"Clunk" sound coming from rear end of car

[Kirthasa]

Since buying my '92 5-speed NSX a few months ago, I have been tracking down and eliminating a few minor rattles and other such noises. There is still one that I have not been able to isolate.

When making quick changes in speed or direction (acceleration, braking, or cornering), I hear a clunk sound coming from the rear part of the car. This sound is much like you would expect if you had a socket wrench sliding around in the trunk, except there is just a single noise with each major change in motion.

The noise does not always happen, and it's not a rattle or other more worrisome noise.
However, in a car this well-built, it seems a little unusual. Has anyone experienced anything like this before?

Thanks,
Aaron

 

[ilya]

I get that occasionally when driving over a speed bump or a poorly paved road. I'd like to know what that is as well. Sounds like it's coming from the trunk.

 

[Sig]

I think it has something to do with the clutch. It happens to my car too, usually when beginning movement from a stand still. So first gear and reverse are the most commone times for me to hear it. I am getting my clutch replaced sometime soon, will let you know if the noise stops.

 

[Kirthasa]

My clutch was replaced 1500 miles ago, so I hope it's not the clutch

 

[ScienceofSpeed]

You may be hearing the differential locking and unlocking. A good test is to go to a parking lot. In 1st gear, cruise around (we refer to this as 'boulevard pimpin' <g>) apply throttle, and get back off right away. You should hear a sort of clucking noise as you describe. Repeat until satisfied

-- Chris

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[Kirthasa]

So is that just something to get used to, or a problem with the differential? BTW, there is another possibility in the Troubleshooting section of the FAQ. If the late FAQ Nazi hadn't passed recently, he probably would have pointed us to it: http://www.nsxprime.com/FAQ/Troubleshooting/noise.htm

I quote:
"Rattling Sound From Engine / Exhaust Area"
"[SR - 2001/2/28] My front header was rubbing in the vertical piece of the front beam that as I understand it is part of the front motor mount. [it was] fixed by pulling out the beam and grinding the flange on the vertical part of the mount."

"[MWE - 2001/2/28] It's the same problem I have. It seems to me that this *is* an issue with the RM headers, as I got about half-a-dozen people email me back with the same rattling/clearance problem. Scott at B&B was going to make me up a new front header at no charge (exchanging my old one). I finally told him yesterday that although I think his product's quality and warranty program is second to none, I felt that going through such a song and dance would really just be a waste of time and money, as the new header would likely have the same problem as the old one. My suggestion to make a slight manufacturing modification on the bend of the #6 tube really did not go over very well. That is, he was willing to do it, but he wanted to see my car, take measurements, etc, and it would take "several weeks" to work out the changes to the jig, etc, etc. So, in summary, like the rest of you guys, I will be getting out the trusty old dremel tool and grinding away at the edge of the front motor mount."

Whaddya think? Could this be it? I'll take a closer look at my front motor mount if I can get a good look at it.

Aaron

 

[ScienceofSpeed]

Aaron -- Did you see my email regarding lunch tomorrow or Wendesday? How about we say tomorrow at 1pm in Kirkland. We can listen to your clunk clunks...

-- Chris

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www.ScienceofSpeed.com - Click for more info
www.NSXClassifieds.com - The internet's only exclusive NSX Classified site!

 

[Larry Bastanza]

Aaron,

I have had this "rattle" issue with the RM headers also. I repaired it the same way as most, with a dremel tool to give clearance. Do you have RM headers?? The sound you describe really doesn't seem to be the "rattle" mentioned. The way you describe it sounds like a motor mount "clunk".

A procedure that has worked for many is to LOOSEN the front and rear motor mount bolts. start the car and throttle up the engine to get the drive train to "rock" back and forth (it actually will rotate on the right and left motor mounts. Then retorque the front and rear mounts. This has cured many "clunking" NSX's.

HTH,
LarryB

 

[Kirthasa]

Wow - Thanks. I'll give it a try. Are there good instructions anywhere on how to loosen/tighten the motor mounts?

 

[Larry Bastanza]

Aaron,

This is pretty easy. The front and rear motor mounts are located as follows:

Front: Located on the front side of the transmission (sort of by the shift cables) It is up above the "front beam", a little hidden, you will have to remove the left rear tire, once the car is up on stands. You will have to get up there with a universal socket, 1/2 inch drive extension, just loosen the bolt about 1/2 turn or so.

Rear: This is located (I am going from memory) in the rear at the center, by the engine/trans seam. This one will have easier access. Again, loosen the bolt a 1/2 turn of so. Start the car a rev the engine 3-4 times. If you have a helper, have him goose the throttle, while you watch the drive train rock back and forth.

If you do get together with Chris, I am sure he can point these mounts out to you first hand. Also, I do not have the URL handy, but the service manual is available here on NSXPrime. Pictures tell a thousand words!


I found the URL: http://www.nsxprime.com/FAQ/Reference/1991_svcman/1991_svcman.htm

Section 5, Page 29 shows all the drive train mounts.

Good Luck,
LarryB



[This message has been edited by Larry Bastanza (edited 01 August 2001).]