this could be heaven or this could be hell

[Mr. ED]

....

But bad surprise at this time: the complete trans is not free....
I verified with changing the diff for the other I own: the diff is the root cause. It seems that MIP gear is not round.
I Try to make it work a few time to get a first wear....better but clearly not at the right level!!!!

So I went back to the standard Traxxas ball diff (but a new one): free trans, but in my point of view, this differential is really hard to adjust. We will check on the track when time will come.

I could be wrong, but I think the diff of those older models has teeth more or less than the current models... or was it the gear on the topshaft that differs???

[jwscab]

the top shaft definitely had different gear count between blue eagle, trx1 and tr3, not sure about srt. There were also 3 or 4 diff gears as well across models. That part of the the traxxas lineup is kinda hard to pin down without looking at the parts lists or exploded diagrams to get the right part numbers. It sounds like he had a problem with the MIP gear in any case.

[peuge73]

....

But bad surprise at this time: the complete trans is not free....
I verified with changing the diff for the other I own: the diff is the root cause. It seems that MIP gear is not round.
I Try to make it work a few time to get a first wear....better but clearly not at the right level!!!!

So I went back to the standard Traxxas ball diff (but a new one): free trans, but in my point of view, this differential is really hard to adjust. We will check on the track when time will come.

I could be wrong, but I think the diff of those older models has teeth more or less than the current models... or was it the gear on the topshaft that differs???

This issue is closed for me at this time: the problem was due to the MIP diff gear that was not round.
The rustler diff is absolutely compatible with the old Eagle and Eagle LS. In an other hand, TRX1 and TRX3 are not the same (smaller).
When you purchase the optionnal ball diff, both gears are supplied.

My question was for a good tuning on track: what oil thikness to use on planetary diff gear ? I mean the rustler one, for example, ref 2388.