petertobin

I'm considering this as a insurance investment - interested if anyone has had a failure since install / general feedback, or if there is a known better way (hopefully that does not involve huge amounts of labour) tbf has kept me awake at night (i had a idle motor failure a few years back while on a road trip - I initially thought it was tbf... not at all pleasant)

- use case is for a 93gts, 180k km

thank you in advance

Schocki

I installed mine 4 years ago and installation was easy. Last time I checked one month ago my TB, it was still at the same value (0.23 mm).
Before, the flexplate lamp was secured with Loctite 290 since 2005 and nothing moved either.

GregBBRD

Roger gave me one of these, to do testing with. I installed it on a client's car and left it on for about 10,000 miles. While there was do sign of flex plate migration, the hardened insert inside the clamp left a significant mark on the torque tube shaft...right where you really don't want any stress risers.
Afraid that the shaft was compromised, we replaced it.

"Testing" over.

I believe that Constantine is no longer making his excellent clamp (which had no obvious negative effects.)
I've gone back to what I did for years, before there were any "clamps" of any type: I simply fit an earlier style torque tube shaft which has the groove for the circlip and fit the stock Porsche washers, retaining washer, and circlip, found on the earlier vehicles. (Yes, it's a bugger to get the circlip on, when everything is installed, but it is possible....and it's actually really simple to measure everything and install the perfect amount of shims, when the torque tube is out.

"Going backwards" in model years to a shaft with a circlip groove actually kills two birds with one stone: You eliminate the 28mm shaft, which has proven to be prone to breakage, and you get a shaft with a circlip groove.

We make 25mm torque tube shafts, with the circlip groove from 300M material.
Crazy strong/durable material.
After years of torture testing these shaft behind engines with insane amounts of torque and horsepower, we have not been able to even remotely "hurt" one.
Guaranteed not to rip, tear, bend, or buckle.

Constantine

For information purposes only, we still have them.

GregBBRD

My apologies.
I thought Mary told me that you were no.longer making your flex plate clamp.

Like Constantine's very robust torque tube bearings, his flex plate clamp is a terrific part and an excellent choice for a long term "cure"!

petertobin

thanks for the reply's, food for thought (and a change of plan then...) - forgot to mention I'm in New Zealand, which makes shipping a consideration. Will have a chat with my guys about what they think / do some googling to find some costs info on the two options mentioned above

cheers

FredR

That the 28mm shaft is prone to snapping there is no doubt and why on earth Porsche modified the design from the 25mm 3 bearing shaft to the 28mm two bering shaft remains one of the big mysteries of the 928 evolution given no one has ever produced a Porsche document suggesting why such happened.

That being said the interesting question is whether anyone has ever seen a 28mm shaft fail once the clamp migration issue has been resolved? I asked my dear friend Constantine this question some years ago and he had no knowlege of such a failure once his excellent clamp has been fitted. To my way of thinking this left the rather obvious question as to whether the 28mm shaft was the victim or the culprit regarding such failure. Just about all the TBF examles I have come across involved the 28mm shaft but I understand it can also happen with the non-shimmed 25mm shaft installations.

We all know where the 28mm shaft fails- at the base of the taper either on the front or the rear. If there was an inherent design flaw with the 28mm shaft then examples like Bill Ball's 89 S4 could never have covered 300k miles yet alone handle a supercharger install on top of it. Clearly there is a random element to the failure and my best analysis to date suggests it might just be a simple question of tolerance ranges between the shaft and the clamp that presumably [?] were outsourced to different manufacturers. Those whose assemblies are at one end of the range are simply "out of luck" destined to grief as I was back in 1999 with my late S4. Once I applied the Loctite solution the problem disappeared and 22 years on has not resurfaced to date over two iterations but then I do not know whether it will reappear next time I start the motor. If nothing else I have the "comfort" of knowing that if it does, I will immedaitely recognise the characteristic vibration that went with clamp slippage 22 years ago.

Upon reflection, I have not been able to find evidence to resolve in my mind whether the 28mm shaft induces a vibration that causes the shaft to slip or whether it is simply a case of tolerances as I originally concluded it was. Either way when one stops the clamp slippage 28mm shaft failure and/or TBF do not happen. That we still have examples with no secondary protection measures all these years on I find "disturbing".

Mark R.

I've been using Cap'n Earl's method with Loctite 290 for nearly 20 years.
I check it regularly, and once applied, the spline has NEVER moved.
In all those years, I only took it apart one time, which did require LOTS of heat.
The Loctite 290 is really an incredibly well engineered product.
Heck, the liquid "wicking" properties alone are truly amazing.
Such a simple and elegant solution to the problem. Thank You Earl..!!!

GregBBRD

I see just as many cars with flexplate preload (and TBF) with the 25mm shafts as I see with the 28mm shafts.
Pretty well convinced that flexplate migration is a direct result of increased torque and more "spirited" driving. I've seen both S4's and GTS's with very minimal flexplate vibration.
And when we start digging, we have always found out that these cars were driven "softly".

I've yet to have seen (or have heard of) a 25mm shaft failure.
Whatever causes the 28mm shaft to fail...whether it is a "bad" batch" or a a design issue, the result isn't worth the time to think about or worry about.
I replace the shafts, when given the choice. (I'm not sure I've ever ordered a set of 28mm Constantine bearings.)

I'm not sure how much "extra" clamping force is actually required to prevent flex plate migration.
I've never been able to make the "Loctite" only solution work.....gave up on that, pretty quickly.
I've only seen one flex plate migrate with the "Porken" (split collar) clamp (and we did not install it, so I don't know how it was installed/torqued)....and I continue to use this style clamp as a temporary/watch it closely repair....waiting for a time when the transmission/torque tube is removed, in order to fit an early shaft or one of Constantine's clamps. (I'm not sure if Porken still offers this product or not. Last time I tried to buy one, I was told that he no longer was making them, so we made up/continue to make similar split collar clamps, for our own use.)
I've never seen flexplate migration with either Constantine's clamps or with the one Ritech clamp I tested.

As I said above, I only rejected the Ritech clamp because of my concern over the possibility of a stress riser being formed on the shaft.
I did not actually have a failure, of any type.....just did not "like" what I saw.

The advantage of the Ritech clamp is the ease of installation.
The advantage of the split collar clamp style clamp is that they are also very easy to install and they are very economical.
Constantine's clamp requires significantly more effort, but would probably survive a "roadside bomb".

FredR

That you have never seen a 25mm shaft snap is very interesting. It tends to confirm my long held suspicion that there is more to the problem with the 28mm shaft than is currently understood however it does seem that stopping the migration saves the 28mm shaft from itself. I also suspect driving style may play a part and maybe a hot climate plays a part as well. I suspect we will never really know the full story but as long as I can keep the motor in one piece that is the main thing. Tomorrow I intend to do a crank end float check all being well.

The main "tricks" to the Loctite approach are cleanliness and letting the Loctite joint cure for 24 hours in the bolted condition. It has served me well in two iterations, one for 5 years and the other for the last 17 years or so but my mileage is minimalist especialy so since I retired and then covid hit. The first time we did the procedure I made the mechanic spray the splines with carb cleaner and then blow it out with air - rinse and repeat quite a number of times. The second time was from an engine out rebuild so less of a problem getting it clean. For some reason I could not get hold of one of Constantine's clamps at the time of the second iteration- when my drive shaft snapped there were no alternatives and Porsche could not fix the problem. When I refused to take the car back until the local agents could fix the problem, they contacted Germany about "the problem that did not exist" and within 10 minutes were told to install a new pinch bolt and over torque it by 10%. The "fix" lasted about 2 weeks and then the tell tale vibration re-emerged.

At least I know that if it does let go I should be able to feel the ominous tell tale vibration that happened at 3050 rpms as soon as the clamp slipped. Whether or not they all do this or my motor is exceptional in that regard I have no idea but I do tend to be very sensitive when it comes to feeling "vibrations". I have heard other owners talk of such a vibration.

If and when the drive line has to come out for maintenance first on the agenda will be a Constantine clamp- it really is a no brainer.

Mark R.

Same here, Fred. I totally agree.
So far, I've never had the torque tube out on my Auto.
The only time I had to break the Loctite bond loose was to resolve this situation:
https://rennlist.com/forums/928-foru...y-looking.html

FredR

Mark,

Interesting how just about everyone i have spoken to who has used this approach struggled to get the joint freed up.

In my case I had to break the joint after wrecking my late 90S4. We pulled the motor first and then had the transaxle with torque tube to work on. I undid the pinch bolt and then used a wood chisel as a wedge- gave it a tap into the open section of the clamp- job done. The joint had seemingly withstood the crash impact even though the drive shaft was slighly bent. I think the Loctite bond is a bit like glass- very weak in tension and it took very little force to get it apart. Then again maybe the crash impact did for it. Dumbest 928 thing I ever did was chuck the torque tube- I should have kept the carcass to fit a new [25mm?] shaft and Constantine Super Duper bearings for future use- durrgh!.

GregBBRD

If the shaft was bent, seems like pretty good odds the tube was bent, right?

FredR

No, not at all- the shaft had a slight deflection at the base of the front taper- the 28mm shaft was running true- it was the splined end section that was out of kilter- we clocked it.

Difficult to visualise how it did what it did but it surely did it. Even more amazing was the fact that the loctite was still holding the clamp in the same index marked position.

It had to happen in the 928 - the crazy thing is that my wife is a bit psychic- as I was about to leave the drive way she ran out of the house and asked me to take my daily driver Subaru- she had a "bad feeling". My response was that if I was going to have an accident I would sooner it be in the 928 because of its strength. 30 minutes later I was in hospital with a fracured L1 vertebra, whiplash neck injury and concussion- and my immaculate 90 S4 was totalled. Some tw*t on a mobile phone clipped me as I went by heading into a tight off camber left hand bend- I thought it was the car stepping out under load and instinctively put some counter lock on- the rear end went ballistic- i counter steered that but could not catch it and ploughed into the inner safety barriers [I was on top of a bridge]. Next thing I know I am in a dead car, the windscreen had gone, the engine was dead and my back was hurting something awful.

On the postiive side I have not needed much in the way of spare parts since and had to sling a lot of real nice trim that I could not even give away.

ROG 100

Over 2000 Ritech clamps have been sold to date - manufacturers numbers - with zero issues.
I fitted one to my GTS over 6 years ago. Over 60k miles in those 6 years and not a smidgen of movement - period.
I drive my GTS very very hard.
Constantine's clamp is also an awesome piece of engineering.