Trans noise on trailing (back) throttle
 

Hi All,

I have had my '86 cab for about six months now and am just driving with the top up since I got it :) Now, I am noticing a bit of noise on back throttle in any gear. It seems fine under load, but it is a bit harder to hear with the engine. I don't seem to hear it with the clutch in and a quick test of clutch in and out at idle in neutral is nice and quiet and no difference in or out.

I just replaced all four engine and tranny mounts with the higher performance standard mounts that our host sells. I have also rebuilt the shift mechanism, replaced the coupler and all the shifter bushings. It seems to shift pretty well; much better than it did and everything including the mounts helped. I also drained and replaced the tranny fluid. Looks like there was Sweepco in there. I replaced it with Valvoline dino oil.

Since this is my first 911, I'm not sure if the noise is normal or not. All I have to go on is our little 356 and it is actually very quiet. The 911 is much more of a beast in comparison and has all sorts of noises, but I'm guessing I shouldn't hear much from the transmission. Seems to happen in any gear, and mostly on trailing throttle. I'll try to listen more and try some higher speed coasting to see if it is much different.

The tranny was removed and had 1st and 2nd gear/syncro work done about 10K miles ago according to the PO's documentation. I don't think it mentioned bearings, but I'll double check.

Is this normal or should I be concerned?

Thanks!

Franny

I had the same concerns as you after a few months of driving. The drivetrain on these cars are very noisy. I heard and still hear things that worry me. Different metals warm at different speeds making all sorts of special noises. I finally brought in an expert to help analyze all the work that I had done to my car... Like you, I replaced all fluids, but I put Swepco in my tranny, new BradPenn, new Ate blue, new brakes, new everything on top of engine, new sound mat, new shifter bushings and coupler. Still very noisy.
---edit... 1st and 2nd synchro about 60k ago ---
Tom Amon was kind enough to take the time and come drive my car. He charges a nominal fee to just drive it, listen, and put it through its paces...he came back and we discussed all my concerns.
The thing that put my mind at ease was he said he would be proud to own my car, and he drives a ton of 911 race/street cars.
I can't say enough about his service. He is the man.
Rich

My best advise is to drive the car frequently and get used to all the common noise/sounds unique to your car. Then, if anything changes, noises get louder, pitch changes, new noises, etc, then worry about it.

I had my car for a little over a year when after a long spirited drive in the mountains noticed significant gear whine that hadn't been there before. I knew something was wrong at that point, and my instincts were correct. Pinion shaft 4 point bearing was going, as well as the bearing retainer. I ended up pulling the motor and tranny doing the repairs myself. Very rewarding, but sucked not having my car on the road for about 6 weeks.

Is the noise a whine or a rattle?

Whine could be bearings or ring/pinion. Rattle could be gears.

Some gear rattle seems not uncommon, or at least you can read about it here enough. I get a litttle gear rattle between 1500-2000 rpm under acceleration. I'm not below 2k rpms much though. Just seems there is a frequency where the gears will make noise then it clears up. -J

Thanks Guys,

I guess it is more of a slower whine. Similar to what you get in most cars in first on trailing throttle which I think is the syncros spinning away. I just haven't heard much in the higher gears before. I suppose I could just drive with the top down :)

I'll spend some more time listening in various situations.

Thanks for all the suggestions,

Franny

After working on the coupler, did you replace the tin cover, held by 4 screws, after you were finished? Without that cover the trans will be unbelievably noisy.

How many miles are on the car?

My 83 cab has always been noisy. When I did the 3.6 conversion I killed second gear. The IM plate was warped by my abuse and track time, the repair and subsequent kinder and gentler driving still has tranny noise.

Consider an oil change, check mounts and couplers.

Thanks Pete,

Yup, I replaced the cover. I bet it would be loud without it! Car has about 106K miles with the tranny refresh at about 96K or so. The car is just a fun driver for me so no track time. It gets driven a couple times a week and has gone on a few long day/weekend trips. The engine has had a good service (valves, fluids, plugs, cap, rotor filters, etc.) right after I bought it and I also did the CVs due to ripped booties. The joints looked just fine so they got re-greased and reinstalled. Just had the right rear sway bar mount replaced along with a complete four wheel alignment and return to correct Euro height all done at a good local shop here.

Tranny and engine oil have less than 1500 miles. Mounts and coupler are new (<500mi).

Thanks,

Franny

There is some normal (the 915's I've heard) gear whine noticeable if you are 'enclosed' in the car coasting/cruising or light throttle.
Actually lots of noises that are deadened by 50 lbs of 'stuff' on the back seat and window tray area.
I've removed that dead weight and the mechanical noises are all over the place, lovely too.

My car has all sound deadening removed with thin carpet throughout. I installed a rebuilt Trans with factory LSD and stiff wevo mounts and couldn't believe how loud the Trans was compared to non LSD with stock mounts. Not sure which added more mechanical noise probably LSD but mounts def don't help. Add a few track days on the clutch and the symphony really gets going!

I drove home with the top down (while we still can!) and I couldn't hear a thing. This mornings commute I was listening pretty intently. I can only hear it when the car is in gear with the clutch out. In neutral clutch out, or in gear clutch in and it is very quiet (this diff is probably just fine) so it is just back throttle. I'm guessing it is just fine and is probably just normal syncro noise. It isn't a problem at all, I just wanted to get an idea if there is some darkness lurking inside the tranny.

Those "Sport" mounts are a bit stiff and that is probably why I hear a little more now. They did help with the shifting though!

Thanks,

Franny

p.s. Why does that car stay with you so much through the day? It is very engaging to drive, but I find myself thinking through the day how much fun it is. Weird, huh? f.

Totally normal! I can see mine from my office window and its a huge distraction. So much so, I park on the other side of the building now.
As for your noise, dont obsess. The more you listen the louder it gets. I once obsessed about a noise so much I just had to sell the car as I had done everything under the sun to fix it. That was 10 years ago and the car is still on the road and running perfect.

Good advice :)

Yep, franny, just listen for change. At 106K miles I seriously doubt if the car has a differential problem, so just have fun with it!

Will do! Incidentally, Your book was a huge help in my entrance into the 911 world! Great info and well laid out. It was a really big help!

Thanks,

Franny