Inner sill and floorpan replacement

Inner sill and floorpan replacement

In today’s episode of ‘Jobs I wish I’d done properly last time’, the rest of the offside floorpan and inner sill are cut out and replaced with new items.

When I replaced this floorpan previously many years ago, I had used a Steelcraft pattern part, which incorporates an additional flange around the entire edge, and which I had seam welded onto the inner sill, heelboard and transmission tunnel, as can be seen above and below, and made a right old mess!

Below you can also see where I had previously welded in a repair section to the bottom of the old inner sill, where it had rusted out where it met the floorpan.

I found that my new favourite toy, the air hammer, was the best way to make short work of releasing that dodgy old welding.

For the inner sill, there is a great Steelcraft repair panel which replaces the whole front 4 feet of the sill, up to the point where it starts to curve upwards at the back towards the heelboard. This was ideal for me since the back end of mine was completely sound, so I marked up a straight line and cut out everything in front of it.

Skipping forward through several hours of cleaning up the remnants of the old welding, wire brushing everything, and epoxy painting the insides of all the box sections, I was ready to weld in the inner sill repair. You can also see below that I’ve fitted a new jacking point strengthener to the inside of the sill – somewhat unconventional and difficult to fit from this side, much easier to do from the outside when fitting the outer sills, but it’s a bit late for that now having already replaced them!

Inner sill section cut to size and being welded in. I was able to spot weld most of it since the access to the flanges was pretty good, which makes it a pretty quick and tidy job, just needed some plug welds along the top front section where it meets the side of the footwell. I butt welded the repair section to the back of the original sill so that it would be easy to dress back and hide the join later on.

This is the tricky bit about fitting the jacking point strengthener this way round, I had to carefully measure and pre-drill some holes in the sill, so that I could plug weld them from this side. I put a couple of self-tapping screws in the middle holes to pull it all tight before welding the top and bottom holes.

With the inner sill done, it was the small matter of fitting the new floorpan next, but I decided to also replace the rusted-through heelboard strengthener on the underside, so whipped that off at this point too.

Only a few spot welds holding it on, so was off in no time. Some surface rust lurking beneath it of course, so cleaned all that up before moving on.

New floorpan in place! I deliberated for a while on my welding strategy for this – mostly whether to weld from inside the car, or from underneath. In the end I went for a bit of both, pre-drilling most of it for welding from beneath (all of the flanges on the chassis rail, crossmember, along the tunnel and heelboard, and where it meets the footwell), leaving only the outer edge along the inner sill, and a couple of other spots not accessible from below, to be welded from the inside.

Many, many plug welds later and it’s all done. Thinking ahead to V8 power concerns, I chose to additionally seam weld the back corners around the rear suspension hangers to add some extra strength in that area – much more to come on this subject at a later date.

Inside things looked pretty neat, you can see where I’ve already welded and ground back the edge along the inner sill.

Tidied up all the welds underneath, and this job is done.

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