That mass-damper isnt in every TT, we have found.

But, if you want me to weigh two empty tubes, I can do that next week.

 

Carl-- Curious and kind of related: Is the dampener a feature found only on stick cars vs autoboxes? I'm thinking that a torsional damper might help with resonances in a relatively springy shaft mounted tight between clutch and gearbox, where the autobox has a hefty hydraulic torsional damper mounted to the input shaft already.

 

Drbob, The damper is in all 928s but roumoured not to be in CS/SE models. It doesn't rotate with the shaft so it won't do any torsional damping . It's basically a mass damper that will change the resonant frequency of the TT/transmission/motor combo. IIRC most were marked with frequencies of around 950- 1000hz.

 

The very early cars suspended the battery box to the rear of the transaxle (it is rubber gasketed to the body)since Porsche was very concerned about vibration and used that weight as an attempt to "tune" it. There was some question about the G forces involved and if the battery could sustain it but that was only 4-5gs and the battery people said ..no problem. As mentioned nearly ALL had the cast iron balance weight but I do recall that part of the lightweight mods for the Club Sport included leaving it out. As Constantine noted the steel 5 speed tube empty is around 27-28 lbs.

 

That's beautiful.

For a point of reference, the 944 GTRs used a 928 torque tube. The engine and transmssion were solid mounted in a full tube cage car. They broke the steel torque tubes like they were made of glass...very common problem. I wasn't involved with the problem or the solution, but it would be fun to know what the problem was.

 

Damper wasn't there originally but its installed to all cars after '81 MY, except CS and possibly SE.

 

Thanks for the info and the diagrams. Very informative! So it's a housing damper and not a driveshaft damper at all. :lightbulb:

There needs to be an oil-filled version, obviously.

 

Did the GTR cars have a body-strengthening crash cage? If the body twists (I think even F1 cars twist SOME amount) and you solidly connect this assembly the car, then IT will twist too. If you support it with rubber, it can be properly isolated.

Just a guess.

 

Dr. Bob:

My information is that there were no mass dampners in the 78 and 79 MY tubes. Of course, those are the "long" TTubes, and the 78 model had the battery box bolted to the transaxle as a dampening measure. In 1979 they moved the battery to its current uni-body incorporated position.

In 1980, when the TTube was shortened, the mass dampner started.

Here are some pics of one: Note it weighs 8 pounds, and what I find most interesting is the sticker on it that shows "87 Hz", suggesting perhaps they tested each one before installation?

Yes, on the aluminum TTube we did not care to replicate the mass dampener.
Also note our bearings are solid mounted to the TTube, and not in rubber blocks as OEM has it.

The RPM ranges noted above in this thread are of no consequence to the racer, as is the little vibration and or noise the TTube will produce.

I will be the first to race this new part, and I will let you know if the noise is an issue. I dont expect it to be.

 

Carl--

If in fact the tube/housing 'rings' without the dampener, it will eventually harden and fail. For fun, you can spread talcum powder on a supported shaft and gently 'ring' it to see where the node centers are. Add some wide/thick rubber strips to the centers and 'ring' again. The noises from the tubes that the factory was working on may have been way beyond normal NVH and into actual mechanical failure modes.

My tongue was only most of the way into my cheek when I suggested an oil-filled tube.

 

They were a complete tube frame car. The "body" attached with Dzus fasteners.

 

Dr Bob: I agree with you completely. I hope to have it at Watkins Glenn this March 23rd and we will see if it "sings" or not. Right now, I have only 3 weeks left to get the car ready and its looking doubtful.

But, your assessment is correct - if we allow the aluminum to work-harden it will crack. Lets see if it work-hardens first. The paln is to see if it sings or not first. If its a problem, we will have to rubber-mount those pillow blocks.