Metallic grinding smell from clutch

[crxguy52]

I've recently noticed a metallic grinding smell when I back my car out of my driveway, it smells just like using an angle grinder on steel. This would seem to indicate that there is some metal-on-metal grinding, presumably in the clutch since it's only present when I back it out of my driveway (it's uphill and I have to slip the clutch most of the way out). The PO indicated that the clutch was replaced in 2017, likely less than 20k miles ago. I'm pretty easy on the clutch because I know how expensive they are, I'd be surprised if I wore it out in that timeframe.

The only thing I can think of that would cause this is maybe one of the flywheel bolts backed out, looking at the service manual it doesn't look like any other bolts could back out and cause this. There is some clutch shudder when it's cold out, but I chalked that up to being a normal NSX thing. Anybody have any other ideas? I plan on getting it up on jack stands to take a look, anything in particular you'd look for?

 

[goldNSX]

I'm not CRX specialist but in the NSX it's natural to smell some fumes from the clutch when you drive backwards. Well, I didn't say it's normal to have that kind of smell from the clutch. Was an OEM clutch installed back in 2017?

 

[crxguy52]

This is for my NSX, and I'll have to go back through the service records. I would imagine it's an OEM clutch though.

The clutch doesn't slip, so it being worn out wouldn't make a lot of sense.

 

[Honcho]

This is for my NSX, and I'll have to go back through the service records. I would imagine it's an OEM clutch though.

The clutch doesn't slip, so it being worn out wouldn't make a lot of sense.

Burning clutch disc friction material smells just like you are describing. It's likely from you slipping the clutch as you back out.

 

[Old Guy]

An observation. The smell you notice may be present whenever you slip the clutch, you only notice it when backing up because you are driving into the 'aroma cloud'. When you drive forward you leave the cloud behind you. I don't know whether that is particularly important.

I am familiar with that odd smell that comes from grinding steel. Without knowing for sure, I had attributed it to the by-product of the burning of the steel particles when grinding results in incandescent particles. If that is the case and that is what you are smelling I would expect that to be accompanied by a fair amount of noise which you have not reported. I have a 2000 with the original OEM dual mass flywheel arrangement. The clutch has what I would characterize as a moderately narrow engagement point which combined with what seems to be the normal lash in the 6 speed drivetrain can make for some lurching take offs if you are not smooth with the clutch - throttle action. However, at > 70,000 miles I don't think the clutch has any shudder. I am familiar with shudder and burnt clutch smell after I glazed the clutch on my Volvo 745 turbo dragging a friends boat & trailer out of the water - his FWD Saab was just spinning the front wheels.

If you have some actual clutch shudder you may have glazed the friction surface or damaged the flywheel surface. If you have created some high spots on the friction surface or the flywheel during partial engagement those high spots are getting a lot of action and may be heating up a lot leading to the smell. Depending on the amount of surface damage the clutch may have sufficient grip that you do not notice slippage when the clutch is fully engaged.

The absence of noise causes me to lean to a clutch friction surface problem. I suggest that you put the car up on jack stands, shift in to a higher gear and use a pedal jack to disengage the clutch. While turning the rear wheels (both depending on how open your LSD might be) listen for noises that might be coming from the clutch indicating a metal on metal contact of some kind. I suspect you will have to be right under the car to get a good ear on things so you will need assistants to help with the wheel turning. Take the appropriate safety precautions! You can progressively adjust the pedal jack to raise the clutch pedal / engage the clutch and listen for new noises. If you don't hear anything out of the norm I am thinking that you have a friction surface problem.

 

[goldNSX]

Hoe steep is the driveway?

 

[crxguy52]

Burning clutch disc friction material smells just like you are describing. It's likely from you slipping the clutch as you back out.

I've only smelled overheating clutches, and to me they smelled the same as overheating brakes. This smells like someone took an angle grinder to some steel which is why I was concerned

Hoe steep is the driveway?

It's not terribly steep, and I'm slipping the clutch for maybe 5 seconds at low (~1500 RPM) speed. I do the same thing with my Integra and don't have any issues.

If you have some actual clutch shudder you may have glazed the friction surface or damaged the flywheel surface. If you have created some high spots on the friction surface or the flywheel during partial engagement those high spots are getting a lot of action and may be heating up a lot leading to the smell. Depending on the amount of surface damage the clutch may have sufficient grip that you do not notice slippage when the clutch is fully engaged.

The absence of noise causes me to lean to a clutch friction surface problem. I suggest that you put the car up on jack stands, shift in to a higher gear and use a pedal jack to disengage the clutch. While turning the rear wheels (both depending on how open your LSD might be) listen for noises that might be coming from the clutch indicating a metal on metal contact of some kind. I suspect you will have to be right under the car to get a good ear on things so you will need assistants to help with the wheel turning. Take the appropriate safety precautions! You can progressively adjust the pedal jack to raise the clutch pedal / engage the clutch and listen for new noises. If you don't hear anything out of the norm I am thinking that you have a friction surface problem.

That's an interesting point. I've never launched the car, but it's possible the PO did, particularly before the clutch was broken in. That could cause high spots like you said and localized heating. I'll try the test you outlined when I get it up on jack stands.


After thinking about it some I've come to the conclusion that as long as it's not slipping, I'll just keep driving it. The shudder isn't bad or even present all the time, and if I need to replace the clutch at some point everything gets replaced anyways - I'm not going to ruin something by not doing anything. Obviously I'll take a look, but short of pulling the transmission there's not much I can do