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Drive train slop, loud bang when shifting

28 January 2019
Hey NSX Prime. New owner, this is a great place for info. Thanks for all of it. I have an NSX with an aftermarket clutch that I just picked up. Generally ok to drive, but if I drive it hard, the shift from first to second is so violent it sounds like the engine is trying to bash through the fire wall. I have heard clunks from driveshafts before and this is no that. If this was driveshaft slop, the u joints would have snapped by now. And hard shift from first to second makes a bang lounder than the radio on full blast and it feels like the car is punching the back of your seat. There is a shockwave of the bang that shakes the entire car. What is going on here?

Checked motor mounts and they are good. Checked driveshafts and they have equal play.

Noise sounds like it's coming from a clunk in the trans or the read diff. Any suggestions on where to look next?

Hate to ask, but could it be a trans or diff failure, or could the aftermarket clutch just be that violent when it engages?

It does it at high and low rpm, higher the rpm the louder, and if I rev out first, lift clutch and gently get into second, I can make it mostly go away, but any shifting under power causes it. Same thing happens in other gears, just not as loud or violent.
First, welcome, you're going to really enjoy the car once you get it sorted out. What you're describing is definitely not normal, and I can't imagine it would come just from an aftermarket clutch. I've been reading about NSX's for 10 years now and I've never heard of anything remotely like that. When I first read your post I thought motor mounts, I would check those again just to be sure.
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Could that really make a sounds that loud. It literally sounds like getting rear ended. I'll dig a little deeper tonight
Actually not if the rubber is just broken and still there. But the added play could let the engine/gearbox combo hit something somewhere. Start with the rear mount as it's easy to check. If the front one let go the rear one won't survive long...
People's assessment of noise is subjective, so it is extremely hard to be definitive about your problem.

As an observation, the NSX drivetrain seems to have a largish amount of lash in it. The 6 speed gearbox seems to be a little worse than the 5 speed in this respect. The OEM clutch on the 6 speed box has a relatively narrow engagement point on it which makes smooth jerk free take offs a bit of a challenge. The lurch, near stall, disengage, rev the engine, pop the clutch again kind of start seems to moderately common with new owners. Aftermarket performance clutches just make this problem worse because of typically narrower engagement points. My observation about some owners is that they deal with the lurch / stall problem by revving the engine up to around 2000 - 2500 RPM and then slide the clutch out. Gets you a very quick stall free start, short clutch life and perhaps a rear ender into the back of the car ahead of you if its rush hour traffic. Getting a smooth start without starting with a 2000+ RPM engine speed requires some finesse.

Do as suggested and check the front and rear engine mounts to confirm / eliminate them as a source of the problem. The front one is a hassle to get eyes on without removing stuff - one of those remote inspection cameras might help. You didn't specify the year / mileage on your vehicle. A high mileage older car is definitely a candidate for worn mounts, particularly if it has been enjoyed vigorously by previous owners. A completely failed front mount could certainly materialize itself at a bang at the back of the seat region following a 1-2 shift followed by full throttle.

If the mounts seem OK, then jack one rear wheel up off the ground and with chocks to prevent movement of the vehicle, the transmission in gear, emergency brake off and the wheel removed, use a bar between the wheel bolts to rotate the wheel back and forth. This may allow you to determine the location of the noise. A lot of rotation in the hub would be unusual. I did this on mine; but, its been 6+ years so I can no longer give you a quantitative number for the degrees of free play. Repeating left to right may allow you to assess the relative condition of the L/R driveshafts. Of course, if you spot split driveshaft boots or ooze from the boots you could have an answer to your noise. Not sure about your reference to U joints since the NSX does not have any. Do you mean the inner and outer tripod joints on the driveshafts?

If your car is still moving, it is clear that you have not had a transmission or differential failure. Wear in the differential will certainly increase drivetrain snatch; but, usually comes with continuous noise / howl telling you there is a problem. Same deal with gearbox bearing wear and its usually the synchros that become a problem first in the box short of outright knocking some teeth off of a gear pair! That would definitely make continuous noise. You can try a drain and flush on the transmission (always good if you don't know the last time it was done). If the fluid comes out with a bunch of shiny metal bits in it, then you have a transaxle issue. If the fluid comes out clean then chances are that the wear levels are probably normal.

If you list your location, you may be able to find another local Prime member who can meet up with you and go for a short drive in your car. This could give you a quick read on whether your noises are abnormal.
Thanks for the reply. I will try all of those things and see. While my first NSX, this is far from my first performance or modified car and the noise is certainly not just lash. This shift it's more violent than the 1-2 shift of my 900hp Supra on slicks. And that has a super single that is the worst clutch I have ever driven.

I also have no trouble with low rpm smooth starts. The clutch chatters a little but that's perfectly tolerable. High rpm shifts under power sounds like the block is rhino trying to smash through the firewall. I am going to swap out the motor mounts early next week. Maybe I just missed something in the front motor mount. This is the first NSX I have ever turned a wrench on, and I know nothing about trans axles or mid engine, all the same concepts but I appreciate the insight. I'll do the motor mounts and reassess the driveshafts then report back and let you know what I find.
when you're wrong you're wrong and I was. The front motor mount was shredded. I didn't get a good enough look at it until I really got under there. It has now been replaced with innovative mounts urathane mounts front and rear..... Also the PO had put the wrong bolts in almost every place under the car and couldn't even spell torque wrench which lead to some drilling and tapping in the trans case and the side of the block. Thanks for the advice everyone
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Also the PO had put the wrong bolts in almost every place under the car and couldn't even spell torque wrench which lead to some drilling and tapping in the trans case and the side of the block.

re wrong bolts. Honda used dacrotized bolts for most of the parts that attach to the body. Dacrotized is notable for a greenish - grey coating on the bolts. The coating addresses galvanic corrosion problems when using steel bolts on an aluminum structure. Make sure that the bolts attached to the body are correct. The dacrotized bolts can be hard to source. In a pinch, galvanized zinc bolts can substitute; but, avoid ungalvanized steel and stainless steel fasteners.
Thanks! I made sure for all of that stuff, by wrong I mean that the front mm bolts we're three different lengths. 25mm 40mm and 60 mm