Potomac-Greg

When my trans lube is warmed up (and only after it's warmed up), I get a rattling sound (sort of like a diesel engine) from the transaxle only when first pulling out with the clutch fully released at very low RPM in first and second gears. Once the revs pick up (over 1,500) the rattle is gone; and there's no discernible noise in 3-4-5th.

I've read about a fifth gear rattle that's supposedly harmless. I hope that's it. The transaxle otherwise works extremely well.

If so, is there any gear lube that's better/worse for this? I'm using Mobil 1 synthetic 75W90.

jstand22

The only time I've heard the famous floating fifth gear noise is at idle...
But that could very well be it as well.

Scootin159

Mine's made a noise exactly like you describe since the day I got it. 60k miles later (and actually a new transmission for an unrelated reason)... it still does it & hasn't changed it's tune at all. No idea what it is, but someone who would know has said it's the catalyst in the converter breaking up.

kennycoulter

same thing here, and use mobil 1. i don't know how long it has been doing it, but i started hearing it about 2 years ago or so. i have tried everything to figure out the rattle and never knew what it was. i also figured it was the exhaust system, but sounded like coming from the rear.
glad i am not the only one, and that it isn't something to stress over...just annoying.

ausgeflippt951

You sure it's not the TT?

knfeparty

I've had this with two different transmissions. I've even had a new exhaust from the catback put in. Mine sounds like it's the clutch throwout- releasing the clutch pedal in neutral makes a ton of noise when the car is warm. Again, it's such a pain to replace the clutch (and right now it's working so well!) that it's definitely one of those things I will let break before I fix it.

Potomac-Greg

But I definitely only experience it with warm transaxle lube. No noise when cold. And clutch position has no effect. So to me the logical explanation is a rattling component that gets cushioned when the lube is cold and thick. It was particularly pronounced this weekend b/c I had the rear carpet and pad out of the car for a PCA DE event. LOTS of transaxle noise, some cool, some not so cool.

Scootin159

Not saying it's one way or another... but the torque tube bearings are also going to be warmer (and thus have expanded) when the car's warmed up. I know the temperature does effect them though, as they are specifically spec'd out for a temperature range. There's a thread out there somewhere in search country where someone replaced them all with aftermarket bearings that has good info.

kennycoulter

well torque tube is making more sense in my situation, since it seems to also vibrate up with the revs.

jstand22

Many people mistake the 5th gear rattle for the torque tube because the sound echos and is amplified by the torque tube....bad torque tube bearings are usually much louder than the 5th gear rattle.

Scootin159

not sure how much this actually means... remember that half of the gears (i.e. the 'input shaft') are spinning at the same speed as the torque tube whenever the torque tube is spinning (which is anytime the clutch pedal is up). I don't know if the rattling gear in the fifth gear set is the input or output gear though.

M758

with the clutch pedal in there should be no gear rattle since the tranny and Torque tube should NOT be turning. I have heard the rattle only with the car in neutral and clutch pedal out.

jstand22

Exactly...both transmissions I've had in my car have had the 5th gear rattle, you should only hear it with the clutch out, it should go away when you push the clutch in (might be like a .5 second delay because things have to stop spinning). When I changed to swepco in the first transmission, it quieted down a little, but was still there. It's no big deal.

ArcticSteve

I just acquired a 1990 S2 and haven't had a whole lot of seat time, but tonight I took it out for a run and when I got home I left it running and did a walk around to check all the lights and HOLY SH*t the noise coming out of the trans axle was just like what you'd hear out of a diesel motor. Could not believe it as this trans axle was purported to be a factory rebuilt SL unit 45k ago. This car has extensive records and I noticed an invoice dated 4 years ago and 33K miles indicating that the trans axle fluid was changed with SWEPCO 201gear oil. 4 months later and 8K later another invoice says "transmission is very noisy" but nothing was done.

Up to tonight I haven't heard this trans axle racket before, but the motor has always been cold. Like Greg describes in the above captioned post, when the clutch gets engaged the sound quickly ceases. I put it up on stands and the noise is present in 2 nd and 3rd at idle. Didn't try the other gears because I was too flipped out until I read this thread.

If this is the "fifth gear rattle" and I'm hoping it is, I must say it's fairly outrageous. I have trans axle whine on deceleration only at city speeds. Not quite the same as my 87 924S which sounds like a turbine spooling up or down at all speeds.

Previously, I ordered a bunch of maintenance parts one of which being Red Line 75W90 gear oil. If I had it to do over again I'd get the Red Line MT90. So I might as well try the 75W90 ... or not?

Tom R.

Is that the R&P?