Best 75w90 gear oil for vibration reduction?

dnewton3 said:
My thoughts on your quest ...
- keep your hand off the shifter when not actively shifting; whether you believe it or not, the weight of your hand over long periods of time can cause excess wear on the internal bushings, etc. Simply put, the shifter is for shifting; it's not a place to rest your hand.
- No oil is going to dampen the vibrations to any measurable degree better than another; I seriously doubt there is any lube that could quantifiably offer any difference if the same grade is used (GL-4; 75w-90).
- in theory, you'd want a thicker lube, which is ironic, because most folks (myself included) want a thinner lube for quicker shifting and more reliable synchro action
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💥

The first point is not something well-understood by most people, and is a very likely cause of accelerated wear (and sloppiness/vagueness) or early failures. The shifter knob should be treated as a "hands off!" location except when actually changing gears. (y)
 
Toaster said:
I got the quart bagged ones at AutoZone.
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That stuff is not suitable for manual transmissions requiring GL4.

Liqui-Moly just released an acceptable 75w90 GL4, but it is still making its way to stores. Part #22275.

There is Redline MT-90, and there is also Triax. There is also Motorcraft XT-M5-QS, but it is expensive even from Rock Auto.
 
Your shifter bushings may be worn out and at minimum should be replaced. As indicated above by several folks, avoid unnecessarily resting the right hand on the shifter; also use the recommended transmission fluid. If the buzzing and vibrations do not go away, replace the transmission and motor mounts also.
 
Did the motor mount test, it's all good. The trans mount is an aluminum bar holding the rear of the trans to the frame and differential. I guess this is just a thing with rear drive trans. That aluminum bar doesn't have any bushings, but I wonder if any could be added...
 
dnewton3 said:
This is the gussied-up Fiat version of an MX-5; a 2019, right? In the ND Mazda, that trans is very light-weight; it was redesigned for quick revs. I am not very familiar with the Fiat version, but I seem to recall that they stuck with the NC trans for some reason (based on a video of a chassis review I saw on YT). Anyone able to confirm/deny this?
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Yes sir you are correct, the Spider uses the Miata NC transmission. Depending on who or what explanation you want to believe, the most widely reason I've seen given is that the NC trans was more suited to the torque curve of the Fiat 1.4t engine so Fiat went with it in the Spider. The lesser explanation provided by the keyboard warriors on the forums is that Fiat 'knew the new ND transmission was fragile' and didnt want their fine Italian reputation marred by a new, unproven gearbox. Apparently the architecture of the ND version is different and there have been lots of failures being mentioned in the Miata forums. Can confirm, I have seen quite a few threads about it. Much less in the newer versions, but quite a few in the earlier ones. Apparently this transmission is on its 6th or 7th update already, while the NC box only had (or needed) a couple.

As far as the vibration being asked about, this seems to be a common occurrence in the Spider when the factory clutch and flywheel have been replaced by certain combinations of aftermarket replacements. Being that the clutch has been replaced in our example here, I would suggest that might be going on here as well. Were factory parts used in the replacement? I cant really say I've heard too many complaints of vibrations or anything else from anyone who is still on the factory clutch.

I have no first hand knowledge of this, my 2019 is an automatic and I couldnt be happier with it, after half a million miles of shifting Rx7's back in the day, I have exactly zero interest in manually shifting this car or any other.
 
ka9mnx said:
Driveshaft balance?
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Perhaps. Not sure if the perceived vibration actually comes from the transmission.

Btw does this Miata NC transmission really require 75W-90? A 75W-90 is thick for
today's standards. Most manufacturers use some 75W today which is the half of the
viscosity. I'd first find the actuall cause before playing with several MTFs.
.
 
Drive shaft balance isn't an issue. It so does is at idle. I do have aftermarket clutch and pressure plate, but I got the one that's closest to the OEM clutch.
 
Toaster said:
Drive shaft balance isn't an issue. It so does is at idle. I do have aftermarket clutch and pressure plate, but I got the one that's closest to the OEM clutch.
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So it does it sitting still at idle? It's likely normal. I've never had a rwd manual that you *couldn't* feel the motor running through the shifter. Even brand new off the lot vehicles.

You're probably just actually noticing it because you just had the work done and your brain is actively looking for issues.
 
someonesomewhere said:
So it does it sitting still at idle? It's likely normal. I've never had a rwd manual that you *couldn't* feel the motor running through the shifter. Even brand new off the lot vehicles.

You're probably just actually noticing it because you just had the work done and your brain is actively looking for issues.
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Probably. Because when I got it I never noticed any kind of noticeable vibration.
 
So kinda off topic, One issue that may be is the harmonic balancer. The thing has 34k miles on it and the crankshaft pulley is a little wobbly. Was worse before but hasn't been as bad. Maybe the dampers have already went bad and it's making the engine vibrate more. Mounts are def okay. I did retorque the spark plugs which helped mostly with the footwell vibrations, but shifter buzz is probably gonna be in any rear drive car. It's a different experience since I've driving front drive manuals. No torque twisting and buzz in the stick.
 
Toaster said:
Saying that I can put that spec of oil in?
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There is no intermediary viscosity like 75W-110 NS, that's why I said to try 75W-140 NS.

It's worth trying, as it is safe to use in a synchronized transmission. It might quiet it down, it might not.

Product URL: https://www.redlineoil.com/75w140-ns-gl-5-gear-oil

1715135930873.jpg


Another option would be the Red Line Lightweight Shockproof gear oil: https://www.redlineoil.com/lightweight-shockproof

The shockproof will stay longer on your gears.
 
aba4430 said:
Your shifter bushings may be worn out and at minimum should be replaced. As indicated above by several folks, avoid unnecessarily resting the right hand on the shifter; also use the recommended transmission fluid. If the buzzing and vibrations do not go away, replace the transmission and motor mounts also.
Click to expand...
Start with this and put the freaking correct fluid in.
 
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