Black Sea RD

Roger,

Really don't appreciate your tone and comments.

I was actually waiting for an explanation to my questions/concerns. Your latest response is the first I've heard this clamp was fitted to multiple 928s and model years with different shafts.

Pictures and a detailed explanation would have done wonders for me.

This is something I have gone through on my own products on many occasions here on rennlist and I welcomed the opportunity to explain them and their benefits. Strange that my questions are seen as a threat to you and this clamp.

Good luck with your sales of this new clamp.

Dave928S

Mongo ... it is clear from the pic you posted that your driveshaft is too far back in the torque tube case, and is as Greg describes.

If you look at torque tube specs, which give dimensions of the driveshaft within it, in relation to the end of the torque tube flange, you'll see that Porsche specified specific dimensions. They did so to ensure that the projection of the shaft each end was such that the grooves for the bolts lined up.

Compare the pic that Roger posted of a shaft in the correct position within the tube, with yours, which I have marked to show the relative positions of the step in the shaft with the bellhousing flange. You may have loosened or tightened the rear pinch bolt ... but you haven't adjusted the drive shaft to its correct position within the tube.

Nothing in this chain of components has a variation in dimension or allowable tolerance of 3/4" ... so with everything correctly positioned there has to be only a trivial tolerance of spline engagement .... and if there isn't (like yours), there is something wrong that needs to be fixed.

This is what I've been alluding to in my previous posts ... if the drive shaft is in the correct position within the TT, and the front flexplate is straight, the spline engagement has to be within a close tolerance. It could/should only vary by the aggregate tolerance of all the components in the chain ... which is trivial.

... and if that engagement is within tolerance, then the new clamp should slip on easily, with the adjustment bolts with locknuts snugging up any tolerance of spline engagement. I'm tempted to buy an auto just so I can buy one ..

69gaugeman

Wonder how it would work if you greased up the splines and didn't tighten the bolt fully, allowing the splines to 'float' as it were? When I get another rogerbox 928, I think I might just try this....

OTR18WHEELER

In this pic below, you can see the markings on the spline caused by the migration of the OE flex plate clamp, and the damage it caused. I believe the Ritech flex plate clamp would have prevented this from happening. The splined shaft itself has not moved, when I removed the rear pinch bolt it had no marks or abraisions whatsoever. The shaft is in the correct position in relationship to the cut out of the bell housing in this case.

danglerb

Grease up the splines, snug tight maybe with loctite so the bolts stay put, take it out for a fun romp, then up on a rack to see where the grease gets pushed around to.

OTR18WHEELER

^^ a foot note to my above post..
I believe the migration of the OE clamp was a result of the front TT bearing gradually migrating rearward allowing increasing wobble of the shaft between the front bearing and the clamp, this and increasing vibration over time. So my theory is that the failure of the OE flex plate clamping force is not the inadeqate OE clamp itself, but also the failure of the front TT bearing. My front bearing was 13 inches rear of original location at this point.
All in all, with Constantines Super Bearings, and the Ritech clamp, I believe this to be a solution.

69gaugeman

Exactly. Sure the splines will wear out, but the engine will be saved....

Adk46

A carbon fiber shaft sounds expensive - not the tube itself but the assembly with the attachments to steel splines or flanges. The wonderful stiffness of carbon fiber is what we're after - it changes vibration/whipping/wobbling dynamics enormously. This stiffness can be obtained at much lower cost with a larger diameter steel tube with welded attachments. Most driveshafts have always been made this way. It looks like there's room in the torque tube (no bearings would be required). I might be missing some details of the design requirements, though - perhaps the axial and angular tolerances of the engine and transmission mean that the shaft must flex.

I'll speculate further on a few points that have come up: Unclamping the shaft removes a restraint that may change its vibration dynamics - beware lower wobbling resonance rpm and bigger wobbles. The twin plates of the flex plate may be there to provide vibration dampening from the two plates sliding a bit across each other, like the dampening you get from leaf springs. Or the torsional strength they needed meant a thickness that, as one plate, would be too stiff axially.

This is all very interesting, since I must soon inspect this issue on my car. It would be nice to know just what to do!

Despite all the bickering, I want everyone to know you are heroes to me, the new owner of a 928. Such passion!

Mongo

Okay, to use this new clamp then, what do I have to do exactly to properly move the splined shaft forward IF my current position of the shaft does not support the mounting?

I am tired of this TBF **** and want to sleep better at night once and for all without having to pull the TT to install a new clamp. Those three letters should stand for a vintage torpedo plane and not a serious issue with auto 928s.

Imo000

Take the rear pinch bolt out and see if it's in the right location.

Chalkboss

My hats off to this solution, looks like a well made piece, and the utility can't be beat. I roll with a Constantine clamp and have no issues. Fantastically engineered clamp. Still, one wonders what Porsche knew, and the reasons for doing what they did. They left us picking up the pieces of their problems. Glad that we have have experts keeping us on the road.

docmirror

Let me preface this by saying: I'm not a ME; I never had an issue with the twisting moments or inertial moments on a driveshaft; I haven't studied it in any way, and this is just one man's opinion on the CF shaft idea.

Early in the development of the Osprey tactical VTOL, the engine designers specified a CF tube)not a solid shaft) for the main rotors. It did not go well, with a lot of shattered tubes(shafts). I believe they also tried a solid shaft, with variations on the dopants of the epoxy, with limited success. It's the ability of steel to deform and return to it's natural shape that makes it so good at power transmission. CF has a Young's modulus that is so very different than steel that I am worried we would find similar faults with a CF shaft or hollow tube. I've heard of some tube driveshafts for cars, but I think it would merely shift the failure point to the next weaker segment of the transmission path. Maybe that would be the pinion gear, maybe the spiders, I just don't know and won't speculate on all the potential failure modes.

What I will opine is that the actual Youngs modulus, and also the shear properties of CF wouldn't lend itself to this application. The steel allows the wind up under torque, and the release which is taken up by the large diameter of the flex plate(aptly named). Remove that elasticity from the transmission path and I think the 928 would maybe experience the same thing the Osprey did back in the beta phase.

YMMV, don't try this at home, closed course pro driver, and may call **** leakage. But - it's been seen before and didn't go well.

Mark R.

Getting back to questions about this new product...

So this new clamp anchors itself against the body of the stock clamp housing.
That seems like an ingenious and sound approach, since that portion is welded in place.

My question involves the other end of the interface and the test observations so far:
Does the leading corner edge of the clamp begin to dig into the splines over time?
The edge of the splines are an incline rather than a nice flat land, so that's why I'm wondering about this.
And I don't know the hardness of the shaft splines, but clearly there are some strong forces involved.
Is it the intent of the four adjustment screws to take up for wear (and thus movement) in this area..?

Absolutely love the ease of installation...

SeanR

Checked mine today after two years under boost. Moved 3-4mm.





This clamp would have kept the drive shaft from creeping.

Mark R.

3 to 4 mm doesn't seem too surprising after two years under boost.
So do you have some experience with this new clamp Sean?

We relaxed the clamp on Brandon's new 90 S4 on Saturday.
The clamp moved back about 3 mm. Not sure about the history there...

I've been using Cap'n Earl's original Loctite method on mine for many years.
It does a fantastic job of completely eliminating all movement, BUT...
It's a MAJOR BITCH to remove when needed (requires LOTS of heat).

So I'm definitely interested in learning more about this new product.
Hoping to hear more regarding the questions in my post above...
.
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