Tony and of course all tuned in, On straight and level track the train rocks back and forth or oscillates while in motion...right? Tony, I will conceed you have a point. Exaggerated movement can be a problem. Physics 101: For every action there is an equal and opposite reaction. Looking at what you indicated and adding a few Ie., 1. Track isn't truly level. 2. If you inadvertently slowed or increased the speed of the train and returned it back to original setting. 3. Dirty track momentarily stalling the locomotive. 4. Track out of gauge causing a restriction. Each of these could contribute to the rocking, floating back and forth, or an oscillating action described as "Slinky". This is still within the realm of "Slack". Remove all of those issues and if you find the train still slinks around the track then "I would agree...with you". The action and reaction of the MTL's may indeed be over exaggerated. I will conceed that much. You may actually see an accordion effect as a train gets under way due to a fast start and it may take a while for the train to level out. I was just thinking about the protoypical loads that would normally cause drag. Most of our train cars are weighted equally so the drag that is normally there with the big boys isn't with ours. I've watched ATSF and SP trains traveling up and down the San Joaquin Valley or state highway 99. I've stopped under a eucalyptus tree to catch a lunch and watch the trains go by. Many a time I've noted slack movement within the train. Unable to detect any real cause Ie. Train speed reduction, hot box, wheels a wobbling and etc.. Until I looked down the track and found it wasn't level. Regarding most modular layouts...with one exception, I've yet to find level track on any modular groups layout. Thanks for the comeback and I will be watching for the action you have described the next time I catch a club layout in action. I really must install a spur line into a new grainery. Shippers are tired of hauling grain in by truck...grin! Tony, Thanks for the comeback. Edited add on: Rather then start another thread I decided to add these comments here. I realize this may seem somewhat diluted to some and just because a bunch of guys are jumping up and down and yelling about a slinky doesn't make them right. As far as I'm concerned it's a bunch of nonsense! I realize to that in some circles this makes me the apparent idiot and I'm seen as the dummy. I have some suggestions for you. May I suggest we go back and revisit a prototype coupler pocket. In the past as well as today there have been springs built into the couplers to cushion the "Slack". Santa Fe's shock control added a strut shock to help reduce the slack. Train cars, couplers and slack have been together ... from the start. The Brit's used two bumper pads on each side of the cars to reduce the slack. Conductors pulling duty and riding in the cabooses of American trains complained about the slack and said "It never stopped". I shared here in an earlier thread about a incident involving my great uncle a conductor for the Santa Fe railroad. You can look it up by searching my handle and posts. Slack isn't something that happens inside the knuckle coupler it actually occurs in side the coupler pocket. The springs will stretch as the train gets underway and crimp up as it comes to a stop. Rollover a gentle hill and the "Slack" will stretch the train and then pull it back in. Get acquainted with the real thing and I promise you...you will understand the action you see. This is an age old problem. One the real rails have tried to solve. I vote we leave the slack alone.