Bronson M

iTrader: (1)

Considering you'd only have a top speed of 120mph I really don't think that's an option for most tracks. Hell at summit point (fairly tight track) I only used 4th gear twice with a 3.9 final gear ratio.

WigglingWaffles

Your next video should be titled "Greg Peters, the six speeder eater"

_integrity

I am curious the results post clutch/flywheel swap and with a bearing that presses in like I'm used to. Would be sad if the trans is failing due solely on a slightly larger power increase. You aren't making unbelievable power to where you expect the trans to instantly fail due to mechanical restrictions. You're making respectable #'s for what you have invested and nothing seems obscene. Other Japanese mfgs I work with are designed to support the original >200whp/tq yet are problem free making 600/400 +whp/tq with an upgraded clutch in countless scenario's as well as many more in the 800-1000 range. Would be unfortunate if this is the case as there aren't many affordable bolt on options for the BP. Friend of mine runs the Turbo2 on his 1.6 (he's had this combo for quite some time now) however it was far from a bolt on affair and required fork to be modified, trans adapter plate to be made from scratch, trans mount, etc.

P.S - I don't want to make the move over to a BMW trans myself either. Maybe 3rd time is a charm.

Have there been any other reported cases similar to yours Greg? You didn't even get a chance to truly enjoy the thing before failure.

Quigs

iTrader: (2)

Would it still be worth tossing the 5 speed in just to troubleshoot any other possible scenarios/issues before possibly inadvertently eating another much more expensive 6 speed? I know it's a lot of extra work to put the 5 speed in, but from watching your videos you can certainly do it pretty quickly it seems. I would just hate to see the same thing happen again because the clutch and trans just don't play nice together for whatever reason.

EDIT: Just kidding, I missed the post where you said you bought the more well-known 949 set up. Disregard...

_integrity

Quigs I was thinking the same however if he loses the latest 6spd on the new parts list....it's time to scrap the idea of using the 6speed to retain that power as there would be no other contributing factors - hopefully Greg tries it in stock configuration with the OEM shifter if it's sitting in the turret area when he purchases. Since there is no rock solid proof of cause, just damage, starting with a static OEM-like configuration would be nice and if everything is vetted then re-add the short shifter back in and let her rip. For what it's worth the MiataRoadster shifter setup does look like a quality configuration but I would still test without so the only aftermarket component is the clutch/flywheel. From what I've read he is replacing the clutch/flywheel combo along with a new pilot bearing + master/slave (I would replace the throwout with OEM as well if it isn't already-I personally never use aftermarket brand bearings, oem NTN Bearing quality etc)

Midtenn

iTrader: (15)

Greg, I don't think there should be a gap between the parts of the 4th gear assembly. I don't have a picture of a NB1 assembly, but here is one of the NB2/MSM 4th gear.

germanmiata

Im not familiar with the miata gearbox specific but the gap has to be normal. When you shift u move the syncros to the gear. They work like a little clutch to match their speed.

Midtenn

iTrader: (15)

The gap between the bronze synchro and the gear is normal (its actually specified in the repair manual what the minimum gap between them should be), but that's not the gap Greg is showing:



See the "smooth" area on the left? That is where the synchro rides on the gear assembly. The gap he shows shouldn't be there at all, possibly. Those two parts should be flush to one another. I've got shots of my NB1 internals, but nothing clear enough that I can say there isn't supposed to be gap. I'll try to get some pictures this evening.

1993z32

Correct. And what happens once it slips down is the steel cone on the left contacts the main hub between 3rd/4th, and it's not supposed to be able to. Once I tapped the synchro cone fully onto 4th gear, and reassembled the countershaft, 4th gear became free floating once again.

Also - I will be running my old faithful 5-speed for a while until I figure out what my next move is.

DarkSwordsman

I agree with Greg's theory about the synchro gear being ripped from the gear because of the force applied from the engine... for the most part.

Usually, when people shift gears, they are off the throttle. You should be able to easily slip out of a gear with the clutch engaged and 0% throttle. This shouldn't matter if it was a 100 hp or 400 hp engine, especially if they are the same engine, so it doesn't make sense as to why it would happen. To me, it would only make sense if you are flat foot shifting and the clutch wasn't 100% disengaged when you went to shift, however, why would it only happen in fourth then?

I was originally thinking the short shifter, but really thought about the helical gears.

Greg, in this picture, the way the gear is oriented, the input shaft gear for 4th should be pushing 4th gear away from the selection hub. Meaning, fourth gear is rotating up, as in clockwise from your hand, as in your hand turning right (clockwise).



From this next picture, it seems that the gear is over the synchro and that the teeth mesh there, then the synchro gear meshes with the counter shaft.



I'm thinking that, under power, the gear itself is pulled away from the selection hub and slides on the synchro gear, and since the clip is holding only the synchro gear against the other gear directly connected to the countershaft (in the bottom of the picture), the synchro gear is able to stay in place as this happens.

Then, when you let off power, the gear tries to return to it's original position thus pushing the synchro gear into the hub. The reason the clip isn't worn is simply because the synchro gear is going the same speed as the counter shaft, so there is no pressure on the clip besides the single force pushing the synchro gear into the clip, which is just pressure, no friction.

While, yes, the hub can push against the synchro gear, it may not be enough force to push the synchro gear all the way back into the main 4th gear. If it could, then every stock Miata should've failed after a few hundred miles from wear on the hub and the synchros automatically engaging 4th and 3rd.

As a result of all this, the transmission just constantly grinds away the hub while even in neutral with the clutch engaged. It would be more extreme the farther away you get from fourth (first and sixth) as the input speed (hub) will be spinning far faster than the output speed (fourth gear). As far as the rear end locking up while in neutral with the clutch disengaged, my statement about two gears being engaged should be true in the instance that the synchro may have pushed over so much, that fourth's synchro pushed the selector onto third's synchros a bit and got itself caught in the hub as well.

Also to note, this pulling motion of the input gear on the counter gear under power should happen in any gear, not just fourth, since the two gears for fourth (input and counter shafts) are always spinning. If anything, the force should be more in fourth gear since the synchros can hold the synchro gear to the hub.

I hope this helps. There may be more to it, but, considering all the contact points of the gears based upon the pictures you supplied and what I found through searching combined with my knowledge of High School physics, I don't think there is any more elevated math required or hidden forces. Granted I have never worked on a transmission and there could be more to it that I don't know, and as a result my opinion may be very wrong, this is what makes sense to be from my knowledge of Physics, what information I have, and the information that I checked against other sources. I hope it at least gives you guys more ideas to work with.

The solution may be to get gears (helical or straight) where the gear and synchro gear are one solid piece, or one where the interface between them isn't just a straight gear, perhaps tapered like a helical gear, or one that literally screws on and has some sort of locking pin or lock nut on it. As a last resort, some red thread locker or some killer bonding agent between the gear and synchro gear may help.

As far as why this didn't happen to any of the other gears is a mystery to me. Third gear should technically be pushed all the way on the synchro gear in this case, I think.

I hope this helps.


Edit: Have you checked if third had any extra wear on it similar to fourth? I think third still could be exposed to similar error, but 1st and 2nd and 5th and 6th appear to have more than just a little ring to push against on the main gear that allowed them to stay in their correct positions.

Also, I'm sure you know this, but the reason the car was able to move a bit in neutral is definitely from that friction in fourth.

sexyicky

iTrader: (1)

Updates on new clutch? Did you give hell to clutch masters?