How common is this failure?

[Missed Approach]

Hi All- Background as always: 1986 911 3.2 Coupe (915 transmission) now 146K, new clutch in 2014 (36K miles ago) with a new clutch cable installed at that time.

The situation: Driving at low speed in a picturesque area (Excelsior, MN) on a slight downhill slope, perfect 72F weather, with a wide area to park on the street. Pressing in the clutch to shift from 1st to 2nd, I hear a bang, and the pedal goes to the floor. Shift into neutral, hazards on, glide onto the side of the street. A nice gentleman eating with his wife in outdoor seating runs into the street, picks up, and then hands me the lower half of Throw Out Lever #915-116-713-08 (with the spring attached)

Essentially, I got really, really lucky on the location and circumstances of the failure!

Quick flatbed to my local shop via AAA. Due to the non-internal location of the part, it was simply a matter of sourcing a used piece (didn’t want to wait for it to ship new from Germany) and installing (no internal damage of the transmission was sustained).

My question- has anyone ever seen this type of failure before? This is clearly a cast ferrous part (it is magnetic) and it sustained a crack quite some time ago that eventually caused it to bend, and then completely fail. If you note in the images, the crack was wide enough to rust on the inner surface as it slowly expanded.

This must be a very rare occurrence, but just wanted to check!








Cooking on a Porsche 911- The compound butter made the difference.
https://www.youtube.com/watch?v=FvXBR50rH9E

[Marc Bixen]

Seen it once before. It was cracked for a while, the darker area, then the rest sheared off, the shinier part of the fracture. Does it look like it had ever been bottomed out?

[GH85Carrera]

Yea, it almost had to have taken an impact at some point and cracked. Maybe a piece of road debris from 20+ years ago cracked it. That dark area on the break indicates were it was cracked.

I doubt anyone ever inspects that part very often. Part of the "fun" of a 34 year old car.

[john walker's workshop]

Seen a few.

[josephvman]

I had this exact failure on an '88 Alfa Romeo Spider, and I can tell you on older Alfa's it's an extremely common failure. My guess is that it's not as rare as you might think on 911's, though I have no doubt the Porsche part is better quality than what Alfa uses.

[porsche930dude]

My clutch pedal broke off once. Glad it wasnt the brake!

[porschyard]

It is probably more common than people think. I have seen several late 915 (77-86) arms break like that over the years. Always about mid point and most of the time no apparent damage and always sign of a long term crack (rusty area)

I have wondered many times if this not a casting issue.
I had a customer show up with his 930 on a wrecker one day with the clutch pedal to the floor and it was the clutch arm broke in half, IIRC it was an 86

This is the only 930 arm i have ever seen break and looking at it closely there is no sign of damage and the crack does not go frt to back but starts at the top center and went about half way down.

This bolstered my suspicion that these are casting flaws but i am not an Eng-o-neer or a metallurgist so this is just my observation and opinions. Has anyone else ever seen a 930 arm break like that, Please chime in.


As a side note i dont recall ever seeing a one piece 72-76 915 arm break.

Richard

[john walker's workshop]

Seen a 930 short arm break it's end off.

[porschyard]

Originally Posted by john walker's workshop

Seen a 930 short arm break it's end off.

Wow ok, never seen one of those break

[sugarwood]

Originally Posted by Missed Approach

Throw Out Lever #915-116-713-08 (with the spring attached)
sourcing a used piece (didn’t want to wait for it to ship new from Germany)

Pelican sells this part for $250
https://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2016.cgi?description=91511671308&command=DWsearch

[Uwon]

Ha!
You have got to be kidding! I thought it only happened to me.



Just happened about a month ago



CAA home for the RST-free. 100 km COVID-19 taxi home for my wife and me-$252.
I have a heavy duty clutch which is quite stiff to handle my turbo motor. I had assumed that the stiff clutch and perhaps that the arm came out of a donor car involved in a major track accident have something to do with it breaking but now I’m wondering if it’s just a general weakness.
How many of you have heavy duty clutches?
Johan

[porsche930dude]

Dang Johan you need to learn to drive without a clutch. Heck once you get on the highway its free sailing

[Marc Bixen]

JB Weld???

[Uwon]

Originally Posted by porsche930dude

Dang Johan you need to learn to drive without a clutch. Heck once you get on the highway its free sailing

Yeah, yeah! True story-I restored a Model A in my teenage years and in the summer of ~‘62 I had a summer job as a labourer for a highway building contractor. One day the super comes up to me and says-you drive that Model A, eh? Can you do it without a clutch, eh? See that Mack truck, it has no working clutch pedal. If you can drive it, you go from $1.69 to $2.20 an hour. Thought I had gone to heaven.....
With a freshly rebuilt 915 in the RST and three towns with multiple traffic lights to deal with, it was probably not a good idea to try.
Cheers,
Johan

[Uwon]

Originally Posted by sugarwood

Pelican sells this part for $250
https://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2016.cgi?description=91511671308&command=DWsearch

Yes, but that is for the arm only. Double that if you loose the omega spring, pin, etc like I did.
Johan

[Missed Approach]

Hi Everyone- Thanks for all the great feedback- Uwon, that's unreal timing- sorry about the taxi ride. I'm somewhat leaning towards a FOD (Foreign Object Debris) hit from many years ago, or casting issue, or both. Porschyard, that's a very interesting data point of never seeing the failure in a 72-76 arm.

Cooking on a Porsche 911- The compound butter made the difference.
https://www.youtube.com/watch?v=FvXBR50rH9E