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just a couple tid-bits i want to interject: Japanese metal is graded differently with different properties than american steel..... if you couldn't already tell from the rust, lol. you should address it when welding more along the lines of t1/spring steel. i would have to say the previous welding was a larger contributor to to the failure. something like 7018 stick, or smoothcore mig wire 25/75 will yeild a much better weld. in the end, don't forget that the frame does typically flex tortional, but flex on the horizontal plane is not nearly as important, so those horizontal gussets to the front beam are ideal, but over-doing it on face rigidity could bite you in the end. that steering box mount plate should at least been welded front moon and then allowed to cool before continuing, or heat relax the section. think of it like when you weld, it's like stapling one small part of your shirt in a pinch because the way it get's tight when it cools. if you pull pressure against it, something concise is going to take most of the load in stead of spreading it out, and start the tearing.
Hi guys , any help or insight on this repair would be appreciated...
The front driver side frame rail cracked and separated from the front crossmember . I'm not sure of the cause , but my 90 4runner is a big rock crawler , so I abuse it pretty good , but the fact that the frame itself fatigued and cracked was pretty surprising . My plan is to fab some custom L-brackets and hit all four sides of the frame to the crossmember , with additional gussets going diagonally to reinforce .
Anyway , this is a big project for me , and I'm considering just taking it to local 4x4 shop to have them do it ....
Actually, while the horizontal forces of the steering box can be a "catalyst", the root cause could be the added strain of the impacts from having a solid mount on the end of the frame horn. Older Jeeps the do the "shackle reversal" where they swap the fixed leafpack mount to the frontal frame ends find that the frame cracks at the hump directly behind the tire(about 24 inches from the frame ends).
The triangle horizontal brace that you added is the best fix for your situation.
Ken