Dr Zarkoff Wrote:
-------------------------------------------------------
> > Water sloshing around in the partly-filled tanks
> reportedly contributed to some of the SDP40F's
> stability problems and may have contributed to
> some derailments.
>
> > This was no longer a problem with the units that
> went to freight railroads
>
> The stability problems were with the trucks, not
> the water tanks, and freight units equipped with
> this model truck had the same problems. The
> solution was those shock absorbers mounted on each
> end of the center axles.

This is the first time I have ever read anything about the HT-C ( aka - Dash 2 ) truck's center axle being the cause of SDP-40F derailments. The HT-C 3 axle truck debuted on the SD-45X units built for Southern Pacific in 1970, and was used on almost all 6 axle Dash 2 SD - Units for many years. ( Conrail ordered their SD-40-2 units with the older style HD truck. ) All HT-C trucks since 1970 have had the shock absorber on the center axles; the SDP-40F units were built in 1973 - '74.
In the wake of the Amtrak SDP-40-F derailments, extensive tests were performed by the AAR & FRA; said tests never determined an exact cause, though the HT-C trucks' hollow bolster specified by Amtrak as a weight - saving effort was suspected as a cause by many. ( The extra water tank located inside the carbody had a different fill separate from the underbody tank, at the discretion of the freight railroads Amtrak operated over; another weight - savings idea. ) The majority of derailments were actually initiated by a light - loaded baggage car derailing, and pulling the trailing SDP with it. It's worth noting that several of the railroads that experienced SDP-40-F derailments were known to have questionable track structure & maintenance ( except perhaps BN ), while Santa Fe never restricted the units and routinely ran them at speeds of 90 MPH on their tracks.