gaerbox issues

[bainsgs]

Car makes a clanking noise which may relate to the gearbox/slip diff. Car has had a refurb recently after not been driven much. Timing belt etc but gearbox not removed just oil changed with one recommended by Honda. The mechanic I use says it could be the slip diff and not sure if a normal gearbox shop could actually do any refurbs. It almost feels as if something is sticking.

Sorry I am not technically minded but would appreciate any feedback. Could it be as simple as the oil?

Thanks in advance

1996 N Plate manual

[Kaz-kzukNA1]

Diagnosing the noise issue over the web is one of the most difficult thing based on my experience.

Quite often, the source of the noise was completely different from the place/parts that the person described.

You could upload the video file but not easy to diagnose without listening to the noise with having the car in front.

The position of the microphone, sound reflection due to surrounding environment, the equipment used for recording/playback, etc all changes the sound frequency, direction, etc.


Changing the oil (MTF) would change the sound frequency depending on the oil spec but if it was replaced with the one recommended by Honda, then it would be the Honda MTF-3.

You already have one of the best option for the street usage.


You can also inspect the MTF meshed metal filter on the trans case but probably not much use for your case if the noise is really from the DF (differential).


You can do basic investigation by listening for the noise under the following conditions but from what you wrote, best if you can take your NSX to someone with the actual experiences with the NSX Gbox.

In the past, something reported as gbox noise was actually from the drive shaft, wheel bearing, loose wheel nut on refurbished wheel as the coating melted after spirited driving and even the cause was from the engine and not the Gbox.


All conditions with the engine running;
In neutral, 0mph, CL (Clutch) engaged (CL pedal up).
In neutral, 0mph, CL disengaged (CL pedal floored).
Drive on straight line at moderate speed, go through each gears to check any noise difference.
Make 90deg Left and Right turns at crawling speed. Any difference between turning left or right?


I won't go too much into technical detail but for your reference, from 95+, NSX started using the torque reactive style LSD with the helical planetary gears, etc.

Unlike the 91-94 LSD of steady pre-set breakaway torque, the 95+ LSD would increase the pressure force against the pre-loaded multiple friction discs resulting in much higher breakaway torque.


Kaz

[bainsgs]

Kaz,
Thanks for that. In neutral there is no noise, clutch engaged and disengaged. When you put it in first or reverse noise starts quickly but not constant as if something is rotating and then catching. In the Midlands if anybody knows of anybody with experience of the NSX G box. I will double check the oil spec.

Gurinder

[214nsx]

Kaz,
Thanks for that. In neutral there is no noise, clutch engaged and disengaged. When you put it in first or reverse noise starts quickly but not constant as if something is rotating and then catching. In the Midlands if anybody knows of anybody with experience of the NSX G box. I will double check the oil spec.

Gurinder

My 91 Nsx recently developed the same noise as you described, rolling speed forward or backward, noise coming from left hand side/ Gearbox. No noise when car is off the ground. Car starts fine, butter smooth select in any gear. Had the passenger side driveshaft inspected by a mechanic but found nothing abnormal.

Gurinder, please report back if you managed to fix your and ill do the same.

Phil

[bainsgs]

Will do. They did use the MTF-3 oil so nothing untoward there

[214nsx]

Hi Kaz, Where is the MTF meshed metal filter located?

Phil

[Kaz-kzukNA1]

https://lh3.googleusercontent.com/pw/AM-JKLWDJ9Qqf8AjHizYwRuBqSPH5bOrrggEKXj7HAV62wfY1Pw-W0phalP-wLcHqlDRwLtcOF3A0xzLSTeh7gpKRYDWCd4oxASIefdtxQQU1x 1G0uWvntkTQrwkGQECJUkweTL-ehEgQiwnTNncJ-vHDbjBgA=w1080-h608-no?authuser=0
The location.



If the noise is from the DF, probably inspecting the strainer won't tell much.

There is a big magnet plate near the MTF pump so any big particles would be trapped there.

At the strainer, normally you would only see tiny particles from the synchro or gear teeth edge or anything that doesn't stick to the magnet such as the liquid gasket.





https://lh3.googleusercontent.com/pw/AM-JKLUH7K1ZNHDDqzXgLhbqhJQFEaKI2Cf5TGWK7FzSGVqGDk31O K98sCRY6smERZCTLZYzP7yG_NV4Goztx-SCIjN3Vkd-a5tqA4mOylzifGS340t_6IgI0AEUTxvNeNE6KO3Zxe6COuGX_z K_GvtcASd-OA=w1080-h608-no?authuser=0
You'll need the replacement o-ring and the MTF filler washer.

The drain washer is the same one used at the oil pan/sump drain.

If never done before, good idea to get spare cover as you could break the tab.





https://lh3.googleusercontent.com/pw/AM-JKLXObp2nPOuK_15NDKtsSqaiUe2uNZwNeEvw2h96jjh9OcDi3 LoNHfIPYrPAMj2a9tknWPPoJXhF6ugMMdF90f216rRlk1hcNnl m45Jrh5QXh8nDuP3BiKxBT8_izq0_nLbo74SN-FbMKa4eQBvPsjqHNw=w1080-h608-no?authuser=0

https://lh3.googleusercontent.com/pw/AM-JKLVwZjD6abey_No-9D_YbVY-lXLvWEJj6gPf1q02GEfFVbaI6o2JpFkzv5tRsiC0yC-xQlPYvPPm-vKyCRKHD6zOqiSmmy2eBZ5F2lBN3gQxii6gQh6dUGUX_2JH2wL fRTkrFRcXmYNfhp9OltdUWjI8Cg=w1080-h608-no?authuser=0
If not treated in the past, by now, the blue section of the strainer cover is already heavily oxidised and bonded to the trans case.

This makes the removal of the cover time consuming if not done previously.

On installation, just coat the blue section and the backside of the tab with the silicone grease.

Never apply leverage force trying to lift the cover using the tab marked in red.

Instead, apply force in the direction marked in yellow to 'rotate' the cover back and forth.

This will break the oxidation and while trying to rotate the cover, change the direction of the force just a little to pull the cover outwards.

Repeat it and eventually, it will come off.





https://lh3.googleusercontent.com/pw/AM-JKLU-krayBV5b8qOZoR4jek6s5Dmax6Dyc9-YSEHuKTBwA8vDnBcGOjivA07Wf_B595DF3sSQIyo9x5V20l6iK NFRS_VWrvQ_izg3ldP1PyHDTC5xZsBrWPkhNq1YXLdx5MM0fVJ R0GdFVgHmmyWMyy5TCA=w1080-h810-no?authuser=0
The example of what you would expect inside the strainer.

Just a tiny metal bits with metal powder.





https://lh3.googleusercontent.com/pw/AM-JKLWjEqR8DhV5UzhMKvD28X2PR2O2EdCck_Ar4eEEgTByA1Zz6 Ju_ArCW675XiwHsew5N-Y0Tz4AKrRJvrF4HlzIyX0U16yTH-85wnsardFIZsFU3Jm_k_Ur3U5SXdnHbDdjIOjmlSwlF68i_l4m ZZoRg-A=w1080-h810-no?authuser=0
The worst one so far….. It's not metal and in fact, excessive amount of liquid gasket.


Kaz

[214nsx]

Thank you Kaz��

[214nsx]

So just a little update on my side. I replaced the diff oil from Honda MTF-3 to Royal Purple and the noise had disappeared.

[Kaz-kzukNA1]

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

[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