Should my 901 gearbox sing along?

Patronus · 09-15-2002, 02:06 AM

I replaced my car's 5-spd 912 gearbox with a 5-spd 901 from a '71 911S. What a wonderful smooth gearbox, the only problem is a whining sound in 4th and especially in 5th gear. It is quiet at trailing throttle. It has new transmission oil, by the way. It doesn't sound 'unhealthy' - quite the opposite - it sounds like a rally car. But if it should be quiet I guess I'll have to do something about it.

Do I have a problem?

pjv911 · pjv911's Garage

I have a 69` 912 tranny in my car which is also powered by a 2.7 motor. I have the tranny noise you describe in 3- 4 -5th gear under load only . I figure its a countershaft bearing thats going bad. Its been making the noise now for 2000 miles and has not increased as far as I can tell. The answer to your question is yes you do have a problem. I have a question maybe(you) someone can answer. Is there a difference in the gearing between a 912 unit and a 911 unit ? My car is geared way to low for my ride to work which is 11 miles of 70+ mph. The engine is screaming at 4k rpm in 5th gear. I plan to do a 3.6 swap in the future but not as soon as I would like. At that time I will be using a different tranny. But I do have a 901 from a 69` T sitting in my shops basement.

Kurt Williams

Peterfrans · 09-15-2002, 06:08 AM

I have it too. It is most noticable in 4th and 5th with little load and around 2500 rpm. The noice seems to be less under load or at higher rpm. Mine was rebuilt about 3000 km ago.

pjv911 · pjv911's Garage

Thats exactely how mine is Peter. Although I can hear it in 3rd gear as well.

1980SC · 09-15-2002, 11:36 AM

I know my SC's 915 is a bit different, but it has been whinning loudly under load in 3,4,+5th ever since I've owned it. In the 20K miles I've driven, the noise hasn't gotten worse, so you may not need to worry about it much. I do hate the noise, but I can't force myself to rebuild a gearbox that still shifts well.

Rob
1980SC

Patronus · 01:04 PM

You guys seem to have exactly the 'problem' that I'm having. It makes me feel better.

Kurt, as far as I can remember the 911T gearbox is geared only slightly higher than the 912 gearbox. The difference was not worth it for me. What you want is a 911S gearbox. To me it feels as if there's a big difference between my new 901 tranny and the 912 one that I threw out a month ago. My 2.7 was over-revving all the time, and now there's lots of rpm left even well in excess of 100mph. Depends on what you replace the 912 tranny with - I got hold of a '71S tranny which seems to be perfect for my engine.

Problem is the fact that 100mph on my speedo isn't 100mph any more. I'm going faster than it indicates, since I replaced the gearbox. I will either have to get the 150mph speedo that goes with the new gearbox or re-calibrate my existing one.