ASK TRAINS blows it on SD-40-2

[filmteknik]

Someone asked about the difference between the SD40 and SD-40-2 in the January 2005 ASK TRAINS

They correctly pointed out the longer frame (for commonality withSD45-2) and modular electrical system and the minor things like the water level sight glass (well, actually the window to see it without opening an access door).

But on the trucks they missed the boat entirely mentioning only that the Dash 2 has the dampening strut. (What, no mention of the three holes in the frame instead of two? ha ha) NO NO NO. The difference between the HTC truck found under most (e.g. not Conrails') Dash 2 C-C's and the Flexicoil truck previously used is much more than a dampening strut and holes in the frame! The HTC truck lines up all the traction motors the same way instead of tucking them all inboard of the axles. This means that one of them is outboard of an axle and you can see how the truck frame is extended to carry it. That is an additional visual difference beside the holes and the strut.

The purpose of this change is significant. It reduces weight transfers that would occur under heavy pulling on the old truck. The traction motors are hung NEXT to the axle with a pinion gear on the motor shaft driving a bull gear on the axle. One end of the motor hangs off the truck frame while the other rides bearings on the axle inboard of the wheels. This allows the axle to ride up and down on its suspension following track irregularities and the motor tilts up and down with it. But the motor also tries, with the forces involved, to either climb up or push its way down depending on which way it is turning. It doesn't really do this but it tries to in a manner of speaking. When two motors are facing one way and one is facing the other way you will have two trying to lift and one trying to push down...or vice versa. This causes a transfer of weight between axles and the axle that has weight taken from it is more apt to slip. Which in turn means the wheelslip control system must reduce power or momentarily brake that axle etc. Either way traction is limited

When all motors on a truck face the same way they will all be "trying" to do the same thing...push down or lift...and therefore there is no weight transfer between them and no negative effects on traction.

Easily one of the most important features of the Dash 2 C-C's.

TRAINS: You should run a correction!

[M636C]

filmteknik,

What was the exact question "Ask Trains" was answering? If it was "How do I tell an SD40 from an SD40-2?", it may not have been considered that this was the right place and time to discuss weight transfer characteristics of EMD trucks. For the average observer, watching a moving unit, with trucks covered in road dirt, the damper strut would be the easiest truck feature to see if you were on the wrong side to see the sight glass. I can't count handrail stanchions fast enough to tell the frame length on a moving unit.

It sounds to me as though "Ask Trains" were correct, if not comprehensive in their description of the SD40-2, and rather than a "correction", additional information could be provided in a letter.

Why don't you write a letter to "Trains" providing the additional information, and if it is printed, you'll get paid for it.

I've only recently discussed this aspect of truck design on the "Steam Diesel and Electric" thread on this Forum, and what I said is pretty much the same as what you said. It isn't news to many of us on the Forum, but I didn't specifically indicate that that motor arrangement was used on EMD Dash 2 locomotives.

You may be surprised to know that trucks of that design were used on EMD export designs prior to the introduction of the Dash 2 line, in particular the GT26C locomotives built by Clyde Engineering for the Western Australian Government Railways, built from 1967, had a version of the HTC truck, at least four years before the Dash 2 units were introduced. Those trucks did not have the damper strut on the centre axle, either!

Peter

[dwil89]

Also, Conrail specified the older style flexcoil trucks with their purchases of new SD40-2's in the 1970's...they were leery of the newer truck design because of the blame( though never fully proven) of the newer style trucks on derailments of the Amtrak SDP engines in the ealy to mid 1970's. Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown

[Randy Stahl]

QUOTE: Originally posted by dwil89

Also, Conrail specified the older style flexcoil trucks with their purchases of new SD40-2's in the 1970's...they were leery of the newer truck design because of the blame( though never fully proven) of the newer style trucks on derailments of the Amtrak SDP engines in the ealy to mid 1970's. Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown

Right , you can't tell a dash 2 by the trucks. The only real way is to open the electrical cabinet.
Randy

[gabe]

QUOTE: Originally posted by Randy Stahl

Right , you can't tell a dash 2 by the trucks. The only real way is to open the electrical cabinet.
Randy

[dwil89]

QUOTE: Originally posted by gabe

QUOTE: Originally posted by Randy Stahl

Right , you can't tell a dash 2 by the trucks. The only real way is to open the electrical cabinet.
Randy

Cool, if I am even on an SD-40 I will open the electrical box and say "cool it is a dash-2." I figure I will have a better than 50% chance of getting it right given the number of Dash 2s compared to regular units.

Gabe