Yes

Yes - the front truck loses power once in a while.  When it does, only the wheels in the rear truck spin.

If I lift it off the track and put it back on, most of the time both trucks start working again.

What is the best way to fix the part you are describing?

the front truck loses power once in a while

If it's like my Atlas N locos there's only one motor so if the front truck stops turning and the rear truck still goes there's a problem with the driveshaft to the front truck or with the gears in the front truck..DaveB

Atlas Drive

Dave, There are actually several parts in the front drive assembly which may be failing mechanically. You can confirm this by taking the shell off and spinning the motor while applying force to the front truck wheels. If you feel any slipping you will have to take the frames apart to further diagnose the problem. Take a look at the exploded parts diagram for the SD-24 which can be found at N SD-24 Loco. As Azbaja indicated the Male Universal has probably failed, but I have also seen the Worm and Shaft Assembly slip and Gear Set in the Front Truck Assembly fail.

Some dealers carry parts, but I usually just go http://www.atlasrr.com/nparts.htm.

ps. If this is the first time you have taken one of these apart, you may want to take pictures of the disassembly.

Gentlemen, thank you

Ken - especially thank you for the detailed response.  I may get some time again today to take it apart and try your suggestions.  If not today, then definitely on Sunday.

In either case, I'll post my findings here.

Looks like I'll be ordering some parts

I tried putting some pressure on the wheels with my thumb while turning the motor, but nothing seemed to slip.  I also removed the trucks and put pressure on the wheels while trying to spin the gear exposed at the top, above the trucks, but nothing slipped there either.

While taking it apart, a small piece of debris fell out from somewhere.  It was very difficult to tell what it was made of.  It was about an eighth of an inch long and curled up.  I don't know where it was either.

I visited Atlas's site and was able to locate the parts in the exploded diagram.  I think I'll order everything on each side of the motor - they're inexpensive and it will be an interesting project to see if I can repair this thing.

I bought the engine about 10 years ago, but only started running it about 4 months ago when I completed the mainline on my new layout.  I had big plans back in 2003, but stuff happened and I wasn't able to do anything but plan, read, more planning and more reading until about a year ago.  It was the first n scale loco I bought, so I'd really like to see it going again (although I would trade it for a Providence & Worcester loco in a heartbeat!).

I'll update this when I'm able to stick the new parts in there.

Keep at it - You will get it running

I do not know where it was jammed but the odds are that the debris you found was blocking the front drive. Since the rear drive was still turning there must be some slip some where in the front drive. I would still suspect the front universal, so replacement is in order.

Additional note on slipping: although very rare there have been instances of flywheels slipping on motor shafts. Apply some opposing torque to the flywheels. If the flywheel is slipping it can usually be pulled off the shaft. Clean the flywheel and shaft, add a little CA inside the flywheel and carefully reassemble making sure that the CA does not get squeezed onto the motor bushing.

Can't help you with the Providence & Worcester, as I left or sold all of my stock when after 30+ years in New England I returned to my Southern Appalachian roots, railroads and rolling stock.

The parts came today!

I'm having great difficulty installing the Main Universal (#540104) on to the motor's shaft coming out of the flywheel. It's in a recessed area, and I'm afraid to ruin this little plastic part.

Is there a trick to that?

What's interesting is this is the first time I've taken the loco apart this deep into it.  When I took it aprt this far, the original Male Universal just fell right out as if it wasn't attached.  Looks like I found the problem.

My other question is what should I use to lubricate the parts?  Or maybe I'm better off just putting the rest of the original assembly back in there, which is already lubed up.

Thanks!

Male universal installation

Dave,

the male universal on the SD24 is the same as that on the Atlas H16-44. I've not had to replace any on my SD24s, but I've had to replace all the universals on my five H16-44s due to splitting (it is a known problem).

If you look closely at the universal you can see that the hole diameter is larger on one side than the other. That's the side to press onto the shaft. I use a small jeweller's screwdriver to position the universal, by sliding it down the screwdriver blade.  Then I press it into the shaft using whatever flat ended tool I have handy that will fit inside the recess. It does require a moderate amount of force.  I haven't destroyed a universal so far, but to guard against future failures I bought a pile of spares.

Regards,
Ron

Ron - Thank you!

Ron,

I didn't notice the two different hole sizes.  I will likely get a chance to look at it tomorrow.  I'll post back here when I have it done.

Thank you!

Tricks

Dave,

I would not call it a trick, but I hold the Worm Shaft Assembly (544103) vertically and place the Male Universal (540100) in the end of the shaft. Then holding the motor with the shaft vertical, I lower the motor down on the Worm Shaft Assembly / Male Universal group while gently rotating the motor with a finger. A third hand would help. The real trick is to keep the first Worm Shaft Assembly / Male Universal / motor group together while repeating the process with the other Worm Shaft and Universal. A fourth hand would help. They do snap together but not significant force should be required to get the parts together.

Since the type(s) of lubrication used on the parts as received is not known, I would not use the old parts or the new parts without first cleaning and lubrication. I use a very light coat of Labelle 108 Multi-Purpose Oil Light on the shaft and gear shafts. I use a very light coat of Labelle 102 Gear Lubricant or Labelle 106 Multi-Purpose Grease with PTFE on the gears.

The 'Ole 401 Is Back In Service!

Thank you all!!  

Ron - The hole being bigger on one side helped a lot!  Figures - I had a 50/50 chance yesterday I would have never known that.  I guess in the long run I'm better off knowing that than not knowing.

Ken - Getting me started and the taking pictures idea was a Godsend.  The most time consuming aspect (other than the cleaning) was figuring out the correct orientation of the plastic motor housing in relation to the decoder and pickups at the top.  The first time I put it back together I inadvertently bent one of those contacts over, so the engine would not fire up.  The lights worked, but the loco would not move.  I panicked a bit, took it apart and saw what I did and corrected the problem.  Rookie mistake.

I feel good about doing this.  Two weeks ago I would have thought this way beyond my capabilities.  I was about a minute away from driving to my favorite LHS about 45 minutes away when I made my first post in this thread.  Now I feel like a master craftsman!  LOL

Thanks again!

Sharing or the joys of having a Modeling Community

Dave,

Congratulations! Although I often spend hours alone working on projects (retiring independent contractor who mostly worked from home), I probably get as much joy out of the interactions (learning, teaching, confusing, pontificating, humbling) with other modelers as I do running trains. Participating in a community weather directly or online is always a rewarding experience.

Again, Welcome to the community.

Agreed

I've been on and off here for a few years.  I have a feeling I'll be more on than off now that I've accelerated my layout build.  It's a great community, and I'm looking forward to making some new friends.

I'm sure I'll have more questions soon enough!  I plan to contribute when I can as well.....

http://model-railroad-hobbyist.com/node/16960

You're welcome, Dave

You're very welcome, Dave.  And congratulations.

I've received a lot of help from online forums myself, and I'm pleased to be able to help somebody else out.

I struggled as well, the first time I changed one of these universals.  Now I've done 10, and all my H16-44s have since had decoders hard wired to them.  If another universal splits it will be a major challenge just to get to it.  In that event, I will probably resort to gluing the split universal to the shaft, as I've seen several people report success by doing that.

Regards,

Ron