The locomotive itself is essentially an EMD GP38 with modified HTC-style trucks and GP39 engine components.only 10 were built, and only 9 out of the 10 still exist after one wrecked in 1983 and was scrapped the following year.
The EMD SDL39 was an experiment in weight distribution using a frame about the size of a four axle locomotive but using two three axle trucks, which made it appear unproportional compared to other common engines of the time.The type of locomotive was built upon special request from EMD and was originally meant to replace the Milwaukee Road's small fleet of ALCO RSC2 types of units (modified from RS2 units built upon MILW request from ALCO); though they were built for service on the light weight branch lines. The entire fleet (with the exception of the wrecked unit) survived into the formation of the SOO Line railroad, who purchased the Milwaukee Road in 1985. towards the late-1980's, the SOO Line retired all 9 of the remaining units and were leased (but soon sold) to the Wisconsin Central (WC), but were later leased by the Illinois Central (IC) due to the Wisconsin Central being purchased by the Canadian National (CN) during the mid-1990's; thus the WC portion of CN deemed that such units were no longer necessary or needed.
The 9 remaining SDL39's lasted on the Illinois Central for several months, but were eventually sold to and leased by various leasing companies before finally being sold to FEPASA in Chile.
They've remained on the FEPASA ever since.
- When the Wisconsin Central purchased some SDL39's from the SOO Line, they were fitted with more advanced radio controls.
- They were originally fitted with the MILW's unique electronic bells that were shaped like horns.