How to cure chassis rust

[James Doulton]

Answer: Screw a sheet of aluminium over the whole underside of the cockpit, covering the rust holes so that the MOT tester doesn't notice. Unfortunately, I wanted to fit my new seats, so I removed the panel only to find this...

and this ...

That'll be why it was sold without an MOT last year by the guy who had owned it for many years. Then some scoundrel got it MOT'ed a few weeks later and then sold it for over twice what he had paid for it.

[Adrian Southgate]

You will have to remove seat belt anchor bolts, roll bar main bolts, front footwell bolts or at least slacken them. They all stop the tub from flexing enough to get clearance. Welding anywhere near glassfibre is very iffy however if you could get enough clearance to insert a plumbers 'asbestos' square sheet between the rail and the tub that would dramatically reduce heat transferIf you can get one or two of those square sheets in place you may as well cut out the old rail and fit a new one.

[1midz0wwbl268]

He's in Bristol Steve,  is there  anyone thats in the area, or near enough to him to offer any help, i,m sure it would be more than welcome , i,m without any transport still, but if i had a car on the road i would offer to go down and do the welding for him , or if its during next winter James i might be able to help, if you have a  mig welding set.

[James Doulton]

It's raining here, so I have not gone out crawling under the car this morning. Looking at those pictures again, it looks like those diagonals are completely rotten and will probably need to be completely removed. Whilst thinking about it in the shower, I remembered a frame that I made up for my neighbour's van. It occurred to me that I could remove all of the current diagonal and angle iron and make up a separate frame to fit into that area instead. I can weld that up on my bench, paint it and treat it and then bolt it in place, simples! It'll end up heavier than the original but only a few kilos - I could save that by going on a diet! These diagonals cannot be important for the normal use of the car because, in effect, I haven't got them there now.

[Adrian Southgate]

That diagonal serves two purposes, cross brace for the seat support and a triangulation for the gearbox and rear suspension. That being said its thinner than the main rails too. I would imagine an X shape would produce more rigidity in the frame but also retain the mounting points for the seats.

Do your seat runners bolt directly to the floor pan James or do you have spacers?

The underside of mine is plastered in oil from a leak in the engine somewhere ages ago, consequently covered in dust and fairly cruddy. Hopefully well protected as I'm loathe to scrape it off now. :-(

[James Doulton]

The rain has stopped for a moment, so I went out and had a look. It looks like the rust was caused by the seat bolts, on both sides there is a small hole that is directly under the seat bolt, as well as the big jagged holes. Once the moisture gets in to the section there is no where for it to go so it ends up rusting more than the totally exposed bolts, and eating its way out.

[James Doulton]

After spending a couple of days sulking about this, flitting from one idea to another and planning how to take the body off and depressing myself, I have now decided on a different plan. I think that I will cut out a large rectangle in the floor on each side and replace the two diagonals from above. It shouldn't be too difficult to repair the floor afterwards and the floor isn't going to go anywhere as it will be supported by the new diagonals. I could chamfer/feather the edge on the top and use adhesive tape on the underneath to stop the resin from running through and then use strips of glass matting on the top to fill the chamfer - it won't matter if there is a little bulge under the carpet. Welding the stuff in from above should be fairly easy.

[Adrian Southgate]

You wouldn't need to cut that much out James, six inches at either end of the box should be enough clearance.

Martin's idea of cutting two holes means a lot less glassing up afterwards and if you use the 'dave adams' method and dissolve the resin out of the edges with acetone then you should be able to join them back up with very little 'bump' at all.

[1midz0wwbl268]

James,  it might be easier to replace the box section first , if i were having to do this i would cut out the corroded small box section first hold the new section  in place with woodern blocks fore and aft, tack both ends into place  from above and then remove the blocks weld fully, then tackle the L section  that way the chassis shouldnt get distorted or tend to twist  because my fear is that if you remove both the L,and box sections there is a lot of chassis without triangulation  then with the top expossed you can get to the seat mounting strips and  weld those in ,  you would have to remove localised areas of floor  at both ends and where the seat mounting weld to the crossmembers , but these only need to be small enough to enable you to weld 

[James Doulton]

Finally found both the time and the mental energy to do something about the car this evening. I have finally removed the drivers seat and the carpets ready to cut out the floor. One of the bolts on the seat was a tough job but when I had removed the exhaust I could get my angle grinder on it - it didn't last long then. I also struggled for half an hour with the door side seat belt bolt. I eventually beat it and got it out in one piece but my muscles ache now. Hopefully I will cut out the floor tomorrow but I might have to treat myself to a Bosch oscillating cutter first!

[Dave Adams]

i would weld "sill" strengthening sections in before cutting any steel out. (the ones usually required to stop the car sagging) Also i wouldn't  ponce about cutting pieces out if the whole box section is heavily corroded but replace the chassis sections as a single piece, less welding overall.

Also i would also tack weld some cross sections (to the new sill sections) onto the car before cutting away any of the chassis members, once you have replaced / repaired them remove the tacked on cross pieces,

[James Doulton]

Now you see it...

And now you don't...

It was really hard work to saw through the welds and it was difficult to get the full benefit of the angle grinder. I will still need to do quite a lot of grinding of the two ends to make sure that I have a good straight edge for the joins. Then I'm going to make up some 38mm square tube by welding two pieces of 35x35 angle together. It is 3mm thick, so it will be quite a bit heavier than the old stuff but it will look like it matches the rest of the frame.

I was really determined to get on with it this evening because I'm getting fed up with having to drive my tintop in this good weather. I just want to get this done so that I can get the seats in and then concentrate on the engine mods.

[James Doulton]

Nearly finished the driver's side. I made the box section out of 3mm thick angle iron. I am reasonably happy with the welds even though the underneath of the one at the front by the gearbox was difficult. I checked the welds when they were less than half done, using the club hammer method. I also had to add in two longitudinal strips because my new seats have 11" centres between their fixings. That meant cutting out more of the floor. I had a whole series of small fires while welding but they all just blew out - I didn't need my water bucket.