Page created: 3-Dec-05

Re-published: 1-Nov-09

A little while ago I discovered that the boot floor of my Discovery had succumbed to rust, which is, unfortunately, a relatively common problem on models of this age. The problem stems from rain getting inside, either from around the alpine light seals or through badly made gutter joints, running down behind the trim where it can't be seen and collecting under the sound proofing insulation where it's held against the steel floor. The way I discovered it was that I climbed in the back and felt a crunch under my knee and a quick look under the carpet revealed the worst - a series of rust spots matching the line of spot welds to the under-floor bracing, particularly bad towards the rear where a number of holes had appeared.

The rust was too bad to repair but fortunately the main boot floor is available as a complete repair panel, which I bought from MPS 4x4 Store. It should be noted that it's only practical to replace this panel if the rust hasn't reached the sides or wheel arches. Otherwise it becomes a much more complicated repair that will require some welding. Similarly, in my case the cross braces beneath the floor were all in good condition but if these are rotten then they too must be welded in place. All are available as repair parts.

The original floor is spot welded around the perimeter to the rest of the body and across to the series of braces that run underneath. To remove it, it's necessary to drill out all the spot welds - about 130 of them! - so I bought a set of Draper spot weld cutters for this task. These cutters, which come in a set of two sizes as shown, comprise a spring loaded steel point and a double ended cutter that's threaded onto the end of a shaft. Although they are two slightly different sizes, I ended up using both ends of both cutters as the teeth wore out quite quickly, and I only just managed to drill out all of the welds before they were completed worn. Also, despite having already diligently centre-punched the centers of the welds, in the end I found it easier to go around and drill a 2mm pilot hole right through each one to prevent the cutters from wandering too much. Despite this minor niggle, they made a very neat job of separating the welds and the old floor was easily removed with the aid of a large screwdriver to pry it loose.

The seat belt mountings on the other hand, which bolt both to the floor and through to the chassis via rubber bushes, needed a bit of persuasion with an angle grinder, as did the screws securing the fuel tank inspection plate! Eventually, we cut out the section of the old floor to which one of the seat belt mounts was fixed so it could be worked on in a vice, hence the rectangular hole shown in the picture below left. The grinder, in the hands of my friend Steve, was also employed to dress the remains of all the spot welds.

Although not strictly necessary as long as you're careful with the drill, as part of the job I removed the fuel tank, both to make access easier and to enable me to paint all of those bits of chassis and body structure that it's not normally possible to reach. After cleaning and wire brushing, I first applied a zinc rich primer called Unidox and then an enamel top coat called Supercote, both sourced from Witham Oil & Paint Ltd. 

In the pictures below the fuel flow and return lines can be seen wrapped in a polythene bag to protect them from dirt. During the course of the work this bag had to be periodically replaced as the diesel eventually ate its' way through the plastic!

As well as  the chassis, I also painted the new floor panel, which arrived with only a primer finish, the fuel tank support plate and the seat belt mounting brackets in the same way.

In addition to these parts, there is also a small bracket spot welded to the underside of the floor that supports the wiring to the fuel tank sender (shown alongside seat belt brackets, left). This was also carefully cut off and painted ready for re-use.

When re-fitting the seat belt mounting brackets, it was my original intention to use small stainless steel nuts and bolts. However, I soon found that these fouled the seat belt brackets themselves so I had to resort to pop rivets as used originally. The previously spot welded wiring bracket was also pop riveted in place.

It was now time to fit the new floor panel. I have no welding skills to speak of but some research had shown that it was possible to fit the floor with pop rivets, so I bought a box of 4.8mm dia. x 10mm long multi-grip rivets with an extra wide head to spread the load more effectively. In the event these were only just long enough - 12 or even 15mm would have been better - but at the time I wasn't sure how much clearance there was underneath.

The newly painted floor panel was carefully masked up and a series of 2mm pilot holes were drilled around the edge and across where the braces were positioned. The floor was then laid in position and the pilot holes drilled through the supporting structure. With the floor removed again, all of these holes, about 100 in total, were then opened up to 5mm for the rivets. Very tedious.

After a liberal application of black guttering mastic to the perimeter bodywork, the floor was again laid in place. Because of the awkward size of the panel and the large quantities of mastic everywhere, two timber rails were used to slide the panel into place and a temporary 'handle' made of wire was employed to do the final positioning. Then the task of fitting all of the pop rivets began. In fact, I was surprised how well my Draper hand riveter coped with this, given the size of the rivets, and it didn't take long before the floor was very secure. The only slight snag I had was that, due probably to the mastic, the panel was a very tight fit at the front edge. So much so that I couldn't get it flat enough to make my slightly too short pop rivets bite. I eventually resorted to fitting two 5mm stainless steel nuts and bolts in the centre of the front edge that were used to draw the panel down flush.

Once the floor was fitted, I sprayed waxoil over the underside of the new panel and in all of the nooks and crannies of the body and chassis that I could reach. After that it was just a case of re-fitting the fuel tank, tank guard, bumper and various bits of trim, the procedure for which as the saying goes, was the reverse of removal!