Transmission Idle Noise - Bag o' Rocks - Post-Rebuild

Hey guys, got my car (2001 c2 manual) back from the Indy I was working with. I'd go up there every weekend and wrench on it for the past few months. Original transmission, original engine, but all new bits ranging from clutch flywheel pressure plate RMS IMS and vario cam. NOTE: flywheel is dual mass, not lightweight anything. At idle, only when hot, I hear a almost bag of rock style rumbling at idle. It's definitely rotational. When I stomp on the clutch, it goes away. When I lift it up/engage it, it comes right back. Again, this only happens when HOT. My biggest concern is not that if it's the transmission dying but if it is the fact that I might have screwed the install up.... Here's the story on how I think I screwed up the install. After about six tries of using the plastic tool (first mistake imho) for clutch alignment, we were NOT able to get it where it got all the way up on the dowels on the transmission no matter how much we rotated the crank or wiggle the transmission... So on try ~7, we were fed up but able to get the bell housing just barely over the dowels on the engine. technically, in alignment but less than 1cm from home. When we finally got it there, him (Indy) and I just slapped the bolts in and FINGER TIGHTENED until we got that nice THUNK of it finally seating (classic que that everything's gucci) The clutch feels great after 1100 miles and the shift action feels good for a 157,000 miles tracked and daily driven car, but that (new?) rattle sound is making me think that maybe I screwed up the clutch install. But the fact that it only happens when it's hot makes me think it's just my transmission dying and not that I screwed up the install. I know the trans is dying bc I have a pinion gear howl on the highway. I also plan to replace it with a lower miles used example Plus wave track diff ASAP Any and all advice is welcome. Note to self, if you do a clutch install, do yourself a favor and use a genuine metal clutch alignment tool, not that plastic crap Peace

Its a bad pinion bearing and thats why i hear the gear whine.

Could be a bad flywheel as well, possibly a bad or damaged release bearing also....sounds like you might need to pop it all out and take another look.

I wouldn't blame the plastic input shaft, I would always check the fit of the tool pilot to the bearing or bushing, if loose, wrap with tape till tight, I always put the trans into the highest gear so I can rotate the input shaft to align with the clutch disk splines, that is usually the biggest hang up in installing the trans to the engine, in neutral you have no way to align the splines.

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This makes sense. Pushing the clutch in would stop the input shaft from spinning and the noise would stop.

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Not sure if you care about above tranny. If you do and want to rebuild or at the least preserve all the very expensive parts inside of it. every mile is taking its toll. The bag of rocks is a bad end stage bearing life noise. With that bearing noise tranny bearing could be ready to explode all its ***** out. Just like an imsb. Then its toast. If the bearing collapses, it can destroy expensive gears, turning a $300-$500 bearing replacement into a massive transmission failure. jmho

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Hey dudes, thanks for the replies. I am fine with running this trans until it blows up. I am sourcing a secondary unit with the same issue as mine right now for 1k. You say its a 300 to 500 dollar bearing replacement? Id like to just bring them the gear stack and the parts and then have em press what needs to be pressed. Who do u know that would do this for such a low price?! Also, the sound wouldn't stop when I press the clutch if it was on the input shaft... no? Peace

Could be a bad throw out/clutch release bearing? It�s making noise when it�s spinning unloaded because it�s a mess, but under load (clutch in) it�s centered/located/quiet? If the last change was the clutch and install had hiccups then that should be the first suspect. Pull it apart and inspect. Maybe that bearing is a dud/DOA.

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Was just saying the bearing itself is a $300-500 part. Vs damaged multiple gear sets+syncros+sleeves/etc, that can cost over $500-1000 each, adds up fast. Labor is another big cost at most qualified tranny shops... https://retro-sport.com/porsche-gear...-shaft-bearing Only trans shop I know/trust personally is Kevin Gross on our forum. He runs Catellus Engineering in Mass. Small shop that knows its way around 996 trans better than most . Like all 996 tranny shops, they're not inexpensive. Instead of tossing out the old tranny you're replacing, He might even want to buy some good parts out of it, if they're still in good shape. Gears are expensive new. Couldn't hurt to ask, worst he could say is no thanks...

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Thanks for the kind words! Yes, the bearing is expensive. To get to it, you need to remove both the input (main) and pinion (output) shafts from the transmission. Usually the sealed bearing on the input shaft is destroyed in the process of getting the shafts out. The whole disassembly and reassembly process for the G96.00 .01 .30 and .31 transmissions is quite difficult, even if you put aside the issue of R&R'ing the interference-fit gears from the pinion shaft. If you dive into the project, a few other things to do while in there. First, there were mistakes made by Getrag in setting up the pinion, ie, its S3 and S4 shimming. So measure and correct. The thrust washer between 3rd and 6th gears breaks sometimes, which gets expensive. CMS has a nice upgrade part that is sensibly designed to get lubrication where it needs to be. The two-spider open differentials used in the early boxes (.00 and .30) have been known to break. Look for a good used four-spider version and install it. Happy hunting!