Transmission case: is this crack going to be a problem?

[Baby]

While cleaning, I noticed this hairline crack. How concerned should I be?

[john walker's workshop]

there are plenty of threads about "cracks" on transmissions that are only casting marks, but yours sure looks like a real crack. it will be a problem now or later if it is.

[Flieger]

Up on the very top where it is on the fin, it looks like it is a raised casting mark to me.

[Hodgey]

can you inset anything into the 'crack'? If not then as Flieger suggests, it may be a raised casting mark.......

[Steve@Rennsport]

If thats a crack, you do have a serious problem.

Zyglow testing is the way to confirm whether its casting flash or a crack.

[BGCarrera32]

Based on how that runs from the very top of the case all the way down to the bearing I would be extremely suspect of that...

[slodave]

I say casting mark...

Looks like it's in the same position as this...

(Taken from this thread and reversed...)
Crack, a big social problem....worse in a 915



Actually, they look identical.

[Flieger]

Nice one, Dave!

[BGCarrera32]

Wow. I stand corrected.

[lucittm]

Probably caused by a crack in the mold. It might take a few castings before they catch it at the foundry and then make a new mold or repair the old one. Ironically with a bit more metal on the outside of the case it is stronger than a case without the additional flashing. Because it was molded in and not machined, it would not be a stress riser.

Mark

[Baby]

Dave, that's almost freaky. I know nothing about casting and assumed the mark was either a sign of insignificant fatigue or of severe stress of what nature I can't imagine. Anyway, this is encouraging.

[slodave]

A link to a thread from Zef, with the same problem.
Is it a crack ?

I'm sure there are a lot more out there that look like yours and the others, they just have miles of crap covering them.

Don't worry about it and keep driving.

[D911SC]

This picture of mine may make us both feel better!! I was sure it was a crack but there are no leaks or other symptoms.

Mine is 915 from ROW 83 SC.

Note pic is upside down to match the other ones in this thread.

[turbojem]

i cleaned my 915 about a week ago went back ,& did a little more today and saw the IDENTICAL crack (or what i thought was a crack ) , i wondered why there wasnt oil all over the garage . Very happy to have found this thread about the casting mark . - Id post a pic but looks exactly like youz allz same location too . '84 carrera Kinda relieved - i think ?

[Jerome74911S]

Evidently that crack remained in Porsche's mold for a serious amount of time. My car is older, but I'm going to crawl under there and have a look anyway.

Nice to know.

[Walt Fricke]

It should be pretty easy to determine if this is a casting mark. Get in there with a power tool with a suitable abrasive - the round small bodywork sandpaper pieces with a fine grit on a die grinder, for instance. If this is raised, rather than indented, you'd grind it off, leaving a smooth surface.

And you could do this in just a small part of it.

If, as I suspect, this is actually an indentation, you could still try this. You could even use another kind of tool to see how deep it is. Maybe do it where it appears on the tip of a rib. If it is a crack, you haven't made anything worse. If it isn't, but is a shallow casting groove, you still haven't made anything worse.

In fact, maybe, if a groove, you could just use a scratch awl or machinist's scribe to scrape it a bit to determine where it stops.

In my experience, transmission cases are most often cracked from two causes. One involves broken parts getting in the teeth between pairs of gears, forcing them apart. The other involves accidents with the car (those I have seen have been on the race track), where a rear tire slams into a wall or another car. The force gets translated through the axle right into the differential housing. Or the rear frame rails get bent enough to break the bell housing portion.

If you know the history of the box, you might be able to rule in or out the chances of something like this happening.

I don't know enough about aluminum to know if a long crack like this could develop but not be full depth - not all the way through. Seems unlikely in a casting like this - I'm not sure it would develop like the typical bolt fatigue fracture, where once it snaps you can see the progressive nature of the failure, starting from a stress riser point and getting larger.

On a 911 gear box, I think the normal side thrusts from the ring and pinion are to the left (driver's side). Which is why you can get aftermarket reinforced cover plates if you have a monster motor. I'd not expect that on this right side.

If your photo is upside down (and it looks a lot like slodave's), then this is in the lower side of the transmission, where there is a lot more oil. Which means the lack of oil suggests it isn't a crack, or if it is, it isn't all the way through. Transmission oil, while rather thick, is quite good at making its way out of things if it has the opportunity.

[Zyglo]

Wouldn't it be nice if there was some way of testing these things without destroying the material???

[ClickClickBoom]

Originally Posted by Zyglo

Wouldn't it be nice if there was some way of testing these things without destroying the material???

While Magnaflux won't work, dye penetrant most likely will!
Nicely played....

[LBEEMING]

Old thread but thought I'd join in. My 1985s transmission has the exact same marking.

[Walt Fricke]

So maybe it was a casting artifact? If so, I'd hesitate to call it a flaw.