Locomotive Descriptions and Phases - EMD SD70M-2, SD70ACe
The SD70M-2 and SD70ACe were a redesign of the EMD SD70 series aimed at meeting new emissions standards that took effect in 2005. While they shared many mechanical components with the previous SD70M and SD70MAC models, they received a substantially altered carbody and underframe that borrowed some features previously used in the SD80MAC and SD90MAC series. The air reservoirs and associated piping were all moved to the engineer's side while the traction motor cables were moved to the conductor's side, as on contemporary GE units. The dynamic brakes were moved from the front to the rear of the hood, and a wider radiator section was located behind a lowered and tapered central hood. The underframe was several inches taller than on earlier SD70 models and resulted in a shorter cab being adopted from the late-model SD90MAC. The radial-steering HTCR trucks were carried over and a new, simpler HTSC truck was introduced that lacked radial steering and rode on a shorter wheelbase.
Unlike the SD70M and SD70MAC (which rode on different underframes) the SD70M-2 and SD70ACe were nearly identical. The main differences were the substantially thicker and more numerous DC traction motor cables, smaller traction motors and absence of inverter cabinet vents on the SD70M-2. Visual changes over the production run were numerous but relatively minor, and as the SD70ACe outsold the SD70M-2 by a wide margin, the latter had fewer variations.
These phases are of my own making. As there was no single major change during SD70ACe production after 2005, Phase 1 denotes pre-production units. These phases do not include EMD's new Tier-4 version of the SD70ACe.
|Jacking pads||open||flat plate (SD70ACe only)||flat plate (both models)||curved plate|
|Panels above d.b. intakes||3 rows of vertical louvers||3 columns of horizontal louvers||short doors||medium-height doors||shorter columns of louvers|
|Cab sub-base panels||hinged||bolted|
|Inverter cabinets||surface-mounted grills||flush grills||no grabirons on panel edges, no slot at top right corner|
|Rear sand fill step||No||Yes||No|
|Rear hood end grabirons||engineer's side||conductor's side|
|Rearmost conductor's side hood door||bolted on all sides||hinged with 4 bolts||hinged with 2 latches|
|Frame and side sill||open sill under cab||continuous sill, slightly narrower under cab||(1)||narrower section extended toward fuel tank,|
removable sill section under inverter cabinets,
shorter vertical extension behind front steps,
2 additional vertical ribs on underframe (above & behind fuel tank)
|Air reservoirs||strap supports||end support brackets|
|Dynamic brake intakes||open at bottom corners||notched bottom corners|
|Rear hood end bottom panels||2 latches||1 latch|
|Engineer's side handrail||6th stanchion from rear moved forward|
|Conductor's side underframe cable shroud||yes||no|
|Conductor's side handrail||straight (SD70ACe) or zig-zag (SD70M-2) vertical section behind inverter cabinet||zig-zag vertical section behind inverter cabinets, stanchions moved rearward|
|Side sill handrail stanchion supports||vertical||angled sides|
|Panel behind inverter cabinet||solid (SD70ACe) or square grill intake (SD70M-2)||small (SD70ACe) or large (SD70M-2) louvered section||rectangular grilled intake (SD70ACe)|
|Fuel system||narrow cutoff switch housing, separate gauge||wider combined gauge and cutoff switch housing||Revised fuel sensor (near bell)|
|Air piping||revised piping ahead of reservoirs||revised piping behind reservoirs|
|Small front hood panel on conductor's side||2 bolted panels||1 bolted panel, 8 bolts||1 larger bolted panel, 10 bolts|
|Traction motor cable shroud (SD70M-2)||yes||no|
|Hand brake||5-spoke or 8-spoke stamped wheel||3-spoke welded wheel, new housing||wider notch above wheel|
|Isolated cab seam||notch around door latch|
|Angled braces behind end plates||no||yes|
|Sand hose supports||narrow||wide|
- Frame and side sill, Phase 2c: Same as Phase 2b2 except narrower sill section extended rearward, farther than on later phases and without removable section.
- SD70ACe units exist in all phases.
- All SD70M-2 units are Phase 2a, 2e or 2f. EMDX SD70M-2 demonstrators are early Phase 2a units with some Phase 1 spotting features (air reservoir straps and no notches in dynamic brake intake).
- As a DC unit, the SD70M-2 does not have inverters but retains the inverter cabinet housing found on the SD70ACe.
- Trucks (HTSC or HTCR-4) vary across all phases, and sometimes vary within a single order.
- Rear sand fills are either on top of the hood or in notches on the hood ends.
I came across a low-resolution SD70ACe general arrangement diagram online illustrating many of the frame and hood dimensions. I used these dimensions in both the 1:36 and 1:18 renditions of the SD70ACe and SD70M-2. The drawing below lists all the dimensions I used from the general arrangement diagram.
- Some dimensions have been rounded off to the nearest 0.25" (since that's the finest increment in the 1:18 drawings).
- The underframe and coupler height were listed as 73.0" and 34.5" in the general arrangement diagram, based on a 43" wheel diameter. However, since I drew my 1:18 rendition of the HTCR truck with 42" wheels, those dimensions in my drawing are 72.5" and 34.0" respectively.
- The specified location of the seam at the front of the hood did not line up with photos (it was off by 1.75") so I based that dimension on photos. The two altered dimensions (as used in my drawing) are listed in red.
- The drawing shows an SD70ACe with HTCR trucks. The inner axle spacing is 4" shorter on the HTSC truck, leaving a 4" larger gap between the truck frame and fuel tank.
- The truck centers are measured from the pivot pin, which is 15.75" outside the middle axle of each truck.