Welding to the subframe.
 

So when I changed my rear track rod ends, whilst undoing the eccentric bolt, I was silly enough to crack off the sub frame tab that the eccentric bolt adjuster pushes against.

http://i.imgur.com/uFCXuGhh.jpg

Originally it wasn't an enormous issue as when it came to aligning the car, they managed to work around it. Trouble is, under heavy load the alignment has shifted, and this bolt now hasn't got any tab to push against if I want to install an eccentric bolt locking kit.

The solution would be to weld a new lip onto the sub frame. My trusty garage told me I'd need to TIG weld it, which is fine, but I want to ask if anyone's done this? And if the weld would be strong enough?

Any recommendations, tips or advice? Thanks!

Just replace the whole part. Check/replace the transmission mount while you are at it.
http://986forum.com/forums/diy-project-guides/63154-replacing-rear-suspension-bracket.html

If TIG welding a lip is strong enough, there's no need and would be a lot quicker, cheaper and easier.

If it's not, then I'll look at replacing it.

The TIG weld will be strong enough but you'll still have to remove it, plus clean it up and as it's a thick part it will need to be pre-heated too before welding. Easier to just swap it out.

Strange. The garage told me that it could be done on the car, but the arm would need to be dropped due to melting the rubber bushes...

So it has to be removed anyway?

Looks like you have a nice new track arm there. You replaced that - why not the subframe half?

Yes it can be welded on the car.

Porsche intended this to be replaceable if damaged. I'd follow their lead.

Again like I've mentioned above, welding is the quickest, easiest and cheapest route to go down. Once done, its function would be identical to if I just replace the part, except it'll be a lot less hassle. It's not on show, it doesn't need to look perfect. To change the subframe part I'd have to have a transmission jack followed by a lot more patience/difficulty, and whilst I'm comfortable with doing a lot of suspension work myself, I'm not comfortable doing that. Changing the arm took me all of 20 minutes and was two bolts, so that's no comparison.

If welding is strong enough and can be welded on the car, there's literally no reason for me to change the part at this time. I may change it in the future for the sake of replacing a part so that it's as it should be, but it'll hopefully make no difference after I've welded it. I'd just be doing it for the sake of it.

Just needed to know if it can be welded whilst on the car and if it'll be strong enough - looks like a yes to both of those. Thanks guys.

Theoretically welding might seem to be the quickest, easiest and cheapest route. One would think that it would be easy to just "reach up there and weld it". but just the fact that you are asking here tells me that you have not found someone to actually do it yet. Talk to a local welder and see what they say. Any welder that I know would want that part off of the car to weld it and would want it cleaned and sand/media blasted to clean it up. Depending on the alloy, they may need special rod and heat treating. Then you need to do a little finish work. Ugh. None of that sounds quick, easy or cheap to me.

My advice, suck it up and replace it. In the end, it will be faster, easier and cheaper just to replace the whole bracket. My guess is that you will be able to find the part is readily available and reasonably priced, as they are not a common failure point.

Just my $.02. YMMV.

First off you can not just "weld" the aluminum without knowing exactly what it is. Forged, heat treated or just cast require different welding techniques. Welding will change the metallurgy of the material near the weld from the heat. Aluminum is much more sensitive to heat than steel and can become brittle if not not done properly. Since this is a suspension component it is likely at least heat treated. You also stated that the suspension is being stressed under heavy load. Since the spot that has failed is directly where the control arm is bolted to and is in the middle of the support you can bet the forces are highest there. Now ask yourself, What would happen if this component fails during any aggressive driving?

those whole brackets are less than $100 on ebay, I paid that shipped to Australia as mine was missing all together, not a hard job to swap out

Want quick, easy, and cheap? Grind a fresh surface for adhesion and J-B Weld a small strip of aluminum on. J-B Weld can fix everything.

<iframe width="560" height="315" src="https://www.youtube.com/embed/aVLoJe3JbFI" frameborder="0" allowfullscreen></iframe>

Want it done right, safe, and permanent? Replace it.

THIS^^

Honestly, if you don't want to replace it, that is probably the quickest, cheapest and easiest method, with little risk that you can do yourself. If it doesn't work, no harm done.

That said, replacing it is the best option.

If I were welding that, I would use an argon-helium gas mix and 4043 filler rod. All the surface oxidation should be removed in probably a 1/2" vicinity of the weld (in all directions including wrapping around the corners) and all bolted and pieces removed probably at least 8" away and all rubber pieces removed probably 12"-18"+ inches away. And it would be an absolute "not fun" job, TIG welding that with the auto darkening helmet on your side/back under the car, filler rod in one hand, TIG torch in another, hopefully some sort of special torch-mount amptrol or at minimum, on/off torch switch set with upslope and downslope settings of a more advanced TIG machine, as a foot pedal sure won't work in this "out of position" job. On/off switch with proper machine settings might do the trick. You will need a very experienced welder and even then, if there isn't a clear path o vision or awkwardness in the access with both hands, I'd still budget on dipping the tungsten a couple times. You'll also need to get a good ground directly onto the subframe somewhere, and there will be a fire risk, so absolute no brake lines or gas lines anywhere near.

It would be much easier to remove the part to TIG weld this. And then, the points are valid about the heat affected zone annealing the material in the vicinity of the weld. Over time, it will regain its participation hardening, but it's a concern on a loaded suspension part. Welding hot and fast (and using helium in the mix) will reduce the width of the heat affected zone, but not eliminate it. This is probably A356 sand cast aluminum, like many other cast aluminum car parts, has silicon and magnesium alloying elements. It welds up pretty nicely actually. Since it's a suspension part, I would seriously consider passing on this job if it were to come my way back when I were doing these sorts of things. Too much liability. These sub frames used are available cheaply, so bolt on part replacement seems a much easier bet. After welding, especially if done "on car", you'll also need the weld deposit ground to proper clearance for the eccentric washer to bear against. It's possible to be done and all, but sounds like no fun to me and not something I'd involve myself with fixing when replacement sub frames are so cheaply available off pretty much any wrecked Boxster.

JB weld actually wouldn't have the problem of the heat affected zone, so could be advantageous in this regard. But if your camber adjusting bolt is moving around, I would question if JB weld is up to the job, and strongly consider just replacing.

Hope this helps. Best of luck!