SD40-2W driveshaft upgrade

[SirTainly]

I'm just in the process of putting a decoder in my IM SD40-2W and I find that both the little black eared collars on the motor shafts have split, and are just spinning. The bits that sit inside the flywheels and attach to the drive shafts. I see IM have moved to a hex drive for the later versions, anyone done a retro fit, is it just new motor with different flywheels and drive shafts?

[SirTainly]

Just looking at it, swapping the motor for an Atlas one and the drive shafts from an SD60 might work. The shafts are in stock at Atlas, but not the motor without the sound cradle. Can you fit the new style motor into the older style cradles?

[mmagliaro]

 I sort of get what you are saying, but not completely.  Is there a piece of plastic tube inserted into the flywheel, with slots in it, so that little "ears" on the drive shaft sit in the slots to spin the flywheel (and worm)?
If that's how it works, perhaps just pry that plastic insert out of there and replace it with a short length of brass tubing with slots filed in it.  A brass insert wouldn't crack and it could be tapped into the flywheel very tightly so it would never spin.

Can you post a close-up picture of this?

[Dirk Jan Blikkendaal]

Hi, had the same problem with Atlas C-628/630 for my RSD-15 Alligator conversion.....
These small plastic parts on steel shafts are just asking for trouble........slipping/breaking.
My solution is very simple: I drilled 2 small holes (0,7 mm) halveway along the flywheel as accurately opposite each other as possible (a little off will not matter) , glued (ACC) 0,7 steel wire inside touching the steel shaft and cut off all excess outside the flywheel.
No slipping ever anymore........ also no problems with imbalance...... [ Guests cannot view attachments ]

[SirTainly]

mmagliaro, it's the other way around there's a small piece of plastic on the motor shaft, with two lugs on it, these slide into the slotted head of the drive shaft.

Dirk, that's a good solution, I like it! I'll have to keep that in mind if I find my C630 has gone the same way. The original is a poor design, the hex fitting on other locos is much better.

I've sort of fudged a solution, borrowing at atlas motor with the hex fly wheels, I shortened to SD60 shafts and thus it's all working again. I've order a few bits from Atlas to repair the loco that had it's motor borrowed so hopefully both will be running again soon.

[SirTainly]

This is a shapeways replacement for the broken parts, shown on a frame here. I'd order these if Shapeways pricing and shipping wasn't so awful.

https://www.shapeways.com/product/VCAZTPE6C/replacment-atlas-n-scale-male-universal-x2?optionId=163572980&li=shops

[jjb62556]

I just order new one from Atlas 

[John]

I just order new one from Atlas 

This should work .. $4.00 plus shipping



https://shop.atlasrr.com/p-1999-n-sd7-9-worm-assembly.aspx

[SirTainly]

Not sure they'd fit, that's not the same part. The ones on the motor shaft are not a ball, but more of a donut shape.

This would be the current Atlas equivalent. Wish I'd ordered a couple of these to try them now though.

https://shop.atlasrr.com/p-3635-n-sd-35-universal-ball-joint-2.aspx

[peteski]

The original Atlas design for SD40-2 and C630 locos used a universal coupling consisting of a donut with 2 prongs and a cup.  The part number for the donut is 540104.  Then they redesigned the coupling to use a ball-shape with 2 prongs and a cup.  AFAIK parts for each design are not interchangeable.  The original design parts seem to be out of stock at Atlas.  I suppose you could try calling their parts department ( 908-687-0880 ) and ask if they still have any 540104s.

In my experience either of the designs is prone to cracking.  I have seen both donuts, and the ball couplings crack and slipping on the shaft. The hex-shape couplings are more reliable, but are not direct replacements.

[John]

Not sure they'd fit, that's not the same part. The ones on the motor shaft are not a ball, but more of a donut shape.

This would be the current Atlas equivalent. Wish I'd ordered a couple of these to try them now though.

https://shop.atlasrr.com/p-3635-n-sd-35-universal-ball-joint-2.aspx

they look pretty similar to the ones above ..

[SirTainly]

same as in the photo, but as Pete said they aren't the ones used, which are the donut style.

[mmagliaro]

Now I see what you mean.  NWSL also makes simple doughnuts with ears on them, made to fit 1.5mm shaft, but the hole in the doughnut is "D" shaped to fit over a flat on the shaft so it won't slip.  I don't know if those are more durable than the IM and Atlas incarnations of this idea, but I don't think I have ever had one crack on me.

I like Dirk's idea with the pins.  In fact, you could tap the holes and put set screws in there instead of glued wires.  Then you could easiliy get it apart if you ever want to. 

[peteski]

Now I see what you mean.  NWSL also makes simple doughnuts with ears on them, made to fit 1.5mm shaft, but the hole in the doughnut is "D" shaped to fit over a flat on the shaft so it won't slip.  I don't know if those are more durable than the IM and Atlas incarnations of this idea, but I don't think I have ever had one crack on me.

You are exactly correct Max.
The reason those donut couplings crack is because the holes in them are made small enough to be tight press fit onto a smooth steel shaft and transfer power without slippage.  That constant stress eventually causes plastic fatigue, and they split.  This happens to many other similar couplings (like ones Kato uses,and even to those infamous Bachmann white nylon axle gears). 

Machining a flat spot on the shaft and using D-shaped coupling eliminates the stress, since the high pressure is no longer needed.

Actually when I fix that type o problem, I take a 400 grit sandpaper and scuff the steel shaft. I then slightly enlarge the hole in the donut (to reduce the pressure, and also scuff it using 400 grit sandpaper.  I make sure both are thoroughly degreased, and the I install the modified donut using thin  CA to adhere  it to the shaft.  That works quite well, and since the pressure is relived, the donut will not split

I like Dirk's idea with the pins.  In fact, you could tap the holes and put set screws in there instead of glued wires.  Then you could easiliy get it apart if you ever want to.

The way I understand Dirks fix, there will not ever be need to remove those pins. The slots in the female part of the coupling are open-ended, so the coupling can be removed with the pins installed.

[Dirk Jan Blikkendaal]

The way I understand Dirks fix, there will not ever be need to remove those pins. The slots in the female part of the coupling are open-ended, so the coupling can be removed with the pins installed.

Thats eaxactly true Peteski! Its a reliable, simple and cheap solution.....