Sunset 3rd rail drive repair? FP7 and running the A and B together under TMCC?

Where are the cover plates that fell off? ….how are they attached to the truck? …….that’s step # 1,….then we’ll look into your running issue,…..my philosophy is always fix known problems first, then see what the locomotives do.

Pat

What ^^Pat said.  It's possible that the gearboxes were loose all along.  Lack of proper gear mesh would definitely impact starting / running characteristics.

You probably know this, but before attempting to run locos in an MU configuration, it's best to place them on the same track separated by a foot or two, and gradually advance the throttle until both units are moving smoothly.  I would test in conventional mode first, in case one of the locos isn't reliably receiving the command signal.  I'm not sure what boards were in those.  But if there's a momentum setting, I would set it to "low" in both locos for the initial test.  Observe the starting characteristics and any speed difference as you increase the throttle.

If one of the locos hesitates at start-up, it could have a mechanical bind.  Take the shell off and turn the flywheel by hand for 15-20 full turns, you should be able to feel if it's sticking.  It might also be necessary to separate the lower drive shaft and check each truck separately.  Check for rubbing brake shoes or debris jamming the wheels.

If the issue is some sort of programmed starting delay, or the on-board circuitry is getting out of synch with regard to forward, neutral, and reverse then it might be preferable to power both units from just one of the TMCC boards.  These are single-motor units if I recall.  Of course you would have to add a tether between units.  But I imagine that you wouldn't ever run the B unit by itself.  And by tethering, you would never have to sync them again!

If you do the test, perhaps you could post a video.  In any case, don't give up, let us know what you find!

I have the cover plates and screws that fell off the inside axles,   you can see them still attached to the outside axles. 2 very short screws hold them on.

OK I will take them apart and look further. Will that TMCC board run both motors they pull a lot of amps?

Thanks for tips. Will take a look tonight.

Like I said, I'm not sure what boards were in those.  I would definitely encourage you to measure the current draw before attempting to run both from the same board.  There are potential workarounds to that challenge.  But the first step is getting both units to operate smoothly and reliably.

You might be able to temporarily disconnect ALL of the electronics, and run the motors from a 9V battery to verify that the drivetrains are mechanically sound.

OK so I got some time to work on these. I took the shell off the B unit and found that there were only 2 screws holding the body on though 6 holes for body screws. I found that all the screws holding the gear covers on the outer 2 axles and  the trucks together were partially un-done or loose not tight. None of the screws were tight. When I checked the A unit all the screws were tight. Note this B unit was produced 2 years after the A unit.

I took apart the trucks, outer axles gear cover plates and center rail pickup rollers mount to the trucks. I found 1 wire on one of the trucks center rail pickup had broken off, I re-soldered a more flexible wire to it as the wires included were a bit stiff. I found that the axles have blunt ends and the side frames hold them in place. The drive line with worm gears that turn the axles are free floating (see photo below) and the gears sit on top of the axles and the only thing holding the axle gears to the worm gears are the bottom cover plates held on by 2 very tiny 2mm screws, so if you have one of these check often to make sure they are tight if they are not your gears could slip. I could see no damage to the worm gears or the axle gears. After properly attaching the gear boxes, cover plates and side frames all together and making sure all screws were tight I tried turning the motor over by hand, comparing the A and B units. They seem to both have the same amount of resistance either A or B unit when turned over by hand. No binding or sticking in an part of the rotation.

When run on the track the A unit runs fine. The B unit now is not running well, some noise from the motor and runs slower? Will tinker with the B unit further and see if I can figure out if it is the motor or TMCC board? Thanks for any further tips!

I took the motor leads off the TMCC board and wired them to DC power pack with an amp meter. I get 2 amps at 8 volts DC and looking at it upside down could see some wobble and noise from one of the U joints . On further inspection found the U joint on one end was loose and the helmut shaft could be slipped out of the spider joint easily.  Here are photos of the U joints and shafts to trucks on either end. There does not look to be much metal holding these on.

Will have to seek replacements. I see a variety of plastic parts on NorthWest Short Line or the Weaver plastic parts at P&D sites, any where else there are parts. Any where that carries replacement metal parts to match the 3rd rail drives? Thanks for any tips.

Perhaps will ask the shops listed on the 3rd rail out of warranty repair page.

Scott at 3rd Rail was aware of the tapping noise, etc.  Improvements were made in later production runs to address these problems.  I would give 3rd Rail a call, and see if they have an improved 2nd-generation part that's a bolt-in replacement.

Some newer model F7s got ball-bearings in the truck sides to hold those blunt axle ends.  It's a low-speed bearing so I don't know how much difference it makes in the operation.  Have a conversation with Scott or his parts guy, see what you can learn and post back.  It seems like you're close, don't give up!

If you’re not able to source parts from 3rd Rail for the busted driveshaft, look into RC car telescoping driveshafts ( constant velocity type ) …..you’ll have to figure out collapsed, & extended lengths, and input & output shaft OD’s to get the right sizes, but there’s a lot of different lengths, and ID’s to choose from. I use these a lot in steam locomotives , and they’re especially handy for broken universal drive shafts in articulated steam, ……especially when stock parts are NLA…

Pat

Here's an old thread from the 2-rail O scale sub-Forum that might have some relevant info:

https://ogrforum.com/topic/sun...7#149239177502502347

Thanks for the suggestions, and interesting link to the topic. If I can-not find an answer or parts will just save these engines as a shelf display and continue running my MTH engines; I have always found the MTH design superior to most; robust and reliable and easy to get replacement parts for the very rare problem. I have an extensive fleet of mostly MTH and they have run many miles/hours with never a drive problem on any of my MTH engines.