88911coupe

Over the last couple of months I've noticed an odd faintly metallic flutter/whirring sound that seems to be from the tranny (G50). The car is an '88 w/ 180k, engine completely rebuilt about a year and a half ago. Nothing was done to the tranny at that time and it shifts fine, maybe a little stiff on extremely cold mornings but otherwise works perfectly. Here are the main points as best as I can recall:
Loudest at 2,500 to 3,000 RPMs sometimes hear it at lower rpms but faint
Definitely in gears 1,2,3 but road noise and wind may drown in out in 4,5, can't be sure.
Seems to be only when IN GEAR, if I take it out of gear can't hear it or its too faint
Same sound whether accelerating, decellerating or steady speed.
I can hear it better with window open and near a wall on left. It's not really a grinding sound, it sounds more like something metallic faintly hitting something at a fairly high frequency.
Any suggestions or what I can do to narrow this down?
Thanks,

g-50cab

Change the fluid - inspect the plug for metal bits.

there is a main bearing that can make this sort of noise - especially if it;s only when it's in gear

88911coupe

Thanks, I'll do that, when you say main bearing you are referring to a bearing inside the tranny correct? One more thing, I changed the tranny fluid about 6 months ago to Mobil 1 75/90 LS. Did not notice any metal bits then but was not hearing the noise either.
Thanks,

User 4221

The best thing for G50 Boxes is Mobil Delvac 75-90. I have heard that the bearings and syncros like this oil best.

I think Boardwalk sells it if you have trouble finding it elsewhere.

88911coupe

Thanks, I'll follow up with them. Does the description of the sound sound like bearings or synchros? I've had Mobil 1 in the box for years and just recently began to notice the sound. Maybe a fluid change will address it?

User 4221

I've read on Pelican that the G50 doesn't like the LS stuff. It is a relatively cheap test and you can look for shavings on the drain plug.

rusnak

Does the clutch slip? Is the engagement/ disengagement smooth?

Peter Zimmermann

When you say "only in gear" does that mean that you've tried to replicate the noise by coasting in neutral while holding the revs at about 3K?

Have you tried revving the engine in your garage, while standing near the left rear of the car? You could have a problem with the muffler, or a broken heat shield on the cat, etc.

88911coupe

Pete, yes, I've put in in neutral and kept the revs in the 2800 range while the car is coasting and I don't seem to hear it. Part of the problem is its not real loud in the first place but it either goes away or is MUCH quieter when in neutral.
Next step maybe this weekend will be to get it on a safe, solid stand and have someone put it in gear to see if I can locate it better.

88911coupe

Rusnak, clutch works fine as far as I can tell, engagement fine.

ron mcatee

Back in 1987, there was what they call G50 rattle. This occurred while in gear and putting a load on the transmission. On some cars, it was worse than others. Basically, it caused the shift lever and shaft to vibrate causing the noise. My 87 Carrera had it and every once in a while my 88 Carrera does it, but only under a load. There was a fix (service bulletin) from Porsche, but in some circumstances the problem still ocurred. It was to have been fixed for MY 1988, but maybe they didn't get all of them fixed. Next time you hear it, put your hand on the gearshift **** and push the direction of whatever gear you are in. If this decreases the sound/rattle, you'll know what the culprit is. For example, if you are in 3rd gear, push forward, 2nd gear pull back. The shifter bushings could also be worn and contributing to the problem. Let us know what you find out.

rusnak

I would probably open the tunnel cover and see if you can hear it better. I was wondering if the pressure plate is somehow prevented from pressing against the clutch, maybe by wear or maybe a bad adjustment of the TO mechanism. Is there oil leaking from the bellhousing?

88911coupe

Just to clarify, well aware of G50 rattle, been driving G50s going on 15 years, this is different but thanks for suggestion.