Hey all,

Long-time lurker, first-time poster. I'm experiencing a grinding noise that I can't identify. I have an '04 G35 Coupe 6MT. The noise occurs in all gears but stops when I engage the clutch or shift to neutral while moving. It sounds like grinding or whirring, leaning more towards grinding.

Correct me if I'm wrong, but I think I can rule out issues with the input and output shaft bearings since the noise stops in neutral. I guess that leaves me with a clutch issue? Or, perhaps something has worn out in the gearbox, affecting all the gears. I'm honestly not sure; would a clutch problem cause grinding in gear but not in neutral? Shifting is not a problem, and it's as smooth as can be for a 20-year-old vehicle. It doesn't appear to be slipping (at least as far as I can tell). I've tried the old trick of flooring it and monitoring the RPM versus the speedometer, and it seems to grab fine, even on steep hills. Could this be the first symptom of a slipping clutch that I haven't felt yet?

I'll try to record the noise, but no guarantees; it's very faint, and I have an exhaust leak on the driver's flex pipe.

Thanks,
Jimmy

 

Have you ever replaced the throw out bearing or the manual pilot bushing?

 

I'd start with a fluid change, inspect the fluid coming out for excessive metal.

 

No, nothing on the transmission has been touched by me beyond a fluid change when I got it 2yrs ago. I'm going to replace the clutch and I think the kit comes with a throw out bearing, I'll buy another pilot bushing to install.

 

I'll do this and see what comes out, the noise does sound stronger in third but that could just be the lack of road noise at that speed compared to higher gears.

 

Looks fine to me. So I guess the clutch is the next step. Any chance this is a flywheel problem?

 

Ohh I thought you had a 6MT manual transmission, you have a 5AT automatic transmission?

 

Uhhh nope? 6mt. I put redline mt85 gl4 back in. Don't tell me the guy gave AT fluid when I changed it 2 years ago.

 

Well that RED COLORED FLUID in that cup sure looks a lot like ATF fluid.

 

Totally, but doesn't it become this color after being used? The red line I put in had a red hue to it.

 

The MT85 fluid you put in is more of a yellow color, not red. And it is significantly thicker in viscosity. What you're swirling around in that cup looks distinctly like ATF.

The smell will be the biggest test though, ATF and high viscosity gear oil have completely different smell. Gear oil STINKS, ATF smells a little sweet.

 

Well this fluid was fairly warm so that could explain the thinness of the oil. But ya, hard to deny that deep red color.

Here's the red line, I see what youre saying, it's more yellow than red, looks red-ish when looking down the bottle.


So, let's assume the mechanic 2 years ago was braindead and gave me the pump to the atf instead of the mtf. Where do I go from here? New oil is in and still makes the noise like nothing has changed.

 

I'd just run it, shorten the fluid change interval and change it out again next year regardless of mileage. Then drain it into a very clean container and strain it to look for EXCESSIVE metal, you're always going to get some metal in the oil with a gearbox.

As for the sound, it goes away when you work the clutch pedal yes? Probably looking like the TO bearing is starting to die, you can usually limp them along for a good long while by being diligent about not having your foot on the clutch when you shouldn't. When you are waiting at a stoplight you should be in neutral with the clutch released, not just sitting there riding the throwout bearing. Fortunately it's a pretty straightforward job getting the transmission out of these cars, if the clutch isn't slipping and you're ok with spending the time then you can just put a new one in without touching the clutch. Use the OEM bearing, they're not too spendy usually around $50 at your local Nissan/Infiniti dealership. If they want more than that just check online for the OEM part number.

Are you SURE the clutch isn't slipping? The best way to test is find a section of freeway near you that has an incline, 6th gear around 2500 rpm (65mph or so) and floor it while you watch the tach to see if it jumps a little, if the clutch is engaged it won't jump it will smoothly increase in rpm, if the clutch slips you'll see a little bump in the rpm that isn't slow. Here's a little 4 second video clip of what it initially looks like, it will continue to get progressively worse to the point where it's slipping in city driving in low gears with only mild throttle.

 

I'll be doing that, I also sourced another cd001 for 600$ encase this one ***** out on me suddenly. Besides the slight grinding, my current trans is near perfect shifting and smoothness.

I'm like 99% sure the clutch is not slipping, I haven't floored it in 6th at low speeds yet. But doing 60kmh in 4th and flooring it is smooth and grabbing fine.

I talked to a guy at my local car club who is also really familiar with the V33 platform and he said its probably my sychros going. Considering all the symptoms (grinding in all gears but not in neutral or clutch in), he was nearly positive. Which honestly is fine with me, I'll just ride this till it dies and either save up for a cd009 or just keep swapping cd001's.

Thank you for the detailed responses!