Driving technique (need help here)

The power divider.

Talked to a couple rookie flatbedders. One was planning to do a lease. Crunched some numbers for him and talked him out of it. I asked him if anyone at his current bottomfeeder company had ever shown him how and when to engage the power divider. I told them about drivers scream and threaten murder when they're climbing a grade in Montana., come around a bend, and a rookie comes to a dead stop to engage the power divider.

My my technique is the same as before, downshift throttle, downshift, throttle, right gear light throttle, no wheel spin, POWER DIVIDER, top the hill, POWER DIVIDER OFF, up shift, light throttle, up shift.

Do not come to stop on a grade. Instead engage the power divider while rolling, but only while your wheels are not spinning. If you have wheel spin, let off the throttle and wheelspin will stop.

 

I'll jump in here. We've got a 10 speed and a single screw tractor pulling doubles. If I stop on an icy/snowy grade - I'm SCREWED. She's all right if you can keep rolling, but it'll go every which way but forward if I come to a stop. Then it's chain time in the middle of the road. Sooooo . . . .

I've gotten good at keeping her rolling, and my technique is to use high revs whilst not completely spinning to try and achieve forward momentum, and when she starts to spin and slip, back off throttle, gear down, try again. If I wind up stopped using that technique, then back to square 1 - chains. But usually I can keep her rolling and find a gear that suits - but it's a fine line.

They took the power driver OUT of these new trucks. Thanks a bunch guys.

BTW - never driven an 18 on bad roads, only 10's. Big jump between gears - Would think a good brain behind a 13/15/18 with tandem drive could get along OK.

A lot of my technique relies on keeping a big following distance to feather my stop/start roll technique. Used to be easier to accomplish - now almost impossible - I get that space eaten up by dummies.

 

Exactly. What I never have figured out is it says right on the little lever ENGAGE AT AMY SPEED EXCEPT IF WHEEL IS SPINNING!!! least it does on my tractor anyway. So why come to a complete stop ESPECIALLY ON AN ICY HILL?!?

Power dividers are a touchy subject most don't even know how it works but that is a completely different subject not intended for this thread and I'm not going to hijack it.

I prefer using the power divider in low traction others may not. Just depends on the driver I suppose. Same way with kicking it out after you crest the hill. Sometimes I will sometimes I won't just depends once again on conditions. Good rule of thumb is this as long as it is slick enough to allow wheel slippage when cornering it is safe to leave the power divider locked in. If its not that slippery best to disengage it after you've got out of the jam.

 

What is the jump between your gears on a 10spd? If I shift my 18 like a 9 it'd about 300rpm or so. About 150rpm for splits from direct to over.

 

First off, your way less likely to spin your drives if you turn on your power divider. a min of 2 (4 with duels) wheels gripping is better then 1. If you have lockers as well you can get all of um gripping. Why nto improve your traction but flipping on power divider and lockers if you have um. No i have SS and had similar troubles when carring a 2000 pound load. Key is also getting weight on your drives. If you can adjust your tandoms and 5th to put as close to 34 on your drives as possible it really helps.

lastly i keep my rpm low. If the truck doesn't have much torque in the low rpms, it seems to spin less. Obviously if a spin occoures, keep down shifting until you regain control. The key is letting off the throttle because to much fuel produces a spin. Also, a pair of auto socks never hurt and they can be used a relatively decent speeds. they are easy to put on and if in light snow all day they ride a lot smoother then chains but provide comparable traction.

 

That's roughly the jump in my truck with a 10 speed.

 

Had to think on that - about the same actually - 9th at 1500 - change to 10th becomes 1100, so about 400RPM, I guess, need to take note on the lower gears.

 

you do have to back off the throttle first to regain grip, but then your truck is going to slow to maintian speed in current gear. I norm downshift at 1200 rpm. in snow i let it go lower. if it starts to slip at 1200 rpm, i let off throttle and its norm ok by 1000 rpm. now i have grip, but i cant maintain anything at 1000 since that's to low for my engine. so I downshift (carefullt to avoid a jolt) keeping wheel speed the same but raising rpms to 1200ish. I want to be in the lower end of the gear to prevent to much tourqe. But yes, you have to regain grip idealy before the shift. But by the time you do, your road speed may be to low for the gear your in.

 

If your wheel is spinning, your trying to slap 2 different speed axles together wich is like a supper bad version of grinding gears. Your likely to break the thing. You don't need to come to a stop to engage it. but you should let off the throttle and let all wheels equalize in speed. Put the clutch part way in and your road speed should get all of them close.

 

TripleSix, you did a fine job of explaining it! Here's the reasoning behind it:

It takes a given amount of HP to climb a hill. HP which can generated at low rpm with high torque or at a higher rpm with a lower torque. But the higher rpm requires a lower gear, which increases the torque multiplication, negating the benefit, or so it would seem. However, it's what happens when the tires break loose that makes the difference. If the engine is making a larger amount of torque, it accelerates much quicker than it would in a lower torque situation. So what, you say? It makes a significant difference, the tire has a better greater chance to reacquire traction if the spin speed isn't rapidly increasing. Look at the power curves of the ISX:



Below 1400 rpm, a traction loss will result in maximum acceleration of the wheel, as torque is constant in this range. Above that RPM, the engine has far less tendency to "run away" when the load is removed by wheel slip, as the torque and thus the acceleration drop the higher up power curve you move. So a small slip results in an instant torque (and power) drop allowing the wheel to regain traction instead of being accelerated into a spin.


Another example of this comes from motorcycle racing. Ducati was kicking the Japanese' butts with a v-twin motorcycle with a lower power to weight ratio, and it took a while to figure out why. At first it was thought the more concentrated power pulses were breaking the rear tire loose in a gentler manner, by temporarily overloading the tires traction ability near the adhesion limits, allowing the riders to find that edge easier and more consistently, and therefore get into the throttle sooner leaving corners. (And so came the big bang 4 cylinders, with concentrated firing orders.) But that wasn't the only advantage it seems; because the Ducks were operating well above torque peak, while the four cylinders were in the meat of their torque curve, the exact situation described above with the trucks came into play: A slip on the V-twin dropped output to the tire, while the Jap bike's tires would accelerate away if they broke loose. The Ducks were both more controllable at the limit, and able to use more power sooner to offset their power disadvantage.


One other thing, if you have a tire consistently breaking loose, get the power divider engaged. While it's not the issue it once was, it still isn't a good idea to have the power divider spinning up because of constant wheel spin. It's hard on the differential section of the divider, and in the old days would actually spin the lube off the spiders leading to rapid overheating and failure of the power divider. And remember that the power divider is actually strongest when locked in, so you aren't going to hurt it running down a slick road with it engaged. I have spent hours at a time running with it locked when needed.

Class dismissed!