![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1232636;image)
Maybe I was not quite clear enough with my words. It connects the differential TO the front drive shaft. It is actually this cup:
I assume that it is impractical to drill out the screw shaft and re-tap the cup. Otherwise, the tinker-dwagon would have suggested that? It certainly is a frustratingly small size to work on. I assumed for 2WD, I would have to go in and remove the loose 12T gear and its bearing. Then on the other side, remove the front drive shaft so it is not flopping about.
Sorry; that was in part my fault. The exploded views I'd been looking at show that cup having a D-cut shaft... or maybe I got that mixed up with pics of the rear diff in my head. ![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
Yes, it is impractical to tap/drill; those cups are usually hardened for wear resistance nearly to the point of embrittlement. While in some cases this is case-hardening that doesn't extend to that shaft area, I wouldn't dare count on it. My first line of attack would be to scribe a slot in the end of that screw stub, then apply heat and use a very small flat-bladed screwdriver to try and back it out.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1232655;image)
Dang... you are in a bit of a pickle here. On mine, the grub-screws (0128) in the driveshafts right at the spur gear (0015) were tight as hell, and had CA rather than LokTite. Getting them off may require enough heat to damage the spur gear.
My gut reaction is... (contrary to my previous warning aboot dismantling the "CV" joints) that since they sell these parts with that joint disassembled, they've made them to be disassembled/reassembled. If so, the course of action least likely to cause more damage will be to dismantle the "CV" joint above and those in the front wheel axles.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1232657;image)
You'll need to remove the radio electronics (they're zip-tied and held down with very sticky double-faced foam tape) and remove the top plate (this means also dismantling the front shocks from the plate to get to the screws that hold it down) from the chassis and unscrew the long screw that goes down through the steering rack slider assembly. It's more work than popping the steering rod loose from the servo or rack, but you want to avoid that as they get loose very quickly if you do pop them, even once. Then remove the spur gear cover.
Then you can take the spur gear and both driveshafts out to work on it. You'll need to work the spring retainer (0127) around the body of the ""CV" joint (0083) like a circlip; try to avoid stretching the spring as that will ruin it. There will be a thin pin (0072) that goes through the joint under that spring; press it through and then you should be able to remove the dogbone shaft (0082).
Watch out when disassembling that joint; there will be a bushing (0079) in the middle of the ball that will try to fall out and roll into the nearest HVAC register (0no0no0mygawdn0), never to be seen again.
Once you have the parts all baggied up for later, you can reassemble the center chassis of the car, then remove the front wheels, unscrew all 4 kingpins, then remove the front axles and dismantle those "CV" joints. Leave the front gearbox alone until you have repair parts on hand.
Actually, while you have this area all apart, I recommend you inspect the main chassis plate very carefully with a flashlight around the back of the front gearbox, servo mount and the spur gear housing. The nature of the damage I'm seeing here suggests to me that this car was run head-on at high speed into something very hard and solid like a wall or curb. You may find hidden damage that really necessitates a rebuild on a new chassis plate. ![Embarrassed :-[](https://www.eevblog.com/forum/Smileys/default/embarrassed.gif)
Cheers!
mnem
![Tweak :-/O](https://www.eevblog.com/forum/Smileys/default/smiliey_cal.gif.pagespeed.ce.yYMcAvxBJk.gif)
I got around to taking a closer look at this the other day.
The theory of head-on collision damage is certainly valid. However, on inspection I saw no further signs of such damage. The broken part is inside the chassis, so I do not understand how an impact could have been focused here. It could be my understanding is wrong in a freak crash.
Do note that the damaged LED lights do not support a crash. That damage was from extracting the truggy from the flower bed by pulling backwards and having the light bar caught in the plant stems. (
Didn't your papa teach you anything? Oh wait, I am papa in this case...)
When I inspected the affected parts, I noticed first thing that the screw used does not match the parts list. This screw that sheared has a hex cap head or a torx head. Most likely it is a torx head. The one in the parts list has a Phillips head. It is too small for any tools that I have (or is that an excuse to go tool shopping for more screwdrivers again), and starting to get too small for my eyes. Unfortunately, the field of view with the camera macro lense is a bit too shallow in the photos I took.
![Test Equipment Anonymous (TEA) group therapy thread](https://www.eevblog.com/forum/index.php?action=dlattach;topic=81471.0;attach=1234326;image)
What can be easily seen is liberal use of CA around the screw head. My theory, and feel free to debunk it, is the load path was changed by use of the CA glue. With the strong glue, the load path became cup-screw-gear. The normal load path would be directly cup-gear, and the screw is only to retain the gear in the cup. If the screw was unable to handle the loads, since it was not intended to do so, then it sheared under torque. It certainly looks possible when looking at the photo in the earlier post showing the broken end of the screw inside the end of the cup.
EDIT: earlier post is this one:
https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3599403/#msg3599403All that aside, I still need to fix the truggy. The cup needed is not available for sale on its own.
However, the differential cups are available. The needed cup is 1 to 1.2 mm longer than the differential cup, shown sliding one into the other. Looking at the wear marks on the cup from the driveshaft dog-bone, it looks like a shorter cup should not be a problem.
![Test Equipment Anonymous (TEA) group therapy thread](https://www.eevblog.com/forum/index.php?action=dlattach;topic=81471.0;attach=1234328;image)
I would like to know what the tinker-dragon thinks about this as an alternate part:
https://www.aliexpress.com/item/32764836662.html?spm=a2g0o.store_pc_groupList.8148356.23.17666925MS3CKaIs this worth trying, or did I miss something with this alternate?
The only way I can find the needed part, beside buying a whole truggy, is in an assembly like this (also comes in all black):
https://www.rc-helicopter-spare-parts-online.com/wltoys-12428-12427-12428a-12427a-12428b-12427b-12428c-12427c-rc-car-spare-parts-drive-assembly-front-green-p-30110.htmlThis is a website I am not familiar with (at least so far). This assembly is a third of the price of the complete kit...
Tinker, tinker, tinker; so much for RTR (ready to race) ...