Where can I see the main input shaft on a G50?

[RobFrost]

To diagnose ecessive backlash in the drivetrain on my G50, a well-known 911 gearbox expert told me I need to get it in gear, rock the wheels backwards and forwards and take a look to see if the main input shaft is turning. If it is, the play is in the clutch (likely broken friction plate springs). If it's not, the backlash is in the gearbox or diff.

Since I don't have a workshop and lift, I arranged for a relatively local porsche specialist mechanic to get the car up in the air, pop off the transaxle side cover and took a look but he said it's not so easy to tell me how much of the travel is transmitted to the input shaft because [excusey type stuff about how tricky it is to do with shimming the side cover and not having enough hands free]. He's not given me an answer, and I'm none the wiser whether my clutch friction plate springs have broken.

Despite not wanting to do the one thing I booked the car in for, he was really keen to give the car an inspection I didn't ask for and for me to do a grand or so of easy fettling jobs I could do at home off a Jack such as tightening up wheel bearings.

Does the Carrera 3.2 G50 have any other inspection cover that can be removed (with the gearbox still in the car) to give easy viewing of the main input shaft so I can counter his objections to doing the job I booked the car in for? I assume the transmission side cover is what MB had in mind?

The situation is particularly frustrating because there aren't a lot of Porsche specialists near me and I've committed to two full days of travelling to get the car to him and get home, and then to get back out to him and drive it back when he's finished with it. Since this massive inconvenience to me is so much greater than the inconvenience to him of having to wind it back up on the lift for half an hour, to balance the side cover or call a colleague over to shine a torch in there, I'm inclined to apply a little pressure for the job I actually booked it in for, to get done.

Thanks in advance.

[andytat]

Hi Rob.
To be able to see the input shaft you need to disconnect both driveshafts
from the gearbox, Remove the drive shaft flanges, drain the gearbox oil
and remove the gearbox side cover and the differential. This seems like
an awful lot of work to check check the backlash in the input shaft. The
G50 clutch doesn't use a sprung centred friction lining, it has a big rubber
damper that is prone to fail and when it does the clutch friction plate rocks
backwards and forwards onto steel stops, giving lots of backlash. I reckon t
hat is your problem and should be easy to diagnose for a specialist who is
familiar with the G50. If the diff had that much backlash I don't think it
would last very long and would think it should be very noisy.
I hope this helps.

Andy

[RobFrost]

Hi Rob.
To be able to see the input shaft you need to disconnect both driveshafts
from the gearbox, Remove the drive shaft flanges, drain the gearbox oil
and remove the gearbox side cover and the differential. This seems like
an awful lot of work to check check the backlash in the input shaft. The
G50 clutch doesn't use a sprung centred friction lining, it has a big rubber
damper that is prone to fail and when it does the clutch friction plate rocks
backwards and forwards onto steel stops, giving lots of backlash. I reckon t
hat is your problem and should be easy to diagnose for a specialist who is
familiar with the G50. If the diff had that much backlash I don't think it
would last very long and would think it should be very noisy.
I hope this helps.

Andy

Thanks Andy. I agree that sounds like the problem. However... It had a new clutch 25k miles ago, and for a long time I understand the vast majority of replacements have been the more conventional friction plate with springs instead so most likely that is what is in place. However these springs have also been known to snap, apparently - yielding pretty much the same symptom you describe.

In terms of noise, there is some metallic rattle from the tunnel under load at low revs in higher gears, which I guess could be play in the diff but could also just be general rattle. They say there's some play in the pinion shaft bearing. Backlash is 12 degrees at one wheel, and therefore 6 degrees if you were to turn both wheels. Notably, it is much less in the lower gears than the higher - indicating play is at the input side of the gearbox - which is the main reason I'm with you in suspecting the clutch.

Your feeling the clutch is the more likely suspect encourages me to drop the engine to have a look - but of course as big a job as opening the diff may be, it seems like a smaller job than dropping the engine when they both fulfil the same purpose. The advantage of dropping the engine is you're already there to fix the clutch if that's the problem.

FWIW I asked the porsche specialist who has the car straight: "in your view, do you think the clutch plate springs have failed?" and he said "no". Maybe opening the diff would be a compromise to confirm he's right without removing the engine & gearbox.

P.S. I have a little scope/camera you could easily poke in to see if the input shaft's turning but I'm not allowed in the garage. I could have got this job done in 40 minutes if I just had some lifts or the use of them.

[Gary71]

That investigation sound more complex than changing the clutch…

[RobFrost]

That investigation sound more complex than changing the clutch…

If so, the engine should come out instead. But I believe the side cover coming off should be sufficient. The oil is already drained.

[Nige]

Sure this isn't G50 gearshift rod rattle? There is a proper factory fix for this, also your shift rod should have a foam/rubber sleeve around it to prevent it vibrating against the tunnel.

http://forums.pelicanparts.com/porsche- ... attle.html

[andytat]

Ah,
I wasn't aware that you had a new clutch only 25k miles ago. The main reason for the rubber damper was to
cushion the backlash of the gear train at low rpm. G50 gears are seriously heavy duty and the firing pulses below
2000rpm can make the gearbox quite noisy, this is why manufacturers went to dual mass flywheels. There will be
an amount of backlash in the diff and gear train and it's difficult to say how much is normal.
Nige made a good suggestion which could be worth looking at first.

Andy

[RobFrost]

Ah,
I wasn't aware that you had a new clutch only 25k miles ago. The main reason for the rubber damper was to
cushion the backlash of the gear train at low rpm. G50 gears are seriously heavy duty and the firing pulses below
2000rpm can make the gearbox quite noisy, this is why manufacturers went to dual mass flywheels. There will be
an amount of backlash in the diff and gear train and it's difficult to say how much is normal.
Nige made a good suggestion which could be worth looking at first.

Andy

Definitely will look at Niges suggestion but that won't fix the excessive backlash in the drivetrain, which is the only problem I have with the car.

[RobFrost]

There will be
an amount of backlash in the diff and gear train and it's difficult to say how much is normal.
Andy

Also, I'm getting another Porsche specialist to drive it next week - hopefully he'll have a better idea than me what's normal. FWIW on the phone he agrees with me it sounds like the clutch plate but it looks like he'll pop open the diff for me and take a look. Thanks for your help.

[RobFrost]

Sure this isn't G50 gearshift rod rattle? There is a proper factory fix for this, also your shift rod should have a foam/rubber sleeve around it to prevent it vibrating against the tunnel.

http://forums.pelicanparts.com/porsche- ... attle.html

Thanks - that's really helpful to learn. It sounds likely that's exactly what the noise is.

[andytat]

Good luck and keep us posted.

Andy