Stress crack in transmission case?

Adrock · 08-16-2018, 10:27 PM

hi all,
I'm trying to work out if this is a crack in my transmission case...
It's hard to tell, even in person. If it's not a crack, it could possibly be from the original casting? It looks pretty fine and doesn't 'appear' to be deep if it is a crack.
If there was going to be a stress crack, it seems a logical place for there to be one.

If it is a crack, I presume this would be fairy easily repaired? It's a 915 case prob from around 83. Does this mean it's likely to be aluminum or magnesium?

Cheers,

Adrock · 08-16-2018, 10:29 PM

Sorry, I just realised I posted this in the engine rebuild forum.
Happy for admin to move this across to the general 911 technical forum if appropriate.
Thanks.

KTL · 08-17-2018, 06:38 AM

1983 is definitely aluminum case. Shoot an email to Roger Brown at California Motorsports/CMS. He's seen a ton of these transmissions and also does repairs to the case. So I bet he's got his own fix for this location. The more common issues he sees at the clutch release fork location is on the G50 trans where the mounting bosses crack off

https://californiamotorsports.net/collections/porsche-g50-transmission/products/cms-g50-993-gt3-clutch-fork-pivot-shaft-boss-repair

He used to weld machined aluminum blocks onto the bellhousing. Apparently he's since developed a more elegant solution above where he screws the pivot blocks into the trans.

He fixed up my differential housing with steel bearing bore sleeves and also welded a crack that he found near the speedometer sending unit recess. He also discovered the threads were messed up in one of the detent holes and installed a helicoil

Matt Monson · 08-17-2018, 07:53 AM

CMS doesn't have a billet replacement for 915 like they do for G50. That's most likely because this failure is uncommon and there are so many 915 cases still floating around.

It does look cracked. I'm not sure how you would repair it. If you weld up the cracks, it might add some strength but somewhere down the road the mount could still rip out. I would look for a new case personally.

Dpmulvan · 08-18-2018, 06:27 AM

First off you need to dynaflux the area, you can purchase crack check off amazon if you wish or have an experienced welder do it for you. The crack check will expose the entire crack from beginning to end. Then it can be tig welded, ground, sanded et.

Adrock · 08-19-2018, 07:40 PM

Thanks team... I had a really close look on the weekend under sunlight (what sunlight we have here in Melbourne here in Winter!) and I'm not completely convinced that it's a crack.
I'll have to do as Dpmulvan suggests above and have it Dynafluxed.
I might try and take a photo with my digital SLR with high Res, so I can zoom in a ridiculous amount and see if I can get a better idea before I start stressing. Although, if it's a crack, I'm sure welding would suffice considering I'd only drive it 4 times per month at the maximum!

mikedsilva · 08-19-2018, 09:38 PM

I don't think that is a crack.

Adrock · 08-19-2018, 09:47 PM

At this point either do I Mike. I think it's like webbing from the casting of that mount. There are similar web looking areas in other corners of casting. Still. Doesn't hurt to confirm.

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Dpmulvan · 08-20-2018, 04:37 AM

Take some acetone and a needle, clean area and run a sewing needle up it, still not sure buy a can of dynaflux. It's impossible to tell with the naked eye. That's why you have to dynaflux welds, joints in a nuclear power plant to be absolutely sure.

cgarr · cgarr's Garage

Seems like an odd place for a stress crack

Adrock · 08-22-2018, 07:27 PM

Quote:

Originally Posted by Dpmulvan

Take some acetone and a needle, clean area and run a sewing needle up it, still not sure buy a can of dynaflux. It's impossible to tell with the naked eye. That's why you have to dynaflux welds, joints in a nuclear power plant to be absolutely sure.

That's a good idea, I'll grab a needle and see how I go... I was wiping it with a rag and brake cleaner, but I think all I was doing was wiping more gunk into that spot.
Will report back after the weekend.

HaroldMHedge · HaroldMHedge's Garage

Not sure where you are at down under so I did a quick check for a Dye Penetrant Inspection and came up with this company.

Russell Fraser Sales Pty Ltd