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Thread: Close coupling MTL heavyweight pssger cars with MTL Z-scale knuckles (905)...

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    Default Close coupling MTL heavyweight pssger cars with MTL Z-scale knuckles (905)...

    After following a thread on another MRR board for a while, I decided to try close-coupling my MTL heavyweights with MTL 905 Z-scale couplers. I ruled out MTL Truescale couplers, because my min radius is a smidge under 17", and the cars also would need to negotiate #7 turnouts... didn't seem that the Truescales would work well with these limitations. I thought my experiences using Z-scale 905s might be useful to others contemplating a switch...

    The good thing, changing out the factory couplers on MTL heavyweight passenger cars for MTL 905s is a very simple swap on all but the dining car... using the same holes and pins that were used to mount the factory couplers. Unfortunately, the stock couplers on the dining car have a longer shank or pocket, and are mounted further back than on all the others, so new holes will have to be drilled. I bought 3 packs of the MTL 905s, sufficient to change out 6 of my 7 cars... leaving the diner til later, since it would require drilling new holes.

    The close-coupled cars looked great... but I must say, I was a bit disappointed with first runs of my now "close-coupled" passenger train, pulled by my Kato FEF-3. Although the close-coupled cars negotiated all my turnouts and curves just fine, there were multiple "random uncoupling events (RUEs)" with each trip around my twice around layout. I check all the coupler heights, and they seemed good... The RUEs did not occur passing over turnouts or track joints, or at the transition point in a grade. They did not seem to result from uneven track. Finally, after a couple operating sessions, I began to notice a pattern. The RUEs consistently occurred in two specific circumstances: (1) when pulling the cars on any downhill turn to the right at road speeds (40-45 smph), or (2) when slowly pushing around a right turn that transitions from level to downhill, a group of cars might uncouple and coast down grade in front of the train.

    The "right hand" nature of the problem was key... When inspecting the couplers, I noted that right hand turns tend to move the knuckles linking two cars away from each other. When combined with the inevitable slinky action of MTL couplers at road speeds running down grade, this caused the RUEs: as the trailing car sped up and bounced its coupler against the leading coupler in a downhill right turn, they uncoupled. Similarly, at low speeds, pushing around a right turn the couplers are in compression while the right turn works to uncouple the knuckles, and if the train then enters a down grade, a runaway results.

    I was thinking of giving up, and going back to the factory couplers... but I THINK I have come up with a two part solution, that has allowed me to get through two operating sessions w/o a single RUE:

    First, I turned each coupler slightly off the cars axis... looking from above the car, I twisted each coupler ever so slightly counterclockwise on its mounting pin. This should cause the knuckles on the two cars to stay better engaged in right hand turns. This seemed to help reduce the frequency of RUEs, but the slight twist did not completely eliminate the problem (too much twist might cause problems in curves, or make coupling/uncoupling more difficult).

    Second, I added one of the "truck restraining springs" supplied with the couplers to one axle on each of five (the last five in the train) of my seven cars (I will probably add a spring to one axle of each car, eventually), hoping to reduce the slinky effect. This seemed to have the desired result... slinky isn't completely eliminated, but it does seem reduced, and no RUEs since. Although adding the axle springs will reduce the number of cars that my FEF-3 can pull, I only have 7 heavyweights right now... and the FEF-3 easily pulls them all (with springs on 5) up the 1.8% grades on my main line . I doubt that I will ever pull more than 8 heavyweights, as that is all my spur passenger depot track can accommodate (and my main line just isn't long enough).

    Anyway, I thought I would share MY experiences... and that they might prove useful to others contemplating using Z-scale couplers to close couple. I am hoping that I have eliminated the random uncoupling. If so, I'll get another pack of 905s and swap out the couplers on my diner. I am NOT planning on swapping couplers on all my freight cars...manually uncoupling the 905s with a pick is a bit more difficult than doing the same with N scale couplers... and the freight cars are coupled/uncoupled much more often...
    Last edited by NDave; 4th Sep 2018 at 11:22 PM. Reason: spelling

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    I tried the same process with similar results: unwanted uncoupling, especially when there is any slack in the train. In addition, recoupling is difficult because the couplers tend to swing way to the side. The pins appear not to hold the couplers sufficiently tight to the underbody. I'm considering replacing the pins with screws, but I'm concerned about derailments on curves if the coupler boxes are not allowed to swing freely.

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