Dual range bogie drives

Reading here about a truck for sale fitted with dual range 34000lb bogie drive with a compound gearbox driving into it and wondered just how successful the ( dual range bogie drive was).
Concept of dual range diffs goes back a long way, mehanically operated, vacuum then electric and with single drive until multi ratio transmissions seemed almost to ring their death knell.
I couldnt quite get just why you would spec a 34000lb bogie up as dual range.
I have never driven any bogie drive with dual range, so cant comment on how efficient they were.
Was a mob not far from where I lived in NSW who had KW quarry trucks specced up with them, either 40000 or 44000lb capacity, didnt have the HP we have today, had the deep reduction 15 speed Roadrangers, but had a pretty steep climb up from the quarry floor.
Used to drink with a bloke who drove for this quarry mob, told me he would only engage low range ( in the diffs) once he was loaded, pull out of the pit onto level ground, STOP entirely, engage High range and then choof off.
This bloke had been around since the days of single drive two speed diffs, added that company policy was to drive the quarry trucks likee that after a couple of failures because some blokes would not bother stopping but change out of low into high on the go.
As I said, I know nothing about them, dont even know if they are still available new.
Reckon my biggest fear being electrical, ( or air?) actuated would be one stuck in low, the other in high.
Comments??
Dave_64

Just went looling on Mr Google and found a whole raft of answers on this subject going back quite a few years ago right here on this site!
Makes good reading, way before I joined as a guest even
Dave

Dave , your fear of one being up and and the other down has happened.
I had a customer who bought an ACCO with those diffs fitted and complained that they weren't working. All the electrics checked out and you could hear the monkey going up and down the pole. It wasn't until I pulled the unit off that I realised that one was going into high as the other was going into low.
No idea how long this had been going on, but the power divider had sure been getting a workout.

In the Sixties and seventies the Commer Bogie was set up as a three speed unit on the gearstick. It would have been a big help with the low horsepower and big loads of the time. I think they were Eatons with a heavier power divider.

Definitely always stop to change ratios either up or down when tandem drive. Single drive obviously no problem. Can get very expensive otherwise.

Brockway trucks used duel range bogies, shift on the go, any speed any gear, they called it Huskie drive

www.bigmacktrucks.com/topic/53771-1970-brockway-361-huskidrive/

So any size bogie Im thinking could be had as dual range

Paul

Dave_64, I remember reading something in this forum a while back where Swishy said that his SAR had 2-speed diffs. But he had relocated the shifter to the floor, so that you had to stop to change ratios. Too many failures in other trucks he reckoned. Good for crawling out of quarries though. And a certain winner in the "who can go slowest" race. I know in the early days, Eaton marketed the "3-speed" diff concept, but it wasn't a success. Too many power divider failures. Looking back now, with the benefit of hindsight, it seems obvious that it would never work.

Often required to move the shift controls outside the cab. More to do with pre electronic engine road train speed limits in some states where they would simply stay in low range until over the border.
Eaton advertised bogie drives as three speed setups, had the tin instruction plate riveted on the firewall.
The third differential compensated.

i think some of you Blokes are confusing the Terms Dual Range & Two Speed....

Dual Range Diffs which were common on Heavy haulage & road Train Prime movers back in the Day(such as Swishy's SAR). The Truck had to be Stationary to change ranges..

Two Speed Diffs Were you Split each Gear on the Go.. Whilst are more Common in Singles Drives were also available in Bogies Drives.. (Such as the DT for sale on Here) I had a little Bit to do with a Bedford with 340000LbsEaton Diffs 30 odd Yrs ago & you drove it the same as any other 2 speed Diff equipped Tuck..


BISTBC..

Thanks for all replies.Guys
The DUAL RANGE bogie drives on heavy haulage certainly makes sense to this old phart, coupled up to a multispeed main trans and/or a compound auxilliary and the way HP has exploded even in say the last 30-40 years.
I guess I was referring more to the "lighter" DUAL RANGE set ups, to my mind a 34,000lb bogie was very light, when just about every second truck seemed to be running around with at least 38,000 back ends.
Don't think I'm knocking that paticular Diamond T, I'd be proud to have it IF I had both the space AND the money.
Were always a grand make.
Of course available engine HP was a lot lower, besides the gross allowable legal weights at the time.
Cheers, Dave