subframe stress cracks!

[rossocorsa]

just been cleaning up my spare subframe intending to use it to build up the spare engine onto then swap over, aside from the usual dents on either side due to indiscriminate jacking (still better than the one in the car) on first inspection it looks pretty tidy but I have found stress cracks where the bracket for the gearbox mount fixes, these will be well hidden on a complete car unless you look very hard so I figure that the one in the car is probably the same.

question is how best to repair the captive threads make it awkward and given its function it needs to be strong, as said I rather suspect I may find the other frame is the same and I need to get this one sorted and built up to save time later



  

[75coupe]

I had exactly the same problem on my 1975 coupe. I managed to weld up the cracks with oxy/acetylene with a smallish nozzle, and it has lasted for over 2 years of abuse - lots of pull power standing starts at hillclimbs!! (Broke the engine stabiliser rod though). You could always weld the the gearbox mount bracket to the subframe too for extra strength, I have never had the need to take this off, and the engine/box has been out three times....

[rossocorsa]

You could always weld the the gearbox mount bracket to the subframe too for extra strength,

yes I'm thinking along those lines myself, I think I might weld the cracks then put a thin reinforcing plate on top  bolt the mount in place and then weld the resulting structure together

[MattNoVAT]

I would cut a hole in the side allowing access to slot a backing plate in behind the stress cracks and then grind back some of the cracks, then weld through to the backing plate, the trick is getting the weld penetration thru to the backing plate, finally grind back to a flat surface.

Then weld up the access hole.
Theres probably a few approaches depends on cost and skill of the person welding i guess.

[rossocorsa]

I don't fancy cutting a slot in the frame it's just a further weakness need to ponder on it a bit 

[rossocorsa]

in the end we welded up the areas around the captive nuts then put an additional plate on top seam welded around the edges and stitched in the centre to give extra strength, knocked out the dents as best we could (so it is still a bit dented) and had the subframe powder coated in black