I noticed something today that I realized has been going on with my 914 for a while. Whenever I get off the power and coast, there's a roaring noise from the car. If I take the transmission out of gear, or if I put the clutch in, there's no noise. And if I add enough throttle to maintain speed or accelerate, no noise.

So it only happens when engine braking.

Any ideas of where it could be coming from? This obviously won't be something that is easy to replicate in the garage...

My thoughts were that it could be the CVs, objecting to being loaded the "wrong" way. Possibly time to repack/rebuild/replace them. Or it might be something in the transmission? I did rebuild the trans relatively recently (especially if you count miles, but not that many months ago) so it could be something I did there...

--DD

One gear only, or any gear?

I wouldn't think it's the CVs since they are in motion when the car is regardless of if you're in gear or not.

Probably something with the transmission since it goes away when it's not engaged. Maybe a throwout bearing? When my throwout bearing failed it sounded like what you're describing.

Sounds like a bad bearing!

I had a similar sound on my 6 and when I rebuilt it I found this!!

Yep, that's a bearing. I'm sure the Evil Doctor will chime in here on precisely which one it will be...

-Josh2

Have you ever rebuilt the transmission?

Might mean you have to take it off the road and stop driving it again for another few years....

I think it may be there in all gears, but I noticed it most in 5th.

I rebuilt the trans pretty recently. Sounds like I may have gotten something wrong.

--DD

Diff whine?

What trans mounts do you have? Some convey more noise than others. I switched to the 911 sport mounts and I definitely hear more noise.

Dave, check the rear trunk for that box of Frosted Flakes... Did you use the same gaskets on reassembly of the trans?

Differential whine possible from the wrong setting which could have been caused by the wrong gasket???

I think Rich, or one of the PNW guys has a tool he may lend you to check it....but you would need to pull it apart again....

Not to bring up the debate over the use of the word rebuilt, but what exactly did you replace in the transmission when you had it apart?



rich

I just opened up a 915 with the same problem. Bad ring and pinion, caused (probably) by a failing clamping plate, allowing the pinion shaft to move longitudinally.

Hope this isn't your problem, but it sounds like that might be the issue.

The Cap'n

We replaced the bearings in the intermediate plate (both), several synchros, one synchro hub, possibly a slider, and the bearing retainer plate that bolts to the intermediate plate. (Mine was quite worn.) The bearings and synchros were new, the retainer plate and synchro hub were used but much better than what came out of the trans. If we replaced a slider, it would have been with a new part.

We measured the gaskets that came off the trans, and used new ones of the same thickness.

I think I need to have a talk with my mechanic...

--DD

One possibility: 5th gear on pinion shaft was installed backwards. Like other splined gears, it has a slight offset; if installed the wrong way, will move closer to underside of synchro hub on input gear. Because of helical teeth, input gear will move forward on decel, and synchro hub could hit gear on pinion shaft.

Jon B.
Vista, CA

.......
(check Fluid)A>K>A...gear oil

Did you happen to replace the carrier bearings and the front pinion shaft bearing in the case?

I recall that the front bearings can oval out the case in some situations...and possibly the seat.

Rich