I have an USA 16V 84 automatic, manufactured in August 84.

It absolutely does not have the circlip set-up.

Its apart now and its most likely getting reassembled with the Constantine clamp. Preventative.


Here's a picture of this particular 84 set-up:

 

There should be no forward thrust on the front flepxlates at all, ever. If there is, the thrust bearing and other bearings are at risk.

Why people want to play around with this is beyond me.

Constantine

 

How did you know it was dead Ben?

I see you have an S2, marked as 85, is that '85 model year car?

 

I thought the circlip set-up was present for all '84 or older cars, meaning you can't have TB failure?

 

I read here somewhere that the change was made mid year. Consistent with what I've got.
I prefitted the Constantine clamp last saturday, perfect replacement for the current clamp. (I have 3 autos and originally had bought the clamp for the 86, which is next in line for the garage bay).

 

anyone have a full "Dwayne" or Sharkskin style pictorial write-up on this process? Thought I saw something a couple of years back, but can't find it on search.

 

I guess you class it as a '85 MY, because it was delivered to the first owner in early Jan '85. Over here in the UK, we take the year of the car from the date the first owner had it registered.

All of the date stamps in the various components show '84 though.

I split the engine out of interest to see how badly damaged the thrust bearing is, and there is still some meat left, although this isn't white metal, its down to the copper backing. There is a groove worn into the crank where the thrust bearing had been riding.

I had 1.4mm of crank end play.

Cheers,
Ben

 

Bill, you know I respect you knowledge and opinion on these cars, but to me it is a known problem with a known solution.

I have to go with Constantine on this one, any forward pressure on the crank is going to push the crank forward into the thrust bearing.

If you release the tension and after a few short hard drives it comes back, to me, this does not mean to me that any kind of equilibrium has been meet, it just means you have a recurring problem due to a design flaw.

I think the reason it goes to 2-3 MM so easy is that there is less rearward force holding it back.

That being said, you can get by with doing just what you said until the wear limit on the thrust bearing is reached, if you catch it in time.

I think it is a lot easier to put a clamp that works in the car before you have a problem than it is to put crank bearings in after you have one.

BTW, Thrust bearing failure on automatics is not just limited to the 928's, I have seen it a bunch of times in American cars, but that is pretty much always traceable to the torque converter.

Just my opinion.

 

FYI -- on MT cars, disengaging the clutch pulls the crank against the forward thrust bearing surface -- so any wear caused by excessive use of the clutch will be on the opposite side of the TB.

 

Just my opinion too. I certainly agree Constantine's clamp is an elegant solution and don't mean to discourage its use.

I've been checking my flexplate and crank endplay since I bought the car almost 9 years and 130K miles ago. The first time I released the flexplate at 72K miles, there was 5-6mm of movement. The crank endplay was 0.008". Every time subsequent to that I've found no more than 2-3mm of preload, and most recently only .5-1.5mm for the last year or two, and the endplay has remained at 0.008". So, this works for me. As a practical matter, I have a lift and it is dirt simple for me to check this periodically. If I had any other reason to pull the TT, I'd install Constantine's clamp or an early style shaft with shims and circlip. But my TT just keeps on turning with no bearing noise or other problems. So, I'm satisfied with my approach and I'm just reporting my observation. People should know that I'm kind of a calculated minimalist. I take good care of my car, but I don't do more than I think is going to make a meaningful difference. But it is hard for me to argue against more cautious approaches. There is reason to fear TBF and do whatever you can to prevent it. For many people that would mean installing Constantine's clamp right away.

Also, note my crank endplay has not changed at all since I started checking it and at 0.008" (0.2mm) is within the range for "factory new." I would NOT ever allow it to get to the wear limit of 0.016" (0.4mm). Even a thou or at most 2 would do it for me.

And Dave, yep, I had that backwards. I've saw forward surface wear on the thrust bearing of a low mile 5 speed just last year and looked at the clutch mechanics and saw it worked the opposite of what I had thought earlier (not having dealt with a 928 clutch before then).

 

Bill, it's an easy mistake to make -- every other clutch I've worked on, the action pushes the crank forward.

 

WSM Page 39-48 states flex plate was introduced for MY 85, that means any car made after August 1984.

(Porsche MY starts in September)

 

 

So Bill, is your flex plate still straight? Reason I ask is I get appr. 2 mm movement each year, but the flex plate has a bit of a curve (it won't straighten out completely).

 

Yes, mine is flat. I'm not sure how I would react to a plate that didn't rebound to flat. You might try releasing the peripheral bolts too.