My Six-speed Hates Me
 

Gentlemen,

Are there some secrets to making six-speed shifts?

This is a serious plea for help. I blew up my five-speed on track a month or so ago, and replaced it with an early NB six-speed I had stored in the garage for about four years. I've done three track days with the six-speed and I probably still miss a dozen shifts during a 30 minute session.

I'm running AmSoil MTG. Second to Third seems notchy on track, but not on the highway. Fifth to Fourth is embarrassing if the car is not moving in a perfectly straight line. I suppose I have some innate muscle memory going on when shifting, but there have been times downshifting to Fourth where I've ended up just putting the transmission in Neutral and pointing people by.

I also rebuilt the shifter with new bushings, so I don't believe anything is to blame but me.

Any suggestions would be greatly appreciated.

Magic Ford transmission fluid fixed my MSM.
XT-M5-QS
Worked far better than I expected.
Smells weird, not like normal gear oil at all

Miataroadster short shift kit transformed how my 6-speed shifts. Expensive but worth it.

Redline D6 ATF is supposedly an equivalent, which explains the smell (ATF is very mild), however I wouldn't suggest using the Redline ATF. I will say that BMWs use ATF in their manual transmissions though...

I have always run MT-90 in my Miata 6-speeds and they both shifted great. One of them I cooked the input bearing -- no idea if that's fluid related or just general track abuse.

--Ian

I found using a bronze shifter bushing and mt90 to be the magic sauce for me

Could the shifter be moving around from worn/insufficient engine or differential mounts? That could explain why the gate your after might not be where muscle memory puts it on the street versus the track.

Mine has Redline heavy shockproof gear oil, a factory shifter and a brass bushing as a data point. No shifting issues.

I can't get your link to open. Did you get stock height or extended?

I purchased two quarts of that Motorcraft oil years ago. I never put it in. They're in the garage. I ordered from the very local, tiny Ford dealership down the street. When I went to pick up my order, the parts guy asked me what it was for. When I said "Miata", I thought he was going to put them back under the counter.

I suppose the cheapest thing would be to try a bronze bushing before draining the nearly new MTG, unless the MTG us just the wrong oil for the six-speed.

I can feel, and see, the shifter move around a bit when accelerating or decelerating, but the five-speeds I've had were the same way. It happens in my stock '90 shitbox, too.

Thanks,

Engine mounts solved mine
 

Engine mounts with a 70 durometer bush solved 90% of my miss-shifting.

Another vote for engine and/or differential mounts. I couldn't hit 2nd to 3rd on track to save my life with stock mounts. Turns out they were completely destroyed when I pulled them out. AWR engine mounts solved all my driveline slop/mis-shifting issues.

When I bought my Ford fluid it had been on the shelf at the Ford dealer for 4 years.
They had never sold any.
I had them check to see what it "fit" in the Ford line up.
They told me the only application they could find for it was the mid 2000s GT40...
I believe it had a "Ricardo" gear box.
It didn't smell like ATF either.
I didn't believe it would really help but it made huge improvements.
All the other suggestions are all spot on.
But, especially if you already have the fluid, give it a try first and see if it helps you too.

I've run the following in all my 6 speeds and haven't had an issue missing shifts. Bear in mind i've clocked maybe 3000 miles ever in 5 speed miatas, so this may just be a muscle memory thing for me as well.

Amsoil MTG
MiataRoadster Tall/Angled shifter
Carbing High Grip knob
Delrin or bronze bushing
Aftermarket motor/diff mounts

Easily the best shifting transmissions i've ever experienced, and my DD is an S2000.

Extended angled version, which places it very close to the wheel for easy shifting. I also installed a stock height version in my '93 street car (converted to 6-speed), mostly for looks. I, by far, preferred shifting with the one in my track-mostly MSM.

The website seems to be a little bit flaky at the moment. E-mail Bill Wilner directly (Bill@MiataRoadster.com) with any questions. Great guy to deal with.

Thanks!

I could just say '+1', but...
I switched from 5sp to 6sp in my track NA about a year ago. It does take some getting used to, and if you don't street drive it, it will take a little longer to build the muscle memory. My setup:

Mazda competition motor mounts
Amsoil MTG
Miataroadster shifter -tall/angled.
Bronze bushing

Probably the biggest difference for me was the Miataroadster shifter (and it was the last change)... expensive but worth it.

Here's a pic of the driver's side motor mount. Replaced with a Mazda Competition mount. I haven't pulled the other side yet. Waiting on an AWR 70 durometer to arrive.


https://cimg3.ibsrv.net/gimg/www.mia...ad49a92001.jpg

That certainly didn't help your shifting.

Please report back how you like the hybrid mount setup. I have mazda comp mounts on mine and was considering trying a poly mount on one side.

Took the car out yesterday with the hybrid mount setup. At speed, I really don't notice any new harshness, but I will admit at idle there might be some added vibration. I need to spend some more time driving her. My next track event is coming up at VIR. I'll know then if the mounts help my shifting.

I've got the MR tall/angled shifter and aftermarket motor/diff mounts but would NEVER describe my MSM as anywhere near the best 6-speed I've ever used.
Looks like I need to add Amsoil MTG and the bronze bushing too.

My MSM's gearbox was so crappy that I'd only find reverse gear about 1/3 of the time (REALLY embarassing in car parks as people look to see where the grinding gear noise is coming from.
On the track it wasn't uncommon to accidentally find 2nd when looking for 4th, or 5th when you wanted 3rd, which really screws up your times and you spend the rest of the laps trying hard NOT to do it again instead of driving.
On the road, especially around sweeping turns, I'd find "almost-reverse" instead of 5th when changing up from 4th - more gear grinding and your rear reversing lights come on to let everyone know you've fucked up.

The MR tall/angled shifter fixed these issues but it's still far from what I'd call acceptable, it feels way too agricultural, as opposed to the slick 5-speeds I've owned or driven in the past (1982 Mitsubishi JA Starion, Mazda 3 and SP23, 1.6L NA MX-5).

If you haven't got a MR tall/angled shifter yet, I thoroughly recommend it.
I originally bought the short version because the tall-angled version looked odd to me when installed.
Bill tried to talk me into the tall version but I got the short version and it was better than the OEM shifter.
Later I upgraded to the tall/angled version and Bill was ABSOLUTELY correct, it made shifting even easier (especially reverse, almost no effort needed at all and you find reverse every time).
I used black heatshink on the silver shaft and it virtually "disappears" in the car now.

PS: Add a VooDoo knob, or some other round knob to the tall-angled shifter for the best combination.

FYI: Many NCs, which use the Aisin 6-speed gearbox too, have 2nd-gear issues when cold.
The AE86 too - one of my friend's sold his after 8 months, calling it a "Death Trap" because he had so many near-misses in morning traffic because he couldn't find 2nd gear when he needed and had to use 3rd instead.
I drove him from Brisbane to Warrick, ~150km, to pick up the car because they were in high demand when initially released and the one in Warrick was the top-spec model he wanted.
After the drive home he complained that the gearbox was shite which I attributed to just being different to his previous VW Golf gearbox but he clearly wasn't impressed with it..
Every time he took it back to Toyota, all they'd do was change the oil to a different brand to see if that worked - sometimes it did initially but the problems always returned a few weeks later.
Apparently the Toyota dealers in Australia had an upper limit on warranty costs so swapping out the gearbox or replacing the car was not an option, which is why they simply tried changing the oil and hoped that it would fix the problem.

Some Aisin 6-speeds are good, some are just shite and need to be avoided at all costs.
If buying one, insist on driving the car in the morning when it's still cold.
If it has 2nd-gear issues, walk away, it will always be problematic.
If it drives well when cold, you've found a good 6-speed gearbox.

I forgot to mention I have installed a bronze bushing since my original post, but haven't done much driving with it yet.

I don't have Second gear issues, and I have no problems finding Reverse. First to Second is very smooth. I get a split-second grind upshifting into Third, almost like I'm either not depressing the clutch far enough, or letting it up a little too soon. The Miata Five-speed, and my '07 Audi S4 Six-speed, don't need much clutch action once the car is moving. I plan to be very deliberate about my shifts at VIR this week. Most of my embarrassing problems were downshifts from Fifth to Fourth (Fifth to nowhere).

Replace fluid with unicord blood you already own. If that doesn't fix, then syncro's are bad so toss tranny in trash. Then new(used) 6 speed with fix your issues.

I want to see what happens at the track first with the bronze bushing and the new motor mounts. That said, I would be amenable to trying some kind of synchro additive in the MTG--I don't want to drain it just yet. I seem to remember a GM additive mentioned here before, but a search for "additive" came up zero for the transmission.

I don't think the fluid is TRULY having much bearing on the shift feel, although each time i've tried Redline, i've been "rewarded" with a transmission that feels straight up broken.

Lot of it is the lottery of starting with a good trans.

"The AZ6 Reverse Shuffle" is a thing on both of mine. (And nearly every other AZ6 i've ever driven)

NC boxes are not the Aisin AZ6, they're the Mazda box found in the later RX8s.

If you throw it in the trash use the trash can in my garage :rofl: id love a busted 6 speed to do...extraneous, nefarious things with

Just spent a glorious day on VIR Grand. In five 30 minute sessions, I only missed a couple of shifts, still Fifth to Fourth. I did a personal best of 3:08.74. The motor mounts (and bronze bushing) did the trick. I love my Six-speed. I like my Six-speed and need to make it work for me...

I drove 216 miles to the track and I honestly did not ever notice the stiffer mounts while driving. If someone had done the replacement without my knowledge, I would not have known. That said, there were just a few times at idle (long wait at a traffic light) when I thought there was more vibration, but again, if I hadn't been looking for it, I would not have thought twice about it. I would have blamed the tune.

The hybrid mount setup (OEM Comp Mount on the driver's side, aftermarket on the right) is stiff in the sense it secures the engine, but not so stiff to shake your eyes out. AWR is using a larger diameter bushing in their 70 duro mounts in order to reduce NVH. I'm a believer.

Things aren't all unicorns, felatio, and IPAs, although they're way better with the new motor mounts. The Fifth to Fourth shift remains a problem on track. Lap to lap, it doesn't make any sense. Six out of seven times, the downshift to Fourth is easily and smoothly completed. But sometimes the transmission doesn't want to downshift from Fifth into any gear. Fourth should be easy to find in a panic--push in the clutch, let go of the shifter, then pull the shifter rearward.

What would cause this?

If motor mounts helped but didn't remove the problem entirely, i would think poly urethane differential mounts would help too.

The XT-M5-QS fluid that was mentioned make a noticeable improvement for the 6 speed shifting for me when I did it on my NC. It didn't have such a big effect on my NB, but it was still better.

70 durometer poly engine mounts on my 140hp NB created a small "zizz" at idle which became less at running speeds. They improved the gearchange quite a bit. Stiffer rubber bushings might also have worked.

90 durometer ones on my 400hp turbo NB had the same effects except the vibrations were so loud and violent they nearly stopped the car be9ing my daily driver.

Gents,

I'm the OP and this is relevant to me again...

I emailed Bill at Miata Roadsters and passed him the story--basically cut and pasted from above--and he didn't believe one of his shifters would solve my problem. I have the magic Ford extra virgin, virgin unicorn oil and am contemplating trying the six speed again.

What is the possibility--all funny/satirical/rude or dickish comments welcome--that the magic oil fixes my problem? She's HPDE only, but I'm averaging more than 25 track days per year.

Thanks,

You're still on the stock shifter? If so, I would spend the $$$ on the MR shifter. It's worth it.

Since my previous post in this thread I've upgraded to BBFW competition motor mounts (don't do this to a street car), and also caged the car. I'm pretty happy with the 6spd at this point, but I also still get the occasional 5/4 fucked up shift. Just the cost of a 6sp, IMHO.

I can't justify that. I'm willing to try the six speed with the virgin unicorn oil. If it doesn't work out to the performance of the five-speed, I've only lost some coin on the oil and some hours in the garage.

Do these shifting problems happen towards the end of a session on a hot day or any time? It's pretty well known that the AZ6 doesn't like to get hot. The aluminum shift forks unique to the Miata AZ6 trans seem to not like high temps, and it doesn't take a bunch of power to get the trans hot since it's related to shaft speed (engine speed). Emilio has brought this up many times and even installs trans coolers to combat this.

I get gear lockouts once or twice a year. Usually towards the end of an afternoon session in July/August. And this is with a whopping 132whp. I rebuilt the box when 3rd started grinding and replaced all the synchros, clutch hubs, and shift forks. Measured all the clearances per the manual, and it made no difference. Basically I'll be motoring down the straight, shifting at 7000rpm, and out of nowhere I'll go from 4th to 5th and it will lockout. Feels like I've missed the gate. But I can stir the shifter around all I want and it won't engage any gear(4th/5th/6th) for a few seconds. Then after a few seconds of flailing around trying to engage something it will finally go in ruining my lap and at that point I just cool it down and park it. And I should note it doesn't grind when it finally engages a gear, so it's definitely the shifter mechanism and not the clutch hubs/synchros/gear cones.

I've tried all the highly rated fluids (Ford, Amsoil, Redline) and found no difference between them, so I just stick with the Redline MT90 since it's readily available locally. I have Innovative engine mounts, poly diff mounts, and the MR shifter. I finally installed a trans temp sensor in the drainplug over the winter, so I'm hoping to find the temp threshold where the lockouts occur in the next month or so.

The "lockout" you describe seemed to happen whenever, even the first session of the morning. Perhaps because I'm making roughly 225whp. My lockouts were always when I wanted to downshift, especially fifth to fourth. I never had a lockout when I wanted to upshift. The stirring around of the shifter is exactly as you described. I recently watched video of me at VIR, in Turn 3, trying to steer and point people by whilst desperately searching for a gear, any gear.

You rebuilt the trans, use the juice, and installed the super shifter and still get the occasional lockout?

Thanks for the very informative post.

I ran an MSM 6 speed for a short time. The ratios were ok for my uses but prefer the 5 speed ratios. My main gripe is the same as yours in that the shifting feel and accuracy was absolute garbage. Tried a bronze bushing and fluid before it started grinding in third gear and then i gave up entirely and went back to blowing up 5 speeds.

To be fair, once I used virtual dyno i realized I ramping in power a lot harder than i though which explains all the other broken gearboxes. I have since dialed it in softer on the bottom and they last much longer at higher WHP levels.

One thing I have always been curious about is fabricating a transmission mount for the factory 5/6speeds. I have poly bush's everywhere else but I've wondered if installing some frame rail braces and fabbing up a transmission cross member with another rubber/poly bushing may help reduce the driveline flex. Im no engineer and haven't seen other do much about this. Had the idea after putting a similar setup in a LS swapped miata.

Correct.

The only thing that seemed to help was insulating the exhaust. It was worse when I had a stock exhaust with cat and uninsulated exhaust tubes. It improved after I fabbed up a custom exhaust (deleting the cat) and wrapped the header primaries with DEI titanium and using DEI form-a-shield on the bottom half of the header and entire midpipe past the diff. Before it would happen pretty consistently toward the end of sessions regardless of ambient temps. Obviously a cooler would completely remedy the issue.

Do you have hood vents?

Thanks much,

Ford fluid and a GR shifter fixed all the mis-shift issues for me

GR?

Motul Gear 300 75W-90 gets a lot of love these days.

No.
I've considered venting, but coolant temps are not an issue at my power level with the Supermiata rad and reroute. And talking with my aero buddy there is a drag penalty associated with the hood vents, which we think outweighs the marginal reduction in lift and the increased heat exchanger air flow which isn't needed.

If it drops engine bay temps significantly, then it may help trans temp slightly. One thing a lot of mustang road race guys run is a trans air scoop. You could use the stock subframe brace to mount a scoop to blow air at the trans.
https://cimg6.ibsrv.net/gimg/www.mia...afbff0dbfd.jpg

The reason I asked is I had read here, IIRC, that hood vents potentially reduce the airflow across the transmission.

Sir,

Could you explain this in a little more detail? I'm going to assume you're turbo...

Thanks,