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This is how the clamp stood before. Unfortunately, I do not have a measurement history, and I haven’t driven much on this car. Just one trip in August and after that I started going through the techniques. I am looking forward on all other benefits that the color will bring to me
At this point, it might be good to note that before I can call it a complete success, I still need to reinstall everything and make the car runable. Proper installation of the rear axle and transmission requires some action. I also disconnected the kickdown wire from the clutch housing to make sure it was moving freely. Hope this worked well. A painful job. There are also plans to renew all transmission oil cooler hoses.
Fortunately, a local expert is just a phone call away. For now, he's still answering my calls. It may be necessary to try to get him to visit the shop.
But I need a new flex plate. I have not found any of the 928 used parts dealers in Europe. Mark should open a branch here The flex plate is available from Porsche as well, but it's a pretty salty price. I wonder is it still worth investing 500€+ against a used part?
When I see a flexplate clamp fail in the manner yours has the first thing I suspect is the poor thing was operating in an unaturally stressed condition such as when the clamp slips given there is only so much misalignment it can cope with. One thus presumes that you have checked the crank end float and hopefully lies in the region of 0.2mm. Of course the end of life float is 0.4mm however that presumes even rather than one sided wear or so I would think.
As to recovery options the trouble with second hand "operationally critical parts" is that one can never be sure what state a used item is in unless of course one knows the full history- rarely the case. As I recall some earlier versions of the flex plate had issues with the rivetting - I cannot remember the specific details but presumably you would not want one of those in your 928.
As for a replacement flexplate you have limited options. Some kind soul on this list may have one and you can try the likes of Mark at 928 International or Roger at 928srus. In the UK you can also try contacting Paul at https://www.928specialists.co.uk/ given he often has spares from dismantled examples.
The crank end float measured 22.9.2021 0.24 mm, so it should be healthy. Given the wide range of replacement engines, I hope the figure is true.
In all procurements, European and Finnish practices favor European suppliers. Purchases from outside are subject to 24%VAT plus customs duty. That is why the EU location would be great. Since these cars have been purchased in EU countries in quantities (?), It is a bit of a mystery that there are so few sellers of used parts here. Boris made sure there is no need to look at UK sellers either. But since the flex plate is pretty critical, I might choose Porsche Original here. I hope I manage to install the whole package correctly to avoid too short a lifecycle
The crank end float measured 22.9.2021 0.24 mm, so it should be healthy. Given the wide range of replacement engines, I hope the figure is true.
In all procurements, European and Finnish practices favor European suppliers. Purchases from outside are subject to 24%VAT plus customs duty. That is why the EU location would be great. Since these cars have been purchased in EU countries in quantities (?), It is a bit of a mystery that there are so few sellers of used parts here. Boris made sure there is no need to look at UK sellers either. But since the flex plate is pretty critical, I might choose Porsche Original here. I hope I manage to install the whole package correctly to avoid too short a lifecycle
Juha,
0.24mm end float should be fine- it may possibily indicate that at some stage there was some clamp slippage- 2mm or 3mm displacement is very common to see and I consider that a pre-cursor to future problems. 21 years ago it was enough to cuase my drive shaft to snap or so I believe. Constantine's clamp is the ultimate solution and it is pretty hard to screw up installation of this unit. Back in 1999 I was extremely critical of the stock clamp design and commented how if I were to design such it would have a taper clamping arrangement. At that point constnatine contacted me, advised me of his plans that were still on the dwg board and we shared some thoughts on the subject- his work is perfection.
Another thought ofr consideration- given where you are at this moment in time remember the stock torque tube bearing depend on the rubber insert in order to function correctly. Hopefully you have checked the location of the two bearings your torque tube has - even so you might want to consider changing out the bearings for the super bearing alternative given the age and what is typically seen. It would also be prudent to carefully inspect the base of the shaft taper [both ends] for any signs of cracking .These shafts were falsely maligned as quite a number of them snapped- however my analysis of the failure told me that they fail due to the streses imposed on them when the OEM clamp slips [as so many of them do] with the resultant catastrophic consequences.
Whatever you do, replace the bolt on the rear clamp with a new one while you are in there.
Fred,
The torque tube was replaced in 2003 and since then 90 tkm have been driven. I need to take measurements and replace the mentioned bolt for sure. Maybe I can convince Erkka to visit the shop for evaluations. There is also a list of other renovation items. Such as replacing/protecting power steering hoses, starter maintenance, replace rdk sensors with dummies, etc. Perhaps these should be documented in other threads. Based on my experience with the rear axle, I might do a complete removal of the body to continue with several expected engine issues, etc., but that will be winter 2023. I do need some driving experience before.
Fred,
The torque tube was replaced in 2003 and since then 90 tkm have been driven. I need to take measurements and replace the mentioned bolt for sure. Maybe I can convince Erkka to visit the shop for evaluations. There is also a list of other renovation items. Such as replacing/protecting power steering hoses, starter maintenance, replace rdk sensors with dummies, etc. Perhaps these should be documented in other threads. Based on my experience with the rear axle, I might do a complete removal of the body to continue with several expected engine issues, etc., but that will be winter 2023. I do need some driving experience before.
Juha,
Interesting that the torque tube was replaced in 2003- one wonders why?- my guess would be a snapped tube due to flexplate clamp migration and that may well explain the fractured leaf in the flexplate. At 90k km I would not touch the torque tube unless of course you are extremely motivated to go the super bearing route. If there is a need you could change out the ATF and filter in the auto box and the diff oil. Another little pre-emptive mod would be to replace the hose and tubing that goes from the vacuum spider [at the rear of the inlet manifold] to the shift modulator on the tranny. These things have a habit of letting go and when they do part load shifts go with one hell of a thump- not good.
At this age power steering hoses and all fuel system hoses are a no brainer if they have not been changed out alredy. I also did the hoses on the ATF cooling circuit last year - good time to do this- I used 3/16th hydraulic hose as I recall. You should also change out the PSD fluid- this often gets over looked but it really needs changing every couple of years or so just as you would the brake fluid- it is not too difficult and there is an easy to follow procedure for doing it.
If you look closely at the flexplate, you can see where it was hitting the "step" on the flywheel (shiney notch/notches on the flexplate about 30mm from the bolt holes. Certainly, this caused the flexplate to break.
This requires a severe amount of preload to achieve...over 3mm!
Very few engines survive this amount of preload!
To be safe, I would suggest remeasuring the endplay and confirm that the crankshaft moves back and forth very freely. (Should be able to move with your fingers or with very gentle prying.)
I've seen several engines where the crankshaft has welded itself to the thrust bearing and the measured endplay is actually the bearing moving in the bore of the crankcase.
This can be detected, because it takes an abnormal amount of effort to move the crankshaft fore and aft.
Also check for metal particles suspended in the oil. Additionally, cut open the oil filter and inspect the paper for metal particles.
I hope everything is normal, but I'd certainly check.
Since right now, you only need the flat plates of a flexplate, have 928 International remove the hub from a used flexplate.
The plates should fit into a Fed X envelope and be relatively cheap to ship!
I don't want to go too much off topic, since it's not really germane to the OP but @GregBBRD , can you please clarify something to straighten up my understanding of options? For your 300M, 25mm shaft, do you put in a provision for a circlip? If so, for my '90, would that be something to help make sure I don't get bit by TBF? ETA: I installed a Ritech clamp, which I believe would not work with the 25mm shaft, so I'm feeling OK about the current risk level of TBF, I'd just like to understand the landscape better, as it were.
I'll have to put in new bearings at some point and my inclination is always to try to upgrade when possible. If I can build in some peace of mind via what you offer I'll start to plan for that route.
Thanks for any clarification
Last edited by Zirconocene; 02-15-2022 at 02:03 PM.
I don't want to go too much off topic, since it's not really germane to the OP but @GregBBRD , can you please clarify something to straighten up my understanding of options? For your 300M, 25mm shaft, do you put in a provision for a circlip? If so, for my '90, would that be something to help make sure I don't get bit by TBF? ETA: I installed a Ritech clamp, which I believe would not work with the 25mm shaft, so I'm feeling OK about the current risk level of TBF, I'd just like to understand the landscape better, as it were.
I'll have to put in new bearings at some point and my inclination is always to try to upgrade when possible. If I can build in some peace of mind via what you offer I'll start to plan for that route.
Thanks for any clarification
Yes, we do.
The factory circlip, special washer, and shims is the one of the most secure methods possible (although Constantine's clamp is certainly another very secure method), and the cheapest option, by far.
Since right now, you only need the flat plates of a flexplate, have 928 International remove the hub from a used flexplate.
The plates should fit into a Fed X envelope and be relatively cheap to ship!
Greg,
I'm sorry I haven't answered before. Something else has caught our attention recently . (The neighbor's idiot is about to start WW3.)
So I have to re-measure the endplay and see how the crankshaft moves. I'll do it soon. I found an unused flex disk locally, so I'm fine with it.
While waiting for the new flex plate, I studied more. I wonder if the plate cracked before that mark on the plate, or whether the mark was created after the crack when the plate was allowed to warp under pressure. The flex plate will hit the flywheel after a 1,5 mm of offset if the plate is broken as it is. Goes by guess and needs more research. I'm looking for an opener for the oil filter to check it out, and if it looks bad I guess it's best to take the oil sump off. The engine will only be fully opened after the next driving season.
I just found a small piece of interesting information about the history of this car. The previous owner had checked the position of the transaxle clamp and flex plate in 2006 (about 49 tkm ago) and the position of the clamp shifted 3.1 mm backwards. The car had been driven 170 tkm at that time. So the tension had been pretty tough. The distance is the same as GB's estimate for the cause of the plate failure as well. So it's likely that the flex plate has been broken from then on! The "good news" here is that there has been extra flexibility on the plate. When I checked this first time the plate was bend some 0.2 mm. But how much damage there is inside....?
As I suggested in an earlier post it was pretty evident to me there would be some "hidden" history here so it is no surprise to read your latest post- quite the opposite in fact.
When my 90S4 drive shaft snapped around March 1999 with about 80k km on the clock it was obvious to me that something was horribly wrong. If the design was inherently flawed then every example would have the same problem but that was just not the case. We have seen examples that have covered 300k miles with no issue and that with the 28mm tapered shaft that has been constantly blamed since I first found Rennlist around the same time. Since then common sense has prevailed for the most part and this shaft does not get blamed the way it did 23 years ago but it is still viewed with suspicion that as I am concerned is based on a false but understandable premise. The difficult bit to comprehend is why Porsche migrated to a 28mm two bearing shaft design when seemingly there was nothing inadequate with the original 25mm shaft design that can and does handle 600 bhp monster motors. Even more puzzling was the migration circa 1984 from the shim locking method to the primitive "bicycle" clamp to hold the shaft in place- mind blowingly stoopid!
Back in 1999 when I had to replace my "snapped" 28mm drive shaft I would not accept a simple "like for like" repair given my professional background but the fact was I had no alternative. The main dealers even advised me to replace the torque converter bearings as they would likely be "toast". We did replace them and one of them was "rough"- how could this possibly be at 80k km? They also advised me to replace the flex plate "just in case" but after careful visual examination I refused to do so unless Porsche coughed up the cost. Since then we read about how torque tube bearings "fail", how rear flex plate bolt fail, how dampers can fail and end up flying backwards and forwards knocking torque tube bearings out of position and all that before we even begin to absorb the thrust bearing failure syndrome. Fact- TBF does not happen to manual transmission cars [some even question that!}. Porsche fitted a damper on the torque tube not because of mechanical issues but because of prototype discovered NVH [noise, vibration, harshness- i.e. creature comfort noise measurements]. However I have often wondered if this NVH concern might be more significant than it is understood to be and possibly the "root cause" of all these issues. We know the flexplate clamp slips and if we stop this from happening the problems "disappear" but just maybe there is a "connection"? Why do some hold and some do not?
The bottom line is that when everything is working as it should there are no issues but as I concluded 23 years ago, when the flexplate clamp let's go all kinds of issues are induced. My driveline was rebuilt by the local agents and hey presto no issues- for two weeks that was- then suddenly a distinct vibration appeared at precisely 3050 rpms- WTF? Back to the workshop, car on the ramp, we undid the front flexplate clamp bolt and boing- the damned thing jumped about 3mm. We reset it and problem gone- for two weeks and then back again- straight back to the workshop. Up on the hoist, pinch bolt undone- boing another jump of 2mm to 3mm! At that point I refused to take the car back unless and until they could fix the problem. The local agents did not know what to do so they contacted Kaiser Wilhelm in Stuttgart and within 10 minutes received an instruction to replace the pinch bolt and overtorque by 10%- yet they denied there was any "problem". I fell about laughing my nuts off! Took the car away and no issue- for two weeks and then guess what?- "boing" another 3mm jump. I literally walked away from the car and left it in the workshop "disgusted".
I then setup a problem solving workshop with two top notch mechanical engineering colleagues and came up with two recommendations- one to search for a solution using some kind of locking chemical [glue] and the other to get the recently introduced "internet" into my home. Two days later i had the internet and immediately found Rennlist. All of a sudden a problem that "did not exist" became a profound problem in the Stateside 928 online community- no such thing as conspiracy theories huh? At that point one of our brothers [Earl Gilstrom] had come to the same conclusion we had over here and he was one step ahead of me having devised a procedure using Loctite 290 and he was about to do the first example. He kindly advised his procedure and I immediately found a bottle of Loctite 270 on the local market that was more or less identical and the following day I implemented that solution. 23 years on and my flexplate is still being held by the stuff and yet some folks still advise that Loctite "does not work"- well it did and still does for me. Since then no TBF issues, no torque tube bearing issues, no torque converter bearing issues- nothing - no known issue whatsoever in the drive line. Is this chance or good luck? - I doubt it is luck! Would the Loctite hold up if exposed to cold ambients like yours?- i have no idea whatsoever. All i can say is I have lost count of the number of owners who have asked guidance in this regard and no reports of failure- zero!
So back to your case- you exhibit crank end float that is a bit higher than "normal" [but no issue]. This will invariably have happened because of the time spent under false compressive stress loads. The flex plate cracking will have been caused by this as well. Is your drive shaft secure at the base of the taper- who knows? I suspect if it was going to fail it would have done so already but...? If you seek reassurance maybe you can carry out a magnaflux test or a dye pen test at the base of the splines if you seek some reassurance. Remember when there is an out of balance force in the system it has to manifest itself somewhere and if the flexplate was the victim then hopefully nothing else will have suffered consequences that might lead to failure.
All things considered and depending on your circumstances/motivation I would consider installing three of Constantine's "Super Bearings" and "dump the damper" [apologies to GB- nothing personal]. Note that the mass of three super bearings is the same as two stock bearings plus the weight of the damper kit- this is no coincidence! Completely different support arrangement that works- no recorded problems on a single example Constantine has rebuilt.
If you are flush you might consider the extra $$$'s and go for a new shaft then you can go for a 25mm design - Constantine does them and so does GB with his upgraded "custom" material spec. Personally I would stick with the 28mm shaft you have but that is me [tight as a duck's *** and that is water tight!]. New TT bearings/supports is good insurance whilst in there.
Bottom line: You are spoilt for choices! 23 years ago not even Porsche could solve my problem and yet I am still a "happy teddy" today! Folks still do not believe me when I tell them what is causing the cylinder head corrosion problem- sooner or later they will!
Get rid of the snow and Pooters and then you will have cracked it for the summer season.
02-13-2022, 04:00 PM
