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Bulldozer care demands eternal vigilance

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In my last column I discussed the importance of using top quality bolts and keeping them tight.


On a bulldozer, grouser plates in particular should be kept tight, because the bolts also act like dowels as on the front end loader I discussed last month. If left loose for long enough, they cannot be tightened. Likewise, bolt on sprocket segments must be kept properly tightened; they cannot be tightened after being loose for a while without as these bolts are a real dowel fit. The only cure is to replace the sprocket centre and new segments, an expensive and time consuming exercise, as the sprocket disc has to be removed, disturbing seals and bearings.
It is bad practice too, to remove a track link to regain track adjustment on a worn track. What this does is hasten the demise of the sprocket, as the chain is now out of pitch with the sprocket.
It is vital too that the front idler is precisely aligned with the sprocket so the chain runs true. Otherwise there will be excessive wear to the chain or centre rib of the idler.
There are wear plates and shims that secure the idler from both vertical and lateral movement; idlers should always be firm, with their only possible movement being along the track frame to tension the track. Also, alligator master links must be properly tightened as loose ones will self-destruct. If worked loose for any time they will not properly retighten.
Dozer tracks are especially prone to excessive wear when ripping rock. To minimise wear, try to have some loose material on top of the rock, to help cushion impact and allow for limited track slip.
Poorly adjusted tracks hasten unnatural wear. I remember watching a D7G working in a quarry, where the tracks were so loose they almost rubbed on the top of the guard that covered the tension spring between the two top carrier rollers. While I was there the supervisor spent 15 minutes with the operator. But no immediate action was taken to tighten the tracks.
The other extreme is tracks that are too tight. This is very poor practice, as it places undue load on sprocket and idler bearings, reducing their life. It also makes a machine much harder to turn.
In the wrong hands, a mounted ripper on a big dozer, is a real tractor killer.
I recall talking to the careful owner of a D11 in a quarry, and he told me track life there, was just a little over 2000 hours. But Ill bet he costed the dozer accordingly though.
There is no doubt that a complete track rebuild is expensive. Even a medium size dozer can eat $30,000 to $40,000. So the question should be: is the rest of the machine worth spending that amount of money on?
The transmission
I have seen giant leaps in transmission technology. Early ones were not even encased in housings. Then housings were developed, and gears in simple shift patterns to provide two or three forward speeds and one reverse, ran in oil.
The early clutch was also very crude. Some had leather facings and others cork. My first D4 had a clutch with a material a bit like old brake lining and it took very little punishment before it burnt out. Allis Chalmers developed a sintered metal, copper like substance, that was a very marked improvement, and it found its way into steering clutches.
Then Cat built the oil clutch, the clutch to end all clutches. But at Sydneys Royal Easter Show in the mid 1950s, the Allis boys at the Tutt Bryant stand told me, a 14 year old Cat convert, that the new clutch with all its wearing parts, would prove the end of Cat. History has proved how wrong they were. Personal experience with these oil clutches proved how effective they were. Where they could give thousands of hours before adjustment was needed, the old dry master clutch could need adjustment after just a few hours.
The only parts we ever bought were very odd oil seals on the main output shaft. Quite obviously Cat learnt from the success of the oil master clutch, and developed the wet back end, by running the steering clutches in oil again dramatically extending component life.
Current transmissions are power shift and hydrostatic, and rely heavily on clean oil. Each has thousands of wearing surfaces that will give a good life only when free of contamination. So they have filters and oil filling facilities that have to be treated with almost surgical cleanliness. These units can run into tens of thousands of dollars just to be rebuilt, let alone purchased outright.
But sometimes the cause of a problem can be difficult to nail down and the repair remarkably inexpensive. I remember hearing about a D7E experiencing problems with the power shift failing to engage. The servicemen arrived, checked all the pressures, and after much soul searching and reading of the service manual, decided radical surgery was needed. But when he removed the top of the transmission he found a clump of gum leaves causing the problem.
Final drives
This area has not changed a lot, except when we saw the intermediate pinion come between the bull gear and pinion, and forced bearing lubrication introduced. Better sealing with such things as the duo-cone seal dramatically enhanced oil retention and kept dirt out too.
The advent of the planetary final drive is not recent but it has been seen to dominate in many late machines as the preferred drive.
It is also interesting to note that Cat has gone back to a conventional track system with the new electric transmission D7. Its track frame resembles the TD 20s with the dead axle in front of the sprocket; previously Cat had the dead axle in the sprocket centre.
Seemingly simple things such as the alligator master link, sealed and lubricated track, and bolt on sprocket segments, have revolutionised track work. Sealed rollers and idlers too only need maintenance once in a while, although a regular check to see if they are overly hot, will catch a potentially expensive failure.
In many instances I have seen large amounts of money squandered on repairs. In some quarters, there is a great desire to replace faulty parts with new OEM parts, even where it may be suitable to use other suppliers of equal quality.
Can we repair this part with local expertise? An example: about 25 years ago with some wear on the spigot of an all aluminium stator out of a D7E torque converter, which was required to carry a bearing, we contemplated buying a replacement.
We checked our suppliers and they told us it would cost $3400. That prompted us to make a trip to our local engineer who repaired the old one for the princely sum of $250.

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