Inner suspension mounting welding

It's been a while since I wrote anything about the inner rear suspension mountings. I'm doing them a little differently this time as there are rustier than normal, and I've got good access with the body removed.

This is a photo of the offside rear chassis with the reinforcing skin removed. It doesn't look so bad, but the reinforcement on earlier cars is taller than on later cars, so the rust spreads higher up the chassis rail. The rust went a long way forward on this car too, so I've removed part of the crossmember for access.

Here the rust has been cut away and the metal prepared for welding. I'm planning to fit later rear suspension (with handbrake on the rear wheels) so will leave out the third suspension mounting hole.

The repair will be on two sides of the chassis only as the third side is in good condition.

I've replaced the original double skinned part with a single piece of metal 2mm thick which should be roughly equivalent in strength to the original 1mm and 1.5mm skins. It's best not to go any thicker than necessary as that might result in stress concentrations at the end of the excessively thick repair.

The shape was worked out with a cardboard template, and the repair panel formed by beating it over the edge of a steel table.

The jig is the one featured on Frederick the Frog's suspension jig page, but has since been modified to mount to the chassis jig. It's been painted up to look pretty as well. Accuracy of the hole positions is very important on the later rear suspension (which isn't adjustable). Get them just 1mm wrong and the car can lean to one side.

The various clamps set everything in position for tack welding. In hindsight I would have braced the rear of the chassis rails across the body mounting holes as the chassis rails moved enough to stop the holes lining up correctly at the boot floor.

I've been careful to overlap the repair onto existing reinforcements where possible to reduce the build up of stress (rear damper forces can cause the chassis to crack).

The bottom of the chassis was overlapped at each end, and the side at the rear. The side at the front is a edge to edge butt weld for reasons I can't remember. That might have been better overlapped too. All the edges were also seam welded.

With the welds ground down the repair is finished (apart from the new closing panel for the rear crossmember which would be fitted after the outer suspension mounting repair).

A little sealant should tidy up the overlap seam weld, and otherwise there's no evidence of the panel having been repaired.