Tamiya only ever made the alloy gear for EvoIV, no other car.
They soldout very early when EvoIV was new and i couldn't find any more
but recently i suspect somebody's found a stash of NOS unsold in japan,
there's a couple appearing for sale this yr.
(haven't bought 1 as my only geenuine EvoIV spool is in the evo5.)
yeah its very harsh on the other little bevel gear
... and you can't buy that little bevel gear except in a pack with the big gear
All shafters need a lot of effort shimming the gearboxes.
the EvoIII used to chewup oneway bevel ringgears... up to 1 every run,
you'd open up the gearbox and find 3-5 teeth missing or squashed.
Practised so much we could get gearbox lid open in under 10s...
eIII had a solid shaft, the bevel pinion sat on the shaft floating.
If you floored the throttle hard with a hot motor or hit something fronton,
the ringgear could bend away and skip a few teeth.
It was solved partially by....
1, 3pc shaft made by Square, stopped the 'javelin' poking in on a smash.
2, Tech racing made a CF backing plate for the ring gear, Tamiya followed.
3, Tamiya beefed up the plastic on the ring gear on the outside edge
4, some tried alloy gearbox casings... very expensive, doubtful if it worked
any better than using the longest possible machine-thread screws in plastic 'box lid
With 1 & 2 done the ringgears enjoyed a much longer life, now seldom
needed replacing until they looked wornout during routine rebuild
(hence leaving me with a ton of spare, hahaha i boughtup real bad).
Interestingly balldiff gears never stripped afaik, even when 2nd balldiff up front.
ok that was the eIII... however that also explains why
1, eIV got the alloy bulkhead gearbox casing
2, and the 3pc centre shaft
3, with the bevel pinion securely clipped &
3a, sub shaft is securely located via 2 bearings, zero float
4, and why they made a metal gear
5, and metal gear only for oneway not balldiff
Ironically the beancounters also wokeup so eIV kit got a lot less
CF & alloy goodies than the eIII inside their pizzabox... now all on option list
Common/typical failures on eIV afaik are:-
a, shaft cups... PLASTIC?!
clear plastics could be more brittle than black too btw,
not that the blacks survive very long anyway.
Alloy highly recommended.
b, rear knuckles are flimsy & flexy.. go alloy or TB03 items
c, 950 knuckle bearings are too dainty for axle duty = don't live long
Keep heaps of spares or go TB03 knuckles with 1050 bearings
but you'll also have to change the stubaxles to longer versions.
d, servo turnbuckle can cut centre shaft in half... don't ask,
no idea how it happens but have seen a few broken centre shafts!!!