Low hanging truck frames on Intermountain FT's

[Cajonpassfan]

Thanks, guys, for the enlightened conversation, drawings and theories
As luck (and good customer service) would have it, today I received a very nice and professionally written note from Intermountain. They are sending me a couple of replacement trucks, free of charge. Unfortunately, there are no other replacement parts available until the next run of FT's arrives in (hopefully) not too distant future. Rather than messing around with repeated fixes, I think I will just replace the trucks, and go work on the layout. Especially since the price is right...
Otto K.

[peteski]

I had the same very positive customer service experience with IM as far as getting free replacement parts, but then I had some not so positive experience with the AC-12 I sent in.

So, are the new trucks any better than the old ones, or are the still low-riders?

[Cajonpassfan]

Well Peteski, I guess we'll know when they get here...

[peteski]

Well Peteski, I guess we'll know when they get here...

Duh!  I don't know why but I thought you already received then. So much for carefully reading posts... 

[Cajonpassfan]

Lol 
Well, here's an update: I did receive a baggieful of replacement trucks from IM, but only three are new, the other four have the same "low hanging" sideframe problem.
Couple of them I was able to improve by filing off the little suspension nubs protruding below the flat floor of the truck, just enough to clear the rail, see pics. It certainly helped with the clearance/dragging issues. So far so good...
Otto K.

[peteski]

So, by examining the good and bad trucks can you see what exactly causes them to hang low?

[Cajonpassfan]

Well Peteski, not easily. The lateral cross section of the sideframes casting forms a wide "U" shape only connected at the ends of the casting with thin bars. It appears that the top of the "U" at the pin is being spread outward and the plastic doesn't have enough substance to stay put. The result is that the little nub at the top of the "U", which should fit snugly under the pickup contacts, has a gap (see pics) even when the assembly fully "snaps" together. Could it be the plastic "U" simply gets tired after some use?

The pics below attempt to illustrate the problem. The bad black truck on the left, gray truck on the right, beginning to fail. A good new truck in gray.  I also disassembled the bad truck and measured the bottom and top of the "U" and there's definitely a bit of a spread. The fact that the inside bearings are grooves rather than dimples doesn't help, see last pic. Forgive the quality of the pics, the iPad doesn't do well with close ups...
Otto K.

[peteski]

Curious.
But there are dimples at the bottom of the grooves in the inside of the sideframes for positively locating the bumps in the pickup strips.  So in theory the bumps in the metal bearing/pickup strips should be retained in the correct location by the dimples in the inside of the sideframes.

I still suspect that the axle length on the low-hanging trucks' wheelsets is shorter than on the trucks which are good.  Didi you measure the total axle length of both proper and low hanging trucks?  The way I see this is if the axles aren't long enough then they don't push the bearing/pickup strip's bumps deep enough into the sideframe dimples.

Even if the problem is caused by the plastic sideframes being spread out more than they should be, lengthening the axles should fix the problem by properly pushing the bearing/pickup bumps into the sideframe dimples.

[Cajonpassfan]

Curious.
But there are dimples at the bottom of the grooves in the inside of the sideframes for positively locating  ....
.......  the axles aren't long enough then they don't push the bearing/pickup strip's bumps deep enough into the sideframe dimples.
.... lengthening the axles should fix the problem by properly pushing the bearing/pickup bumps into the sideframe dimples.

Peteski, allow me to paraphrase a very old chocolate ice cream joke: there ain't no "f" in dimples!
Sorry about the lousy photos, so here I took another one. As you can see, there are no dimples, and perhaps that is the problem. Maybe I'll try to epoxy the brass strips in their proper place, although it's hard to glue anything to engineering plastic (Delrin?) the sideframes are made of... It would be so much easier to be able to obtain new sideframes. [ Guests cannot view attachments ]
Otto K., not having much fun with this ...

[peteski]

Ah - got it!  I thought I saw dimples in the other photo. I no clearly see that there aren't any.    Now I see how that can be an issue.

I really need to dig my set out of storage and check those trucks out.

[GaryHinshaw]

That slot looks like a flat-out design error.  Do the good trucks have dimples instead of slots?  Do the side frames mechanically attach to the gearbox at all, or just via the wheels/axles?  If the latter, there is nothing holding them up but friction.   

[Cajonpassfan]

Not quite just friction, Gary, the bottom plate (with sideframes attached) "snaps" into slots at the ends of the rounded truck frame. Unfortunately, the thin plate is only attached at the center and isn't strong enough to keep its shape near the ends, the ends flex upward under least pressure. And yea, all trucks are like that...good and bad.

[central.vermont]

Just out of curiosity has anyone tried simply swapping out the IM trucks and putting in Atlas GP7/9 trucks?
Otto, have you tried this?
Jon

[mmagliaro]

Can you take a close-up shot of the UNDERSIDE of the truck, completely assembled.   I want to see where
the gears poke through.
It looks to me like you could drill and tap a couple of 00-90 holes right through the cover and into the rest of the truck,
and put some screws in there to hold that whole cover up and off the rails.  I don't think I like the idea of glueing the
contact plates into the sideframes.  I tried that on an engine once and while it works (I used Walthers Goo, so it would
stick to the Delrin), the plates and wheelsets can't float as freely as they should and it didn't run as well, so I backed out
my glue attempt.

By the way, I've got some Kato F7's that had this exact same problem.  Even though the truck design is different,
the little tabs and other hold-on mechanisms for the truck
cover just have a little too much give in them and they let the sideframes sag enough to almost touch the rail.  I took them apart
and snapped everything back together firmly, and it was better, and it works, but I try to avoid touching the trucks when I
rail the engines because the sideframes won't tolerate much squeezing or other fussing before they work loose.

[Cajonpassfan]

Max, an interesting and creative idea. I'm not sure there's enough meat in the truck frame to accept a screw...it's pretty lightweight. And the bottom plate is quite thin to countersink a screw in. See pic below.
Jon, if the Geep trucks would fit that would be great, I just don't own any....is this feasible, anyone?
Thanks, Otto K.