SCX10 Powertrain not smooth. Tried everything!

[KingRaptor]

I bought a used SCX10 I (original) and I can't figure out why it won't have a smooth power train. It is a 2012 Jeep Rubicon model but it was only ran about 4-5 times it barely has any signs of use. I really need your help on figuring out why it won't run smoothly. With and without power the truck feels like bogs down every 1/5 or 1/6 wheel rotation, like it's getting stuck on something.

It looks exactly like this video. almost like something in the drivetrain is too tight or rubbing on something.

https://www.youtube.com/watch?v=LLMPq57YumQ

I have tried...
- with and without motor attached to transmission
- with and without power
- individual drive shafts attached (rear only, and front only). It happens whether I have only the rear, or front driveshaft attached.
- reseated/remounted transmission a million times
- tried a different motor
- set pinion/spur gear mesh a million combinations from very loose to very tight
- rebuilding transmission, adding grease/lube/oil wherever I can think of
- transmission has been rebuilt with tight screws and loose screws
- slipper clutch set loose and tight

The driveshafts are lubed up, and feel fine, nothing is caught. The motors are fine (new holmes hobby trail master, and new torque master).

Please help me. I have no ideas on what else to try. My main suspicion is bad mesh on the transmission (but no idea how to adjust mesh in the transmission). Or just bad driveshafts that don't like the angles.

[Growler]

Are the driveshafts aligned properly? Refer to SCX10 Jeep G6 kit manual for example, pins on both sides need to be parallel. One other thing I can think of could be badly molded plastic transmission gears. Have had few of those out of the box. If you spin the gearbox shaft with your fingers without motor or driveshafts attached, does it run smoothly?

[DRED805]

Do scx10's usually have extreme driveline angles like that? Looks like the driveshafts are just binding up.

[kincer]

Driveshafts in phase? Sounds like a bad plastic gear in the transmission to me. Go all metal gears in the trans. and it should be greatly improved, even if that's not it the plastic gears will eventually give out and you'll need to upgrade anyway so may as well do it now.

[KingRaptor]

Thanks all. The transmission seems to rotate just fine on it's own without a driveshaft, and with or without a motor attached. That's what's crazy. Everything on it's own seems to be completely fine but together it's a mess.

Maybe it's the driveshafts? After more testing I notice the "bogging down" occurs about every 1/2 turn of the driveshaft. However, when I remove the pin that connects the driveshaft to the transmission, and just left the driveshaft spin freely on the transmission gear, I roll the truck without power and it seems smooth and completely fine, which I don't think would be possible if the driveshafts or driveshaft angles were the problem. The truck seems to roll fine when everything is completely assembled except with motor removed, however I have tested two brand new hobby holmes motors and the problem gets worse with the motor installed and a variety of combination of pinion gear meshes. Could the problem be the spur or pinion? Or could the problem be unrelated to the spur/pinion/motor and just amplified by the motor after the motor is installed?

I checked and re-aligned the driveshaft so that the alignment marks are aligned as shown below. It helped maybe 10%, but the problem still remains.




How do I check for driveshaft phase? I just rebuilt the final drive gear (that connects to the driveshafts) exactly as shown in the picture in the manual and problem remains.




I really need your help guys. I want to make this rig work out. It looks great, it's a classic, and it has tons of potential but this is just driving me nuts. Should I buy a completely new assembled transmission unit?

[KingRaptor]

SOLVED IT! Thanks to Growler, Dred, and Kincer!

It was the driveshafts! I assumed the guy before assembled them correctly and I just lined up the marks on the driveshafts, however, after taking them off again I noticed that even with the marks aligned the shaft ends (pins) were not! He screwed the driveshaft ends incorrectly not paying attention to the marks and alignment of the other shaft pin. They weren't parallel!

[Timmahh]

Ya, that lobeing movement you described left me thinking out of phase drive shafts as well.

Glad you have it sorted.

[kincer]

Glad you got it figured out!