915 transmission knocking/tapping

[Dan Young]

I have an 84 Targa that has a transmission knocking noise. The car has a short shift kit and I just replaced the shift coupler. It was very worn. I had hoped that maybe the shifter was not properly engaging the gears and that was causing the knocking noise. The car drives and shifts normally it just has the knocking sound. The noise is the loudest in first gear. If the car is coasting in neutral it does not make the noise. It does not make the noise in reverse. As you shift to taller gears it is much quieter. It is not a grinding, it sounds more like a tapping noise. More like a playing card in the spokes of a bike when you were a kid.

[4sd911]

CV joint?

[Joe Bob]

Cards in the spokes sound on my 3.0 was broken head studs. Pull the valve covers and see if anything is rattling around under the rockers.

[callard]

I've got a small Toyota P/U with a tooth broken off 3rd gear. Makes a knocking sound if engaged. All other gears quiet. Three years now, two - four shift.

[Peter Zimmermann]

More info please...
Is the knocking noise worse when car is cold?, warm? or hot?

What rev range is it most noticeable?

Does the noise happen only during acceleration?

Did the noise start after having work done, or during normal use?

FYI: Having the noise fade in higher gears is not unusual, noise will be muted by road noise.

[zippy_gg]

Have you checked the transmission and engine mounts?

[Flat6pac]

Drop the CV joints and see if its still there. I had a trailing arm bearing go in the past and thats the way I found it.
Bruce

[Tom '74 911]

Originally Posted by Peter Zimmermann

More info please...
Is the knocking noise worse when car is cold?, warm? or hot?

What rev range is it most noticeable?

Does the noise happen only during acceleration?

Did the noise start after having work done, or during normal use?

FYI: Having the noise fade in higher gears is not unusual, noise will be muted by road noise.

Hi Peter & Others-
I live down the street from Dan and went for a short drive the other day w/him to try to help him diagnose the noise. It seems to be definitely coming from INSIDE the transmission. As Dan said, it only happens when the car is moving and in gear. When coasting in neutral, the noise is not there. The "ticking" increases as speed increases and decreases as speed decreases - like the card in the spokes analogy. It's loudest in 1st gear, but road noise could easily be masking it in upper gears I think. Cold or warm I think is the same. I don't remember if it's more apparent during acceleration - I think it ticks regardless of accel/decel. Noise appeared all of a sudden, no recent work done on the car.

The first thing I thought to check was the shift coupler and bushings. The coupler bushings were loose, so Dan replaced them w/some from my stash. While he said that his shift lever feel is greatly improved, the ticking is still there. . . We didn't look at the bushings below the shift lever - he had a short shift kit installed installed a year or so ago I think and they did the shifter bushings then (allegedly).

Could coupler misalignment cause the shifter input shaft to be pushed in/out too far? So it'd be in gear, but not cleanly enough so that something inside is rubbing? I'm not familiar w/the insides of the 915 to visualize. . .

Anything else we might check - that we can get to from the outside?

Thanks for the help,
Tom

[Dan Young]

Tom is right the the ticking happens while in gear and when you are accelerating or deccelerating. Whether the car is warm or cold has no effect.
The sound is there at any rev range, as soon as you are in gear and moving you hear the sound.
One evening I was driving the car and I noticed the sound while I was parking. I was in first pulling into parrking space. Then when I left the noise was there for the whole drive home, which was about 10 miles.

[Peter Zimmermann]

OK, I'm clear on the symptom - good job! I seem to remember a similar problem maybe 15 years ago, but I'm not getting any brain waves yet.

I think that what I would like you to do is get the car up to about 30-35 mph, when you can clearly hear the noise (2nd gear should be fine), then pull up the handbrake handle. First one click, then two clicks, and see if the noise disappears. When you activate the e-brake add a little throttle to keep your speed consistent. Don't leave the handbrake "on" for more than a couple of seconds, don't worry, you won't hurt anything.

Please try that, and I'll continue to do the think, think, think deal!

Tom, if a shifter is adjusted to favor a certain gear, it might pop out of the opposite gear, but you shouldn't get clicking/knocking noises. Have you checked to be sure that the CV joint bolts are tight?

[Tom '74 911]

Originally Posted by Peter Zimmermann

Have you checked to be sure that the CV joint bolts are tight?

Hi Peter - We have not checked the CVs yet. I assumed that since the noise disappears when coasting in neutral (at any speed), that it was not CV or brake related. The noise is present at any speed when in gear - doesn't matter if you're under accel., decel. or coasting in gear; if a gear is engaged and the car is moving, the clicking is present.

Dan can do the handbrake test & then post back!

Thanks for your help Peter!

Tom

[arbita1]

Is the noise present at idle or only while moving?

[Tom '74 911]

Originally Posted by arbita1

Is the noise present at idle or only while moving?

Only when moving.

[arbita1]

Ok. Is it more of a clicking or a metallic knocking?

[Tom '74 911]

Originally Posted by arbita1

Ok. Is it more of a clicking or a metallic knocking?

Ticking, like something is coming in contact w/one of the spinning gear teeth inside the transmission. . .

[arbita1]

I had sort of a similar issue with my 944. One of the gear teeth on first gear (on the input shaft) broke. It caused a tapping sound. But it was constant (moving or idle) and only stopped when I pressed the clutch.

I'm wondering if you possibly have something similar on your pinion shaft (which I think why it would explain why it would only happen when the car is moving in gear). Maybe a broken gear or something coming in contact with one of the moving parts on the pinion shaft. Perhaps maybe even in the differential section? Hopefully this might help Pete Z to hone in on the problem.

[McG]

So Dan...what happened?

I afraid to ask as I am hearing the same sound. But please elaborate on your findings!

Thanks

[Flat6Heaven]

Dislodged speedometer ring magnet?
That happened to me on a 1982 915/62 and made a ticking sound as described above...

Good luck in any case,
Ben.

Edit: magnet failure is accompanied by speedometer reading error.

[DRACO A5OG]

have you had the throw out bearing replaced?

I did a duh by installing the assembly backwards and it caused a ticking noise. assembled it properly per bentley, noise be gone

if not, I would try to re-adjust the coupler, it must be pretty precise.

[McG]

Thanks for the feedback!

No to the bearing.

speedometer ring magnet...the seemingly random things that go amok!