So while I've been building up my NP231, I was given 2 Tera 4:1 cases, both of them were trashed(thus free). I decided to pull one of the Tera cases the rest of the way apart to look a little closer as to what happened. Both tera cases had the same failures at the planetary gear set, here is why:
Here is the Tera case ring gear that the planetary gear rides in:
Planetary gears: Tera on the left, 231 on right
Tera, 5 pinion:
231, 3 pinion:
The pinion that fell out of the Tera planetary set, and the shaft that is supposed to hold it in place
This is the problem I see with the Tera 4:1, the smaller straight cut gear is all that rides on the ring gear in the case, the larger helical cut gear rides on the inner gear(sun gear?)
But there is nothing on the opposite side of either of those gears to help support large torque loads. The straight cut gear is pushed in by the ring gear, and the helical gear is pushed out by the sun gear(may not be the right name for it, but thats what I'm going to call it until someone corrects me), causing large amounts of stress on the shaft that holds the pinion in place. EVERY ONE of the pinions on the Tera planetary gear had large amounts of play, the shafts probably don't look too much better than the one that fell out, there was so much play, that the pinions barely make contact with the sun gear as it turns.
The 231 planetary set has much wider contact surfaces, the ring gear, pinions, and sun gear, are all the same width, so the ring gear supports full width of the pinion under heavy torque loads from the sun gear, and vice versa. I do not have a detailed pic of the 231 planetary gear, but you can get an idea of it from the pics above, I'll take some more pics of it tomorrow and post them up.
sub. Was thinking of the Terra low option in the distant future, now i dont know.....
Building my junk with more junk, so Im always on the look out for more junk....Free to cheap preferably. :D
My junk http://www.jeepforum.com/forum/f22/survivor-project-driveway-frame-swap-33s-build-1280626/index3.html
Mark me down as another Jeeper that's NOT impressed with the TeraLow. I had one, and it sounded like a piece of misadjusted farm equipment in low range. The Atlas that replaced it is much quieter and WAY stronger.
'11 JK Unlimited Sport S, stock for now...
'08 JK X, OEM rear locker and swaybar disco!
That damage might have been caused by over-revving the planetaries by driving at higher speeds in 4Lo than recommended. Too many drive in 4Lo at higher speeds than is good by shifting into 3rd or even 4th gear which REALLY revs up those planetaries gears, they are screaming at those rpms.
Not really vouching for Tera as I had my go around with them years ago but the Tera case in my truck is 10 years old and has never caused me any grief. Now the first case I got from them exploded within 500 miles of installing it and I had a friend with a similar experience but this second case has worked out really well for me. Jerry does make a good point about over-revving the case... it's not built for that style of driving.
Originally Posted by samgm2
And yes, I am an exceptional scientist and engineer.