I used a caliper to measure the shaft diameter : 2mm. Okay, my bad. How come I found that the pinion was loose ?

If its an aluminum pinion it may just be wonky.

But a time of thumb I've learned is:

True 380 sized motors have a 2.3mm shaft

370 sized motors use a 2mm shaft.

But keep in mind their are variations on this rule. All of which I do not know.

Thanks for sharing your experience. Much appreciated believe me.

I just received my thing and putted in F1 kart from turnigy. I hope that can write in this thread about problems with it because I'm disappointed and I can't find answer to that that my own unit is malfunctioning.
I find two problems.
First that it's easy to spot. this esc doesn't have enough power to maintain steady reverse speed, it just jumps back. Even when this thing is working in air.
Second thing, the more important one is that when I push hard the trigger it often maintain low rpms for sec or two, and just after those 1-2s if I'm still holding the triggers it goes up to a proper rpm's. Going on low speeds it's hard to, it's go stedy for second or two and then kick a little in rpm's.
This thing kills joy of driving that kart and I'm starting to regret that I didn't buy a standart 380 brushless motor like that Donkey and normal esc.
Can anyone of You tell me if that thing is broken or is it that way?

Strange problem you have got here. I use my ESC on my duratrax vendetta and everything works flawlessly. I don't use the motor though. Have you try to change the parameters of the esc ? Perhaps the motor timing or something like this ?

I don't have programming card and I didn't try to reprogram it manually.
I checked this thing on two drastically different tx/rx and it acted just the same so it leaves that its esc/motor thing.
HK help center didn't say anything useful only that I can fill formula and send the whole combo back. One thing is that it would take about two months to receive new one and second is that I'm not sure if this thing is broken and what if after sending they say that it is OK...

I'm thinking about getting this ESC to work with my Mamba 8100kv in my project Mini T and was wondering if anyone has done this set up and whether it would work.