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So I’ve done a decent bit of reading since this happened and have only found threads pertaining to the infamous 5/R lockout woes that the 6 speed experiences. I think this was a different issue.
Coming home late last night. I did a 3rd to 6th gear pull, taking the car almost all the way up to top speed. I got on the brakes and coasted down to hit a 270* off ramp onto the next freeway. Shifted 6-5-4, no weird noises, notchiness, nothing. Went to shift from 4th to 5th, locked out. Tried a few times putting varying degrees of muscle into it, still locked. Tried to go 4th to 6th, locked out and the trans would grind if I pushed toward 6th.
Got to a stop light, blipped the throttle a few times, took off, 1st through 4th operated totally normal, still locked out of 5th and 6th with a grind in 6th. Luckily I was only a few miles from home and was able to drive it home in 4th. Got to my garage. Tried shifting around with the clutch disengaged. Still locked outta 5th and 6th. Turned the car off. 5th and 6th no longer locked out. Started it up, I can get into 5th and 6th again. Didn’t try reverse, haven’t had a chance to drive the car again.
Anyone run into this before? I’m not familiar with the internals on these transmissions aside from what little I’ve seen from inside the shift turret. Can’t imagine I bent a shift fork or something like that as the issue went away as soon as the motor stopped spinning.
Transmission is a 6speed with 120k miles that was claimed to be rebuilt with new syncros ~4k miles ago. The fresh silicon protruding from each of the case sections seems to back that claim up. It’s got what’s claimed to be an MR short shifter in it and I replaced the plastic bushing with a brass one (the correct one for a late model vin) when I got the transmission. Car details are in my signature but it’s likely making a little more power as the cam timing was off when it was dyno’ and it was coooold out last night.
Gonna drive the car to work tomorrow and will report back.
Edit: For some reason, my signature isn't showing up in this post. Car's a VVT-swapped built motor with a GT2650r on e85. Made 295whp/270wtq on the dyno but was probably making more last night as it was cold as hell and my cam timing was incorrect when it was dyno'd.
Had a very similar issue.
got locked out of 5/R the first time i ever shifted 4-6, i think it caught the reverse gate but im not sure. A journal bearing had dislodged from the shift fork next to part of the selector on the bell housing side and caused misalignment going into reverse and interfere into 5th. There's another part further in the trans on the same rail i loosened and used to tap it back in (with red locktite)
Copy that, thanks for the insight. Sounds like my issue is a little different still but I'll keep in mind that it may be related to that system. When you got locked out, was it permanent until you went in and fixed the journal bearing issue? Still trying to figure out why my lockout went away after turning the engine off.
I have seen two causes of this sort of problem in the 5 speeds I race.
1) One of the shifter forks has locked a gear in place, due to some detent failure inside, or some damage to the fork
2) The spring fingers the throw out bearing interacts with on the clutch pressure plate are damaged and are interfering with proper disengagement of the clutch.
Copy that. Thanks for the insights guys. I'm gonna see if I can duplicate the issue again later tonight. If so, the trans will come out and apart soon.
Took it out again tonight. Got it up to top speed a few times. Issue happened again once of the three. Shifted down to fourth, no fifth or sixth, then fifth and sixth returned after driving at surface street speeds for a couple minutes.
My clutch pedal was adjusted somewhat low, with the clutch bite point probably a couple/few inches from the floor, and I also haven’t bled it since I replaced the slave cylinder probably a year and a half ago. Gonna adjust the pedal higher and bleed the system before venturing further, as I should probably do both anyways.
Yep, new clutch hydraulics on order. As someone who religously flushes their brakes every 3-4 track days, I'm embarrassed I let this slip past me lol.
I'm still gonna bleed the system tonight and see if it makes a difference. Got a hefty supply of Dot 4 fluid at work and nothing to lose from an extra flush. I'll keep the thread updated afterwards.
this trans wouldn’t go into 6th at laguna this weekend, eventually wouldn’t go into 5th either, then this happened. You can shift without using a clutch on a modern transmission all day long if you’re patient enough. Yes, you should change your clutch hydraulics, but I don’t think that’ll fix your issues. Awaiting results.
I’ll keep you guys posted. Drove the car to work today but didn’t have time to bleed the clutch there. The transmission drove totally fine on the way there and back. Bled the clutch just now. Feels better but yeah, I’m not gonna bank on the flush fixing what seems like a plausible internal issue.
It’s pretty possible that on the last couple passes, the motor was making more than the 280wtq mark that’s generally considered the limit of these transmissions. I’m gonna take it out tomorrow night and see if it does the same thing again. Maybe turn the boost down a bit too.
I was beating on it hard in the canyons all Sunday afternoon and had no issue with the transmission at any point, but obviously didn’t pull it to the top of 6th gear. Wonder if whatever’s going on inside has been an issue for a while, but never reared its ugly head until I took the car up to top speed.
ugly stuff, looks like dirty mercury. I suppose mercury would make a decent hydraulic fluid.... so long as you kept it well sealed with no bacteria or water. But it looks like you may have a bit of everything in there!
I should get a Blackstone report done on it and see what they say lol.
Haven't tried to duplicate the concern again yet but I drove the car to work again today and noted that the occasional 5th to 6th gear mini-grind I've been getting during warmup seems to be gone. More to come later.
I'm not saying I'm ruling out Miata transmissions, but my current search history is full of words like "Getrag" and "ZF". Why am I like this, man.
Took it out again tonight. Same issue still, regardless of input torque (tried in both low and high boost). Trans will shift all the way up to 6th under full load but after downshifting to 4th, it won’t allow upshifts until it cools down. Shift lever gets super notchy moving from left to right as well. Once it cools down, it’s fine. Looks like I’ll be pulling it out and apart at some point soon.
It's possible that you're starting to see an issue like @WigglingWaffles posted. Aisin put press fit journal bearings in the shift forks and with abuse they can work their way out. I had a transmission that was sold to me as "good" that wouldn't go into reverse at all. 1 thru 6 worked fine. Upon tear down, we found that the 5-R fork had a bushing that had backed partial out and wouldn't allow R to engage. It could be that it's locking up while in motion because of load on the shafts, but when its sitting without the motor is can move more freely. As Emilio has pointed out many times, the cast aluminum shift forks in the Miata's AZ6 are its Achillies heal on track. They expand more than the other steel components they are responsible for moving.
Copy that. Makes sense and these journal bearings seem to keep coming up when talking about this issue. If I pull the case apart and find one of them backed out (but not critically damaged like sliding loose inside of the bore), is the general fix just to pop em back in with red loctite? Apologies for the super rookie questions, last time I pulled a manual apart was almost five years ago and I never work on em.
I pulled the shifter out this morning and found the turret dry and one of the locating pins backed out as well. Doesn’t sound like this is the likely culprit still, but figured I’d share anyways.
01-15-2024, 10:13 AM
6 Speed Trans Locked Out of 5th/6th Temporarily
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at least where I'm at its way too cold to even think about touching a transmission.
