sd-45 coupler

[rustycoupler]

 I have a Reading sd-45 and i tried to couple it to a lifelike gp-20 with the truck mounted coupler and it keeps derailing the gp-20, i tried using a long shank coupler no change. The curves i am using are 11.25 any suggestions.

[Albert in N]

Don't have a Bachmann SD-45, so I used my Bachmann Spectrum GE Dash8-40CW (also has twelve wheel drive like your SD-45).  Also, I own an older LifeLike GP-20, but noted that it also had body-mounted couplers like the Bachmann.  Are you sure about LL being a GP-20? All three of these diesels originally came with Rapido (non-knuckle) couplers and none were designed for plug in and play DCC.  All three were sold as Direct Current (non-DCC).  My Dash 8-40CW and LifeLike GP-20 were converted years ago to Micro-Trains Line operating magnetic knuckle couplers.  First, I placed both diesels (without train attached) about two feet apart on the inside dog bone 11-inch radius portion of my Kato Unitrack layout.  Power is an MRC Tech4.  Even after warming up both for 5 laps around the layout, the LifeLike GP-20 ran faster than the Bachmann.  They were not ideally speed matched, but I hooked both up to a 10-car train (either can pull this train alone easily).  They ran OK paired, even switching lead engine and direction of the locomotives.  They did not derail and went around the reverse 11-inch curves without problem pulling the train.  The LifeLike was faster, so it would stress it to pair it with the Bachmann for extended periods.   If your locos run OK unpaired, run them unpaired.  If it is important to run two or more locomotives, get ones that run at the same speed and have matched couplers.  At least, this is my opinion.  BTW, I enjoyed running my old Dash 8-40CW!