captainOCD

So driving the car around this week since swapping in the 5 speed I've noticed some noise with the trans in neutral but the clutch engaged/pedal up. Having never been around another manual 928 (or any 928 for that matter) I really don't know if this is just normal noise from the driveshaft turning or if it's bearings or something unhappy. So far I can't hear anything when driving along and I'd think that if I had a bad bearing it would scream when winding out to 6k rpm, so I'm hoping it's just me being paranoid.

I poked around with a stethoscope last night and the noise sounds pretty uniform throughout the torque tube, but the bellhousing seemed a lot louder. Not sure if that is just resonance though. Didn't hear anything on the transmission case. Tomorrow I'm planning to disengage the intermediate shaft from the driveshaft and check the driveshaft for anything out of the ordinary, as well as see if the noise is present with the driveshaft disconnected.

I put new torque tube bearings (reused the carriers since they looked) and sleeves in from garage9, the vibration damper with new mounts from 928intl, a new *** pilot bearing, and a good used oe throw out bearing.
More info on my swap in case anything I did wrong here can be spotted.
https://rennlist.com/forums/928-foru...l#post16022883
https://rennlist.com/forums/928-foru...l#post16064515

Here's a video clip from in the garage to make it a bit easier to hear:

Does this sound normal or does it sound like something bad?

Kiln_Red

Throwout bearing?

Not really sure. The noise is definitely not normal though.

SwayBar

Not normal, more than likely the throwout bearing.

captainOCD

Maybe something is different with this car, but wouldn't the throw out bearing make noise with the clutch disengaged/pedal down?

Geza

Since the noise appears once the driveshaft spins with the engine, I would think it's related to the bearings in the TT.

captainOCD

That's what I'm worried about too. Would really suck if I got sold bum bearings. They seemed fine when in hand though, but I'm pretty sure they were made in china, which I was honestly a bit disappointed with after paying about $100 for them with the sleeves. But before I come to that conclusion I guess I need to disengage the driveshaft from the clutch and make sure the noise isn't present then.

Kiln_Red

Not necessarily.. Most of the cars I have owned that made throwout bearing noise did so with the pedal up, engine running, neutral selector.

Of course it could be TT bearings, but it doesn't sound much like TT noise from my experience.

Your diag effort to suspend the driveshaft from the clutch is a good one. What is the nature of the sound at 1500rpm in first, clutch engaged/pedal up?

captainOCD

So far nothing that I can hear while moving over the engine. I have a set of 4 wireless chassis ears that I can put in various places. Maybe I can run it on the jack stands in gear and see if the noise can be picked up by those things.

Mrmerlin

Did you add any grease to the TOB?
If your careful you can drill a small hole in the bearing shield,
then inject grease with a hypo needle,
then seal the shield with silicone,
the grease will usually restore the life of a out of grease TOB.

The TOB runs at engine speed all the time so it needs fresh grease to live a long life

Kiln_Red

These are the reasons I am thinking it is the TO bearing. Isolate the driveshaft and observe the noise. You'll know what direction to go from there.

Bookmarked!

captainOCD

I greased where the the bearing contacts the release arm, pressure plate, etc, but didn't put any grease into the bearing itself. I'm gonna head out to the garage now and see what I can find isolating the driveshaft.

captainOCD

Before messing with anything I decided to poke around with the chassis ears and stethoscope with the car running and in neutral (which is why I'm back inside now waiting for the exhaust to cool before I can remove it). The wireless chassis ears made it sound louder at the transmission, but that doesn't agree with what I was hearing using the stethoscope which I think I trust more here since it's a completely analog device.

With the stethoscope I heard pretty much no noise on the release arm. The bellhousing (lower removed) and the front of the torque tube sound the same. The transmission (poked around on the case a couple places as well as right about where the input bearing is) and the back of the torque tube sound the same and seem to be pretty much the same as the front of the torque tube. Right around the middle of the torque tube (from underneath, I believe right below the shifter) seemed a good bit louder though.

Here's a picture of the torque tube where I used tape to illustrate the locations of the bearings and damper to myself when putting it back together. Right in the middle below the shifter is the center bearing. The only other thing right there is the mount for the shift rod, but it's isolated with a rubber bushing.



As soon as the exhaust cools down enough to drop I'll decouple the intermediate and drive shafts.

SwayBar

When reinstalling the clutch, what needs to be greased/lubed besides the intermediate shaft, and using which lubricant?

Petza914

You need to grease the splined shaft very, very lightly with the "super sticky Porsche special grease" but if you use too much it will sling off onto the friction discs and create a slipping clutch - ask me how I know.

This is the grease from Roger and doesn't feel like any other grease I've used on anything before






See the grease spray lines




And the hot spot created from slippage due to the grease

Also, make sure the guide tube bolts are tight and loctite and that the nose of the splined shaft is greased and slides into the pilot bearing smoothly.

My manual transmission makes a rattling noise with the clutch out but I have the 6spedd Z06 setup and they all do this, whereas the Porsche ones do not. The zo6 TT doesn't have bearings in it, just bushings and the shaft is centered by what it attaches to on both ends so it rattles.

GregBBRD

As someone who works all day long on these cars, let me assure you....It's very difficult to isolate a torque tube/transmission/clutch noise in a 928. The entire area acts like a giant speaker and the noises radiate all over.

It's important to remember that both 5th gear spins on its ball bearing and the layshaft spins on its roller bearings, when the clutch is released, in nuetral.

While 5th gear bearing noises are very common, I'm seeing a tremendous amount of destroyed layshafts, these days. Rebuilders tend to replace 5th gear bearing and leave the old layshaft bearings....and most of these bearings are way beyond their service life. ($60 worth of bearings ruining $4,000 worth of layshaft is very sad.)