Turbo Tercel shreds transmission

[SirFoxx]

Just posting this so the forum members can see it. This is the FWD variant transmission in my '81 turbo 4age tercel. I dont have dyno numbers yet, but ballpark number is ~240 crank hp in a 1900lb tercel. It let go while casually driving at ~25mph when i shifted between 2-3, and as soon as i let off the clutch the trans sounded like a grenade went off. My guess is 2nd gear took a few too many hard clutch releases and "bucking" sessions while I was trying to sort out fuel and tune issues, a tooth fractured, broke off and shredded all the teeth off. I've got parts from a blown 4wd Im going to use to fix it -- I will have to cut the end of the counter shaft off to make it work with the fwd trans, but thats a small price to pay to keep it on the road.

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[CornerConqueror]

what machinery are you using for the fix?

[SirFoxx]

what machinery are you using for the fix?

i have spare parts. i put another shaft in, replaced 2nd gear, cleaned all the metal out and its working fine again.

I have a theory that the failure wasnt caused by the motor, but was an "internal" failure, if that makes sense. I dont have pictures of what I initially found, so trying to explain it wouldnt make much sense unless you had an understanding of the transmission.

[Nordical25]

It could be internal failure since only one teeth has cracked. But adding some power won't have lifetime improving effect either on stock 3A transmission.

We did some basic gearbox calculations on a university mechanical engineering course and usually the gearbox is dimensioned to spin for "indefinitely" amount of cycles on a certain momentum. Adding higher momentum won't necessarily cause a disaster but it won't improve lifetime expectation either.

Therefore adding more power output to transmission is basically a gamble in my opinion. The higher engine output, the higher bets. And these transmissions were not desined to spin wheels either. So way of driving and condition of gearbox oil will affect too similarly to mileage of gears as well.