JET951

It did more than helped , it shows you the issue lay in the first place , once you replace the bolts with new ones NOW , this is very very important because the old bolts ( rear one mainly ) is actually stretched & should not be re-used at all

Depending on the 928S4 / GT / GTS ( yes the manual trans has the same issue with the rear coupling clamping force reducing because of the index bolt stretched )
, we will reset the T Tube shaft , install 2 X NEW Porsche bolts with light lubrication on the threads & then say ( example only ) 10,000kms or 15,000Kms or 20,000kms later ( its up to you ) , I would recheck the torque value of the rear coupling index bolt , we will "generally speaking " ,re-torque the rear coupling index bolt ( that was replaced new say 15,000Kms before ) once or twice , all depends on what we see & the individual car in question , the ones that get flogged hard get new bolts every "check time "

Regards
Bruce Buchanan

touay001

Thanks again Bruce. I'm compiling a list of parts ATM that I need and it will include a couple of sets of bolts. After setting down for 5 years you will need to replace lots of parts

Constantine

Touay001,

Can you replace the rear bolt back into the rear coupler?

If the drive shaft moved back 2mm, the bolt cutout in the drive shaft will no longer line up allowing the bolt to be placed through the rear coupler and drive shaft cutout without forcing it through due to the misalignment.

touay001

Hi Constantine,

Good point. I have not tried to put back the old bolt since I'm getting new ones. I'l try to do that today. If I can't do it, what shall I do? I can't move the front coupler. I might need to get a stronger torch!

JET951

Think about it logically

If you have previously Loctite-ed the front coupling bolt & shaft splines ( I take it ) , then using simple logic & the basic fact that the front coupling most certainly has NOT moved at all since( because its seized solid ) , then ALL the movement of the T Tube shaft has originated from the rear coupling ( as it always does )

So by removing the stretched "old' rear coupling index bolt( I bet it was the original one with a red painted mark ) & you have mentioned the T Tube shaft then moved back OK , then you have only put the shaft back to the same position you had it when you attended to the front T T coupling a year or two ago ( or when ever that was ), so that means the rear half moon cutout in the rear of the slipped T T shaft will be or should be OK , going by the info you have given

If you want to un-seize the front coupling I would ( with the bolt out ) }

A ) spray lots of Wurth Rostoff or similar high quality rust / anti seizing liquid& let soak for at least 4 hours
and if still no joy then onto B )

B ) with the bolt still removed , heat with a oxy set , but this is the last resort

Never ever use Loctite in these areas at all

The male & female shafts splines to be lubricated with a light oil , same goes for the index coupling bolts

Live & learn

PS } we sometimes see an old rear T Tube coupling in-hex bolt with teeth marks on their flank , where the non threaded side of the bolt has been riding up and into/onto the male splines of the T tube shaft( wears the spline away in that area a bit ) & its always in the same direction ( Forward ) , I have posted pictures of some last year & the year before & the year before that

PS 2 } sometimes when one looks up into the inspection hole at the rear of the 928S / S4 /GT/GTS T Tube , be it the Auto trans version 1984 onwards ( 4 speed )or the manual trans version ( ALL ) & you see what we call the "Red Talcum Powder Look ", meaning oxidised fine metal particles , then be afraid , because that means the rear coupling has been loose enough for so long the male & female splines are rubbing / chattering against each other & wearing away the steel metal particles ( metal filings) on the male & female teeth contact areas( hence the red coloured rust particles) , when this happens two things become clear

1 ) There is now less metal between the male & female teeth contact areas= much harder to clamp tight & this rear coupling has to be looked after a lot more frequently

2 ) In this state we have seen quite a few ( 1984 - 1995 Auto trans and particularly the 5 speed manual ) were the rear coupling has been not tight enough( index bolt stretched) & there is not just the Red , but its gone the next step , it has broken one third of the circumference of the stupid HOLLOW shaft ( split in three places )
Hence why for the last ten years or so we have to keep in stock new Auto Trans "rear flex plate/hollow shaft assembly ( 1984 - 1986 & the same for the 1987 - 1995 ), because we get so many ( New to us ) 928S / S4 / GT/ GTS that we have never seen before and because the rear coupling has been neglected for so long the hollow shaft is actually cracked ( like I keep saying , this was a bad design ), but it can be looked after , but that means just that, the rear coupling must be maintained REGULARLY
Its funny because the original 3 speed auto trans 928& S ( 1978 - 1983 ) had two solid splined shafts coming together & there is a female splined sliding sleeve over the top with two bolts , this never ever gives any issue at all , in fact its the same sliding sleeve used by Porsche on the 944 , 944S,944S2 & 951 ( all ) works fantastic

But the best they ( Porsche ) ever used was on the 968 , female splined sliding sleeve on two solid shafts with 4 index bolts , this is evolution in design that there 928 completely missed out on , like they say = **** happens

Regards
Bruce Buchanan
Buchanan Automotive

Constantine

Well let's see what you find when you try to re-install the bolt.

Mr. Buchanan has given you a good tutorial on how to proceed if you have to take it apart.

This is why we never liked the Loctite method of arresting the drive shaft pullout at the front coupler.


Best regards,
Constantine

touay001

Thank you Bruce for your valuable advice. It does make sense. Please see below.

touay001

Constantine, Bruce
I was able to insert the bolt into the coupler. The interesting thing is that I can move the collar over the rear hub longitude quite easily. The collar on front hub is welded to the hub. Is that how they are? I had to realign the hole (rear collar) after I rotated the shaft to insert the bolt. The bolt looked in very good shap and the unthreaded section was intact. There's was no red dust that I could see or any other damage.

JET951

Yes thats is correct , the front of Torque Tube coupling "square shaped" clamp is spot welded to the outside of the female splined shaft ( some times you see them broken free , makes no difference )

The rear of T Tube coupling "square shaped " clamp is not

Regards
Bruce Buchanan
Buchanan Automotive

touay001

Thank you everyone. It was very informative to me. So we can't totally prevent preloading the flexplate? The rear coupler can still get loose and allows the shaft to put a forward pressure on the flexplate.

Adk46

The nervous metallurgist speaks: All those who use a torch need to have a sense of tempering temperatures. Below is a curve for hardness, but other properties are affected roughly in parallel. Tempering time for this graph is two hours, so perhaps a brief exposure above 600F is OK. The shaft et al would already be tempered to some degree. Still, Stan's advice of 250F is wise, meaning measured.

Who knows, the splines might have received special treatment (induction hardening, peening) that a torch might disrupt. Careful with that torch, Eugene!

NoVector

Just curious, is your flexplate now flat?

touay001

Almost flat. It still has slight deformation due to being under Load. Definitely is not bowed anymore.

Mrmerlin

does the flywheel stay where you pry it?

Try cranking the engine over and see if its moving to a forward position

touay001

Hi Stan,
Yes, now the flywheel stays in the forward and back positions. I was not able to do that before removing the rear bolt.