High speed reverse.

[Oxbow]

Back in the dark ages when I was being taught to run a dozer my employer said never run in 3rd gear reverse due to increased undercarriage wear. This was pertaining to a D7G, but he also did not want me to back his 17A or 9U tractors in the higher gears. I understand the mechanics of the track slack bunching between the sprockets and the ground on conventional tracked dozers, but it would seem that the high drives would be less likely to have a problem with this.

I now will travel in 3rd gear in the high drives, but only at a reduced throttle level that roughly matches 2nd at full throttle, and even then I can hear my old employers words in my head and feel a tinge of guilt.

When finishing topsoil or cleaning up (going forward) I find myself in 3rd gear quite often, unless the topography is is such that you have to chase the contours quite a bit.

I am curious to hear others thoughts, and I enjoyed the slot dozing thread so much that I thought this may be interesting as well.

 

[AustinM]

HAHA Oxbow, I know exactly what you mean. I was told "never put a dozer in 3rd gear unless it's an emergency." and I too have done it on occasion depending on the circumstances. ( for the same reasons you describe. When finishing topsoil, etc.) The same thought goes through my head, "should I be doing this?" and feel the same tinge of guilt.

Anytime I am on a job and hear the sound of a dozer in 3rd, I immediately look towards it because the sound is unmistakeable.

 

[vapor300]

The newer dozers (tier4) actually kick the dozer into ECO mode when trying to back up in 3rd gear which is just about as slow as full throttle 2nd, but if you have to back up at an incline forget about it.

That being said i have been running a new 7E (not tier 4) And its geared different 2.2 in the 7E is the same as 2.5 in a 6T, and it recommend to backup in 2.6-2.8, and 2.8 in the 7E is about what 3rd is in a 6T

 

[Nige]

The deal about reversing at high speed is to do with the way the track links (rails) are built. If you think about it each link is "cranked", as shown by the diagram below. The link assembly is designed so as to work properly when pushing forward because obviously that's when the most load is on it. When pushing forward there is no relative movement between the bush (which is pressed into the narrow end of the links) and the teeth of the drive sprocket. In reverse the bush "rolls" round the sprocket teeth and so you have relative movement between the two which will cause accelerated bush/sprocket tooth wear. This is why using high speeds in reverse is not recommended. On our tractors we blank off 3rd gear reverse so the operators can't use it.

 

[Nige]

To add a comment, it's nothing to do with bunching or the slack in the track, high-drive or low-drive. It's the simple mechanics of the sprocket tooth/bush contact in forward and reverse directions, especially at speed.

Maybe I can explain it a bit better. in the diagram is looking down from above the spocket on the RH side of the machine. The left side of the diagram is the rear of the tractor, the right side is the front. You'll have to imagine the whole thing being inverted as the link group on the bottom side leaves the track rollers and arrives at the sprocket.

So when the machine is moving in the forward direction the links/rails are moving left to right. The track bushing (3) that is presed into links (9 & 10) engages the sprocket and the next pair of links (5 & 6) which are pressed to the track pin (4) trail behind it. But because of the relative rotation of the bushing 3 & pin 4 the position of the bushing stays pretty much fixed with respect to the tooth of the sprocket from the time it picks up at the bottom until the time it lets go at the top.

It's different when the machine is moving in reverse. As links 5 & 6 arrive at the sprocket (moving from right to left) they rotate along with the pin 4, then when the bushing 3 arrives at the sprocket because it's fixed to links 9 & 10 (that are now trailing behind it instead of leading it) it will rotate somewhat as it engages the sprocket teeth and also will rotate again with respect to the sprocket teeth when it disengages as it leaves the bottom end of the sprocket. That's where the difference lies.

 

[Oxbow]

Thanks Nige, I new there must be more to it than the bunching. I still am foggy as to why higher speed would wear the tracks proportionally more than lower speeds, but understand what you are saying about more wear in reverse than forward.

So, if I understand correctly, the new style chain on a D6N for example (System 1?) that has links that both ends are either inside or outside the adjacent links, are less prone to accelerated wear in reverse? After reading the System 1 thread I understand that there are other issues with them.

 

[Nige]

With the issues of which I am aware of with SystemOne undercarriage (and I've never had to maintain one so it's all anecdotal evidence) high speed reversing should be the least of the tractor owner's worries ...............

Because of the lack of relative bushing/sprocket movement in the forward direction high speeds forward are not majorly detrimental unless of course the ground the tractor's running on is so uneven as to cause major impact wear issues.

The fact that there IS relative bushing/sprocket movement, which will obviously cause wear, in the reverse direction the higher the travel speed the more rapid the relative bushing/sprocket movement therefore the more pronounced the wear will be. Imagine taking a variable-speed grinder to a piece of metal. If everything else remains the same (e.g. the wheel, the pressure you apply on the metal, etc.) then the faster you rotate the grinding wheel the more metal you will remove in a given time. Same principle applies with undercarriage.

 

[dozerman400]

High gear is where it's at (when safe to do so). All the foreman I work for, want stuff done now. Even pushing scrapers, if you use high gear backing up, you could probably ad another scraper.

The bosses/foreman I've been around want to see how much more you can do today than yesterday. Go Go Go.

Oxbow, my first boss (dad) never liked high gear either. He always said "make every move count", you will have less passes than the operator in high gear not making every move count. Now, I operate in high gear (sorry dad) combined with making every move count, keeps my boss happy, keeps my job, happy happy happy.
I don't plan on changing bosses, but if I do, and the next boss don't like high gear, I will respect him and do it his way.

I also think the slot dozing thread is interesting.

 

[Nige]

The thing is of course that the foreman generally isn't paying the bill for the replacement undercarriage, neither is he the one who has to get greased up to the elbows changing tracks, rollers, & sprockets. That's why we don't give our ops foremen the choice, they get the tractor from the shop with just 1st & 2nd speeds in reverse and that's it ..........

Your dad had wise words about high speed reverse, you should listen to him. My first thought any time I see or hear a dozer in 3rd speed reverse is "cowboy", working without thinking ahead and planning his moves.

 

[Scrub Puller]

Yair . . . I have often wondered what the point was of the third slot on a Cat, even in forward. The two speed on the Allis worked well and should have been more simple and reliable, they were plenty fast and responsive . . . I suppose converters work better at twenty one hundred.

It was quite an elegant design, the side to side movement of the shifter selected the range and direction in the transmission and the back and forth movement actuated a clutch in front of the converter.

Cheers.

 

[Meangreen]

The thing is of course that the foreman generally isn't paying the bill for the replacement undercarriage, neither is he the one who has to get greased up to the elbows changing tracks, rollers, & sprockets. That's why we don't give our ops foremen the choice, they get the tractor from the shop with just 1st & 2nd speeds in reverse and that's it ..........

Your dad had wise words about high speed reverse, you should listen to him. My first thought any time I see or hear a dozer in 3rd speed reverse is "cowboy", working without thinking ahead and planning his moves.

I learned in the 50's. My Dad had a cowboy and an operator. The operator some times looked like he was in slow motion compared to the cowboy but at the end of the day he did at least a third more work with half the wear and tear. Clearing land or pushing dirt, he was the one to learn from.

 

[Oxbow]

I believe Nige has already answered the question that I am about to ask, as he is probably as knowledgeable about large scale outfits and the cost per yard/cost per our/etc. as anybody, but:

It would be interesting to see a graph of cost per cubic yard running no faster than 2nd gear vs using 3rd. In other words, is there a point at which cost per cubic yard goes down due to increased production at a rate that is higher than the increased cost per hour caused by running faster?

I suspect that in some scenarios where operator pay, bonuses for early completion, seasonal time windows, etc. are factored in there may be circumstances where it does indeed net a higher return, although they are probably few and far between.


Food for thought!

 

[bigshow]

Another good dozer thread, Nige hit it head on as usual. My neighbor is our master mechanic and I worked/hung out in his shop while still in high school, so I got to hear all about this topic long before I had a seat. Him and Nige explain almost exactly the same way too. I don't make a habit out of high ballin but every now and then on a hot to trot trim project I'll bump it up. It all depends on what the situation dictates, I'm usually a 2nd and wide open kind of guy, I don't touch the decel, usually sit with my legs crossed and trim away. So now that brings up another controversial subject, decelling when changing F-R, I generally don't, haven't since I never believed it to do any noticeable damage. Any more I'm on smaller hydro trim tractors just doing trim work, I don't believe it hurts them, but I've been wrong before. Now if I'm on bigger tractor working up and down slopes I'll decel when I get to the bottom before shifting to go back up. Shall I start another thread, as to not hijack this one?

 

[kshansen]

I learned in the 50's. My Dad had a cowboy and an operator. The operator some times looked like he was in slow motion compared to the cowboy but at the end of the day he did at least a third more work with half the wear and tear. Clearing land or pushing dirt, he was the one to learn from.

This reminded me of a new operator we had on the 988H pit loader a few years back. Boss tried to tell him he had to pick up the pace. They then switched to a couple other operators who were "faster". Thing is when they kept track of the number of loads each one sent to the crusher in a day they found out the "slow" guy was actually getting more loads a day!

 

[bigshow]

Slow is smooth, smooth is fast. Simple as that, consistency pays off. I have found routine helps as well.

 

[Scrub Puller]

Yair . . . bigshow.

Slow is smooth, smooth is fast.

I believe that's exactly right in most callings, for instance the top tally hand (ringer) on a sheep shearing board often looks relaxed and slow.

I have no experience and am quite unqualified to comment on the modern machines and the decel question.

I would have thought the main issue was for the machine to come to stop before changing direction . . . apparently these days it isn't necessarily so and some transmissions are built to modulate and accommodate full power/speed direction changes.

Rather than building complex transmissions for dummys I believe in most cases improved production could be achieved by a bit of tuition in machine control and basic operation techniques such as slot dozing.

Cheers.

 

[JimBruce42]

I believe Nige has already answered the question that I am about to ask, as he is probably as knowledgeable about large scale outfits and the cost per yard/cost per our/etc. as anybody, but:

It would be interesting to see a graph of cost per cubic yard running no faster than 2nd gear vs using 3rd. In other words, is there a point at which cost per cubic yard goes down due to increased production at a rate that is higher than the increased cost per hour caused by running faster?

I suspect that in some scenarios where operator pay, bonuses for early completion, seasonal time windows, etc. are factored in there may be circumstances where it does indeed net a higher return, although they are probably few and far between.


Food for thought!

I was on a job years ago with two D8's. One in the T model insisted on doing everything in 3rd gear "cause it gets stuff dun faster", while the guy in the R never went higher than second... The second guy would constantly get more done. For one simple fact, the higher the gear, the less power to the tracks you have to push, so the smaller the "blade full" Course that's got nothing to do with reverse. I think it's standard that the reverse gears are set a bit faster than the respective forward, but I could be wrong.

 

[vapor300]

The decel thing with going from F to R is another thing i love about the 7E! I dont know how it does it but no matter how fast your going or how quick you do it, its always so smooth.

Does anyone know anything about the tracks on the 7E and why they recommend you back up in that high of a gear???

 

[Nige]

Slow is smooth, smooth is fast. Simple as that, consistency pays off. I have found routine helps as well.

Jim makes a good point. The amount of torque available in 3rd gear (forward or reverse) is almost non-existent, pretty much just enough to drag the machine itself around let alone do any meaningful work with it.

I probably have the "Big Load Slow" video clip somewhere, maybe it's even on YouTube. Get the biggest amount of material you can in front of the blade on every push, and like a chess player plan a dozen moves in advance and you don't need to charge around like a horny rhino ....

When it comes to decel a lot of the modern electronically-controlled transmissions are allegedly capable of going from full power in one direction to full power in the other without needing to hit the decel pedal simply by the electronics figuring out what the machine needs - a true powershift if you will. If you're in the seat you can feel it, you flick the shift to change direction and you can hear the engine decel, plus then you feel the clutches start to slip. The whole process takes about maybe 2-3 seconds. I'm still sitting on the fence on that one as to how transmissions hold up. One thing I can tell you it doesn't work on 16M's (doesn't make the tranny live any longer than it), but that's a story for another day......

 

[Heavey Metal]

Accelerated wear on the bushing due to highspeed reverse is a non issue

What it does to the sproket tips will get in your pocket