Charley B

I think everything after '86.

the flyin' scotsman

Dave ..........good write up as usual; great use of KY, condoms and shafts...........should make a movie.

Which MY's used the 28mm shaft?

Edit: Ryan beat me to it.

RyanPerrella

if this is true then i am sorry but i have to question the idea that these shafts are BAD

I heard of a shaft breaking before, but its not anywhere near the issue that say TBF is or anything like that. I think i honestly heard of 1 shaft shearing. I cant say that those numbers would lead me to believe that they MUST be upgraded.

Or maybe the shaft shearing is under reported? But if all 86 and later cars manual and auto have this driveshaft then i think the problem is being over stated.

SharkSkin

I've said all I can say about price. You'll have to take this up with Constantine.

I imagine the order would be filled, but you'll still need a 25mm shaft...

If so that's really unfortunate. Maybe Constantine's stronger 25mm shaft will take the sting out of that?

I'm not sure that movie would be "G" rated, Malcom.

I have seen the one below with my own eyes, and have heard of others. One theory is that when half the injectors shut down as a result of uneven EGT readings it can stress the shaft and cause this. IMHO it would suck to have this happen right after putting in upgraded bearings. Not everyone, facing that situation, would assign blame appropriately. You'll have to wait for Constantine to weigh in if you want to know what his full line of reasoning is --I am only speculating.

Black Sea RD

Back on again, having a day job does have it's limitations for being on Rennlist.

David, thank you for answering most of the questions on these!

Ryan, we are very aware that the price point needs to be at or below the rebuilt TTs currently available at $500.00 plus shipping. Hate to really corner ourselves yet since we are waiting for a few more details before finalizing the kit price. Think around $500.00 for a two steel bearing unit, which most 928s will work fine with to include the 5 speeds versions due to the new version's robustness, and about the same price of a rebuilt TT including shipping both ways for a three bearing unit, meaning a bit less than $700.00. Once you understand what you are getting for these prices they will seem like a bargain. These pricing schedules should be viewed as introductory pricing and will probably climb up as all things do. Although pricing will always be a concern of ours, we are not positioning ourselves as the low price leader but as a vendor of quality upgrade parts that, for the price, can't be beat.

As far as the 28mm drive shafts, they came in sometime after 1987. From the research we've done they are problematic enough to not offer rebuild kits for them and then be liable for problems. Due to age even the 25mm drive shafts are starting to show some shear problems. That's why we're investing in developing brand new 25mm drive shafts of stronger material.

Thanks for the interest,
Constantine

RyanPerrella

Ok so now you still have my attention

Does this price include the driveshaft, or that is something that would be extra? In which case rebuilding a GT or GTS 5 speed torque tube required the 3 bearings ($700 +/-) and a driveshaft? ($ unknown)

i guess i just need to wait as everything is very vague. Its very hard for me to get excited about it with so many unknowns.

Then again i dont need a rebuilt torque tube and it seems they are much less problematic on 5 speed cars (which is really all i would have anyway)

I look forward to more firm answers when you get them

Till then, im out.

Black Sea RD

Hi Ryan,

From the research we've done and email discussions with the Porsche engineer responsible for the 928 driveline during the change of the 25mm to 28mm, we obtained some facts which I think will be help answer your questions.

The automatic 25mm drive shafts were changed to 28mm sometime after 1987 to control the S4 model's increased torque. What Porsche did not change was the front coupler which needed the 28mm drive shaft to be necked down to 25mm. This neck down, found only in the automatic 28mm drive shafts, is the shear point problem.

HTH,
Constantine

RyanPerrella

So then a 5 speed GT or GTS would have a 25mm shaft in which case i would replace only these bearings and reuse the shaft?

Black Sea RD

Yes, sorry. All 5 speeds have the same 25mm diameter drive shafts, no need to change them unless there are problems with them, such as stripped splines.

Constantine

RyanPerrella

now im interested again........

Black Sea RD

Hi Tony,

To expand a bit more on what David said:

The inner bearing bushing was designed to have a bit more rubber and with a different profile than the original design for a few reasons.

One was to make it easier to push the drive shaft through the bearings without having to use a hammer, which could damage the bearings, or having to use a fancy contraption which is a pain to make.

Another was to have the new rubber bushing grip onto the drive shaft better. This better grip will not allow the drive shaft to merely spin inside of it as the older versions do. This spinning in the old bearing inserts is evidenced by the ghost rings being left on the drive shafts.

Another reason was to allow a bit of mis-alignment of the drive shaft to be taken up by the increased rubber between the drive shaft and bearing. This relieves a bit of the pressure from the internal bearing surfaces making it last longer.

Sorry to hear about that pesky leak! I had the same thing happen to me after my first TT R&R, aargh!

Kind regards,
Constantine

JHowell37

So does the price guesstimate include a new drive shaft or not?

Black Sea RD

No. Use your own 25mm drive shaft or one of our new ones which needs to be purchased seperately. Or get a used one from a used 928 parts supplier.

Cheers,
Constantine

JHowell37

Is there any way to determine if you have a 2 or 3 bearing tube without disassembling it?

RyanPerrella

autos have 2 bearing tube, manuals 3 bearing tube. The manual tube is longer, the automatic trans and torque converter are longer so require a shorter tube, and one fewer bearing.

This pic shows the difference in tube length