Thank Vlad, for blessing me so this happened only 3 miles from my house instead of in Sac the other day.
Ummm, I guess I won't see you guys at Laguna Seca tomorrow. I was ready to try and limp home but my passenger wanted me to call a tow, my insurance handled it, no problem.
Ouch!

Hopefully I can figure out my shim/bushing for the input shaft in time for Wednesday night.

 

Damnit. Now I know I need a 6 speed. The dream is dead.

 

Don't be silly, the 5 speed trees in my neighborhood are just coming into season. Not to mention my shim bushing idea, and of course there's the torsion axles.

Besides if you want to reliably make this kind of power you better be looking at a BMW swap and not some pansy, flimsy 6 speed.

 

I just finished reading this entire thread, a ton of inspiration. Keep chugging along cause its amusing/surprising everyone involved.
Also in for VD plot.

 

Please let us know what you end up doing for the shimming. I'm curious what work around you've found. Are you planning on adding more bracing to fix the PPF as well?

 

Thanks J, sorry you had to suffer through my thread.
Rish, you should know by now that I will share my ideas as I implement them, don't worry.
Old broke junk tranny out, no I ain't half way done, I need to pull the flywheel and measure for my shim.

 

By the way, if anyone wants an old broke tranny, just let me know. It's not very functional anymore, in other words it's not working, but it sucks like you wouldn't believe. Yeah, I got a fresh young one that's not ready to retire, it doesn't suck yet, but I'm okay with that.

 

The 8am time stamp makes me wonder if you started drinking early, or late

 

 

You called it, somehow it always seems to happen on the street. This actually happened in 2nd, wanted to pass a space case, and I passed them, but didn't get too far. Oops!

So I made this in my haste to be ready for Wednesday. It is about 1.1" in diameter and I am guessing that the thickness might be different for every car. The nice way would be to have my machine shop make a small brass or aluminum piece with a pilot hole that I could use to clearance it. Not sure how effective this will be since I am erring on the side of a large clearance. The idea is that it will prevent the input shaft from moving forward too much under extreme torque.





And actually installed in my car.

 

Is the theory that the helical gears put too much thrust load on the input shaft when the torque is higher? What about the output shaft?

--Ian

 

That is my hypothesis, yes.
​​​​​I think torque, forces the helical gear on the input shaft forward. When that happens, other gears on the main shaft can move. But the real problem is, once the input shaft moves forward, it is only making contact with 3/4-7/8 of the counter shaft. The counter shaft is pushed to the rear, deep into the relatively solid tail housing come on Vlad I know you can do a good quote on that.

 

I'm told that the main problem with the 5-speed is that the case flexes and allows the shafts to move apart from each other laterally, with similar effects on tooth strength. The 6-speed case has considerably more external reinforcement ribbing on it than the 5-speed.

--Ian

 

 

I will say that I think any Miata transmission with the 5 bolt bearing cap in the bell housing would benefit from something like this. Not sure if it will work, and probably something else will happen next time, but I want to see what that is.

 

zip ties!

--Ian

 

Interestingly, the failure of my 6-speed last year seems to have been the input shaft bearings, rather than the teeth on the gears. It still drives fine in all the gears, it just makes a ton of noise whenever the input shaft is spinning (when idling in neutral with foot off the clutch, for example) and the drain plug came out with half an inch of fuzzies on it.

--Ian

 

Sounds pretty normal, the input shaft bearing gets zero lubrication when accelerating at high load. But I just don't want it to move forward.

 

My oil was silver, and I am scared to open this one.

By the way Nigel, I was still hungover.

 

Hm, OK. Most Miata 6-speed failures seem to be gear teeth in either 3rd or 4th.

I had speculated mine was due to excess heat thinning the oil.

--Ian