G50 transmission Grinding noise

[911cedric]

Hello Guys,

i unfortunately have another problem with a 993 Twin Turbo.
It has the G64.51 transmission and of course AWD.

The problem is that the transmission makes a grinding noise at low rpm only,
after shifting the speeds, and disappear when the car is launched at higher speed.

The noise is only related to the transmission as is occurs only when a speed is engaged at low rpm.

The noise and vibrations from the transmission are transmitted to the central tube with the shift mechanism and the front differential. It misleaded me first as the sound seemed to come from the front of the vehicle and not the rear.
We only noticed that the sound actually comes from the trany when we lifted the car with the wheels spinning.

We tried to swap the central tube and differential with another, flushed the transmission, but the problem remains.

Few items remain on the suspect list, like the planetary gearset in the rear limited speed differential, the viscous clutch, or transmission bearings.

I didn't find any related Technical information bulletin.

I'd like to know if this is a well know problem and if any of you had a similar experience with a 993 AWD; any suggestion is welcome

Thanks!

[911cedric]

i forgot,
this could also be clutch related; however, the clutch works perfectly; i couldn't say how many miles on it.

[john walker's workshop]

G50s are noisy,as you describe. gear rattle. take them apart and find nothing. hopefully yours is normal and not something else. hard to hear it over the web.

[911cedric]

i have at the garage 3 993 twin turbos and 1 993 4s, all fitted with the same g64.51 transmission, and this is the only one making this grinding noise.

I did noticed that the c4s has this same noise problem, but way less noisy.

I owned a bunch of 993s, and i think i can tell when something is wrong with a car.

The problem is that we just got the car at the shop with this problem, and we don't know much about what was done before on the transmission or clutch.
I can just say that despite this alarming noise, the transmission and clutch works perfectly.

A guy told me, and i believe him, that if the dual mass flywheel was already replaced with a single mass, this could get the trany more noisy and shaky than stock.

Beside, i just noticed that the lower transmission silent bloc / bushing is really worn; can t tell about the upper one but i guess its gone as well.

however, i don t think this could be the cause of such a noise.

any idea?