greg1234

Hi everyone.

When I'm slowing down in my 964/5 Turbo, for example when approaching a junction, and I change down into second gear, I get a sort of "chugging" noise and sensation from the rear end. Is this what's known as transmission shunt (heard the phrase somewhere, not sure what it means)?

It's almost like the sort of feeling you'd expect the engine to make if you were pulling away in the wrong gear.

Is it normal?

horst

Glad to hear of your problem, greg. Actually, I think mine does the same thing, and has for years. I just take it as a reminder that she wants more "r"s

Randall G.

Hmmmm .... when my Freudenberg dual mass flywheel failed, its most obvious symptom was drive-line vibration when lugging the engine--in particular, while on a grade.

Then again, Horst has a (very reliable, but not failure-proof) LUK DMF that is making a similar noise, so perhaps it is nothing.

Do you also hear transmission rattle at idle? Per the shop manual, this is another sign of a failed DMF.

The DMF is supposed to (and does) make for a pretty quiet transmission. If you have a LWF, you should expect more gear noise.

Here's hoping your noise is harmless and not too out of the ordinary!

Adrian

Dear Greg,
The first question would be, at what RPM are you doing this. If you are dropping the RPM too low this reaction is quite normal in a single Turbo, Turbo. Needs RPM as Horst says. I hope of course that you have no other problems. DMF failures in the Turbos are not as common as in the Normally Aspirated 964s but they still happen.
If you leave the clutch pushed in and you roll up to the intersection do you still get the same noises and feeling. Yes I know people are going to say but this and but that. However this little test eliminates the rear differential from the equation. The Turbo 3.6 has a LSD. These LSDs are known in this part of the world as a bigger problem than the DMFs on Turbos,
Ciao,
Adrian
911C4

PS: It might also be idea to make sure that your rear bumper is correctly mounted and nice and tight. In this part of the world we have rigid bumpers and I have seen broken mounts cause similar horrible sounds. Not just on Porsches either.

greg1234

Hi Adrian.

I haven't checked the rpm, but it's when I'm slowing down for a junction or a corner. The fact that it seems to be more pronounced when slowing into a corner (for example when turning into my driveway) might suggest the LSD... but it's a very obvious "chugga-chugga-chugga-chugga" kind of feeling, with a sort of knocking sound at the same time, from the rear of the car. I'm pretty sure it doesn't happen with the clutch fully depressed - it's only as I engage second gear whilst slowing down. It's also not simply that the rpms are too low for the engine to handle, because I can slow down, engage second (producing the chugging) and then pull away quite happily without having to drop into first..

MB965

Greg,

If the noise occurs only when the car is being turned then I believe the noise you are hearing is from the LSD unit.
I encounter this noise on my Turbo 3.6 whenever I am turning with the throttle closed, forward or reverse. The cause of the noise is the steel plates in the LSD unit rattling in the housing as they are slipping. The reason for the slipping is that the design of the LSD uses a 20% forward/100% reverse (or braking) "lock-up" factor. What this means is that anytime the car is turning (one rear wheel turning faster than the other)and the throttle is closed, the LSD sees this as a reverse, uses the 100% lock-up factor and the LSD must slip to allow one wheel to turn faster. The internal design of the LSD mechanically chooses the forward or reverse lock-up factor.

A simple way to determine if what I am describing is occurring is to select a low speed 90 degree corner and try turning with a little throttle opening and then try the same corner coasting with the throttle closed. Always with the clutch engaged. If you get the noise with the throttle closed then you can experiement with applying the throttle on and off while going through the corner. This should cause the LSD noise to come and go with the throttle application.

Porsche issued a TSB on a noise coming from the LSD on the C2 Turbos however they describe the noise as a "growl". It sounds a lot worse than that! Perhaps this is due to the translation to English of the German term for rattle. I wonder if anyone has the TSBs in the original German. I can get the TSB number, I do not have it now.

Let us know what you find out.

Mike
Turbo 3.6

greg1234

Interesting, thanks Mike.

I'll try that experiment.

You must be the other Turbo 3.6 owner I heard about...

greg1234

Hi Mike.

You were right - it seems to be the LSD. It happens almost exclusively on corners, with a closed throttle. Once it's started and I open up the throttle a little, it disappears. If I back off the throttle again, it comes back.

So I guess that's one I don't have to worry about, right? You're implying it's perfectly normal?

MB965

Greg,

I am not sure that what we are experiencing is perfectly normal, as I have only discussed it with one other C2T owner who had the same noise.
Mine has done it since the first day I have used the car and it has not changed during the 1 1/2 years that I have used it. I see nothing in the transmission oil to indicate a significant problem is occurring.
My conclusion is that the noise does not occur on every C2T (the TSB was for all 964 Turbos [the first to use the 20%/100% locking factor], not just the 3.6) which is not a surprise given the fact that is a loud and disturbing noise which I would think would have caused many more people to complain about.
I will get the TSB number and for the hell of it persue the language/translation question.

I do not worry about the noise, but I pay attention to it so that I can track any changes.

Have you heard any complaints from other 964 Turbo owners?

Mike

Adrian

Dear Mike,
This is quite a common problem or complaint from the Turbo owners I know around this area, 964 3.3s and 3.6s. Enough most of them claim the noise is loudest when reversing. I have heard the noise myself in a 3.3. We know 100% this had the old linings,
Ciao,
Adrian
911C4

MB965

Adrian,

I also experience the noise most predominately when reversing. I believe the 964 RS also used the 20/100% LSD

I checked the TSB, it is number 9101 and applied first to the 1991 911 turbo.
The TSB has a more detailed and technically correct description of the problem (I always get in trouble when I try to describe things in a less than technically thorough way. However if I am too technical no one will read it!).

Anyway the TSB uses the term "growl" to describe the noise. Not that it really matters but do you think the TSB, if it was written in German, described the noise using a different term?

Thanks,

Mike
Turbo 3.6

Adrian

Dear Mike,
I have to be honest and tell you that the TSB as we have come to know and love is only available in English. The German ones I have seen and other nations as well are dealer issued documents. There is no source here in Europe outside the dealers (no alldata.com) where these things can be accessed.
The German word for Growl is Knurren. I would doubt that this word would be used.
I will check around but I have a feeling I am not going to find anything,
Ciao,
Adrian
911C4

PS: I believe you are correct with the LSD in the RS. I do not have my notes with me but I am sure you are right.

greg1234

Adrian, what was the consensus here? I think we've established that other people experience this problem, but are you saying that it's normal and can be ignored, or that it's a problem that needs to be sorted?