930 gearbox whine. Normal?

blacklotus99 · 07-04-2009, 04:54 AM

My new to me early 930 is back on the road after a couple months. I like to think of this car (early 75 turbo) as the grand daddy of the turbo cars. Guy in a 996T came over for a chat today while it was parked. I looked at his car like it was some kind of offspring...

Ive just had 1st and 2nd gears refreshed and its now really nice and easy to shift. I dont get those people that say its hard to daily drive. 2nd is so flexible its almost like an auto car!

Have just noticed though that the car has a really obvious transmission whine. Its most obvious in 4th when off boost on a very light throttle. Doesnt matter if the gbox oil is hot or cold (thought it did originally) but seems to be related to how quick the gbox is spinning which is why its most noticeable in 4th at 60mph. The whine gets louder and quieter as you go on and off a light throttle.

What could be causing the whine? I dont remember it being there before the gearbox was refreshed but I was driving it on boost a lot. Once on boost you cant hear it anymore which is why its most obvious in 4th at 60.

Any thoughts?

A930Rocket · 07-04-2009, 06:05 AM

When the trans was worked on, did they do anything to the diff? It sounds like the lash is off as that will cause a whine.

BTW. Check your fluid level.

mark houghton · 07-04-2009, 07:57 AM

Just curious: When you had your tranny refreshed, "while they were in there" did you also have them rebuild the shift linkage bushings? The reason I ask is that when I rebuilt mine (the linkage), the old bushings (which were rubber) were replaced with the new space-age urethane. As a result of the more rigid material, I noticed that it transferred and accentuated the transmission noise through the tunnel and shifter. I've always had a low level whine (mostly in second gear), but it became more pronounced with the urethane bushings.

JFairman · 07-04-2009, 09:32 AM

That kind of whine is usually from the differential and usually means the ring and pinion are not shimmed correctly or the differential carrier bearings are worn.

My 930 4speed with lsd does it a little too, and an old '72 BMW 2002 with 3.64:1 ZF differential I had years ago also did it. Not from being assembled out of spec, but from mileage and bearing wear.

dsiegel360 · 07-04-2009, 09:54 AM

At 70 and 80 mph in 4th gear, what rpms are you at?
This will tell us if your gears or r and p has been changed.

blacklotus99 · 07-04-2009, 09:25 PM

AFAIK the shift linkage bushings were not done but I asked them to check them and didnt hear anything about it. I forgot to ask when I picked it up but would assume they checked out ok. If they needed to be done they would have given me options as to whether to use urethane or not. I will remember not to go down that path...

The diff wasnt touched as far as I can tell from the invoice but Im sure the whine wasnt there before. Carrier bearings or lash settings are a good thought.

At 60mph in 4th the car is doing about 2200rpm. Dont think the R&P has been changed, would have been expensive and I would have some evidence in the documents.

Thanks for the help. This kind of noise will get annoying on the motorway...

WERK I · WERK I's Garage

Did you change your motor/transmission mounts to solid type?
Are you sure you ended up with the same transmission(serial numbered) you started with?