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Rear Upper Toe Control Arm Cracks

 
Old Jan 2, 2019, 11:33 AM
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Item 2 in your diagram, the arm that has the toe adjustment on it.
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Old Jan 2, 2019, 11:35 AM
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Originally Posted by ayoustin View Post
Item 2 in your diagram, the arm that has the toe adjustment on it.
Thats what i thought

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Old Jan 2, 2019, 12:44 PM
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i should probably know better, but do we have a common faults/issues to address on evos kind of official stickied thing anywhere?
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Old Jan 2, 2019, 12:49 PM
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Originally Posted by kyoo View Post
i should probably know better, but do we have a common faults/issues to address on evos kind of official stickied thing anywhere?
Not that i know of Sam. This is it

That would be a good series of threads that covers all the major categories
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Old Jan 2, 2019, 07:43 PM
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Looks like Mitsubishi should have made the wall about 1-2 mm thicker.
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Old Jan 8, 2019, 08:46 AM
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interesting. That forging line should be sanded flat with a die grinder and flap wheel to help to prevent this from happening.
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Old Jan 8, 2019, 10:59 AM
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Originally Posted by Steve_P View Post
interesting. That forging line should be sanded flat with a die grinder and flap wheel to help to prevent this from happening.
Grinding produces a damage layer in the remaining material that is more prone to crack initiation, so while the local stress riser is removed by grinding, a new weakness is produced. Its a "damned if you do, damned if you don't" situation.
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Old Jan 15, 2019, 08:26 AM
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Originally Posted by mrfred View Post
Grinding produces a damage layer in the remaining material that is more prone to crack initiation, so while the local stress riser is removed by grinding, a new weakness is produced. Its a "damned if you do, damned if you don't" situation.
I said sanded with a flap wheel on a die grinder. Not grinding. Don't go into the main forging, just remove the riser. Properly done, it will certainly reduce the stress riser from what's shown in the pictures. This procedure is done on factory forged steel connecting rods all the time.
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Old Jan 15, 2019, 01:52 PM
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It's a flash line crack. Basically a forging defect. Removing the bit of flashing won't change anything.

And grinding or sanding is the same thing. You're removing material with abrasion. Whether its a sanding disk, grinding wheel, or carbide burr. The only difference is the size of the chips coming off the part.
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Old Jan 15, 2019, 04:30 PM
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Originally Posted by Steve_P View Post
I said sanded with a flap wheel on a die grinder. Not grinding. Don't go into the main forging, just remove the riser. Properly done, it will certainly reduce the stress riser from what's shown in the pictures. This procedure is done on factory forged steel connecting rods all the time.
Any degree of sanding that removes that much material will produce a more crack-prone material microstructure. It would have to be taken to a fine polish to get rid of the undesirable microstructure. People may perform such flapper wheel sanding operations all the time, but that doesn't mean no harm is done to the microstructure. Perhaps in the case you describe, the harm to the material microstructure is not has bad as having the stress riser present. This may be the case for the control arm too. Or it might not.

LGTD, I wouldn't call that a flash line crack in the sense of forging. However its possible that the microstructure in that region is less optimal due to it perhaps being a last-to-solidify region that would contain more insoluble or lower melting point elements.

Last edited by mrfred; Jan 15, 2019 at 06:34 PM.
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Old Jan 15, 2019, 06:24 PM
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i dont think its a forging defect...

i think the end starts out as a U and is forged into a O.... with a very small gap where the tips of the U touch...
then they are welded.

stress fracture on the weld.
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Old Jan 15, 2019, 08:08 PM
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It's not a forged piece, there is no weld. The entire piece is cast as it looks and both bores are machined to properly fit the bushing and ball joint. The line that is the cause of this issue is a parting line, it's essentially excess material that was squeezed out between the mold halves. You can tell it's a cast piece the same way you would a crankshaft, by looking at how thin the parting line is. Forged pieces usually have a parting line that's about 0.5-1" in width, while cast parts are thinner like this (usually 1/16-1/8").
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Old Jan 15, 2019, 08:46 PM
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Was also a bit confused by these alum suspension arms & beams & how they are made

Are they forged or just a simple sand casting? Heres a snip from Mitsubishi's EvO announcement from Cypress CA
Heres the article for verification:
http://media.mitsubishicars.com/rele...6fbed?page=142

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Old Jan 15, 2019, 09:08 PM
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Forging is a very vague term and is often misused in marketing material. It is probably cast and ran though a forging press while still hot and finally annealed in an oven. That's pretty typical for lots of mass produced aluminum parts.
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