Undesirable Noise when Shifting

[RPGs818SNA]

My 818’s unaltered 2006 Impreza 5 speed transmission or clutch makes a brief grinding sort of sound when I change gears. Here’s a link to a video that includes the worrisome sound shifting from 2 to 3 and 3 to 4, but not 4 to 5. https://www.youtube.com/shorts/MSCh-Uh0Mck

It doesn’t often make that sound when the engine is cool, but always does after the engine is warmed up and turned off for 5 minutes and then restarted and driven. Once I’ve driven it 2 or 3 minutes, the noise stops. It seems to be heat related, although I’ve had one instance of hitting a pothole causing the noise. I’ve checked the clutch release lever stroke and that’s in spec. The engine and transmission have 92,000 miles on them and the clutch has not been replaced. The oil level in the transmission is 2” above Full on the dipstick.

My questions are:
What does it sound like is causing that noise?
Am I damaging something by driving it in that condition?
What is required to fix it?
If it requires replacing the clutch, is it easier to pull only the transmission or pull the engine and transmission?

Any advice or feedback would be most appreciated.
Thanks,
RPG


https://www.youtube.com/shorts/MSCh-Uh0Mck

[idf]

Sounds to me as if the clutch is not fully disengaging.

[Bicyclops]

I agree. Have somebody push the clutch while you look to see how far the clutch lever is moving. Maybe even with the rear on jackstands, in gear, clutch pushed, see if you can turn the wheels by hand.

Ed

[RPGs818SNA]

Thanks guys, I appreciate your suggestions. I measured the clutch release stroke to be 13.2mm. The spec is 12.1 to 13.5mm, so it's being pushed according to spec, but that doesn't mean it's being pushed as far as it needs, I guess. I'll raise a rear tire and see how hard it is to turn in gear with the clutch depressed vs neutral. Thanks for that testing tip.

RPG

[RPGs818SNA]

As suggested, I lifted one rear wheel off the ground and measured how hard it was to turn the rear wheel in neutral and in gear with the clutch depressed. They both required between 3 and 3.5 ftlb of torque. I also measured how far up from fully depressed the wheel became hard to turn. That happened at 1 3/8” up from fully depressed. So the clutch seems to be disengaging properly at least when it’s not spinning. Are there any other diagnostic tests that might be illuminating?

Thanks,
RPG

[Bicyclops]

Synchos maybe? Does it do the same downshifting? Oil level?

[idf]

Synchos maybe? Does it do the same downshifting? Oil level?

Synchros was also my next thought.

[RPGs818SNA]

Thanks for your responses.

I put 3.7 quarts of Subaru 75W90 gear oil in the transmission and mounted it per the manual. The oil level is 2” above Full on the dipstick.

I belatedly read the 2006 Impreza Clutch System General Diagnostics Table and came across a problem called Clutch Drag characterized by a “harsh scratching noise”. See photos. The diagnostic for that is to shift quickly from neutral to reverse at idle. I’ve done that many times without any unusual noise, but I’ll try it again after warming up the engine and transmission.

221288
221289

So I plan to run the following diagnostics and report back.
1. After heating up the engine, stop, turn off the engine, and heat soak the warm engine and transmission for 5 minutes. I haven’t yet cut out any of the engine compartment vents, and there’s a hot muffler in there too, so it gets pretty warm. Then try quickly shifting into reverse at idle.
2. After getting up to speed, try downshifting to exercise the synchros.
3. Try simply disengaging the clutch without touching the shifter.

I hope these results will suggest what’s wrong and what needs fixing.
RPG

[RPGs818SNA]

Well, today I ran diagnostics on a clear, sunny, 61 degree day. I drove 2.5 miles at around 45 mph with 3 stops, shifting through all 5 gears. No clutch noise. I stopped in a parking lot, turned the engine off, and waited 5 minutes.

I first tried the quick shift into reverse from idle to check for clutch drag. I tried this 5 times shifting as quickly as I could and heard no noise other than the normal click whenever I shift into reverse.

Next I left the parking lot and when upshifting into 2nd, I heard the sound again. Same going into 3rd, and a little into 4th. So no change there.

I tried downshifting and had no problem with synchronization.

While in 3rd, I depressed the clutch without touching the gear shift lever and got the same grinding sound a split second after the clutch hit the floorboard. As usual, the sound lasted about half a second.

I’m beginning to suspect the pilot bearing. Any thoughts or suggestions?

Thanks,
RPG

[Bicyclops]

The nose of the transmission main shaft is in the pilot bearing in the flywheel full time. I think what you are talking about with a depressed clutch pedal would be the throwout bearing. Either way, the tranny is going to have to come out to get to it. Oh boy!

Ed

[idf]

I also don't see how it could be the pilot bearing but TOB could be the cause.

[RPGs818SNA]

Thanks for the feedback!

OK, I agree, it’s most likely the throw out bearing. I now have a theory regarding what’s making that grinding noise. This is based on my diagnostic test of depressing the clutch while in third but not touching the shifter. I got the same quarter second or so grinding noise about a quarter second after the clutch was fully depressed. So my theory has to explain 3 events, each separated by about a quarter of a second: Clutch is fully depressed, noise starts, noise stops.

I understand that the throw out bearing fits between the clutch fork and the diaphragm and is held in place by that part of the transmission cover that surrounds the input shaft. Tabs on the fork side prevent that half of the bearing from rotating. When the fork presses the bearing against the diaphragm, that side of the bearing spins up to flywheel speed while the fork side does not rotate. Is it possible that the bearing is old (90k miles) and slow to respond, and the surface of the inner part of the bearing has gotten rough, and initially rides over the diaphragm fingers when they are moving at 2000 rpm, but as the rotation speeds begin to equalize, it begins to catch on the fingers and make noise until they equalize their rotation speed? That may explain the noiseless period between the clutch being fully depressed and a quarter to half second before the harsh grinding begins. It would also explain why the grinding noise lasts no more than a quarter to half second once the bearing and diaphragm reach the same rotational speed.

If that’s the case, I think the fix is simply replacing parts, although not easy (for me). Can the transmission be removed from an 818 without removing the engine? Once it’s being lifted out, can the axles be pulled out without undoing the rear suspension?

Is it likely that the noise and any debris is contained in the clutch compartment and will not contaminate the transmission or engine if I drive it that way on the few remaining warm days?

Thanks for all the help,
RPG

[Bicyclops]

Both the engine and transmission have oil seals. I don't know about yours, but my bottom flywheel cover is partially open and anything in there would fall out.

You should be able to get the transmission out leaving the axles in place. If you need a little more play, you can unbolt the upper and forward arms so the hubs can swing out a bit. Of course, this is after you've pulled the back of the body off. The tranny needs to move aft to get the nose shaft out of the clutch before it can go out the back. Good fun. You should take a look at the clutch disk, pressure plate, and flywheel. The throw out might not be the only thing wearing out in there.

Ed

[Bob_n_Cincy]

RPG
Whenever you push in the clutch, the flywheel moves a little bit forward as a result of axial play in the crankshaft. Thicker or cold oil would prevent some of that movement. I think it might be possible that the teeth on the flywheel are hitting the dust shield on the bottom of the transmission. It is simple to remove that dust shield as a test.
Bob 221556 221569

[idf]

You can pull the tranny without pulling the engine. As Ed said, to get the axles out of the trans you need to unbolt the upper links to swing the hubs down and slide the axles out. It is easy to damage the axle seals so be careful. Colonel Red (on this forum) sells an inexpensive tool that prevents damage to the seals when reinstalling the axles.
Ivan

[RPGs818SNA]

Thanks so much, Bob, for the dust shield and flywheel idea. Anything I can check without pulling the transmission is well worth doing. I'll get right on that.

Thanks Ed and Ivan for your tips on pulling the transmission. Anything that makes the job safer, easier, or less likely to cause damage is most helpful. It's good to hear from anyone who'd done this before as I haven't yet.

Wish me luck with the flywheel shield,
RPG

[RPGs818SNA]

Per Bob’s excellent suggestion, I removed the flywheel dust shield and examined it closely. It had a light coating of oil and black dust, but no sign of shiny metal flakes.
221901

With the dust cover removed, I was able to see the flywheel and clutch cover. There were no visible signs of rubbing or shiny spots.
221902

By rotating the flywheel a little, I could see inside the clutch cover and the edge of the clutch disk. There is a frame member that sits just below and in line with the clutch disk that kept me from photographing it directly. I had to use a small mirror set just right to photograph the remaining disk material on both sides of the disk.
221903

The flywheel tooth pitch is 8mm, so the visible disk material is about 1mm on both sides. I can’t tell how much may be hidden in a depression on the flywheel or pressure plate, but I’m guessing not much.
221904

The disk material spec is 3.5mm and the rivet depth spec varies from 1.35 to 2.15mm. If the disk material is really only 1mm thick, it should be rubbing the rivets already.
221905

I used an endoscope to check the fork, throw out bearing, and diaphragm, but couldn’t see anything amiss.
221906

I suspect the only way to solve this noise mystery is to pull the transmission and replace anything that looks worn. But I’d welcome any other ideas.

Thanks,
RPG