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MG MGB Technical - rusted side member

I was checking out the work required on my 74 GT floor pans and had a knock on the LH side member/front chassis rail noticing the dreaded crunchy rust sound. So proding further opened up some big holes underneath and screwdriver going through the sides....bad.

I'm after some advice as its on the main LH front chassis rail where it turns the corner and heads up from the bottom of the car up to the front suspension cross member/engine. What's required here? I can get hold of the member running from the bumper to the chassis cross member but replacing the whole lot is a hell of a job. Assuming there's enough good metal heading up towards the front end cross member can I weld in a half section all the way back under the floor to the chassis cross member.

Thanks guys any help much appreciated.

Craig

C Hardwick-smith

Craig,
That's going to be a bug*** to fix.

Obviously it's better to replace the full leg but as you say it "is a hell of a job" and not one I've undertaken.

In principle it is acceptable to join at any point where there is sufficient good metal. An example of where this is done on a regular basis is the rear chassis leg repair sections (rear 3/400mm including the rear spring eye).

It's common practice to add strengthening plates inside the repair spanning the join and plug welded to both sections in additional to a full butt weld at the join. These plates are not strictly necessary if your welding is up to scratch i.e. full penetration, no undercut and a continuous weld containing the right amount of filler wire.

Best of....

MGmike
M McAndrew

The horizontal flip doesn't help! I'm also tempted to say that's what you get with rubberised underseal. It all depends on where the rot ends and good metal starts. There's nothing wrong in buying a repair section and only using the part you need.
Paul Hunt

Craig,

I had to section one into my BGT. I found good metal maybe 8 or 10 inches above the curve, and replaced from there till it met the cross member. I also had to replace the cross member and floor pans. It is a bunch of work. I did mine with the engine out, and I think you may have to do the same.

Hard to say for sure, but it looks to me like someone slathered it with roofing tar after it rusted out. So, you might have more surprises still to uncover.

Charley
C R Huff

Thanks gents,

Charley, what did you have to do for bracing whilst you cut the member and floor out? Or are the sills and the other chassis rail enough to take the load?

Craig
C Hardwick-smith

It has been a while since I did it, Craig, so I may not remember correctly. But, I don't think I braced it. Remember, the load was somewhat lightened since the engine and trans were out, and the roof (GT) and side rails are pretty strong.

Charley
C R Huff

I did this repair a long time ago. I carefully cut and shaped and bent pieces of sheet steel of the correct thickness to the required shape and length, cut the rusted bits out of the members and then held the replacement parts in place with self tapping screws. The pieces were cut to cover the rusty part of the member completely plus about 10 cms onto good metal.

To make sure the arms didn't "droop" I cut the rust out of one side of each member and secured the new piece with the self tappers. Then cut the rust out of the other side and secured the new piece, and then repaired the bottom of the member. To keep the arms in alignment I re fitted the engine cross member.

A very experienced welder then came along and welded the whole lot together. Each member required 4 pieces of replacement material.

The car was upside down at the time giving excellent access to the work area, but that is because the whole car had been taken apart and nothing else was on the tub. I don't have any pictures of the repair now, but the side pieces were welded to the member and to the body shell. The bottom piece was welded to the member and the side pieces and I had a small piece welded from the top of the member where it straightens out to the body shell "to be sure to be sure". That piece was probably not required.

After a few more weeks or months the whole car was put back together and it worked fine until I sold it.

I seem to recall seeing complete side members for sale somewhere so that may the be the easiest way to go, but alignment may be more of a headache.

Good luck

Tony
Tony Oliver

This thread was discussed between 02/06/2014 and 05/06/2014

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