6spd Manual Transmission Problem: 3rd Gear Keeps Popping Out

It's been a while since I've been on the forums but necessity has brought me back in...

I had noticed over the past few years that my car would periodically slipping or jumping out of gear. Wasn't even sure what gear since it was infrequent. I thought maybe I was not pushing in gear possibly and tried to ignore it knowing a resolution would likely required a large wallet.

Well.... I took her out this weekend for a long drive and there is no longer a question. It's very specifically 3rd gear. It jumped out of gear at least 7 or 8 times over the course of 4hrs. That's not great. Odd since aside from the early snap ring, I don't recall too many transmission issues. Here is my baseline data, I'm interested in thoughts on what could be wrong and then the big question is, where do you get that fixed?

2000 NSX-T
6spd
68k Miles
Had the fully serviced by Larry B at 58k miles (timing belt, slave cylinder, etc) so she is really taken car of generally.

I do have a short through shift kit from SOS and I have an NSX-R stalk so it's a pretty tight throw. I don't think this is the cause but do need to include that information. Note, it has gotten worse over time.

My thoughts: I speculate it's a Synchro. I do always blip the throttle on down shift. Not sure if that is positive or negative in relation to synchro wear but I would think at worst it would be neutral. I only put a few thousand miles a year on the car so I was thinking of waiting a while and maybe until I needed a clutch. At that point, may need to send the tranny out for a full rebuild/check. I recall hearing about having an option of having the gears hardened with a coating but frankly this may be my own urban legend at this point. I'll be in a position to potentially remove the tranny out myself in a year or two (making some new house and lift plans for next year). I enjoy working on the car more now that I have a spare toy for when she is down (GT350). That said, I'm no mechanic.

Thoughts?

SUMMARY CONCLUSION (10/9/2021): Tranny had a lot of problems and many parts were replaced. Mechanics Direct in Lowell Mass did the work and seemed excellent to me. Source: Best guess from them was the car may have been hammered on in its early life, my Short Shift Kit was binding a small amount, resting hand on shifter or some combination. Clutch was also in really bad shape. Details in a further post in this thread but that's the rough summary. Wallet now empty but car runs great...

Well, I think there's a problem with the gear/synchro sleeve/hub/shift fork.

A short shifter kit does accelerate the wear on the synchro but I don't think it's the problem of a gear popping out. So no easy solution.

Do you have the habit to rest the hand on the shift lever while driving?

You might check the easy stuff first, like the engine/trans mounts, shift cables & adjustment, transmission fluid condition and level, that sort of thing. That said, I would lead towards an internal transmission problem since you say it's only 3rd gear so far.

You should throttle blip/rev-match when downshifting, if anything that should reduce overall wear when done properly. Another note is not to rest your hand on the shifter when driving. There is a direct mechanical link between the shifter, cables, shift forks, and slider hubs, so applying constant pressure on the shifter can cause accelerated wear on all those parts. At only 68k miles, I don't think most people would expect to have a gear pop-out issue yet.

It is possible that an internal part related to 3rd gear has abnormal wear, which can include the 3/4 slider & hub assembly, the shift fork, and 3rd gear itself if the dog (engagement) teeth are worn. As long as the synchro spring is in good condition (provides some detent action for gear selection), the synchro is probably not the main cause, but it should be replaced during a rebuild regardless.

Here's an example pic of engagement teeth wear on the left. Same story with the gear slider/hub teeth, and the wear on the shift fork should be checked. I would budget a bit more than usual for an upcoming rebuild during your clutch job to account for having to replace a "non-wear" item like a gear or shift fork. Coating or WPC treating the gears seems like overkill to me for street or occasional track use.

Car shifts very smooth. I consider myself being a particularly “easy shifter”. Meaning I will hammer on the car a bit as far as running out the RPM up to 7,500 but very conscious of being easy on the tranny. Never shift hard, never quickly with a lot of pressure and never dropping the clutch. So I think I’m as nice to it as I can be. I bought it with 43k miles which of course I can’t speak to.

Resting on the stick... I keep my hand on the side to some degree. I’ve been suspect of that being an issue that is always flagged if light pressure. I’m not leaning on it. When I left go it’s in no way “recoiling” which tells me I’m not impacting it’s position. I do get if your really putting downward pressure. That I’m not doing.


Sent from my iPhone using Tapatalk

“BIG” I see your note also. Will certainly try to start easy but I’m already budgeting in the $10k range for the next service to account for the $120k full service and this transmission deal. I would like it to be less but like to be surprised downward not upward...


Sent from my iPhone using Tapatalk

Even a light pressure on the shifter of an MT has serious consequences in the long run. The shifter is there to shift gears only, nothing else.

I guess you have time to wait 1-2 years. It won't hurt the gearbox. Do plan to collect/order the parts you want to change early enough. Some parts are backordered.

You can try the easier things first like oil change, adjusting the cable but I doubt it will cure it. I'm pretty sure you have to open the gearbox and this means all new synchros and bearings and some more parts involved.

Sounds like a classic synchro issue but as mentioned here.. try the easy "fixes" first.

I can't remember exactly when, but the 6 spd synchros were redesigned/improved in the newer years. I want to say it coincided with the facelift but my memory fails me on exactly when that was done. When rebuilding 6 spds (e.g. for a aftermarket LSD for example) it's standard practice to use the new conical synchro from Honda.

RYU said:

Sounds like a classic synchro issue but as mentioned here.. try the easy "fixes" first.

I can't remember exactly when, but the 6 spd synchros were redesigned/improved in the newer years. I want to say it coincided with the facelift but my memory fails me on exactly when that was done. When rebuilding 6 spds (e.g. for a aftermarket LSD for example) it's standard practice to use the new conical synchro from Honda.

Click to expand...

According to Larry B. the 6spd transmission in the '97-'99 & '04-'05 have dual synchros on every gear EXCEPT 5th and 6th. For 2000-2003 the transmission had dual synchros on every gear.

NSX_n00b said:

According to Larry B. the 6spd transmission in the '97-'99 & '04-'05 have dual synchros on every gear EXCEPT 5th and 6th. For 2000-2003 the transmission had dual synchros on every gear.

Click to expand...

Thanks for the clarification!

goldNSX said:

Even a light pressure on the shifter of an MT has serious consequences in the long run. The shifter is there to shift gears only, nothing else.

I guess you have time to wait 1-2 years. It won't hurt the gearbox. Do plan to collect/order the parts you want to change early enough. Some parts are backordered.

You can try the easier things first like oil change, adjusting the cable but I doubt it will cure it. I'm pretty sure you have to open the gearbox and this means all new synchros and bearings and some more parts involved.

Click to expand...

....I'm still not buying this for a linkage transmission but will work to stop this regardless since obviously no downside. Oddly I had to go into work today (been working from home since March) and its 70 which is new to those of us in New England. Point being, I drove the Acura since it was on my mind. I was seeing how much I leave my hand on the shifter. I would say a pretty good amount with light pressure. That said, directly downward pressure there just isn't anywhere to go. It's a hard stop at the lever mechanism underneath to my recollection so I can't see how that would make a difference. Leaning on it sideways would be a different matter IMO. I would really like to see the science for this specific transmission. I've had a direct drive tranny before and it made more sense. Even my Mustang is affected to some degree because it has that stupid push down to be able to go into reverse. Summary: I'll work on it but I'm not sold it has any effect.

NSX_n00b said:

According to Larry B. the 6spd transmission in the '97-'99 & '04-'05 have dual synchros on every gear EXCEPT 5th and 6th. For 2000-2003 the transmission had dual synchros on every gear.

Click to expand...

Helpful, thank you. I have to look for an expert to rebuild it. If it's coming out of the car (whenever that is) I want it back to new or better. No point skimping after all that labor.

The way I envision the linkage connection is that the shift fork is basically directly connected to your hand through the shifter, even with steel cables instead of a turret or direct-mount shifter. The fingers of the fork push against the gear selector sleeve, which pushes the sleeve across the synchro and spring to match the teeth of the sleeve with the gear engagement teeth.

The sleeve is keyed to the hub which is keyed to the shafts of the transmission, so the sleeves and hubs always rotate with the transmission shafts when the engine is on. By applying pressure to the shifter in gear (either forwards or backwards), the fork fingers can press against the sleeve (which is always moving), which can wear down the fingers of the fork and the sleeve itself. That's why the fork and the sleeve have specified service dimensions in the manual, if they are worn (i.e. too much clearance) then it will be difficult to fully engage & disengage a gear. In your case, this might mean that 3rd is not completely engaged by the sleeve when you shift because of the worn parts, which makes it so that the sleeve occasionally pops back across the synchro spring and disengages the gear. This can be further exaggerated by worn gear engagement teeth, which can allow the sleeve to slip back off the gear.

Similarly, applying side pressure on the shifter can apply undue force to the shift pieces via the select lever that controls which shift fork is moved, and those all have service limits of <1mm of wear.

Pic of a 5-spd for reference. You can see the distance between the fork fingers and the edge of the sleeve is quite small. We're talking about <1 mm here, if the clearance is over that limit you're meant to replace the fork or sleeve & hub. Take the time to find a quality transmission expert that's willing to take all the necessary measurements and recommends replacing parts that are out of spec instead of just replacing synchros & bearings and calling it good.

Big McLargeHuge said:

The way I envision the linkage connection is that the shift fork is basically directly connected to your hand through the shifter, even with steel cables instead of a turret or direct-mount shifter. The fingers of the fork push against the gear selector sleeve, which pushes the sleeve across the synchro and spring to match the teeth of the sleeve with the gear engagement teeth.

The sleeve is keyed to the hub which is keyed to the shafts of the transmission, so the sleeves and hubs always rotate with the transmission shafts when the engine is on. By applying pressure to the shifter in gear (either forwards or backwards), the fork fingers can press against the sleeve (which is always moving), which can wear down the fingers of the fork and the sleeve itself. That's why the fork and the sleeve have specified service dimensions in the manual, if they are worn (i.e. too much clearance) then it will be difficult to fully engage & disengage a gear. In your case, this might mean that 3rd is not completely engaged by the sleeve when you shift because of the worn parts, which makes it so that the sleeve occasionally pops back across the synchro spring and disengages the gear. This can be further exaggerated by worn gear engagement teeth, which can allow the sleeve to slip back off the gear.

Similarly, applying side pressure on the shifter can apply undue force to the shift pieces via the select lever that controls which shift fork is moved, and those all have service limits of <1mm of wear.

Pic of a 5-spd for reference. You can see the distance between the fork fingers and the edge of the sleeve is quite small. We're talking about <1 mm here, if the clearance is over that limit you're meant to replace the fork or sleeve & hub. Take the time to find a quality transmission expert that's willing to take all the necessary measurements and recommends replacing parts that are out of spec instead of just replacing synchros & bearings and calling it good.

Click to expand...

I hear you on the shifter resting. The only movements that affect the cables are left/right and fore/aft; down does nothing. Admittedly if you had enough pressure on the top of the stick it may deflect in any direction then making your argument sound. Always a chance, but I'm still doubtful. Regardless, I'll work on my habits.

I completely agree on the final comment. I want 100% inspection back to factory for sure. Definitely not the place to take a short cut since just getting the transmission out and back in is probably $2k in labor (unless I man up which is questionable at this point). I will not be going cheap on the rebuild.

N-Wing said:

I hear you on the shifter resting. The only movements that affect the cables are left/right and fore/aft; down does nothing. Admittedly if you had enough pressure on the top of the stick it may deflect in any direction then making your argument sound. Always a chance, but I'm still doubtful. Regardless, I'll work on my habits.

I completely agree on the final comment. I want 100% inspection back to factory for sure. Definitely not the place to take a short cut since just getting the transmission out and back in is probably $2k in labor (unless I man up which is questionable at this point). I will not be going cheap on the rebuild.

Click to expand...

Pushing down on the shifter doesn't hurt theoretically, that's correct. But the angle is always different in every gear. When you hold the shifter in your hand while in gear you can feel some fine vibrations. The more you push it in one direction the more vibrations you feel. The lack of free play kills the involved parts in the long term. If you remove the shifter cables you'll notice that there's no H-schema in the front (unlike a Ferrari for ex.). It is only defined by the gearbox internals. Adjusting the cables only moves the center of it a little bit. Unlike it's completely off adjusting won't cure it.

When I did mine I've found this:


Guess what gear? Yes, 5th. Not sure if shifter resting was the cause as I don't own the car since new. And yes, the 5th popped out on special circumstances.

Good luck!

Clearly the only solution to less resting of hand on shifter is to encourage more white knuckle driving on steering wheel! haha

you'd be surprised how many novice drivers liked to keep touching their "knobs" at hpde's.....

Pretty common even in Europe when sportcars were MT. It looks too cool not to do it.

N-Wing said:

Car shifts very smooth. I consider myself being a particularly “easy shifter”. Meaning I will hammer on the car a bit as far as running out the RPM up to 7,500 but very conscious of being easy on the tranny. Never shift hard, never quickly with a lot of pressure and never dropping the clutch. So I think I’m as nice to it as I can be. I bought it with 43k miles which of course I can’t speak to.

Resting on the stick... I keep my hand on the side to some degree. I’ve been suspect of that being an issue that is always flagged if light pressure. I’m not leaning on it. When I left go it’s in no way “recoiling” which tells me I’m not impacting it’s position. I do get if your really putting downward pressure. That I’m not doing.


Sent from my iPhone using Tapatalk

Click to expand...

No its not pressure on the shifter , I drive my 97 (6 spd) very similar , no speed shifting or power shifting . the fact that it shifts without grinding proves the 3 rd speed blocker ring is ok ,your problem is there is not a total engagement of the shifter sleeve dogs (detents) that hold it in gear . I am not familiar with your after market shifter but i suspect you have a engagement travel problem . You have to put car in 3 rd gear ,remove cable to transmission shifter fork and see if you can move shifter fork for more engagement . This is not first time i have seen this ,difficult to diagnosis without seeing car ,

ralph cerbone said:

No its not pressure on the shifter , I drive my 97 (6 spd) very similar , no speed shifting or power shifting . the fact that it shifts without grinding proves the 3 rd speed blocker ring is ok ,your problem is there is not a total engagement of the shifter sleeve dogs (detents) that hold it in gear . I am not familiar with your after market shifter but i suspect you have a engagement travel problem . You have to put car in 3 rd gear ,remove cable to transmission shifter fork and see if you can move shifter fork for more engagement . This is not first time i have seen this ,difficult to diagnosis without seeing car ,

Click to expand...

Excellent point - I, too, have seen popping out gear caused by short shift kits and even leather shift boots that have shrunk with age. The only other thing that I have seen causing this failure of the gear to remain locked to the shaft that hasn't been mentioned is worn bearings.

tucsonsx said:

Excellent point - I, too, have seen popping out gear caused by short shift kits and even leather shift boots that have shrunk with age. The only other thing that I have seen causing this failure of the gear to remain locked to the shaft that hasn't been mentioned is worn bearings.

Click to expand...

yes you are correct ,worn bearings cause the shafts to move . How ever the indicator will be as you accelerate and release the throttle ,you will see movement in the shifter , depending how worn the bearings or housing are . When the gear box slips out of gear we call it walking out of gear ( techs with 50 yrs experience repairing trans will know what i"am talking about .

Those of us who have been wrenching for 50 also remember when techs were called mechanics.

.....ahh the good old days when we had head nurses....

So the "Old Tech".....should be able to set the points and adjust the Carbs eh?

Bram

Certainly, and the only electronic stuff a mechanic needed was a dwell meter, a timing light, and a VOM. The keys never got lost because they never left the ignition the entire time the car was in the garage. The shop rebuilt engines, transmissions, and differentials ( find a " tech " who can explain how a diff. works ). The heavy line guys started the day with a coffee Royale. Why I remember when....

And, docjohn, we patients miss the head nurses too.

:biggrin: