2 speed rears

I prefer an air shift two speed brownie over 2 speed rears. I had a truck with them that only shifted the front axle one time. When that ####### bound up the rear rear end exploded.

 

Love my 2 speeds w/18b trans. Use them all the time. running 3:90/5:36. Its just so much easier on the clutch. Normally gross 200,000 and can start a load on a 6% grade.
I never run them at highway speeds, just up shift after I get moving. Have 760,000 miles with no problems, also never replaced the clutch. Also running 2400 ft. lbs torque.
Do not like Aux trans, only hold about 8 pints of oil so they heat up fast. Must install
a cooler and fan.













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Oscar, with the 4.33s what was your max speed when empty?? Not to mention how much
fuel did you burn.. (MPG)

Thanks

 

I have 4.10's, at 65mph I'm at 1625 rpm. I've been averaging 4mpg on 7 axles with 25-30% empty. I mostly run 60 when loaded and 65 empty if I'm in a hurry.

 

I have one with 4.33's. Top end is between 68 and 70 turning around 1850 it'll get to 72 if you run right up to 2000. They are behind an 08 cat and pulling heavy like over 140k it gets just under 3 depending on wind best I've seen pulling a pneumatic loaded to 80k is 3.8.

 

This is an old thread, but I thought I would add my thoughts.

I am an excavating contractor that hauls primarily our equipment, and equipment that we rent. We end up hauling into soft job sites often, and do quite a bit of work on jobs in the mountains accessed by Forest Service roads.

We have an old 89 378 that started out life as a logging truck; B model Cat, retarder, Jakes, RTOF 15618, DT461P 46K 2 speed rears (4.11/5.60), on tall 24.5's, tag axle, pulling a 50 ton Aspen 3 axle RGN. The most I gross is 140K.

Like chunkchange01, I love the two speed rears. They make starting out in soft ground so much easier on things, and when driving the Forest service roads at speeds less than 40 mph the splits are enough closer that it makes shifting a bit easier.

Do I think they are necessary, certainly not, especially with newer high torque engines and B model 18 speeds, but I sure enjoy having them. Our old truck has 1.1 million miles on it, and about 36,000 hrs., and to my knowledge the rears have not been gone through, although I am the third owner and do not have records of maintenance prior to purchasing the truck.

Typically I use the deeper reduction just until I get on to firm ground and the load is rolling easily, then shift out as easily as splitting an 18 speed. When I shift, I usually get into fifth gear, then put trans in neutral, shift rears, and then return to fourth in the trans. The split ends up being about like a normal gear doing it that way. I had no experience with two speed rears prior to owning this truck, and was afraid to shift them when moving at first. Numerous times I would forget to shift out before getting on a highway and would pull over and stop in order to shift them. After talking to several folks that have them, I finally got brave enough to try to shift into the higher (faster) gearset while moving, and it was as smooth as can be. I have never attempted to shift into the slower gearset while moving, and probably won't.

Words of caution; DO NOT HAVE THE INTER-AXLE DIFF LOCK ENGAGED WHEN SHIFTING. This will require both rears to engage at exactly the same time, and that (I'm told) is when one or the other usually blow up. As long as the diff lock is not engaged it allows each axle to shift independently of the other, and the power divider takes up the slack.

One other drawback is that I do not believe one can get full lockers with 2 speed rears, or at least not that I am aware.

If I were to order a new truck for what we do (which I have no intention of), I probably would not get 2 speed rears due to the cost, but if I were anticipating pulling much heavier loads in mountainous areas it might be worth considering, especially if full lockers are available with them.

 

As far as I know you can't have full lockers with 2 speed rear ends still. All our guys that haul heavy have aux trans and full lockers.

 

I wasn't sure if they made aux trans (brownies) in torque ratings high enough for modern engines, Obviously they must. Do they use a 3 or 4 speed brownie married to the main trans, or do they have a 2 speed trans separated by a length of driveline?
That seems like the ideal set up.

 

To be honest I have no idea.... Lol

 

If you get an A-box with any torque rating over 1800 you just don't get any warranty. They aren't rated much above 16-1700. They are separated by driveshaft, & basically become your center bearing