]

It locks the front axle to the rear axle, not the left to right. It sounds like it was working as designed. If you need ALL wheels pulling then get a differential locker.

[bobcotkg]

I thought Macks had power divider (front/back) or "peanuts" which were supposed to lock the wheels (right/left) together. Peanuts are automatically engaged when the wheels spin. The power divider is engaged manually. The trucks with power dividers get around better than trucks with peanuts. I guess peanuts don't always engage correctly. Power dividers engage always. I know in my log truck the power divider helps the most. Lock the wheel locks in and it goes good, but it slides sideways easy.

Bob

[Packer]

I'll give it a shot!

At any one time, there is only ONE tire turning!

If only ONE tire is turning, there is no power to the other three.

Now, if the power divider is engaged, it 'locks' the drive lines togother.

Now there is one set of tires with power on each diff.

If one tire has traction per axle, and the other tires are in the air, nothing happens!

A power divider will only work if you loose traction on one pair of drivers, not two.

Remember back in the good old days when you smoked the tires at a stop light?

Torque lifted the right rear tire, and that is the one smoking!

The left one just followed along.

If you put two axles in tandem, same thing as having the power divider 'locked' in.

The tires with the LEAST traction will turn.

Posi-traction is a horse of another color.

Now every thing turns!

Packer

[niceguypmp3]

Ok, so from what i gather from all of the replies, is that in the case I had, the truck should NOT of been able to turn both right side sets of duals at the same time when off the ground and the power divider Not locked in. I'm assuming that if it is locked in and shouldnt be and it is being driving all the time like that, that it is not very good on the rears, correct? boy, oh boy, isnt this just great!

[theakerstwo]

I thought Macks had power divider (front/back) or "peanuts" which were supposed to lock the wheels (right/left) together. Peanuts are automatically engaged when the wheels spin. The power divider is engaged manually. The trucks with power dividers get around better than trucks with peanuts. I guess peanuts don't always engage correctly. Power dividers engage always. I know in my log truck the power divider helps the most. Lock the wheel locks in and it goes good, but it slides sideways easy.

Bob

Some rear could have the peanuts in the carrier but not all and if you have that rear end then you do have traction from left to the right. That was the same set up as was in the non air locking power divider nose cone.

[Lmackattack]

Ok, so from what i gather from all of the replies, is that in the case I had, the truck should NOT of been able to turn both right side sets of duals at the same time when off the ground and the power divider Not locked in. I'm assuming that if it is locked in and shouldnt be and it is being driving all the time like that, that it is not very good on the rears, correct? boy, oh boy, isnt this just great!

If you had one wheel on the forward axel off the ground and one wheel of the rear axel off the ground you are stuck... with the power divider in or out.. your stuck (most of the times) . as said before the power divider just sends power to both axels. a power divider does not lock in the diffs to send power to both side of an axel. you need a diff lock to get the power equal across the axel. the automatic power divider locks in when it detects a diffrence in drive line speed. tha manual has to be operated with a switch.

a diff lock will send power to both sides of the axel if so equipped. I think most trucks with a diff lock only have it on one axel this means that even with a diff lock you will only have 3 powered wheels if the truck weight on the rears is badly unbalanced. I know its a PITA to under stand on a message board LOL!!!

the old trick with macks power divider when stuck was to tap/stab the brake pedal to stop the free spinning wheel and try to transfer the power to the other side. works sometimes but if your stuck bad your done

Trent

[ThaddeusW]

Okay I think there is a terminology problem here.

Power divider (aka inter axle differential)- Differential that divides the transmission drive shaft power between the two driving axles. Located on the axle that connects to the transmission and rear most drive axle. It splits the incoming torque between the two drive axles evenly and takes up any slack between the two axles. The automatic power divider locker (peanuts) engauges when a significant difference in speed between the first and second axles occur. A transfer case also has a power divider to split the power between the driven steer axle(s) and rear driving axle(s) (can be locked). A power divider is also found on the second axle of a tridrive axle setup, the front most does a 33/66 split and the second does a 50/50 split.

A power divider isn't engaged, rather it is locked. Just like the differential locks. So trucks often have two locking switches: the cross lock switch which locks the power divider and the diff lock switch which locks the differentials.

Differential lock (ake diff locks)- locks the differential causing both tires on the same axle to behave as if they were both connected to a single shaft. When engauged, if one tire has no traction and spins its opposite will turn at the same speed.

If you are stuck the best bet would be to engage the power divider lock and leave the diffs unlocked. It should get you to move but it still allows one wheel to spin while the other just sits (with an equalizing suspension like camel back that shouldn't be a problem). If that don't work then the diff locks should be locked and very gently in a low gear crawl out of the mess.

But from memory I believe Mack axles do not have a diff lock option at all. It has the auto or manual power divider lock but no diff locks. That's why some operators prefer the meritor/spicer axles as they have the both locking options. But like I said with the proper suspension all the wheels should be evenly loaded so if one slips the other 3 still have plenty of weight on them.

[niceguypmp3]

*scratches head* ok.... yea, sometimes figuring out things on message boards can be fun lol. I am just wondering if what my truck did is normal for the power divider switch being "out" which i assume means unlocked or disabled because when you put the switch to "in" then the buzzer turns on and when you put it back to "out" then there is the air release hiss. I just didnt know if when it is "out" then both axles should have power or not because it turned both axles when off the ground. I hope that a previous poster isnt correct when saying that the power divider shift motor might be stuck engaged. I dont know how long it has been driven like this. we bought the truck about a year ago and have never used the power divider. You'd think that if it was stuck engaged all this time, that it would of tore something out or there would be a weird noise going down the road, but everything free wheels fine.

[bobcotkg]

Some rear could have the peanuts in the carrier but not all and if you have that rear end then you do have traction from left to the right. That was the same set up as was in the non air locking power divider nose cone.

Correct. "peanuts" are automatically locked, (left/right). Power divider locks front/back. As you said not all rears have "peanuts" or a power divider. I have never messed with an auto power divider so...

My log truck has "full locking" rears. Power divider, and wheel lock on both axels, which equals true 4 wheel drive. But like Trent said, not all are sut up that way.

And I have tried stabbing the brakes while spinning and sometimes it helps.

As far as to answer the original question, If the wheels were off the ground it would be possible for the set of duals on one side of the truck to spin, as long as they were completly off the ground and the other side was touching. Thus being said, engauging the PD wouldn't have made it look like anything happened.

It could be the engauging mech. is stuck on, but I'm guessing something would have shown signs by now. I've left my PD in for a long time in the woods and didn't hear any other noises. Maybe just a wisker more of a whine on pavement, but nothing an untrained ear could hear.

If it were mine and I was worried I would pull the engauging mech. out and check. Don't remember what it looks like on Mack rears, but its simple on Rockwells.

Good Luck,

Bob

[Lmackattack]

If I read your first post correctly it sounds like the power divider was working fine? are you sure the switch is for a power divider or is it a diff lock?

If the power divider was in for a long time you should have noticed that it might be lugging down in tighter turns. most noticeable on pavment. and yes if it was engaged it will be harder on the drive line as in a tight turn the forward tandem axel will move at a diffrent speed then the rear tandem. At least one wheel would have to slip across the ground to keep moving in a turn.

For an example of how it would feel if it was locked in on dry pavement with a load on.. in a tight turn (1st gear) you likely would not get to 2nd gear becasue the truck would louse to much speed because of the friction and stress on the drive line..

but again it all depends how your diffs are set up.