gaerbox issues

[Old guy]

A suggestion as to a possible cause.

At some prior point in time, was a friction modified transmission oil such as Red Line MTL or GM Synchromesh Modified used in the transmission? If the oil was used undiluted (not the 1:2 or 1:3 cocktail mix) the friction modified transmission oils canl lead to erratic operation of the limited slip differential (premature locking). There was one post on NSX Prime from > 15 years ago describing the differential problems that emerged from using 100% Red Line MTL. The problem was resolved after the oil was changed; but, did not completely resolve until after a couple of flushes. The first oil change with Honda MTL and subsequent change with Royal Purple may have succeeded in cleaning the original fluid out of the LSD clutch plates.

Just a hypothesis.

[214nsx]

Thank you for the update, Phil.

Interesting. OEM DF (differential) or aftermarket one???

I know fair amount of owners in US used 'cocktail' mix for the MT oil when they experienced difficulty in gear shifting.
For me, this is just hiding the issue and not a fix because for street driving, one should not have any shifting problem with the Honda MTF3.

Some even reported new issue on DF by using the cocktail method despite the significant improvement on the shifting difficulty.


The earlier spec DF has multiple CL disks with embedded friction material and soaked in the MTF.
It's pre-loaded and constant locking force regardless of the input force difference between the R & L shaft.
The spring washer/plate sets the friction force and the locking won't start slipping/break out until after exceeding the pre-loaded torque.

So, using different MT oil will change the characteristic of the locking/slip behaviour.
For the clarification, this doesn't mean good or bad on the DF friction disks.

Would be interesting to hear the update in longer term as I know some owners in Japan are using customised RP fluid in their MT box.


Kaz

Kaz, I'm not sure if it had an aftermarket diff, I can only put 2 and a quarter liters of oil in.
What is the correct amount from your experience?

So long story short.. my car had a clutch change at (A S MOTORSPORT end of 2019) not sure what oil they use after they replaced the clutch. Soon after that the engine needed a rebuild so the gearbox oil was drained out and stored in a plastic container.
4 months later when the engine was ready to go back in I thought it would be better to have new oil in the g/box. I put 2 liters of Honda MTF 3 in but not enough so added about half liter of the old oil in, perhaps it was mixed with 2 different type of oil.

[Kaz-kzukNA1]

Kaz, I'm not sure if it had an aftermarket diff, I can only put 2 and a quarter liters of oil in.
What is the correct amount from your experience?

So long story short.. my car had a clutch change at (A S MOTORSPORT end of 2019) not sure what oil they use after they replaced the clutch. Soon after that the engine needed a rebuild so the gearbox oil was drained out and stored in a plastic container.
4 months later when the engine was ready to go back in I thought it would be better to have new oil in the g/box. I put 2 liters of Honda MTF 3 in but not enough so added about half liter of the old oil in, perhaps it was mixed with 2 different type of oil.

Not scientific measurement but I normally pour about 2.7 - 2.8L of MTF into the Gbox and wait for the excess to drain out.
So, if you were only able to put 2.25L in, very likely to be aftermarket LSD.

With our MT box, only part of the mechanical gears are submerged in the MTF.
There is a small trochoid pump at the bottom of the trans case driven by the final driven gear.
Thus, unless the wheel starts rotating, trans oil won't be pumped out to properly lubricate the gears, bearing, etc.

This is the reason why you need water like viscosity even at cold temperature but really strong oil film at the same time.
That is the characteristic of Honda MTF-3.

On the other hand, instead of using the ordinary widely used synchro key mechanism, Honda went with unique (though I would say 'strange') spring method for their synchro.

It relies on the tension of the spring and with such thin body, don't know how the manufacture can control the tension spec.
Probably this is the reason why many people experienced shifting difficulty and searched for the aftermarket 'cocktail' solution.

On track, even just after few laps, the trans oil gets so hot that you would notice the changes in shift feeling if usimg the Honda MTF-3.
Potential cause of using such strange spring tension based synchro with trans oil chemical change/breakdonw under extreme temperature.
It's not that expensive so just replace it after the event.

A suggestion as to a possible cause.

At some prior point in time, was a friction modified transmission oil such as Red Line MTL or GM Synchromesh Modified used in the transmission? If the oil was used undiluted (not the 1:2 or 1:3 cocktail mix) the friction modified transmission oils canl lead to erratic operation of the limited slip differential (premature locking). There was one post on NSX Prime from > 15 years ago describing the differential problems that emerged from using 100% Red Line MTL. The problem was resolved after the oil was changed; but, did not completely resolve until after a couple of flushes. The first oil change with Honda MTL and subsequent change with Royal Purple may have succeeded in cleaning the original fluid out of the LSD clutch plates.

Just a hypothesis.

Yes, I heard similar story from one UK owner.

His NSX had to be rescued to Honda dealer due to sudden huge judder/vibration from the gbox only when making the turn. Straight line was fine.

At the end, the dealer had to flush the gbox like 5 times and the judder was gone.

Kaz

[Old guy]

On the other hand, instead of using the ordinary widely used synchro key mechanism, Honda went with unique (though I would say 'strange') spring method for their synchro.

It relies on the tension of the spring and with such thin body, don't know how the manufacture can control the tension spec.
Probably this is the reason why many people experienced shifting difficulty and searched for the aftermarket 'cocktail' solution.

On track, even just after few laps, the trans oil gets so hot that you would notice the changes in shift feeling if usimg the Honda MTF-3.
Potential cause of using such strange spring tension based synchro with trans oil chemical change/breakdonw under extreme temperature.
It's not that expensive so just replace it after the event.

Kaz

Perhaps that explains why my 2000 6 speed is very 'cranky' when cold. You need to be relatively slow and deliberate on the 1 - 2 and to a lesser extent 2 - 3 shifts to avoid balking or a grind. Once the transmission gets truly stinky hot the shifting turns perfect; but, getting stinky hot does take a while if the ambient temperatures are around 20 C.

I tried the cocktail mix and found that it made no material difference to the cold shifting so it was back to straight up MTF. Honda / Acura does not sell MTF-3 in Canada, only MTF. The on-line vendors for MTF-3 all appear to be non North American. Does Honda sell both MTF and MTF-3 in GB or is MTF-3 just the latest version of MTF in GB? Some packaging from the US calls it MTF HG