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Front end clunking noise while hitting bumps (with a video)

24 October 2017
Hi guys, I owned a 1991 NSX for about a year and a half now. When I first bought it the car came with the newer 7 spoke nsx wheels and stock suspension. Every once in awhile I would hear a loud clunk noise from the front end when hitting big bumps. It did not happen often so I never looked into it, than I put aftermarket wheels and tires on it when I did the noise went away on all bumps. Fast forward to now I put a comp tech spring on the car which lowered it about an inch and the noise is back and happens a lot more since going lower. It is a higher mile nsx at 182,000 so I am paying special attention to the steering rack maybe being worn? I am still new to this car and not 100% familiar with diagnosing this, what are common causes of front end noises in these cars?

Things I have done...
-Checked the entire front end and nothing is loose, or seems out of place
-The wheels and tires are not rubbing or coming into contact with anything (its made the noise on my Stock wheels, and my Volks)
-I unbolted the front sway bar and hit some bumps with it like that and the noise still persisted
-I did jack the car up and noticed a slight play in the steering arm coming out of the rack on the passenger side, and noticed no play on the drives side (maybe a Knock bushing could help?)

The car drives straight and gives me no problems, it does not matter if the wheel is straight or turned it will make the noise either way when I hit a bump. And the noise is made on both the driver and passenger side.

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I was going to suggest your sway bar, but looks like you already checked that.
Did you check the spare tire mount and battery?
Thats a good idea about the spare tire mount, and battery I will check those. I probably should of mentioned this but the struts were replaced about 30,000 miles ago they could be the cause of the noise but the probability is low. Im going to look into the steering rack, my only doubt with that is the noise is made with both sides not just the passenger like what a worn steering rack suggest.
Have a deep look into the special feature of the front suspension. On hard bumps the front wheel moves to the rear. There are bushings and joints you can't check by applying force on the wheel only.
Weird question but does your steering wheel move in and out over large bumps?
I can check into the struts to see if they are missing something. I'm not too familiar with this cars suspension what exactly is the "special feature of the front suspension"? And I've never noticed my steering wheel moving back and fourth over bumps I doubt it but will pay attention to it next time it happens just to be sure. Would that suggest something is loose with the steering rack?
....I'm not too familiar with this cars suspension what exactly is the "special feature of the front suspension"?.....

The feature that [MENTION=10201]goldNSX[/MENTION] was talking about is the compliance pivot.

See page 131
Section: Double wishbone Front Strut Suspension
https://books.google.com/books?id=Y...=compliance pivot assembly suspension&f=false

You can also see the description from SOS. I'm not suggesting you need to buy the clamps....instead, just pointing out the description.

Check out [MENTION=18194]Honcho[/MENTION] build. He removed the front assembly and provided some glorious photos for reference.
I can check into the struts to see if they are missing something. I'm not too familiar with this cars suspension what exactly is the "special feature of the front suspension"? And I've never noticed my steering wheel moving back and fourth over bumps I doubt it but will pay attention to it next time it happens just to be sure. Would that suggest something is loose with the steering rack?
If you have play in the steering rack it'll be on the right side mainly or first. Grab the tie rod. wiggle it and listen.

Thanks to [MENTION=32903]natcc99[/MENTION]: that's the 'special feature' There is ball joing and a rubber bushing, (let) check both.

Who installed the new shocks back then?
When your front struts were replaced, was the rubber bushing in the upper shock mounting plate replaced? If that bushing is worn or the mounting has become loose it can create noise. Its difficult to identify the problem because the spring keeps the part 'loaded' eliminating movement when the car is on the ground or up in the air. The noise may only show up during the transient unloading that occurs with large scale suspension movement. That is why the push down on the front end / shake the suspension test may not result in any noise. Unfortunately, I think disassembly and inspection is about the only way to determine whether it is the source of the noise. You can have the same problem with the lower bushing on the strut; but, I expect that will be new if the struts are new. The only thing conspiring against this as a noise source is that it would be unusual for both the right and left side mounts to fail at the same time.

Unfortunately, I think that diagnosing noise in the compliance pivot assembly requires the same kind of 'removal to inspect' approach.

At 28 years and 182,000 mi, it would not be unreasonable to expect that some / all of the (original) pivot points in the suspension are at or approaching the end of their operational life. A plan to do a partial tear down and full inspection of the front end suspension pivot points might be prudent.

Edit: As an additional test, try driving along on a quiet road at about 40 - 50 km/hr and apply the brakes briefly with 'typical' pedal pressure. Listen for clicking or clunks. This brake application will cause a rotational torque to be applied to the A arms which tries to move them in a horizontal plane (and vertical). Absence of noise would not eliminate the compliance pivots as a source; but, perhaps suggest that you look elsewhere first.
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I got some new (used) OEM springs from someone here. I am familiar with the clunk sound when going over holes/bumps on the road. Not so much anymore. I believe my suspension system was shot. Simply replacing with OEM did wonders, even with 50,000miles already on them.
Okay guys we are going to take this too another level, I bought some used struts and plan on putting them in which should help further diagnosis this, while I am in there I am going to replace the bushings too. I located and bought the smaller set of bushings, but am having trouble finding the large rubber bushing that sits between the spring and top hat does anyone know if that part is available?

To be specific I am wondering where i can get the "spring mounting rubber"

Screen Shot 2019-02-28 at 8.30.40 PM.jpg
Forgot to mention maybe I should replace the bump stop as well, does anyone know if I can order that bushing alone?
The "spring mounting rubber" is part number 51686-SL0-003. Roughly $40. The bump stop is part number 51722-SL0-003. Roughly $30. Can be ordered from any Acura dealer or from www.acurapartsforless.com They offer a 5% discount using code 5NSX.
Okay guys got an update for everybody, first thing the cars injectors are at RC for a cleaning so no test drives to really validate anything.

However I bought a used set of Bilstein Struts to replace the originals, bought the upper spring rubber mounts to replace the existing, and replaced the remaining bushings in the strut and spring assembly. Not only that but as I puled out the originals I noticed the two front struts had no bump stop in them what's so ever so I believe that is most likely the cause of the noise.

Now onto another thing a few weeks ago before I put the new struts, and bushings in I noticed the cars left front was lower than the other side, I measured the distance from my driveway to the front fender line and the right side came in at 25 inches (what it should be) and the other side is about 1.2 inches lower. I didn't think much of it as I knew I was going to replace the struts and bushings but once I did the car is still 1.2 inches lower on the driver side so it is not a strut or strut bushing issue. I can't say i've done a full inspection yet but I was wondering if this was a common thing with nsx's to not sit even, and if it was what are some issues that cause a side to sag?
The chassis might have been bent due to not having bump stops in place and to excessive lowering. Put the car on jackstands on a perfectly even ground and see if it sits on all points.
Yes I made sure it was on the identical perch, this up and coming weekend I will pull the strut and spring assembly out measure them just to check. When reinstalling I will also put each strut on the opposite side to see if the sag follows maybe it is the spring (unlikely but worth a shot). And once the car runs again I will get it to flat ground to see how square / level the car sits.
In regards to the uneven ride height, did you check the lower spring mount to make sure it is not upside down? It might be on the right perch, but the mount itself is upside down?

Going back to the clunking sound, were you able to address that?
Take a look at the battery tray. It may not be obvious that it is loose. Retorque the bolts to make sure the plate/tray is sitting snug against the frame and lower radiator mount.
As you can image, if it is loose, a bump on the road will cause the plate to bounce against the frame causing the clunk.

Good luck :)
I did check and they were in the proper position thats a good point. So I got the car all back together with new struts, springs, and rubber bushings, including bumps stops which were not on the old struts. Sure enough the noise is gone so I am assuming the lack of bump stop was causing the noise over bumps. Now the weird but good part is after driving the car around testing this stuff out it righted itself and now sits level. Maybe jacking it up and down caused it to sag on one side i'm not too sure why but it sits level now and has a proper suspension with bumps stops so things have been resolved!

2 Side note's too:
I'm pretty surprised one of the cars previous owners decided to just get rid of them for what ever reason, and I never would of thought about a bump stop missing if it were not for the new struts.
And also you guys were pretty helpful thanks, considering I am newish to these cars there is a lot of good info and suggestions in this that helped me know more about nsx's
It's the steering rack bushing. "knock bushing" they sell a brass replacement that will quiet it down for about 5k-10k miles then it comes back. I have the same issue on my 92 and the only way to fix it is replace it with a new one and they are not cheap. Good news is it's not going to cause things to get worse or damage anything or cause a dangerous situation its just annoying.


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Sure enough the noise is gone so I am assuming the lack of bump stop was causing the noise over bumps.

Congratulations on fixing the issue. It is always nice when things work out.
Yes, completely agree with you. We would have never guessed that the bump stops were missing. Hard to tell without taking apart the suspension.
Yes thanks,I scheduled a alignment for it and was actually going to ask one more question....

I searched around and was curious about the importance of camber bias from front to rear? This forum went into a lot of explanation about toes, and caster but something I'm am a little vague on is camber bias. I was originally thinking on doing -.5 up front along with -2 in the rear (The factory Type S specs) but people seemed to complain that -.5 up front may not be taking full advantage of turn in traction. So if i increase the negative camber up front should I maintain that original 1.5 degree camber difference and increase the rear or is it okay to break that and have a 1 degree camber difference from front to rear? (-1 up front / -2 out back)

I also found a suggestion for alignment specs I am tempted to try out which breaks the 1.5 degree guideline
Front: -1.5
Rear: -2.5
Front: 2mm OUT
Rear: 3mm REAR

This car is driven on the street on a lot of curvy empty roads and I did notice it has a little push to it entering corners which I would like to minimize while not giving up rear end stability. So naturally I was thinking on increasing the fronts negative camber while following 2mm outwards toe, and something like 3-5mm inwards toe in the rear

The car is on the Bilstien struts (stock perch) along with a comtech lowering spring. With 215 front tires and 265 rear RT615 tires, I might drop the rear to a 255 to help reduce the push on turn in's.