'Clunk' coming from the back end

[TxGlenn]

My 97 has a random 'clunking' sound coming from the back end. After researching, it seems the 3 most likely culprits are:

1. Worn motor mounts
2. Worn CV joints
3. Worn control arm bushings

How can I go about determining if one of these is the issue? I do not see any obvious leaks around the CV joints. The bushings appear ok. I am leaning towards the motor mounts as the rear motor mount looks like it is worn but the sides look ok. Does the 'clunk' from worn motor mounts sound different than the other issues?

 

[Superhatch]

I have the same clunk, replaced springs and strut assembly and thought that would solve it but it's still there. Does yours sound like its coming from a specific side?

 

[TxGlenn]

I can't really isolate it. Perhaps coming from the right but I'm not sure. I bought some CV joint rebuild kits and may end up doing that just to rule it out. The rebuild kits aren't too expensive... it's just not a 'quick and easy' type of job. These motor mounts are quite pricey so was hoping to determine definitively if they were the issue before going that route.

 

[jwmelvin]

In my experience, you can see the torn rubber in a motor mount. The front one especially though would be tough to see. An inspection camera would be useful for that. I can confirm also that clunks happen when a motor mount is not installed or half installed.

It's not so hard to repair a motor mount by filling it with 2-part polyurethane. It increases vibration a little, but if you're looking for a less-expensive option, it does work.

Determining the cause - how do you reproduce the clunk? Is it really random or is it related to acceleration/deceleration, cornering, road bumps, etc?

 

[vf2ss]

Can you establish a possible relationship with the 'clunk' on, say, either a hard accel/decel, going over a speed bump, fast cornering, etc.? There is another 'clunk' sound that leads one to believe that it's tied to the motor mounts because it occurs on occasion upon hard acceleration/sudden deceleration when gravity/torque is shifting stuff around. If you notice that the clunk or knock noise happens to you only in the low gears upon WOT or a sudden letting off the gas (i.e. never heard in 4th or 5th), it could be that the grease in the RH inner CV axle is just prematurely worn compared to the other axles. This happens due to the proximity of the RH axle and your engine headers and can be exacerbated by lack of a heat shield and/or aftermarket headers. In short, the constant heat cycling in that area wears that grease down quicker. If you think it could be this you might try just injecting more grease into the inner CV axle and rebanding the boot on that side and see if that makes the clunk go away.

 

[TxGlenn]

I notice the noise at low RPM when I am backing out of my driveway or pulling into it as well as when coming to a stop, etc. I thought I just couldn't hear it at higher RPM due to the engine noise but may be wrong. I made a video recording to record the audio. This is me pulling into my driveway.

@jwmelvin - I see torn rubber on my rear motor mount as well. Is the polyurethane repair job just a matter of filling in the space with some kind of polyurethane compound?

 

[LJSB]

I suggest before you start repairing or replacing things you get it properly and professionally diagnosed. Coming here and having folks guess is a great way to waste money, time and possibly create more problems. JMHO

 

[MexiRicer]

The easiest thing to do first is to unbolt your sway bar and drive around! If the clunking goes away then your issue is bad sway bar end-links. In my experience, when the sway bar end links go bad they do make a clunking noise. Good luck!

 

[jwmelvin]

@jwmelvin - I see torn rubber on my rear motor mount as well. Is the polyurethane repair job just a matter of filling in the space with some kind of polyurethane compound?

Pretty sure I used this urethane. I just filled the mounts after sealing one side with tape.

I hope you can figure out what is causing your clunk.

 

[LJSB]

Wow.

 

[jwmelvin]

I suggest before you start repairing or replacing things you get it properly and professionally diagnosed. Coming here and having folks guess is a great way to waste money, time and possibly create more problems. JMHO

My car has been "professionally" serviced by a couple places that are both highly regarded on this list and nonetheless had some serious issues. One of those was an uninstalled front-motor-mount bolt, which led to a clunk that took a long time to find, given the lack of visual access. I agree that blindly following advice could waste time and money, but giving a car to a mechanic with an unknown problem is another great way to waste those things. I guess it depends on a person's willingness and ability to track down problems.

I find this forum pretty helpful for suggestions. Sway bar end links, CV joints, motor mounts, etc. in this case.

Wow.

Sarcastically derogatory and unhelpful at the same time. Nice.

I'd think that anyone who might fill a motor mount with polyurethane is informed enough to understand the potential risks of transmitting more vibration. My approach is one taken by a popular aftermarket company, as here, with a note that the lower mounts are appropriate for this approach without overly increasing vibration.

 

[Old Guy]

I suggest before you start repairing or replacing things you get it properly and professionally diagnosed. Coming here and having folks guess is a great way to waste money, time and possibly create more problems. JMHO

Professional just means that you are a member of a profession and get paid for practicing that profession. The reality is that it is increasingly difficult to find professional mechanics who are NSX knowledgeable. These days, at a dealership you may be paying $150 / hr for a professional who has never set hands on an NSX which then ends up being an expensive parts replacement exercise. If you have access to a good tech with lots of NSX experience then that is a valid observation.

 

[LJSB]

Wow again.

 

[MexiRicer]

Wow again.

Can you play Blackeyed Blonde from the Red Hot Chili Peppers? Flea went wild on that album.

 

[NSX9]

My experience with a clunky back end!
My 96 Coupe had a noise like a drink can rattling around in the trunk, going slowly uphill made it appear or sudden hard acceleration. Looked/checked numerous times at everything...no luck. Then I saw a post re loosening the forward and aft eng mounts, giving the car a rev while the mounts are loose, torqueing everything back up. FIXED.
I was fairly amazed. No probs since.

 

[LJSB]

Can you play Blackeyed Blonde from the Red Hot Chili Peppers? Flea went wild on that album.

I can tuna fish and paint a piano. No fleas.

 

[MexiRicer]

I can tuna fish and paint a piano. No fleas.

WOW!

 

[TxGlenn]

My issue was a loose toe control arm.