Sportomatic - cracking drive plates, now torque converter noise

[93nav]

1976, 3 Speed Sportomatic, Stock

Short story: The drive plate keeps developing cracks, now noise in torque convert area

Long story:

- engine was rebuilt about 2000 miles ago by a non-porsche, but old european car guy. Other than a few seals, no work was done on transmission
- Just prior to my purchase of car, the prior owner had the drive plate replaced because of a ticking sound determined to be caused by a rivet on the drive plate (loose, sticking up??? I am not sure). Nothing mentioned about any cracks. Place that replaced the drive plate was a modern VW shop.
- I purchased car less than 1000 miles ago
- Car developed a 'ticking' sound when in gear, car moving or stopped.
- Engine and transmission was pulled. Many cracks in drive plate, see pic, drive plate replaced. This was done at a Porsche shop.
- Less than 400 miles after drive plate replaced by my shop, another, slightly different 'ticking' sound when in gear. With car on lift, sound seemed to be coming from torque converter area. Sound was NOT present when in gear with wheels off the ground.
- Engine and tran split, and cracks were developing on drive plate again (no pics but had not developed to the point shown in 1st pics). No other obvious issues. Clutch was worn down evenly.
- One suggestion from a old Porsche mechanic was to check end play. Shop said no end play found.

Right now plan is to replace torque converter, drive plate, throwout bearing, and some seals. Clutch is being looked at to be resurfaced (down to 25%).

Anyone have any ideas, anyone have a NOS clutch? Part #925.116.254.02 according to PET.

[chrisg252]

I can't diagnose your problem but you will probably find the answer to your problem in this thread:

Ultimate ?maybe? Sportomatic Gearbox Rebuild

Check out Post 34 and on- he deals with the clutch and torque converter at that point.
The clutch is still available from Porsche and our host lists it as well.

[93nav]

Thanks for the reply chrisg252,

I was aware of the Sportomatic rebuild thread, just went thru it again and did not gain any new insight.

I have been told by someone who has been looking for a 925 transmission clutch a long time that they are not just not available/to be found, the earlier clutch for the 905 is though. If I understand correctly, the later 925 tran used a 190mm disc, the earlier 905 used a 180mm disc.

I did contact another longtime Porsche mechanic and his only thought was:

"I've never seen that happen. My first question is are the different part number flywheel bolts being used? The sporto flywheel bolts are shorter in length. Almost seems that the problem started with the rebuild."

[chrisg252]

The clutch part # is 925 116 254 02 and a search of Pelican's part inventory shows

Photo Description Price Add to Cart
Genuine Porsche Part: CLUTCH DISC
- This is a special-order, non-returnable, Porsche part
(availability and shipping charges may vary). [More Info]
Note: We can't confirm this part will fit your Porsche 911 (1974-1989).

OEM-92511625402
$279.50

Perhaps you could send a PM to the author of the "Ultimate" thread for his opinion. Your theory re the bolt lengths seems plausible, but it could also be related to incorrectly torqueing the bolts.

[rodoredas]

Hi 93Nav,
got your PM, thanks, but I'm no expert really, and yeah I agree it could any of the things you mention, sadly you won't find any tips on this issue in my other thread. But just looking at your pics and how the drive plate connects to the crank shaft and torque converter, it's obviously flexing.



Assume it's connected properly to the crank and bolts #7 are correct it's flexing around the edge. Something is not balanced or the converter is not connected properly at the 4 points bolt #8

Imagine if the converter was out of balance it would cause some wobbling/flexing of the plate. If bolt #8 are broken or the drive plate connecting bracket on the converter is faulty/craked I guess that too would cause some flexing. That in turn may break something inside the converter. You say that now you have some noise in the converter.

I guess that whole assembly is not aligned. Remember that there are two halves to the converter and they are not mechanically connected, so if the outside shell is oscillating the internals could be knocking against each other causing the tick noise you hear even when the car is stopped because the outside shell is still rotating.

I think all your points are valid and you really just need to pull that whole assembly apart and take a good look, there is not doubt something's broken or loose for the plate to flex and then crack like it has.

Reading your sequence of events again, it seems obvious that something is braking the drive plate, you had it replaced and now you have noise from converter - it's out of balance, not connected properly or faulty which will cause the plate to flex and crack again.

Interested to know what you find because it will help us all diagnose these problems with the Sporto, and the more written about them the better.

cheers
Shane

[93nav]

Shane,

Thank you for the reply. Just got back from vacation, or I would have responded sooner. The car is at the local Porsche shop and they feel confident that the converter going bad is the root cause. I am not so confident on what is the root cause and what is the effect.

The shop did not report any broken or loose bolts which considering how much I have questioned them, I am sure they would have mentioned.

So....the converter, drive plate, throwout bearing (it needed to be replaced) and I assume associated seals etc will be replaced. Once I get the final parts list, I will post here, with a further followup after driving the car for at least 1000 miles.

Yes, the more written about the Sportomatic problems (and hopefully solutions), the better.

Thanks again

[93nav]

20160515 - Porsche 1976 911s - 9116201446 - Still cracking drive plates

An update:

As described in the original post, my car was/is cracking the drive plate.

Short story:
Line-bore done by previous owners shop was bad, crank not centered in block. Ollies re-linebored, engine rebuilt. However, within very few miles, driveplate is cracking again.

Long story:
The shop doing the work figured out that the crank was not centered in the block. The previous owners shop apparently had to grind down the 'nub' on the end of the torque converter to get the transmission/torque converter/torque converter housing to mate. Determined that the line-bore done for the previous owner's shop was done incorrectly.

THe case was sent to Ollies to be checked and re-line bored. Bearings are std/Std.

Motor went back together fine after fixing other 'work' from the previous shop.
Among parts replaced with new where:
- Drive plate
- Torque converter
- turbine shaft
- Assorted seals

On assembly, the transmission/torque converter et al all went together fine. I was told 'slid right on'.

Now, with very few miles since the rebuild, the drive plate is cracking again. My shop does not know why and does not really know where to go from here except try replacing the converter housing, $$$$. One thing noted when trying to figure out the problem, there are marks on the converter housing like someone had put a prybar thru the openings on the converter housing and really put some muscle into it. Probably when the previous shop had attempted to mate up the transmission and motor and it would not go.

In pic below, the parts replaced are circled in red (#11 is a mistake). Marks on the converter housing are at the location circled in yellow.