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Rear crossmember


Bluemoon
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just noticed the dreaded rot at the back and I'm going to replace with a C channel RSJ type, cut and welded the same shape as original. but I remember hearing about a guy who made a removeable one , like the front bumper, just wondered if he was on here or seen it done, or had any problems down the line, and also whether it is any think to do with the vehicle inspecters etc. also is it still best to box it out even though it about 10mm thick, cheers inadvance for any input

Brian

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I know this is a touchy subject with some but here goes.

If you change the design of the rear cross member you have modified the chassis and in principal would need SVA/IVA.

Your removable version would definitely fall into that category.

Repairing the chassis is perfectly acceptable. The fact you used some heavier gauge material you happened to have in stock also is not an issue. If you then boxed it (even with lighter gauge material) you would leave it looking pretty much standard and remove the likelihood of someone looking at it and declaring it an issue.

All just IMHO.

Steve

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Why would you want to make it removable? By doing so you are likely to reduce the torsional rigidity of the frame.

If you make it out of 10mm (!) it's not like it will need replacing in your lifetime.

ps You might need to consider some HD rear springs too :)

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Just a thought.

The chassis is fairly flexible anyway. If you fitted a very stiff crossmember would that just move and focus stresses onto the chassis rails where it meets the new crossmember?

When I used to do this I would spread any loading from chassis flex through to the rear chassis rails with flitch plates and some triangulation. That made the chassis rails become gradually more rigid rather then a sudden stiffness change at the crossmember welds.

The extra work would show up on any inspection.

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I have already 4mm steel tread plate welded on the rear face , its the horizontal edges which have tripled their thickness and the inside boxing which is rotting , looking from back ,top and underside it looks as new, already repaired one side of the chassis up to the crossmember last year, the side that now needs repairing was solid last year after checking with a pointed hammer and nice clanging sound, gave it a good check as the opposite side needed quite a lot of work. I just thought if I made the legs beefy with a bolt on cross member , access would be easier to weld and paint, but just thought I could fabricate it with longer legs , all prepainted, just to paint over where it joins the chassis, its amazing what happens when you talk away to yourself, cheers guys

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