Transmission cracks

[Jim_Brown]

After cleaning 30+ years of crud of the housing of my mg case 901, I discovered two cracks. One next to the breather and the other on the opposite side next to the side cover.





I have no idea when or how they happened.

Can these be repaired? or is it time for a new housing? Will a 914 housing work with a breather relocation?

Thanks,
Jim

[yelcab1]

You can potentially have those welded up by a good shop with a master TIG welder. Although my attempt to have my tranny hole welded up did not fare well. I ended up getting a new case.

[Grady Clay]

Jim,

YIKES

Is this the 901/13 S/N 7193323?

I have never seen that before. I would carefully inspect inside around the bearing support area between the differential and gears.

I wouldn’t reassemble without checking the pinion position, differential bearing pre-load, and the pinion-to-ring backlash.

If the structure turns out OK, all you should do is add epoxy to prevent leaks. I would not try and weld on the casting in that area other than as a last resort.

The mid-’69 901/13 was Porsche’s first attempt using a magnesium alloy investment casting in a transmission. They had started with production engines in ’68 (and 906E, 910, 911R earlier). The ’70 Type 911 casting is dramatically different from the ’69 901/13. Mostly it was to accommodate the 2.2 clutch but clearly everything else changed. There was another casting change to/in ’71.

I have never tested for this but I think there was a metallurgy alloy change from the 901/13 to the 911/01.

I apologize for being so far behind on my e-mail.

Best,
Grady

[paslantnose]

Crack repairs can also be effected quite well with metal stitching.
It is well known in industrial shops and is stronger than the case around it.
If it's good enough for the NRC, it's certainly good enough for automotive.

[Jim_Brown]

Grady-

"Is this the 901/13 S/N 7193323"

Yes it is. I haven't opened it up enough to see if it extends into the bearing support area.

No worries on the email and thanks for your help.

Jim

[tumalo]

I'd take the +30 years of crud and paste it back on there! Bet that was the glue holding it together

[Grady Clay]

Jim,

Before you loosen the nose piece, is there someone with a P258 0r WV 385 who can measure the position of the pinion as it sits, undisturbed? If you do some repair you will want to return the pinion to this number.

Best,
Grady

[Jim_Brown]

Grady-

I'd already loosened the nose cone. It doesn't matter anyway. The cracks are terminal. They extend all the way through the bearing support area. I took it to Dan Hall's here in Portland to see if anything could be done. Dan pronounced the case dead at 1030am.








YIKES! indeed.

[Grady Clay]

DAMN!
Pardon my French


What could have caused this? We need to do some careful forensic analysis here. I wonder if Henry Lee is involved with Porsches.

Is there anyone else with a 901/13 exhibiting these symptoms?

What is the condition of all the gears, etc? Any sign of prior damage?

My sympathies,
Grady

[Jim_Brown]

I have no idea how or when this happened. It is well above the fill plug so it doesn't do much more than weep. From where the cracks are located, vertical impact load on the mainshaft? Something caught in the 5th gear?

The piece (cast iron?) that the bearing races mount into is intact and securely attached to the magnesium housing. It could have been like this for years. I'm very tempted to try some type of JB weld pressure injection into the cracks method of "repair".

Gear conditions... this is the first transmission I've had opened so I don't know. They look OK to me. No scoring, pitting or uneven wear.

3rd through 5th...

[randywebb]

are there any shiny spots or dents any where inside the case?

[davidppp]

Hello there.

I've worked on doxens of 911/914 mag case boxes..never seen this.

Manufacture fault, leading to fatigue fracture is my guess..

It would be instructive to separate the box parts along the crack to look at the fracture surface, inclusions etc...

Kind regards
David

[Porsche_monkey]

If you try to salvage it you should drill holes at each end of the crack to prevent them from propagating.

[Jim_Brown]

Randy - No I didn't see any signs of impact or contact inside the case. The drain plug was very fuzzy with iron filings but there was nothing larger free inside the case.

David - If I find a really good deal on a replacement mag case I'll do some destructive forensics. Right now my plan is to:

1. Drill full depth holes at the ends of the cracks as PBH pointed out - thanks.

2. Drill a series of shallow blind injection holes along the cracks with a bit sized to match the end of a large gauge syringe.

3. Inject jb weld into the blind holes with a syringe until it oozes out of the other side of the crack and the adjacent holes.

I need to get a syringe and mock this up to see if it'll work. JB weld may not flow well enough to fill the cracks. Maybe there is a more suitable gap filling structural adhesive that I should use? Any suggestions?

Thanks,
Jim

[charlesbahn]

Alumaloy might work.

www.alumaloy.net

[Bob's Project]

I think this problem might be coming more common. Although I do not have alot of experience with transmissions in general, 2 out of 3 of the 70/71 year cases I have dealt with had these cracks. However not as bad. I didn't attempt to repair them.

[Porsche_monkey]

I would warm the case with a heat gun and use warm JB Weld. It will flow over a one hour period.

[randywebb]

Jim - you're in PDX - you might talk to Steve W. and run it by Gamroth's to see what they think...

Good luck - this is (unfortunately) very interesting...

[PorscheGuy79]

Jim, firstly very sorry but this a very interesting thread...im hooked! I thought if Grady hadnt seen it before it didnt exist!

[TimT]

I think you can still get new 901 cases from Porsche. I know of a person that rebuilt a 901 box and sourced a new case. Im thinking it cost about $650 for the case.