Well, if wheels DO NOT rotate freely when you remove worm, that means that something inside gearbox is either damaged or moved from its position. Fact that when you install worm and use motor under power to move locomotive and it binds just proves what I wrote.
In any case, only the complete removal of wheels and dissasembly of gearbox (remove part 131), and then pull out all gears, remove all grease from gearbox and gears, inspect all and replace damaged with new one) wil lshow what happened. To do that, I am afraid it is too much for you. You managed a lot, but without a help from side (on spot, not on line), it is very difficult. It would be great if you could find some modelrailroading club near you or some modeller closer than me willing to help.
To post pictures, you must first upload them somewhere on the Internet - this forum does not offer service to upload pictures, as any other does not, only allows you to put a link to picture uploaded somewhere on the Internet. You must find some (free) service provider for that, I use German one but do not recommend it because it is in German (if you know German: link here. But there is one in English: https://postimages.org/
I am sure other members of this forum can give you good recommendation where to upload the pictures.
In any case, do not give up - find somebody who can help you nearby, because this locomotive is a beautiful piece of American railroading, and very probably, repair should not cost a fortune.
If gear(s) are broken and Athearn cannot provide them, either NWSL or some other store can help you. It is important though to know not only the teeth number, but also module (European term) or pitch (I think this is what you use in USA) and gear bore. I assume Athearn gears have 0,5 module/pitch. Such gears can be found here: https://shop.kkpmo.com/ It is store from Poland, but they ship worldwide (flatrate 6,15 Euro). There is one possible problem: worm gear (part 122) is in fact two gears in one - so if this gear is damaged, it is not easy to find exact replacement. But you can glue two different gears to make one, it is important to choose exact teeth number and of course, bore that is appropriate for that locomotive (hope it is 2 mm).
Hrvoje
The frustartion increases, no answer from Athearn. Not surprised!!
If I coud just figure out how to remove the frame and inspect the other gears,it would be so much easier to determine if there is damage.
But to no avail.....
Spalato68 One question: when you remove worm from gearbox, and put locomotive on tracks and gently push it forward - backward, do wheels rotate freely without any binding or hesitation? If yes, than you could assume at least that nothing has fallen inside when part of gearbox broke off. If this happened, this small piece could heavily damage gears inside and cause binding. It would be of course good if you could dissasemble the whole locomotive and inspect everything, which can be done, but is relatively complicated. If you look at the exploded diagram that you posted above, there are many parts when you unscrew the screws holding bottom lid that should be removed before wheels can be removed. So if you do it, be careful not to loose anything, especially two small springs (part 129). Also, it is good to make a photo before you remove some parts, to know how to put them back (or make sketch). Another question: after you repaired broken gearbox, did you try to put worm and clip back and try to move the locomotive (motor under power, carefully)? I just understood from your post that "worm gear is spinning" - but when? With or without worm at place? If it is spinning and worm is in its place but worm is not moving and you push drive wheels with your fingers to rotate them, that means worm gear is probably damaged. Btw - if you posted exploded diagram by yourself, than just follow the same procedure for any other picture you want to show here. Hrvoje
One question: when you remove worm from gearbox, and put locomotive on tracks and gently push it forward - backward, do wheels rotate freely without any binding or hesitation? If yes, than you could assume at least that nothing has fallen inside when part of gearbox broke off. If this happened, this small piece could heavily damage gears inside and cause binding.
It would be of course good if you could dissasemble the whole locomotive and inspect everything, which can be done, but is relatively complicated. If you look at the exploded diagram that you posted above, there are many parts when you unscrew the screws holding bottom lid that should be removed before wheels can be removed. So if you do it, be careful not to loose anything, especially two small springs (part 129). Also, it is good to make a photo before you remove some parts, to know how to put them back (or make sketch).
Another question: after you repaired broken gearbox, did you try to put worm and clip back and try to move the locomotive (motor under power, carefully)? I just understood from your post that "worm gear is spinning" - but when? With or without worm at place? If it is spinning and worm is in its place but worm is not moving and you push drive wheels with your fingers to rotate them, that means worm gear is probably damaged.
Btw - if you posted exploded diagram by yourself, than just follow the same procedure for any other picture you want to show here.
The answer to question 1 is no, they do not rotate freely they partialy rotate not a full circle when I put the loco on the track, if that is what you mean.
I would like to dissasemble the loco, but the instructions on the schematic are horrible.
I have gotten as far a removing the shell, but the damn frame (89) I don't know how to remove it!
Answer to question 2, I put the worm back on and tried to move the loco with power and that's when it spinned without moving.
If the worm gear is damaged, how do you know?
To me, it looks fine, but if I take a picture and show you, then you will know better than me.
Problem is that this website makes it difficult for novices like me to post a picture.
As I said before, I have tried in the past without success, why this website insists on this method is beyond me!
These are the instructions:
Whenever someone new joins the Forums, they often have trouble figuring out how to post a photo. Here's how.
Step 1: Prepare your photo. It should be saved in JPG or GIF format, and no more than 1 megapixel in size (approx. 1000x1000 pixels).
Step 2: Upload your photo elsewhere. You can't actually post a photo in a Forum message. What you can do is post a link in your message that calls a photo posted elsewhere. So you'll have to put your photo somewhere on the Web that's publicly viewable. Many Forum members use Imgur, Flickr, or their personal websites
Think about it, I have to create a link and post it somewhere on the Web that is publicly viewable?
Why?
It would be a lot easier for one to down load photo on the computer, then copy and paste.
Anyway, it would be so much easier for everyone to understand if
1. I post picture picture of worm gear to see if it is still good or damaged
2. try and figure out how to remove the frame (89) and post pictures of gears (122) (125) (128) to see if they are still good or damaged.
Very very frustrating!!
Overmod,
Your suggestions sound good, I would like to take a better look at the other gears, to see if they are still undamaged, problem is that I have gone over the schematic and can't figure out how to remove the wheels without screwing up the drivers.
Again, Athearn sucks at instructions as well! Bachmann much easier in my experience.
Also, I would like to post pictures of the worm gear, the loco and the other gears, but sadly, I have tried in the past without success.
As you all know, I am not that computer savy and still cannot figure out how to post pictures with this website!
I know that once you have a chance to see the pictures, it will be easier to find a solution!
So, this is where I am stuck.
Hawks RuleBad news even with cover on the worm gear still spins.
If you aren't averse to tinkering, you can carefully make up segmented bearings to 'bed in' at both ends of the gear tower, with flush thrust faces toward the worm at both ends that would let you use washers to control longitudinal worm position. I think a number of people here could talk you through how to make actual bearings for both ends of the worm that would make the 'snap-on' cover with its integral worm shaft hold-downs unnecessary for running.
If you can see any teeth on the driven gear, you can mark one with a pricked dimple or a small dot of paint; by rotating the mechanism you can count teeth until the marked one comes back into view.
Hello Everyone,
Here is an update on my FEF 4-8-4.
I managed to fix the broken piece with JB Weld and it is solid and bonded well.
Bad news even with cover on the worm gear still spins.
So, back on then Athearn website I went and guess, FEF 4-8-4 is discontinued and the only parts available are trucks and some gears.
Athearn is owned by Horizon Hobbies, so I went on their website, they do not sell part (126) gear box frame, no matter because I fixed mine with the JB Weld glue.
However, I was curious as to how much it would cost.
The type of worm gear part (123) which is made of brass is no longer made by Athearn, the only other type is a plastic one which looks different than the brass one.
I also checked out the other gears, Athearn makes two types one with 23 teeth and the other with 16 teeth and I have no idea which one is the kind used in my FEF.
I emailed them, no answer yet.
Spalato68 Try to call them, or write. What is offered on their web site is very probably not everything they can sell. But I would first try to repair broken part. It can be done except a part that has broken off has been crushed to dust. Hrvoje
Try to call them, or write. What is offered on their web site is very probably not everything they can sell.
But I would first try to repair broken part. It can be done except a part that has broken off has been crushed to dust.
I have spoken to them before, they sub contract out to a company called Horizon Hobby and they aren't that co operative!
Again,I think it is sad that Athearn cannot even handle their own servicing that they have to sub it out to a third party.
Anyway, I think I will try to fix it myself, if not it goes on EBAY for parts.
Thanks again for your knowledge and help Hrvoje.
Spalato68 Gearbox (126 - in fact, locomotive chassis) should be made of diecast (at least Atheran BB gearbox is) - so if this part is broken/about to brake, then you could try to save it with 2K glue (for metal is maybe the best). But I am not expert in glueing die cast, so somebody here probably has better experience. Again, part(s) that have to be glued must be completely degreased. Also, you must be very careful when glueing - if glue drops inside further, it can prevent proper functioning of gearbox, i.e. prevent free rotation of other gears, or worse - end on some gears inside, making gear unusable. Of course, the other option is to buy new part #126, but this could be very expensive. Hrvoje
Gearbox (126 - in fact, locomotive chassis) should be made of diecast (at least Atheran BB gearbox is) - so if this part is broken/about to brake, then you could try to save it with 2K glue (for metal is maybe the best). But I am not expert in glueing die cast, so somebody here probably has better experience. Again, part(s) that have to be glued must be completely degreased. Also, you must be very careful when glueing - if glue drops inside further, it can prevent proper functioning of gearbox, i.e. prevent free rotation of other gears, or worse - end on some gears inside, making gear unusable.
Of course, the other option is to buy new part #126, but this could be very expensive.
Hrvoje,
I just finished trying to find that part on Athearn's website and guess what?
They don't even sell it!
This company has become a joke in the world of model trains!!
The quality, especially for what one pays is crap!!
They irony is that they still sell the FEF 4-8-4 and the only parts they carry are trucks and a few odd pieces.
Unbelievable!
The original founder must be turning in his grave!
I have owned blue box locos for over 35 years and never had these type of problems.
They were easy to clean, easy to take apart, parts were well built and hardly ever broke down and they sold for 1/8 the price of the junk the Athearn now sells today!!!!
Think about this, 35 years ago a Blue Box Athearn engine was around $30-$40 and the quality was excellent.
That piece of crap, CHINESE made Athearn Genesis FEF 4-8-4 retails for over $500.00 and the pieces easily break!
What a joke!!! What a rip off!
I can take pictures of the worm gear and loco, but my problem is that I do not know how to download and send the pictures, again I am not that computer savy.
I have tried in the past and failed.
So, maybe someone can guide me as to how to do it?
The part of the gear box is cracked and ready to break off.
Hello Eveyone,
Looks like I found another problem which is probably the main culprit.
It is not the clip (121), it is not the worm gear or other gears, but it is (126) gear box!
If you look at the schematic, the worm gear sits into the gear box (126) one of the ends is cracked and about to break off, hence why the worm gear would jerk up and the clip would not stay down!
Hawks rule:
"Do you have a picture of this? I am curious as to how it looks."
Yes, it is first picture I posted - this is worm clip from Athearn FP7, but the principle is the same - but before glueing, you must thorougly degrease all parts because this small brass piece/shim must be glued perfectly - if it falls off and comes inside of gearbox, gears will be destroyed. The ides of this brass insert is that to make worm clip thicker, so it gently presses the worm bearing, and does not allow it to "jump", especially while worm is rotating at high speed.
If there is no mayor design error with this clip, than new one should do the job. I am still in doubt if wormgear has "survived" all that "jumping" of worm above it - it could happen that one or more wormgear teeth in this situation have been damaged (partially at least). Especially if worm is made of brass.
I would try with new clip - but first, you can try with brass wire as I proposed, and old, damaged clip. If there is a space problem when you use wire, than make space - maybe if you cut/grind some part of the locomotive upperstructure (inside), it will be enough for wire, and this part that was "treated" will not be visible from outside.
Kevin:
This guy makes amazing things. He is modelling military vehicles, he made a gun for one such vehicle from one piece of brass that was at least 5-6 mm thick at the beggining. Gun is just 1-1,5 mm thick at the narrowest part (thickness varies along the gun) and 2-2,5 inches long. So making such small bearing is "a piece of cake for him". Bearings have outside diameter of 4,25 mm, while inside diameter was custom made for each worm (bore for Life Like worm and bore for new brass Athearn worm do not have the same diameter). Bearings for Life Like are slightly wider than for Athearn Genesis, so they also do not have the same width.
I really do not understand why Athearn is selling really excellent brass worms with bearings that have bore too big for their worm shaft. Probably most users do not notice this noise because motor noise is usually louder, but as I replaced original motors with coreless ones (practically silent), noise coming from worm asembly was very noticable. Now, these locomotives just glide on tracks (especially Athearn).
Spalato68It was not easy to find someone to make new bearings for me, but I found one fellow modeller with appropriate machinery, so it was done.
Hrvoje: Thank you for sharing those pictures of fabricating the bearings. That is amazing.
-Kevin
Living the dream.
Hello Hrvoje,
Thank you for your input.
I have a strange feeling that even if I order a new clip, the same problem will persist. Before I removed (121) clip, the Loco was still jereking when I applied power so buying a new clip, is futile.
I like your suggestion of using thin brass wire and wrapping it around and twisting it until it gently presses the clip tabs.
You also suggest "If second is the cause, you could glue a small piece of e.g. brass sheet of appropriate thickness, to stabilise "wobbling" worm bearing. I had to use this method in my Athearn Genesis FP7"
Do you have a picture of this? I am curious as to how it looks.
Also, maybe it is the worm gear, but when I inspected it, it looks normal and not damaged unless as you state "it is because worm bearing is smaller than the place where it is positioned"
Great pictures by the way!
I would first try to replace damaged clip with new one, so I would order one (or better, two, just in case). Then, if worm is still jerky, you should find the cause: is this happening because clip is not firmly held in its place, so it allows worm to raise from its position, or is it because worm bearing is smaller than the place where it is positioned i.e. the whole worm/bearing assembly is not held firmly in its place, despite clip is firmly in its place?
If first is the case (clip is not held firmly), you could try to solve this using thin brass wire and wrapping it around, and twisting it until it gently presses the clip tabs. Very gently because you do not want to deform the whole assembly, or crack the clip tabs.
If second is the cause, you could glue a small piece of e.g. brass sheet of appropriate thickness, to stabilise "wobbling" worm bearing. I had to use this method in my Athearn Genesis FP7, and one Life Like E9, beside making new bearings for worm shafts or both locomotives, because in both cases, there was also too much play between worm shaft and related bearing. I used brass sheet approximately 0,1 mm thick. You need to experiment here, because if sheet is too thick, it will cause worm to be pressed down too much. After this procedure, noise caused by vibrations of worm in bearing and bearing in gearbox completely dissapeared.
I doubt that there is so much play in shaft bearing to cause your problems, but I raised it here because it can contribute to jerkiness/vibration of worm shaft, which can cause noise.
I do not have your locomotive, but have Athearn Genesis Big Boy, and must admit that this locomotive performs excellently in this department - no wobbling, jerkiness of worm or any other part of drive train. This locomotive has more precise drivetrain compared to e.g. Athearn Genesis F7's / FP7's I have. In FP7s, I even discovered that bore of idler gear is not absolutely centered, i.e. it is positioned off center of a gear. Not much, but noticable with naked eye if you put locomotive upside down (without a shell), remove bottom cover and observe movement/rotation of gears inside gearbox after connectiong power to motor clips.
You can check when you receive new worm clip if worm/worm clip is sitting firmly by grabbing worm shaft coming out from gearbox with tweezers and trying to move it a bit. If there is no excessive play, shaft should not wobble.
In both locomotives I have, shaft (and worm) wobbled considerably. When I removed worm out of the gearbox, I noticed the same with worm bearing and worm shaft.
It was not easy to find someone to make new bearings for me, but I found one fellow modeller with appropriate machinery, so it was done.
Brass tabs glued with 2K glue on worm clip (Athearn Genesis FP7):
Making new bearings:
New bearings for Life Like worm:
New bearings for Athearn worm:
Hello Lastspikemike,
Your suggestions sound very good, but I think space is an issue and gluing is not a good solution, and like you say "You'd need to preserve removability" in case one would have to remove or repair a gear.
I thought of just ordering a new (121) clip, but I don't think it will stop the worm gear from jerking up and will leave me with the same problem.
The Loco itelf has a very poor design for the worm gear and the quality of the plastic model is sub standard!
I tried reversing the cap as you suggest and the same outcome.
Drilling might work, but limited space is also a problem.
If only Athearn had designed a better way, for such an expensive model, this would not be happening.
Overmod Some of the highest force in this drive is exerted by the worm longitudinally on the teeth of the gear it drives. This force tries to push the worm longitudinally but also up. The only thing resisting this upward push is clip 121. First thing to check is that all four of the little plastic 'teeth' that hold 121 on are firmly engaged. If one corner is not solid it will try to lift there and perhaps push off the other tab on that side. Check to be sure you don't have 121 on backward if its ends are different If the tabs got sheared off, rounded or deformed at some point, you may have to carefully drill holes for short pins or screws or for pieces of plastic to be solvent-welded and filed to shape. Others can advise you on best ways to set up to do this. I have never liked models with those one-piece side rod assemblies -- they bind with even slight difference in relative quarter, and binding is what puts greatest upward resultant force on the worm. I would be tempted to think about some method of making more positive 'journal' retention of the worm shaft at its bearings in the tower. I can think of a couple ways that could be tried; perhaps some on here have actually had to do such a thing.
Some of the highest force in this drive is exerted by the worm longitudinally on the teeth of the gear it drives. This force tries to push the worm longitudinally but also up. The only thing resisting this upward push is clip 121.
First thing to check is that all four of the little plastic 'teeth' that hold 121 on are firmly engaged. If one corner is not solid it will try to lift there and perhaps push off the other tab on that side. Check to be sure you don't have 121 on backward if its ends are different
If the tabs got sheared off, rounded or deformed at some point, you may have to carefully drill holes for short pins or screws or for pieces of plastic to be solvent-welded and filed to shape. Others can advise you on best ways to set up to do this.
I have never liked models with those one-piece side rod assemblies -- they bind with even slight difference in relative quarter, and binding is what puts greatest upward resultant force on the worm.
I would be tempted to think about some method of making more positive 'journal' retention of the worm shaft at its bearings in the tower. I can think of a couple ways that could be tried; perhaps some on here have actually had to do such a thing.
Thanks Overmod,
You are right I don't like the way this one-piece side rod assembly cover method as well.
After further inspection, one of the teeth is broken on clip (121) and I have reason to believe it was always broken when I bought the model, hence the Loco jerking and the worm gear spinning!
Athearn' quality is horrible as to the way this model is made.
The model's plastic is thin can easily break and this is the price we pay when manufactures insist on having products made offshore.
NO QUALITY CONTROL and poor craftsmanship!!
Hopefully, there is a method to fix this, as I mentioned before all the gears are not damaged.
Spalato68 Well if you cannot remove it, better wait until hobby store opens and then ask for help. If you could observe, it would be valuable. You advanced a lot during this past few days, I am sure what you have learned will be useful in the future. But this is a big step, to dissasemble such locomotive, so take you time. And report to us when UP FEF finally starts to roll! Hrvoje
Well if you cannot remove it, better wait until hobby store opens and then ask for help. If you could observe, it would be valuable. You advanced a lot during this past few days, I am sure what you have learned will be useful in the future. But this is a big step, to dissasemble such locomotive, so take you time.
And report to us when UP FEF finally starts to roll!
Well after a few months of trying to solve this problem and model train stores still not open due to Covid, I decided to take your advice and tackle the issue myself!
1. I checked the gear on driving axle first, in case it was damaged. I removed bottom cover (197), held by 4 screws. It wa not damaged
2.Then I removed the gear box cover (121) held by two clips, I checked (123) worm gear made of brass and it was not damaged.
All the other gears (123) (125) (128) are not damaged as I moved by hand the wheels and they turned.
When I put the gear box cover (121) back on, I put the loco on the track applied DC power by putting one pin to the blue wire and the other pin to the yellow wire on the PCB.
The worm gear spinned , and the cover (121) jerked up and the loco did not move.
As soon as I put my finger on the cover and pushed it down the loco finally moved!
So, is the problem the cover (121) that does not keep the worm gear down and if so how can it be secured?
Thank you.
I will keep you updated if anything were to change.
I did step 1, "check the gear on driving axle first, in case this is damaged. This is easier to check than any gears below worm. To do that you need to remove bottom cover (197)" Everything looked ok.
step 2, remove cover 121, no such luck.
I can't get it to budge, for fear of breaking it!
Athearn, diagram not user friendly, to say the least.
Looks like I have reached the end of the line!
Will have to wait, until the hobby store re-starts the repairs.
Again, if I were more adapt to electronics and understanding of model trains, it would not be so hard
But, I am not!
Thanks to everyone for your input and help.
It was an experince and a lesson well learned.
Yes, it has a strong smell after hydrocarbons. It is impossible not to recognize it. Therefore, when I got corona virus but was stll not aware of it, I immediately knew something is wrong, because my smell was 100% switched off - I cleaned something with it, and did not smell a bit. Luckily, that was the only what was wrong, and after 4 days it started to come back - I used Algorex as an indicator that my smell is coming back - very slowly, though.
Yes, it can be found on ebay, but maybe somebody is selling it in the USA. For around $7.5, it is at least worth to try.
Here a technical info can be downloaded (in German): https://www.meyer-chemie.de/wp-content/uploads/2019/03/TI_ALGOREX_Silicon-Entferner.pdf
Google transaltor (purpose and hazards):
ALGOREX silicone remover is a high-quality cleaner with a short evaporation time for the complete removal of silicone oil residues, fats, oils and waxes in particular from lacquer or sheet metal pores before painting.
Hazard warnings:
Highly flammable liquid and vapor.
May cause drowsiness and dizziness. Can be fatal if swallowed and enters airways. Toxic for aquatic organisms, with long-term effects. Repeated contact can cause too brittle or cracked skin.
Seller "industriefarbe" on eBay has the silicone cleaner from Meyer Chemie ("Algorex" is their product-line tradename; unrelated companies also use it) for just over $7.50 ... the kicker is likely to be S&H to the United States.
I have not yet been smart enough to find the MSDS on this in English, although I have for other Meyer Algorex products and I'm sure it exists, perhaps searchable by the correct edit in the URL. Here is the German version: it indicates among other things that it principally contains a hydrocarbon with "7 to 9 carbons" combined with up to 10% acetone.
https://www.meyer-chemie.de/wp-content/uploads/2019/03/sdbALGOREXSilicon-EntfernerDE.pdf
Randy, I used dish soap and warm water always - until a friend draw the attention to a product I have shown here. It is remarkable stuff, and I think it is impossible that more or less the same chemical cannot be found in USA. The advantage over soap and water is e.g. if you have old locomotive, hardened grease, and gearbox not easy to dissasemble. In such cases I use a small brush, soak the whole gearbox and just wait until all gunk comes out - gears although plastic, are not damaged. Then I use Labelle and that is it. You cannot do that with a soap - or, you can, but, water and soap will not evaporate quickly and maybe some soap will be left. This thing evaporates in several seconds. I also occasionally used paint solvent - but, it attacks plastic & color, so it must be used quickly and then washed out. I use it also when I want to paint something, e.g. locomotive wheels or some plastic parts. Wheels are usually greasy, so they must be cleaned before painting, or paint won't stick. I just use a brush, wipe the surface to be painted, and in half a minute it is ready for painting. I simply did not find until now any disadvantage of this - except, of course, it is chemical, so it must be used with caution, as any other chemical, like e.g. solvents.
I'll admit I don;t hang around auto body shops, but I don't recall seeing a product here that claims to do the things that stuff does. Could be very useful. Warm water, some dish soap (especially Dawn brand) and a toothbrush have usually worked for me to clean gears back to bare plastic. And that very Labelle kit is something every modeler who actually runs trains should have in their toolbox. Your local shop should have it. Some newer brands make all sorts of claims, but Labelle is tried and true, they've been around for a long long time. And even their lighter oil in there, meant for bearings, is just sticky enough to not get thrown all around the inside of the loco (as long as you don't glob it on) so it stays in place and does its job. Unless they've changed the packaging since I bought my last pack, it explains briefly what the different weights of grease and oil are for, if you aren't sure which you'd use for what. So despite it being oen of those most annoying heat sealed packages, carefully cut around the outside to avoid tearing up the orange card since it has some useful information on it.
Too many new locos come with either no lubricant, or way too much. ANd when one has been sitting on a shelg for 10+ years, anything can happen. It's not unheard of for time-hardened grease to prevent a loco from running, but even when they do run, you don't get the best out of them without cleaning out the old gunk and adding a proper amount of fresh.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
You may check the gear on driving axle first, in case this is damaged. This is easier to check than any gears below worm. To do that you need to remove bottom cover (197), which is held with 4 screws.
Before you start, prepare some jars or similar where all small parts will be stored - to prevent losing them. Observe small springs under driving axles (129), be carefil not to lose them.
Also, if you do not have it, you should make a foam cradle, to be able to hold securely your locomotive - especially when it is positioned upside down. This can be done from foam sheet (at least 1 inch thick) and scalpel (to cut a "groove" in the middle), as shown on picture below. That is my Trix Big Boy, it had to be opened just to replace ugly yellow SMD for fronth light with something more appropriate. Observe also small white plastic box - this is originally used for spread cheese, now it serves to keep small parts from being lost
If drive axle gear is ok (probably it is, but why not check this first), then you must dissasemble the locomotive so far until you can remove both worm and side gearbox cover (130) that Randy mentioned earlier. This cover is held by two clips of top clip 121, but also with one screw (130). Make some sketches, photos and observe exploded diagram. Do not use excessive force, especially with small plastic parts. Top clip 121 has four small clips, you have to spread them but not too much - use toothpick to keep them in position while working on another one.
When all gears are out, and broken identified, all that are intact should be completely cleaned (including worm). Not just because grease/oil is old and maybe hardened, but also because it can hold/hide debris of broken gear, which can again destroy new gear(s) when installed. At first, you can use ordinary paper kitchen towel to carefully wipe and clean all gears (and gear box as much as possible - for that use some pointed object but not extremely sharp and wrap a part of paper towel around it to clean the gear box). Then you can use old stiff brush or used toothbrush to more thoroughly clean all gears and their teeth. If you want to completely remove any trace of grease/oil, you could use some chemical that is used for such purposes, applied with a brush. I use this, but it is probably not available in the USA. It is used to prepare car body for painting - it removes any trace of grease/silicone, and penetrates and cleans very deep into material. It does not attack plastic or paint, which is a great advantage for your (our) purpose. I am sure similar stuff but under some other name is available in the USA. Here 1 litre costs less than 10 dollars. I use it also to clean wheels/tracks. Despite those were already cleaned with alcohol, it removes even more dirt that was not visible on cotton ball used for cleaning with acohol.
Hope this helps, and report your progress!
P.S.
I forgot to mention, after all gears / worm is cleaned and new gear arrives, before you install them, you should oil all gear shafts and worm bearings, and apply a small amount of greas on all gear/worm teeth. I use Labelle, this set is excellent choice (it will not harden with time):
You can use the same oil for driving / trailing wheels, linkage etc.