THESE NEW SD 40 2S....

shamoo737 wrote:

when somebody says, I dont want nothing. They really want something, because they dont want nothing.

Now you're making my head hurt ... STOP IT!

According to Joe at MTL,

They work pulling everything we have in house around a 195mm curve. The Marklin 145 is questionable, it hobbed a bit due to the length between the wheel centers on each of the trucks...we removed the flange on the center wheels and that helps on 160mm and above.

I cannot find anything online about Joe saying the center axle is also raised, so that may or may not be true. Nor can I find any reference to it not being part of the geartrain, and since I don't have one of these (and have no need for one), I can't confirm anything.

So, it might be possible to drop a regular flanged wheel in there and gain some performance--someone will have to try. If, however, the axle is raised and/or it's not geared, then the center wheels are indeed just for decoration, and do not do anything.

I don't know what the spec is, But I just measured the height difference, and the center wheel measured .006" gap between the rails whit the other 2 wheels touching.

I think a good and reasonably safe experiment would be to put a layer of bullfrog snot on 2 of those wheels and measure before and after tractive effort with one of these:

Digital Meter Measures the Drawbar Pull That Your Locomotives Develop

pray59 wrote:

I don't know what the spec is, But I just measured the height difference, and the center wheel measured .006" gap between the rails whit the other 2 wheels touching.

I wonder if this difference is a consequence of turning the wheels down to remove the flange, and not necessarily due to the axle being any higher?

The fact that there are unused dimples on the power pickup strips in the sides of the truck suggests that M-T may have originally designed the trucks with all six wheels being the same, and then later revised the design by blinding the center wheels to improve performance on tighter curves.

I am pretty sure the axle was turned down to allow the engine to negotiate tighter Marklin radii than MTL's 195mm. Do not at present have any proof of this but it is a guess at best for now. I would like to try and get a pair of standard axles and replace the blind wheels and see what the difference in pulling power and power pick-up. However, I do not think it needs more pickup points the power system on this engine is a miniature version of the Kato and Atlas method used in N-scale so successfully.

I am pretty sure it will get around the MTL 195 just fine with flanges on all three axles. AZL engines with class C trucks have a longer wheel base such as the SD75 and they have flanges on all three axles. I came up with 5 thou clearance between blind tire and the rail top and Robert Ray came up with 6 thou. We both think that you might get some mileage out of Bullfrog Snot on this wheel if you do not replace it with a standard one.

When I took the truck apart there is no evidence that the middle axle is raised and the gears on all three axles are visible through the bottom of the truck cover.

Pure speculation here, but I wonder if the flange may have been removed to help these locos negotiate MTL turnouts. With the tight clearance between the inside rail guards and the outside rail on the curved portion of the turnout, there is no play. Four axles locomotives don't have a an issues, but longer multi-axle locomotive such as steam locos can bind slightly since the long frame has no play going through the curved portion of the turnout. The six axles issue may experience the same slightly bind due to the long wheelbase trucks trying to negotiate this area on the turnout. Remove the flange and there is no bind. Again pure speculation, but these locos run great through 195mm curves and I can't see an addition of a flange affecting this. I wouldn't even bother with tighter curves.

Rob

ztrack wrote:

Pure speculation here, but I wonder if the flange may have been removed to help these locos negotiate MTL turnouts. With the tight clearance between the inside rail guards and the outside rail on the curved portion of the turnout, there is no play. Four axles locomotives don't have a an issues, but longer multi-axle locomotive such as steam locos can bind slightly since the long frame has no play going through the curved portion of the turnout. The six axles issue may experience the same slightly bind due to the long wheelbase trucks trying to negotiate this area on the turnout. Remove the flange and there is no bind. Again pure speculation, but these locos run great through 195mm curves and I can't see an addition of a flange affecting this. I wouldn't even bother with tighter curves.

Rob

Interrresting, but I doubt this is the obvious reason, as AZL 6-axle stuff negociates flawlessly MTL turnouts once their gauge is adjusted with a MTL trackgauge (initially AZL locos had a slightly tighter gauge than MTL's and needed to be "regauged"). ).

Dom

Pictures of the first samples of the SD40-2 in grey plastic and black cab roof had all three axles the same. It was sitting on a piece of plastic and you could see all 6 flanges on the one side. I do not recall when handling the samples seeing the center axle with a blind wheel.

cheerz Garth

I sure would like to hear Mr. Joe's side of this story. He sure has been awefully quite.

Hey, Joe! Too busy to dish out some information on the trucks... or, do you prefer not to wade in to this one?

Guys, calm down, what's the drama? The SD40-2 have enough pulling power as all GP35, GP9, GP7, SD70 and so have and more power then most people own cars ... And running MU, it's always looking better, or? It's only a waist of efforts to have this axle powered in the first place.
4 axles are always good enough for reliable power pickup. A Zthek SW1 has 2 powered/ power pickup axles and it works fine with DCC....

Just my 2 cents

I heard Joe say that with three axles, the trucks don't negotiate the tighter curves as well with the flange on the center axle. On broad curves three axles with flanges would work fine. Three cents worth?