Dipped...

I wonder if it could be dipped in the hot water? Not like, as it's boiling, but just as the bubbles stop? It's plastic, so I don't see water damaging the gear itself...

Bachmann 44tonner

I attempted to buy gears from Shapeways for mine, and one was shattered on arrival, and one more shattered as I tried to fit it... so this might be a good option!

Loco generation

When you say first generation, two motor? You do say driven by the motor.  I had two motor 44 ton with cracked gear. Never looked that close.

I do have the single motor with LokSound now.

Rich

Dipped and Loco Generation

As to whether or not the water has to be boiling hot - not sure. Actually, the steam coming out of the kettle is hotter than boiling water, so it's probably enough on it's own. I just figured that a few extra minutes of heat wouldn't hurt.

And yes, this is for the two-motor versions of the 44 and 70 tonners. When I said "driven by the motor", I was trying to differentiate between the gear that is closest to the worm on the motor, as opposed to the gear that gets its power from the series of three intermediate gears.

nice idea.  I purchased a 2nd

nice idea.  I purchased a 2nd generation (first version of the single motor, dcc-ready) engine for an On30 conversion, and found it had the cracked gears.  I ordered 3rd generation trucks from Bachmann and fitted them to the chassis with no trouble, just had to use the newer retaining clip that comes with the trucks, and the shorter driveshafts that came with the engine.  Of course, that was one of last weekends projects, and now I'm seeing your post!

cracked axle repair

Charlie..please keep us informed periodically as to how this fix holds up.  Brilliant.   Applicable to a lot of situations.  

Update

Once some lube gets into the works, the tubing seems to lose its grip on the axles shafts. It still retains its diameter, but "walks" a little from side to side. This doesn't seem to be much of a problem on the longer end of the shaft, but I had to disassemble one of the trucks and the tubing on the short end just fell right off. I slipped it back on and will keep an eye on it. I think I'm eventually going to have to revisit the idea of using brass sleeves, at least on the short ends.

@BklynXPat re: Gear repair

Have fun! 

Alternative Gear Repair

geoffb:

Sounds like a viable alternative. Unfortunately for me, the eyes ain't as good as they used to be and the fingers ain't as nimble. Hell, I need a telescope and and two spotters just to keep from strangling myself while flossing. But I do appreciate the suggestion - thanks!

I have a similar 2 motor 70-tonner, w/ different issues

This is very interesting to hear that other modelers also have issues with these old two motor 70 ton GEs. I have one that wouldn’t run well and had motors that were loud and produced a smell like an old slot car. I replaced the motor in a vain attempt to solve the issue, which didn’t work.

It seams to me that a gear issue is a possible culprit of the poor running characteristics I have had. I will have to check next time I get it out (and fix other issues with it...). Perhaps I may be able to try this technique!

Bachmann gears again?

Thanks to the Corona Virus I am getting to a few sidelined projects on my list.

Have a Bachmann Doodlebug that I wanted to put a decoder in, Cracked gears!

Have 2 44 tonners Cracked gears. Bachman doesn't have parts.

I read somewhere that the 3rd Gen trucks fit but I hear they crack.

I am going to reach out to NWSL but are there any new solutions out there.

Thanks MARK

Falling back to brass collars

Well, it was a nice dream while it lasted, but not a permanent solution. The heat shrink tubing is 'passable' for the long end, but not the short end. Once the lube works its way under it, it 'walks' around. It also looks like the lube eventually softens the tubing, reducing its effectiveness at containing the cracking.

So, it's back to brass collars. Since the shafts are 3.0mm O.D., I decided to use this:

This required "machining" the shaft ends down to the point where the tubing could be pressed on for a snug fit (with a little CA added for grins). I didn't want to use my Dremel knockoff because I knew that the combination of a minimum 1000 RPM and my impatient nature would result in the smell of burning plastic. So, I found the right-sized brad, ran it through the axle hole, and chucked the "jig" into my 3/8 variable speed drill. Using low RPMs and a couple of grades of sandpaper got the job done without incident. The results are shown below (please pardon the poor quality - both my phone and I have the same level of photographic incompetence).

1 down, 7 more to go.

I am a little confused

In the case that BklynXPat is talking about, the gear is ok, the shaft is cracked?  Is it cracked near the gear.  That is a stress concentration point.  Also is this the “tower” gear?  The gear that is directly connected to the motor.  
I have recently taken on a project from a client to improve the performance and noise signature on six of these GZg 70 models.  As usual, Bachmann has multiple variations of these units.  The ones I’m dealing with are all single motor.  This is a conventional diesel motor with a shaft extending from the motor rotor on both sides.  These shafts are directly coupled to the truck tower gear with a small dog bone.  
That could be accomplished with two motors with one shaft each as well.  
there are two versions of the truck “tower” gear.  One is a small diameter gear, about the same size as the coupling for the dog bone.  The other is a larger diameter gear, maybe 2.5 times a large as the first.  Needless to say the gears in the trucks are different.  The truck attachment is also different.  The firmer snaps on.  The latter is bolted on.  
so far the only gear failures I have found are on the out side axle gear on the same engine.  Here half of the gear teeth were sheared off, so it would run erratically and had a clicking sound.  The configuration is the former discussed above.  The parts between the two truck design are not interchangeable.  The only parts that Bachmann has on their site are the latter design.  At this moment I do not see a source for the failed axle gears.  

The latter design is also much noise than the former.  I believe that this the larger diameter gear making a siren type noise.  This noise is amplified by the shell.  Haven’t come up with a fix for that yet.  
 

Would like to know what gears/shafts are cracking, so I can look for the problem.

Will be quantifying the impact on my site when finished.

Thanks for any insight you can give.

These are the drive gears on

These are the drive gears on the two-motor 70 and 44 ton models. They're the ones the half-axles  fit into. The photos in my original post show the location(s).

Bachmann gears again?

The gear that seems to crack is the axel gear that is a press fit on the two wheels. This results in wheel slipping and noise if the actual gear is cracked and not just the shoulder. some time ago i purchased a new set of trucks and just recently finished the repair.

Only the 3rd generation trucks are available and these are a solid axel with the wheels  insulated. Unfortunately the worm is smaller and a different design. With a NWSL puller i was able to remove the wheels and the square bearings. I reassembled these in the 2nd generation trucks. So far all is good and it runs very smooth. I also installed a bachmann decoder and Led headlights. It all tested fine but I cant take it to the club right now for a good run due to covid.