While running my D model grader last week cutting in a drainage ditch beside a private road I bogged it down with too deep a cut. Before I dropped the clutch though there was a dull thump from down low in the machine.  I also stalled it at that moment and was subsequently distracted by a coincidentally broken starter cable. When I got it running again I discovered that the right hand tandems were not driving - but the left side still is.

[Edit] I checked the right hand chain box and both chains are intact, so the problem is definitely not chains.

Having had a look at the diagram for the rear axle assemblymy conclusion is that the right hand drive shaft must have broken.

I have found a replacement (new apparently) driveshaft with seals and bearings for $2,000 delivered.  I think that is a reasonable investment to keep the machine operational as I have a lot of work to do with it and it's working well since the hydraulic rams were rebuilt.

Has anyone ever replaced a drive shaft in a D/DD grader? From the service manual it doesn't look like a difficult task and I can probably do it without even removing the rear axle assembly.

Any thoughts and experience welcomed.

Langdon

Hi Paul and Steve,

I should have mentioned in my original post that I checked the chains and they are both fine, so the problem has to be (as far as I can see) between the drive sprocket in the right hand tandem/chain box and the bevel gear in the axle housing, which also drives the left side which still has power.

Hi Mike,

No I don't have a part number sorry. I bought the service manual, but not the parts manual. It would be easy enough to get though. Do you have a line on a driveshaft?

Hi Coke,

Yes I plan on pulling the right hand axle to confirm that it is in fact broken, but I didn't want to go ahead and do that until I knew that the probable part was available and affordable. Since it is, the next step is to do that investigation and confirm the failure. If I'm right, then I'll take the plunge and order the parts.

We've found that AC 45 graders have a habit of breaking the welds that attach the chain sprockets to the axles of the wheels.

Any chance that could have happened to the sprocket that drives  your chain?

As soon as the chains were off it was clear that the shaft was broken near the chain box end.  When it came out (with a little help from a slide hammer) you could see that it had sheared off very cleanly right at the point where the drive shaft had been machined to create a shoulder for the outboard bearing to sit against. The shoulder had created a stress concentrator and it broke from a crack that had started working its way into the shaft from the shoulder.

I don’t have any photos currently (as it started pouring rain just as I got the shaft out).  I’ll take some tomorrow and post them here.

New drive shaft is ordered along with a new outboard bearing and seal. I should have them by next week and hopefully will have the grader running again the following week!

I will say though that I’m disappointed with the shaft design. Not machining in stress concentrators was pretty much “design 101” when I was studying these things.

Oh, something else I noticed with I pulled the broken shaft: the castle nut that holds the double sprocket onto the end of the drive shaft was missing its locking wire! Seems the last person to work on this machine just didn’t give a toss. I’m going to have to give it all a good look over at some stage and find what else has been ignored.

My driveshaft doesn’t look like it was repaired though, as I mentioned above I think it’s just a design flaw. The shoulder for locating the bearing creates a stress concentrator and it just snapped clean as at that point.

I’ll post some photos.

So when I pulled the drive shaft out, this is what I found!

On the left of the image is the outboard end of the shaft with the bearing still in position. You can see that it’s a very clean break thankfully.

On the right in my hand is the inboard end of the shaft that fits into the gear box bevel gear. The break occurred right on the shoulder that locates the bearing. I’m supposing that the very sharp corner created a stress concentrator that lead to a little crack forming.

The last time I ran the machine I was improving an old V ditch and I got the left side chain box hung up the berm of the ditch and the wheels lost contact with the ground, so the all torque of the motor was going through just one shaft - which had this fatal flaw. And then it broke.

Anyway, I should have the new shaft next week and assuming the inner bearing is ok I can put it back together. Frankly, cleaning out the years of gunge in the chain boxes is going to be a bigger, nastier job than replacing the drive shaft. I’m seriously considering drilling and tapping a new drain hole in the chain boxes as the one that is in it is about 10mm above the bottom of the box, which isn’t very helpful.

Hi Codger,

Yes I figure that the weight coming off the left hand wheels (even though it wasn't exactly sudden) probably just overloaded the right hand drive shaft. Also my grader (which originally had a petrol motor) has been engine swapped and now has a Cummins diesel which probably makes significantly more torque than the original petrol motor, so the shafts may just be a bit under spec'ed for that motor.

Yes the bearing sits against the shoulder - I assume that the shoulder is machined there to prevent the bearing migrating inward (the break occurred on the inboard/gearbox side of the bearing) there is a spring clip that I had to remove on the outboard side of the bearing to retain it in that direction.

Yes the part in my hand is the long section with the splined end that slides into the bevel gear in the gearbox.

Coger - yes, definitely worth clarifying. In the future I'm going to be a bit more careful about not pushing it too hard - it is after all only little!

Yes I am really lucky that there was a brand new part available on the shelf. And I agree about these small machines. I can do work with it that I couldn't do with a bigger machine and it's cheaper to get it trucked from one site to the next because it's so small.

I think that the owner of the farm I'm working on at the moment would buy it off me just to maintain his roads if I offered.

Codger - yes they are still very productive machines. Not as comfortable, powerful, and fast as modern machines, but they will get the job done if you let them. Take small bites, repeat. There is literally no other machine that will do the same job.

As for price - they are a lot more expensive (still) here in Australia, even for a very tired old junker like my D Model than they are in the US. Mine cost $14,000, but it has paid for itself in a couple of projects. If I get even a couple of years out of it without too many issues then it will have been very profitable to own.

The key thing here though is that the machine doesn't do a lot of hours - but having it lets me win jobs that I wouldn't otherwise get that include a *lot* of hours doing other work. The project I'm working on currently will only require a day of grader work probably, but I'll rack up 100+ hours of excavating gravel/clay on site to use on the road that the grader will finish. Without that machine I wouldn't have gotten the job at all, so it's been an excellent investment.

The only grader I was ever around was an older Caterpillar 12. Guy that owned it used this to maintain his "Standard Bred" horse training track. I'd have to get it going a couple of times per year after he'd starve it out on fuel but somehow never caught on to the simple fix for that.....   

Hi Codger - that's a pretty cool dozer. I'm working on rescuing an old D6 8U that's a similar size. I have a lot of work that i could do with a machine like yours. Yeah the transport cost can be a real killer, especially here in Australia where heavy trailers cost a *lot* to register ($14,000 per year for a two axle low loader).

Yes - the same thing has happened to me multiple times.  I get onto a job then have a neighbour come over and ask if I can do something for them!  Love that photo of you walking the dozer over the road.

Ha, yes keep that fuel topped up - especially in older machines so you don't pull the crud in the bottom of the tank through!

TramwayGuy - I have to say that I'm loathed to make any modifications to the new shaft. Given the age of the machine and the amount that I use it, my inclination is just to run it as it is. I have no doubt that it will give me a few years of work - which will be more than enough.

There is also the question of: if I fix that flaw where does the stress go to? The answer may well be: to the splines on the inboard end in the bevel gear (which I'm told is another common failure in these machines), which would be a much bigger problem to fix!  If I have to choose a failure point then I'd definitely rather it broke at the chain box end like this.  Call it "sacrificial"

And sometimes the design and engineering is correct but manufacturing gets it wrong.

In my last job before retiring I worked in the engineering department of a company that builds industrial rotary encoders. Compared to earth moving equipment, these gadgets are tiny; we started having some field failures of a certain model, the 1/4" diameter shafts were breaking inside the unit right where there was a shoulder for mounting the code wheel.

The engineering specs and drawings called for a small radius at this juncture (I forget the exact number) and even specified the part number of the tool to be used for this operation.

Whoever it was that set up the CNC machine either didn't read the specs or simply ignored them, because they used the sharpest most pointed tool available to cut that 'radius'. We had a really nifty high-powered optical inspection system there so it was easy to diagnose the problem (I sometimes wish I still had access to all of the wonderful tools in that engineering lab).

We replaced those units at no charge to the customers.

When you get into the D6 check out Antique Caterpillar Machinery Owners Club forum. Membership gets you into the library that is still growing. But all the operators, repair manuals, and parts books are there. As well as all the books for attachment such as the cable winches and hydraulic parts and repair, and dozer blade manuals.   As well as a good number local clubs are active in your county.

I now have all the pieces in place to get the grader back together.

It's weird that the cheapest supplier (including shipping) was from the other side of the country.  But anyway, I'm all set.  Now I just need it to stop pouring rain for a day so I can do the work!

And a pump to get the oil into the gearbox. That I don't have yet.

I see your gear oil is in steel pails. Is that still common down under? Plastic pails are the common container any longer here.

Codger - thank you, yes fingers crossed!  I'm looking forward to seeing it all buttoned up again and back to work.  I think putting the new drain bungs in is going to fun too.  It's nice to do an actual upgrade like the hydraulic rams rebuild.

Honestly I've never bought oil in bulk like this, so I don't know what's standard and what's not.  Anything up to about 6 liters is always in plastic at least.

So today was the day and I finally got to start putting the new drive shaft in the grader!

First job:drill a new drain hole at the back of the chain box because there was no way I was going to bail the remaining 15mm of oil out through the side hatch. That oil was nasty...

Drilling of a 10.8mm hole was followed by tapping and the installation of a sump plug with crush washer. Took me forever to find the right size drill bit (10.8mm - seriously? I had to buy that online couldn't find it anywhere on a shelf) 12mm (UNF I think) taps (which everyone had sold out of) and bungs to suit (which were thankfully easy enough to find), but it worked out really well - and the (horrible dirt laden) oil made the tapping pretty easy - free lubrication!

A side note here - when I was measuring up the chain box to work out where to put the drain hole it became apparent that Allis Chalmers A. weren't playing - those chain boxes are made of 12mm / half inch steel that my HS drill bits took their own sweet time getting through and B. did not care in the least how the result looked. The end plate is just slapped on there and welded in place. Alignment? Who cares? it won't matter once it's welded on!

Next step, clean out about four liters of oil, 3mm of mud, and - I kid you not - enough ball bearings, split pins, and shards of metal to make a disaster movie. Bad things happened in that chainbox somewhere in the past (yes that a little bit of foreshadowing). But it all cleaned up pretty nicely in the end - after repeated flushing with diesel (shaking the grader around to slosh the diesel was the hardest part), then lots of wiping out with cloth rags that went straight in the bin!

Looks rather nice in there now:

Next step: insert the new oil seal. I didn't have anything to press it in with, so I went for the "lump of wood hacked into a workable shape" option. It worked. I don't think that the seal suffered any real damage.

The eagle eyed among you will notice that something bad happened to the bearing seat in the photo above. Here's a better view:

I have no idea what, but I'm guessing that it was involved in the installation of the scrap bin of metal parts and shards in the bottom of the chain box some time ago. Still, I think it just looks nasty and shouldn't effect anything. And yes I did clean out the bearing and snap ring seat before I proceeded.

Then it was time to pull out the new driveshaft:

Don't ask me how but the (phone) camera makes these two *identical* shafts look vastly different lengths. Thankfully they aren't and I have other photos to prove it - but look at that shiny new metal! Mmmmm... shiny.

Shaft went in nicely, then I pressed the bearing in.  Thankfully while firm, it wasn't nearly as tight a fit as the oil seal, so I managed to slowly, gently tap it in, again with appropriately hacked wood. I got it in flush with the housing, but ran out of time to shape another piece of wood to let me push it in further. But it's in place at least!

So, having run out of time I buttoned everything back up to keep the water out and called it a day.

I'll be back to it on Sunday hopefully. Get that bearing finished, install the snap ring (I have a bad feeling that is going to be a fight), install the centre sprocket, reinstall the chains, fill with oil, make up new gaskets for all of the chain box ports, then bolt the ports down.

Then I have to go de-sludge the other side... (at least I get to use my expensive, weird drill bit and expensive, rare taps again).

So more photos and narration will follow!

Good progress and thanks for the update. I've seen all kinds of bearing bores destroyed over the years and that one won't hurt anything as the outer bearing race is tight to the bore.

Before you button it up, I would get some oil into that bearing whether it be a thing gear oil, or even a thin bearing grease. Reason being is that even though that is a lubricated bearing, it has none upon initial startup. It is perhaps submerged in oil and if the case then no pre lube is required but I always grease them upon installation as the grease will disolve into the lubricating oil but dry startup is never a good thing with roller bearings.

I have used a welder to WELD on the race.. This actually looks like they were trying to BURN the race in half.. Carbon arc.. or HIGH AMPS on that stick.

Lots of loose parts... Don't you wish these things could tell us their stories sometimes?

The rear sprocket on the same side was slightly loose on the tapered shaft. The washer and the nut were tight to the boss on the shaft but the wheel was still loose on the shaft. It had been this way since new so the taper and the keyway on the wheel had suffered some wear. Some spray welding and machining to the inner hole of the wheel match the taper of the axle made the wheel tight to the shaft. The keyway was machined and a new key was made that fit the keyway on the wheel one one side and the keyway on the axle on the other side. I had a cupped washer made so the nut could now push the wheel tightly on the shaft. New chains for that side and it was good to go. Spent a lot of money for this fix but never had any more problems with the wheels. Apparently some others had encountered similar problems with bad machining by AC.

The spacer that is meant to go between the bearing and the gear…

Oh well. Have to take a trip to town and buy a gear puller tomorrow, pull it off, install the spacer, then put it back on again. I live and learn, but making progress.