I found the solution to 2speed problems. Yeah racing aluminum 25t servo saver horn pn#axsc057. This allows you to use the supplied arm/spring. As seen in my photo it is the standard 25t. The tr4 power HD is a micro servo with standard 25t spline. I installed it and reset epa. It works great.
I had thought about this, so I emailed them...and, they wouldn't give me any straight answers. Their products says great, but their CS is sorely lacking. Word-for-word, this is what their reply said:
"AXSC-057 is design for micro servo of scx10 III"
Now, I knew this couldn't be accurate, and for two reasons. First, as everyone who knows the SCX10-III knows, the stock servo (SX107) has a 20T micro spline, not a 25T spline. Second...as I suspected, and as you, yourself, found out...the Yeah Racing piece has a 'standard' size spline, not a 'micro' spline. However, if my first "final solution" doesn't pan out, I just might get the Yeah Racing part.
For right now, I've temporarily given up on the PowerHobby 59MG. This is not to say I am completely done with this option...I did find a file on Thingiverse - someone designed a bottom servo saver piece specifically for a 25T micro spline. I don't have a 3D printer, so I've got someone nearby printing two pieces for my (one from PLA, the other PETG). Hopefully, these fit...and, as long as both do, I'll see which is the stronger (ie. lasts longer).
In the meantime, I removed the 59MG, and replaced it with an EcoPower 640T, which has a 'standard' 25T spline, thus I'm using the 25T piece from the AXI31009 (aka AXIC3009) "Hi-Low Servo Saver Kit". The only downside to the 640T is that it's only rated to 6.0V...so, if the 3D printed pieces don't work out, I'll need to find another micro servo w/ 25T standard spline (such as Reef's 99, etc), in which case I'd get the Yeah Racing part.
Speaking of the 2-speed shifter, I discovered something else...why so many people (myself included) have had problems with the shift level 'sticking'. Someone else came up with the idea of removing the Guide Pin (which, honestly, I initially thought was ridiculous)...but. With my lever also 'sticking', I decided to remove the transmission cover, and try to determine the cause. What I noticed is that the Guide Pin is not perfectly parallel with the 2-speed shift rod....or, to be more specific, I'm thinking the holes in the transmission case that hold the Guide Pin in place are not in proper alignment to each other.
Here's what I think is happening. The hole in each trans case half that holds the Guide Pin need to perfectly aligned with each other, no different than the pins holding the gears. Using the trans gears as an example, if even one hole is not properly aligned with its counterpart, that would cause the entire transmission to bind. I don't know if this is happening in all trans cases, or only some of them, but one of the two holes is off just enough that it puts the armature responsible for sliding the "shifter" at a slight angle. This could/would cause the "shifter" to be at a slight angle to the rod holding the 'high' & 'low' gears, which, in turn, leads to the binding. Put another way, the 'Guide Pin' is miss of a 'Misguiding Pin'.
So, I tried what the previous person did...I removed the 'Misguided Pin', reassembled the trans case, and, instantly, the 'shift' rod was freely sliding back & forth. If anything else is having a "binding" problem with the 2-speed shifter, this solution is (virtually) guaranteed to permanently fix the problem.
Now, back to your regularly scheduled program.....
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