This is the companion thread to the noisy cold start thread.

My '99 6sp tranny gets noisy when fully warmed up (I didnt notice at the test
drive probably because the tranny was cold).

1) On idle with gear in neutral, there is some clattering sound. If I step
on the clutch, the noise disappears. Seems to be some sort of bearing noise.

2) Coasting in 2nd gear (ie, lifting the throttle so there is engine braking),
there is a roaring noise. This noise doesn't seem to occur in other gears. This also seem like a bearing noise of sort.

Both 1) and 2) only happen when tranny is fully warmed up, nothing to do
with engine temp. If I sit in heavy traffic for a long time, the tranny cools
and the noise goes away.

Previous owner warned my of some tranny noise, saying it was due to
the lightweight flywheel he put in (along with a new clutch) 10K miles ago.
I didn't notice any noise back then probably because I didnt test drive long
enough to warm the tranny. I've read lightweight flywheel instead of
dual-mass can break the crank, just more info to scare myself.

I drained the tranny (old fluid was perfectly clear) and refilled with
AMSOIL 75W-90 GL-4, no difference. I want to see if heavier
weight oil will alleviate the problem, but seems like all 75W-110 or 75W-140
at the parts stores are GL5 and my understanding is GL5 will hurt synchros but I may be wrong.

Any suggestions?

 

6 speed oil : we have beaten this subject to death and concluded the best choice (reluctantly) is the OEM spec oil.
Read about the 6 speed bearings - they are greased & sealed - just like the IMSB ! The seals fail,grease leaks out,bearings wear. Replacing them requires a very specialized puller.Sound familiar?
You will find very little diy info on this so far.As these cars all age,the gearbox will become like the IMSB issue almost imho.
There are only a few competent gearbox rebuilders and nothing like Raby's "Solution"
Suggest 2 sources of advice but ask Rennlisters for others:
GTgears in Loveland Co. He posts here sometimes.
California Motor Sports.aka CMS.
The repair usually seems to involve removing the 'box and shipping it in an old cooler box to someone in Coloradro. A "good used" gearbox is unlikely unless it is less than 50k miles.
Let us know what you do ,it may help others who experience the same issues in future.

 

The light weight flywheel will cause a rattle when hot at idle in the gearbox when the gearbox is in neutral , goes away when put in gear..also will cause a noise under low RPM "lugging" conditions in higher gears. If you have noise under coasting conditions and high speed bearing noise , the problem is the output shaft main bearing , part# 99630280800 .I've got a source for the *** OEM bearing for $300. It requires full disassembly, pressing off all gears and reassembly to replace the bearing.The transmission can only be disassembled 4 times due to the press fit gets looser each time, so 4 times off and on is the limit.

 

And while you are in there .... 2nd gear pop-out fix.

 

My car had the same issue a couple of years ago, before my ownership. The invoice states:

"Clean trans, teardown to remove input pinion shafts. Teardown shafts to replace "sealed" bearings, press off gears on pinion, install new bearing. Inspect all sync's (OK). Assemble shafts clean housings, replace front housing mount. Seal up & install housing, check selector. OK."

Part nos for the replaced bearings were 99630280800 (as above) and 99630280700. Total invoice was a little over $2.5k, which doesn't I think include trans R&R. Work was done by Auto Sportsystems in Fairfax, VA - but that's perhaps a little far away for the OP.

hth

J

 

Very helpful data.Thank you.
Important to realize this gearbox is much more difficult to work on than the 'box in the older air-cooled cars.

 

For #1 normal, though the amount of tranny rattle will vary from car to car.

FWIW, my Boxster 5-speed very infrequently produces a bit of this rattle and when it does it is very faint.

OTOH, the Turbo will produce this rattle quite often and it is more pronounced. But a press then release of the clutch pedal makes the noise go away.

A lightweight flywheel will almost certainly exacrebate this rattle tendency.

BTW, the short term acceleration/deaccelerations in engine rotation speed that causes the tranny to rattle is also having the same effect on the crankshaft: it too experiences short term acceleration/deacceleration events which stresses the crank and the rods and the rest of the rotating/reciprocating hardware of the crank. That's what the dual mass flywheel is intended to dampen.

For #2 that can be normal or from a transmission bearing or gear. But it is hard to say without hearing the noise. And I'm not hinting you should provide an audio clip. Even with a clip the diagnosis would be little better than a WAG.

My advice in these situations is to solicit the opinion of a professional Porsche tech. Be sure you know under what circumstances the noise occurs and be prepared to reproduce the noise when asked or describe to the tech how to reproduce the noise when he drives the car.

Best to stick with the OEM transmission/diff lube.

The transmission is designed to use this fluid, its multi-viscosity attributes.

Using a thicker/higher viscosity fluid probably won't help the rattle -- installing the correct flywheel would help more -- and the thicker fluid might not lube the transmission sufficiently. The transmission's internals are splash lubed and the wrong lube's splash characteristics could be different enough to result in a subpar lubrication of some areas of the tranny.

You end up with the same old noisy transmission but one that possibly suffers from inadequate lubrication.

 

Thank you guys. I actually feel better after hearing what you guys have to say.

Sounds like my rattling noise in neutral is partly or mostly to do with the lightweight flywheel, so
if I ever take off the tranny (to do IMS or RMS (both are original and never replaced)), I will probably
swap a dual-mass back in.

The 2nd gear deceleration noise may be a real problem, but I suspect it is urgent to fix, just a minor
annoyance for now.

Since I've only had the car for a few hundred miles, I'll wait until I feel comfy/confident that
the engine is in decent shape (no D-chunk, cylinder scoring, oval shape, ..etc) before putting
money in the tranny.

Sounds like a plan?

 

Post a pic of the rear end...motor mounts may be shot.

 

Sounds like a plan...I would be making a plan to get the trans repaired before to long, although I had a friend who's noise started out yours and he went 10k miles before it got REALLY bad. But no collateral damage was done( unlike IMS failures). And even if you drive too long and destroy the trans you can pick up a used one for 2k( unlike IMS failure 15k). Also personally I would reinstall a dual-mass flywheel on any m/96 engine except for competition use only. The DMF just quietens it down so much , and smooth's out the power pulses and vibrations of the crankshaft( that's what the extra 13lbs is for). Its a fact that as weight conscious as Porsche is, that they would never have the extra 13lbs if it weren't extremely necessary.

 

Has anyone actually had their tranny pop out of 2nd gear? I hear a lot about the 2nd gear detent but have never had any issues that require it.

 

The second gear pop out problem is very common on the G96 transmission. Three different fixes for it, the Porsche way involves disassembly of trans and shim second gear, G-box has a modified detent that can be installed without transmission disassembly, Calif trans (CMS)has a modified detent lever that requires the case be taken off. Only one of these fixes should be used, do not use all of them on same transmission. The Porsche fix is the cheapest if you are already in the transmission, if not the G-box fix is more economical.

 

On the 6 speed , the problem with replacing the worn 2nd gear dog ring and synchromesh is that it is a press fit on the shaft. The puller required is a Kukko 20T. Very expensive. A press may be required to reinstall even if you used the oven/freezer technique. I am aware of only one diy 'how-to' of this task and that has disappeared. You also need a very specific size tube to use to press the new parts on the shaft.
If anyone has a simpler approach it would be wonderful if you would share the details here.

 

The pinion bearing in the transmission is a possible reason for the roar in second gear. See my thread below for some information on what's in what's involved in the rebuild, I did mine over the winter.

https://rennlist.com/forums/996-forum/911850-my-first-911-1999-996-c2-with-pictures.html

I'm thinking about making a dedicated thread for this as it seems to be happening often now.