camboinc

87 auto supercharged. No real symptoms other than a thunking 2-3 or 3-2 shift, and have to mash the gas from a standstill in 2 in order to engage first gear.

So the shark was driving along fine, in D, I hear a couple of clunks, some rattling, and the car starts to coast. No engine power to the rear end. Just coasting as if in neutral. I'm hoping it is a failed torque tube but there is no metallic, rattling sound when I engage any of the gears.

From park, if I put the car in a forward gear for several seconds, then move shifter quickly back to park, there is a ratcheting sound before it appears to be in park.

Car will roll as if in neutral when in any gear but park.

I left the car a few miles from home. Going back for it now with a flatbed and AAA.

Any ideas? I lost engine power to trans the several years ago during the group drive at SITM. Put a known working trans back in but it was obviously not up to the task (supercharged and all). Obviously, if I choose to repair the car, an NOS trans or fully rebuilt one will go back in.

Thanks for the help,

Brian

928 at last

Rhudy,
Good to see you're still with us....missed you at SITM this year......
My Bet, or the first place I'd look would be the driveshaft (sounds like what happened to me a couple years back....).
I don't recall off hand if the '87 had the tapered shaft which seems prone to this...
Particularly if you had just "mashed the gas" before it happened. (I remember what your car has for power....).
You may want to consider the other goodies while you're in there.....
i.e. Constantine's complete package.....

GregBBRD

The fact that "park" still works and holds the car (from rolling) means quite a bit. It means the axles are still hooked up and the ring and pinion are still doing their job. You could have broken a torque tube shaft....these shafts are doing things way, way beyond their design limits, when hooked up to high output engines.

Long story to tell....and I'm not really ready to tell the story....but I have new shafts made from 300M in the final phases of production....anyone with a high output engine needs one of these!

I've still got a couple '87/'88 NOS complete transmissions, with limited slips....still in the factory Porsche boxes.

And I've got rebuilt exchanges of the highest available quality.....

Or I can rebuild yours.

I do not have any "flat rate/flat price" rebuilds with the "least parts replaced to make the profit as high as possible" transmissions.....but if you want one of these "low end" rebuilds, I can guide you to one.

camboinc

Correction. Car rolls in park... I'm getting er towed now.

GregBBRD

Ahhhh.....that's different.

Axle (C/V joint) broken or bolts came loose at transmission, most likely.

Less common would be a failure in the final drive (ring and pinion).

camboinc

And yes Greg, I'll be wanting one of those tasty transmissions you have

928 at last

Hope you had the wheels turned into the curb before you discovered that.....

Black Sea RD

The symptoms still could be that of a broken drive shaft.

Below is a picture of a broken drive shaft at the rear of the torque tube, where they usually fail, one picture when you look through the rear torque tube hole and one as it looks when you remove the torque tube from the car.

In your inspection of your 928 we would check both ends of the drive shaft for this shearing.

We have R&D'd and currently stock stronger than stock 928 automatic drive shafts (not 300M but can be special ordered) since we have seen many 928 drive shafts coming in with problems which make them unusable for rebuilds, to include this type of shearing.

Good luck with your diagnosis!

MjRocket

Hey Greg may I as what one of your new 87AT go for?

Also where are you located?

Thanks

MainePorsche

https://rennlist.com/forums/9792447-post1.html

MJ,
Greg published the above re the transmissions.
I installed one of these 0.4 LSD units. These units are 'brand new'. It gets a significant Greg Brown prep as well. I even cut the original descriptive labels off the box it came in. Truly unbelievable find and enhancement to the car. I have the old one on a pallet to ready return to Greg. I am very glad I made the investment. I also posted a thread with pics of the unit.

the flyin' scotsman

^^^ Gregs contact info and location are in his posts above

GregBBRD

Guessing that this is one of the infamous 28mm shafts? Concentrating all that "torque twist" into the "neckdowned" area doomed those shafts, from the very beginning.

If the torque tube shaft had broken.....he'd still have the "park" function. Problem has to be "aft" of the "park" mechanism, if it rolls when put into park. (The "park pawl" is just forward of the differential.)

BTW....you ever wonder why the "problem" with the torque tube shaft twisting and pulling out of the front flex plate never happened at low mileage? You will never see this on a vehicle with less than 30,000 miles, regardless of how hard the vehicle was driven.

jorj7

Dang it Greg, you keep coming up with ways to spend money. My wife doesn't like it when I read these posts...

George
90 S4 Grand Prix White (Murf #5)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

GregBBRD

Step 1. Drive down to Harbor Freight
Step 2. Locate their set of "wheel tightening" extensions that only allow a certain amount of torque to be transfered to a lug nut. Note that different diameters allow different torques, virtually irregardless of how much torque you "put into" that extention.
Step 3. Ponder the difference between those extentions and your torque tube shaft.
Step 4. Realize that Porsche built a "larger diameter extention" for the increased torque of the GTS vehicles. Yes, the "neck downed" part of the design did not work, but the increased diameter did transmit more torque, until it failed.
Step 5. Once you figure out that there is very little difference (there is some) and what is happening to those extensions is very close to what is happening to your torque tube shaft....a "light" will go off in your brain and you will understand.
Step 6. Get your wife to understand all of this.

jorj7

Now your assuming my wife what's to understand this, especially when she doesn't want me to go any faster. She has different motivations then I do. Of course that make life more interesting....

George
90 S4 Grand Prix White (Murf #5)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com