High speed reverse.

[Dozerboy]

Houston dozer "operator" are the kings of 3rd gear. When I hit 3rd I'm at 1/2 throttle because I'm traveling.

I have a green "dozerhand" on my site now that I'm working on making an operator out of. He ran around for 5hrs in 3rd gear with a new D6K and barely spread 240yards. And wasn't keeping up with the trucks...I got my work cutout for me.

 

[DPete]

Two things I hate to see a dozer do is spin around short and run in 3rd

 

[bigshow]

Just because it will counter-rotate doesn't mean it has to.

 

[kshansen]

I wish I could have made a video of one operator. I was working on a transmission problem in a 988 87A Cat with a dealers mechanic and we wanted the normal operator to run it while seeing how it was working. The dealers mechanic could not believe how this operator ran the machine. Only way to describe it would be a violent attack on the controls! We both wondered why the machine didn't have more problems.

Another time I was checking out a problem with loss of power in an old Mack tractor, found a bad fuel suction hose. After replacing it driver asked me to go for a test run of his normal 30 trip. This was one of those good old Triplex 5 speed with 3 speed aux. Twin stick transmissions. You would swear those levers were not hooked to anything. He would go through the gears so slow and smooth with never even a click as they went into gear while running through city traffic and some Interstate miles pulling a bulk trailer full of stone dust from a BC plant.:notworthy

 

[GregD1]

We had about 6 old D-9 G`s and H models where I worked at years ago. The slot for reverse had a bolt in it so there was no way to back it up. All set up with push blades and rear cushion blocks. If memory is correct the reason was the ungodly cost of the planetary final drive set up it uses

 

[JDOFMEMI]

Nige and others have explained the reverse wear well.

One thing I would add that I have not seen mentioned is the internal stress on pins and bushings. During forward travel, there is stress from the contact with the sprocket, down to the ground, and just a slight ways forward. In all, probably less than 1/4 of the track length. During reverse travel, the stress is from the sprocket, all the way to the front idler, then about halfway to the rear. This would be about 2/3 of the length of the track. I seen a very good pictoral description of it in a John Deere manual once.
Another problem with high speed operation, forward or reverse, is heat build up. This can cause seals to fail in the sealed links, rollers, idlers, as well as hurting the heat treatment of the steel, further accelerating wear.

On the issue of decelerating for shifts, the new iron seems to be made this way. When I run my D-8T, I will sometimes go for hours without touching the decel pedal. One day, the pedal fell off, as I had not noticed the bolt cam loose. I ran for over 4 hours that way. I will pause in neutral during the shift to let the tractor slow before engaging the other direction, and there is no harsh shift. The older machines would jerk and bang when shifting wide open, and I am sure that is not good. Running H and K model D-8's I would always idle down between shifts.

 

[Nige]

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

I'm interested to know why you think that should be so, because if you do a Rockwell hardness test on a bush and a sprocket segment they are as near as damnit the same hardness. So if that's the case why should one wear different to the other..?

 

[OCR]

Nige and others have explained the reverse wear well.

One thing I would add that I have not seen mentioned is the internal stress on pins and bushings. During forward travel, there is stress from the contact with the sprocket, down to the ground, and just a slight ways forward. In all, probably less than 1/4 of the track length. During reverse travel, the stress is from the sprocket, all the way to the front idler, then about halfway to the rear. This would be about 2/3 of the length of the track. I seen a very good pictoral description of it in a John Deere manual once.

OPERATION TIPS... Page 8.

http://www.deere.com/en_US/docs/con...ts/parts_by_industry/undercarriage/DKB765.pdf



OCR

 

[alco]

Regardless of wear or stresses on the machine, I don't like third gear because I don't like beating myself up.

 

[OCR]

I don't like beating myself up.

Yeah, it gets damn old... mighty fast.



OCR

 

[JDOFMEMI]

OPERATION TIPS... Page 8.

http://www.deere.com/en_US/docs/con...ts/parts_by_industry/undercarriage/DKB765.pdf



OCR

Thats the one OCR

Thanks for helping out. That little book has some good operating tips in it, but what stuck in my mind was the track picture of forward and reverse. It makes it easy to see for some people who struggle with understanding the issue.

 

[OCR]

Thanks for helping out.

:thumbsup... Any time if I can...




OCR...

 

[CascadeScaper]

Out here, there are some big companies that love to see an 8 or 9 going 3rd gear wide open in reverse. Those are the outfits I wouldn't want to work for. I think beyond the wear on the machine, as someone else pointed out, 3rd gear is just too hard on the operator. Dare I say a safety concern for long-term well being of the hands running the dozers? I ran an 824C wheel dozer that had the worst seat imaginable, so I started wearing a kidney belt and everyone gave me weird looks. 2 jobs later I came across the same unit, seat was replaced.

 

[R.D.G013]

Something no one has mentioned is the increased distance a machine travels per day when using 3rd Rev is also a big part in the sprocket/ bushing wear rate. You might get more production using 3rd but you travel more mies in doing so, so therefore there is a correspondingly increase in wear and tear on the track system because of the increased distance travelled per hour. I have been on several machines lately that have 3rd blocked out on them, both fwd & rev. Just my 2 cents worth.

 

[R.D.G013]

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.

Higher the speed = more revolutions the sprocket does in a given hr = greater distance travelled / hr = more times the sprocket & bush rotate against each other which in turn creates more wear. So a machine does a 1000hrs in 1st 2 @ 2.5 mph is going to travel 2,500 miles in that time, one that does 1000hrs in 2nd gear @ 4mph is going to travel 4000 mies in that time, the same would go for using 3rd gear would mean a much greater distance travelled therefore much more wear has taken place because of the greater distance travelled.

 

[Nige]

I'm not sure about that. To me it appears as though the reasoning for using 3rd speed is generally to get the tractor from A to B faster. I think we are all in agreement that you wouldn't be pushing a load in 3rd speed forward.
During operation "A to B" is generally (but not always) backing up the cut from the end of one push to the start of the next one.
So in that case the distance (100m, 150m, whatever) is fixed, the only variable is the time taken to cover that distance. All the undercarriage components will move pretty much the same number of rotations to travel that distance whatever the speed (1st, 2nd, or 3rd) that is selected. Also there's plenty of evidence out there that the operators who are able to move the most dirt in a shift are the smooth steady ("Slow is smooth - smooth is fast") ones, and I can't say I've ever seen one of them tracking in 3rd gear.

 

[ih100]

3rd gear in reverse = greater chance of something flying off the track and shattering the door glass. Also I’ve seen someone doing the high speed reverse thing and struggle to open the door from the crap thrown onto the step.