2 speeds?

[RonG]

Stondad,the windshield wipers were vacuum and it was just accepted that you lived without them on a pull,that was cars and everything back then.My,how times have changed.Chrysler Corp was the first,back in the '40s to have electric windshield wipers and I was not yet in my teens but they won me over at that tender age because I figured "duh",what took everyone so long?
Now,power dividers.......this is what I remember as applied to the Mack bogies......they are designed to distribute the power to all four drive wheels according to which wheels had the most traction with only a certain percentage going to the wheel with the least traction and I cannot remember the number but lets say it was 60% then the rest of the power went proportionally to the other three axles.The purpose of the power divider lockout switch was to eliminate that power dividers help which then guarantees that one wheel on each axle will get power.
If you happened to have the truck in a situation where one wheel was freewheeling which happens quite often doing site work,mixers etc then an old trick that most drivers don't know about and the old f*rts like me just smile when they use it is to leave the power divider engaged and when you attempt to move the truck out of the helpless situation is to pull the trolley brake on a little or even just step on the brake treadle a mite and the truck will walk right out with everyone scratching their head wondering "why couldn't I do that"?I have done it many times over the years now here I am telling everybody.Of course what happens is that the brake pressure on the freewheeling drum stops the wheel from turning and the wheels with the traction now get the power to drive the truck out.Ya' gotta love it!Now everybody knows.lol.Ron G

 

[stondad]

td25c,
You are spot-on mate.
That would cause a BIG problem !

RonG,
Sorry to tell you mate, but your secret is out.

I dunno if they can all do it, but some trucks (UD for example) with ABS will detect a spinning wheel and brake that one wheel to make the other three work a bit harder.
It makes anyone look good.

I didnt spend much time in or under Macks, but I read a lot on them.
The Mack power divider was a piece of mechanical genius that had two sets of plungers walking in and out of a central hub, as they negotiated the inside of a cam-ring on the outside when there was a difference of speed between the main tailshaft and the jackshaft.

If all was 1:1, the whole thing rotated as a unit and allow small differences such as new and old tyres.
If one wheel (or both wheels) on an axle was going too fast (say spinning on a slippery patch) the power divider would restrict the speed of the fast axle, therefore putting some power to the other axle that has some grip.
The power divider did nothing at the level of the differential between one side and the other of the same axle.

To my knowledge, Mack was the only one to have an actual Power Divider. *
All others are just an inter-axle-differential, which may be lockable.
If you are lucky, you have cross-locks as well that lock the drive wheels from side to side and turn you truck into a traction engine that is hard to steer and gets you bogged far worse than if you never had that fancy stuff !

*Not to forget the Albions and Thornycrofts (?) that had individual tailshafts to each axle, or trucks such as the Relay Duo that had seperate engines, gearboxes and tailshafts to each axle.

Please, someone tell me they are interested in the Relay Duo-Drives because I am obsessed with them !

Cheers. M.

 

[RonG]

Stondad,you obviously know a lot more about it than I do and the beauty of this board is that it allows access to answers to questions that might have never been asked without somebody planting the "seed" and we can all benefit from for the flow of Q/A that result.
It sounds as though Mack may have developed the technology that the military used to control their front wheel drives on their trucks and that is where I got the term "sprag unit" which could sense the difference in rotational speed between the front and rear axle and provide the power to the front axle automatically with the added benefit of not having to worry about the axle being powered when you didn't need it.
The process seems to be what you described with a drum that served as the drive part of the drive train and a "driven" drum inside it,both drums having matched slots in them with roller bearings riding in the slots at equal shaft speeds but interfering with unequal shaft speeds to power the front axle.Ingenious to say the least with the added benefit of being simple.
All the differentials that I saw being used in my army days were Rockwell so I attributed the technology to them and maybe it was Rockwell but it sounds like Mack may have gotten it somehow to use in their differentials.Thanks for the heads up.Ron G

 

[RonG]

I should have added to my last post that this selective control of wheel speed is the technology behind "traction control" as we know it on the vehicles of today except that they go about it in a different way.The high tech braking on todays anti-lock equipped vehicles and individual wheel speed sensors allow selective computer controlled braking on the wheel that needs it to allow maximum traction in poor conditions.
The end result much the same but is controlled electronically rather than mechanically.Ron G

 

[pushbroom]

I still see 2 speed rears but on very limited applications. The electric 2 speeds are common on all 3 ton grain trucks in our areas. The brandt road and rail trucks often have 2spd rears but they are a very unique truck. JD powershift trans and a dropbox.
Some of our heavy haul customers use a normal 18spd then couple with a 2 spd auxiliary trans. I have seen them with a 4spd aux trans as well. Now outboard planetary trucks seem to be picking up in popularity in the oilfeild.

 

[stondad]

RonG, Thanks for the compliment but you seem to know lots enough yourself.

I think you are right about the traction and cornering controls.

ABS has been a nightmare for 4WD light and heavy vehicles in soft sand on Fraser Island.
All they want to do is let the wheel roll as soon as it locks when you WANT the wheels locked.

Pushbroom, We see mostly European stuff with hub reduction.