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MG MGB Technical - Replacing sills etc

Hi all

Having had my '66 midget for a few years and done quite a few jobs I'm happy with where she is, I've recently bought a project MGB GT, that I am looking to restore over the next 3 (ish) years.

The floors are shot on both sides as are the inner sills (step sill?). The outer sill and membrane appear to have been replaced and are in fairly good nick. The castle rail on the LH side has been replaced badly over part of the old one, so I have decided to replace that as well.

I have started on the LH side and have already removed the floor panel. I believe I will be able to use a repair for the inner sill, however with the outer sill and membrane still in place it looks like it will be a bit awkward to cut out in places so I was wondering whether to remove the sill and membrane and start from the inside and work out?

Before I get carried away and cut out the rest I would be grateful of any advice on my planned method whilst the car is on a rotary frame mounted on the bumper mounts:

1 tack new floor panel to body
2 remove outer sill and membrane
3 repair / replace inner step sill and jacking reinforcer
4 replace membrane and outer sill

I intend to check door fitting at numerous stages and paint as I go on the inaccessible places.

As the other side is still intact do I need to brace the car across the doorway or is there sufficient strength with the floor tacked before I remove the outer sill?


Tony Brough

most of the front to back strength is provided by the castle rail and the step sill and therefore I'm in favour of bracing the door aperture when one or other is to be removed. Tacking the floor will not provide any additional strength.
I would use temporary fixings for the floor panels until you have the step sill repaired. The lower edge of which needs to be welded to the castle rail and this is easier to do from the top (under the edge of the floor pan).
Working from the inside out is the way to go but the chances of reusing the sill and membrane are fairly slim and I would budget for new ones.

Best of...
M McAndrew

I agree with Mike. I rebuilt mine a few years ago and I can't imagine how you would repair or replace the inner sill with the outer sill and membrane in place. On the GT it may not be necessary to brace the door opening because the roof provides some strength, but I welded a brace across mine anyway. As you can see, I got away with a patch on the inner sill. The rest had surface rust but was completely sound once cleaned and protected.

Mike Howlett

Thanks For the replies guys.

Belt and braces it is then, no pun intended!

As for the step sill on mine I would say it has disintegrated rather than rusted. It had been overplated and welded to the original floor pan.

Tony Brough


leave that castle rail in place whilst you replace the inner step, it'll help with the positioning and alignment. Once that's in remove a small bit of the castle at the front and do the repairs to the bulkhead, this is fixed to the inner step before the castle goes on. When you refit the castle you'll need to replace the outer few inches of the cross member.
Last to go in is the floor but also use it as a temporary guide for positioning the step sill.

Best of...
M McAndrew

This thread was discussed between 04/12/2014 and 05/12/2014

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