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MG Midget and Sprite Technical - Reinforcing the ARB mount

Despite having the chassis rails seam welded a few years ago the ARB mounts are beginning to tear themselves off the chassis rails again. In addition to having the welding done again, I've added two brackets (one each side) to give extra support to the ARB mounts. Top bolt goes in the rear bumper bracket hole (I have no front bumper) and the bottom goes on the ARB mount. I don't know whether this will do the trick or will just shift the problem and stresses to elsewhere in the chassis - what do you think?

A picture is attached although it is not of the best quality.

Chris Hasluck

Well it sure couldn't hurt!

But reinforcing only one of the pair of fasteners might not be fully successful. I wonder if you can make a bracket like that for the rear bolt as well?

The key thing is to try and make the attaching points go all of the way through the chassis rail. For instance, if you cut out the bottom plate for access and then weld a thick tube inside the rail so that you can run the mounting bolt clear through to the top and the thick tube will prevent crushing the frame rail when the bolt is done up tight. Replace the bottom frame sheet metal with a thick piece which will resist twisting will also help.

Out of curiosity, what diameter is your sway bar?


Norm


Norm Kerr

Hi Norm

I think it is 5/8ths (it's certainly not 3/4)

Chris Hasluck

It looks from the pic that the welded seam is splitting away from the side of the rail so it's the side of the rail that is the weakness. Brackets might transfer the loads to other parts of the sides of the rails but ultimately the whole rail needs to be stronger. In the time it would take to fit crushtubes, brackets and through-bolts and lining things up you could just as easily measure everything up then remove the bottom of the rail and make a replacement out of thicker guage steel. If you then strengthened the sides of the rail on the inside (plug welded from outside)it would be super-strong when all welded up and a lot neater too.
Nick Nakorn

Hi Nick

I can see from the photo why you would think that the seam is pulling away from the rail. In fact the photo is a bit deceptive. The rather ragged gap above the ARB is the bottom of the bracket that holds the radiator and not a tear in the chassis rail. The failed weld is out of sight behind the bar as well as a slight tear across the bottom o the chassis rail.

I take the point about fitting heavier gauge metal and strengthening the general area. I will probably go down that route but with the car in use over the holiday weekend I did not want to embark on a big job that took it off the road and just wanted some reassurance that the ARB was not going to rip out (a short term fix).
Chris Hasluck

Why not drill through to the top or the rails weld in a tube and bolt through.
Could not get it stronger than that I think.

And indecently that is what is going to happen on mine ;)
but also because I want to move the ARB to the top of the rails to aid clearance for jacking and speed bumps
Onno K

We fixed the problem much more simply by plating right over the existing mount, plug welding through to it, and joining at the edges of the chassis rail. (See photo. The odd-looking patch around the mount is what happens when you tape over the holes and sandblast the rest around it)

Together with the bottom of the chassis rail and the ARB mounting block, this forms a truss with a depth of about 1/2". It spreads the loads much further - out to the perimeter of the plate, which is longer that the original mounting plate for just this purpose. It has been well up to the job in over a decade of vigorous competing with a 3/4 bar fitted.

Paul Walbran

Im doing the same as onno and placing the arb on top of the chassis rail, instead of on the bottom

Theres a old website that shows the modification ... but I cant find it at the moment

Prop
Prop and the Blackhole Midget

This thread was discussed between 20/04/2014 and 21/04/2014

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