Renew a corroded dumb iron

Need to know

Time: 8 hours
Cost: £75 plus consumables
Difficulty: 4 out of 5
Models: Series models.
Tools needed: Tape measure, marker pen, angle grinder, cutting discs and grinding discs, drill and drill bits, axle stands and jack.
Work safely:
• When using an angle grinder always wear gloves (preferably cut-proof), ear protection and goggles but ideally a clear face visor. Check cutting discs for chips or fractures before use and always operate the grinder so it won’t kick back towards you if it grabs.
• Suitable protection must be worn when welding. Long sleeves and heat-resistant gloves, ideally fire-retardant clothing or similar, such as a welding jacket. Always wear a welding helmet/visor.
• Be careful of stray sparks and flammable materials.
• When working underneath a vehicle, always make sure it is securely supported on suitable stands (never rely on a jack). Make sure all axle stands and jacks are on a solid, flat, even surface, safety pins in the axle stands and stands positioned under a safe and structurally sound location.

Rust in a Land Rover chassis is not always as obvious as it may seem. Even the most solid chassis will be hiding rust somewhere – it’s just down to the nature of the design and the age these vehicles have reached. Now, with the ready availability of a reproduction chassis it’s all too easy just to write-off an otherwise sound chassis because of a repairable amount of corrosion.

This Series I has been in our workshop for a couple of months, undergoing a recommissioning, an engine re-build and a few other jobs to get it back to a roadworthy and safe condition. As with any vehicle in our workshop for re-commissioning, our approach is always to make the vehicle completely safe and up to and beyond MoT standards, not just get it running and driveable. Upon inspecting the chassis on this car, it had received a few patches and repairs in its time, but was visibly very sound and the repairs had been completed to an adequate level for ‘in service’ repair work.

Hidden corrosion

Rust on Land Rovers, however, has a way of hiding and even if the chassis appears visually good, chances are there’s something hidden.

In this instance the corrosion showed itself after we removed the bumper, having attacked the square cap to the end of the front dumb iron, which is a typical water and mud trap. As we poked away at the corrosion, more and more damage was revealed, resulting in the need to replace the entire dumb iron.

Choose with care

There are a few different suppliers of chassis repair components, but my recommendation would be to purchase your parts from reputable suppliers, and preferably from people who also make a full chassis. There are plenty of decent suppliers of solely repair sections, you just have to be a little more cautious in our experience. There a few suppliers of budget chassis repair sections and these typically are not fabricated out of steel anywhere near the original thickness, and the dimensional accuracy of these components can also be off. Even repair sections from time-served suppliers and manufacturers can be different to original, but are usually closer than most. Make sure, too, that you have ordered the correct dumb iron for your vehicle as there are changes between models and years. The key, especially with something like a dumb iron replacement where suspension is involved, is to take plenty of time to set-up, measure and to double-check everything and then slowly and methodically work your way through the repair.

Clear access: Firstly, I recommend removing as much bodywork as you can around the area, in this instance the radiator/front panel and wing panel was removed from the vehicle, along with the wheel on the relevant side. Whilst you will be able to make this repair around body work, it will massively increase the difficulty.

Safe support: I then jacked the vehicle up, placed axle stands under the chassis, letting the suspension drop freely. Leaving three wheels still on the vehicle, one axle stand behind the spring (on the side I will be repairing) and one under the front crossmember, makes sure the vehicle is safe to work under. With the front spring bolts removed and in this case, the brake hoses too, the front axle can then be dropped down, allowing plenty of room around the dumb iron.

Seriously weakened: Hidden by the front bumper, the corrosion didn’t look like more than a simple repair at first glance. However, further inspection and testing proved otherwise.

Accuracy: Measurements are key in this instance: get them wrong and the characteristics of the vehicle can be massively altered. On a leaf sprung vehicle, much of the steering geometry is dictated by the dumb iron, so being as close to original as possible in this repair is key. Note chassis weight is supported on two stands – one not visible – with jack left in position.

Keep a record: Take photos of the measurements and their relevant components to keep a record. You can compare these to the other side of the chassis but only do this if you are sure it hasn’t been previously repaired or suffered accident damage. If you’re not sure, some dimensions can be found in the workshop manuals.

Essential jigging: Before removing the dumb iron, I made a simple jig, just to help with the alignment and the re- welding of the repair section. I cut a bar equal to the exact distance between the two dumb irons. I then welded two tabs onto the top of the bar to clamp onto the dumb irons (all done whilst the bar was clamped to the chassis). This will aid getting the correct dimensions and levels.

Marking out: With a chassis repair, it is always best to avoid perfectly vertical joins, and to try to make the length of the joint as long as possible. Mark out the cut lines appropriately to your circumstances, but also remember that you have to mimic these cut lines accurately onto your repair section.

Cutting back: Remove as little of the original chassis as possible, but obviously be sure you have cut out all of the corroded and thin sections of steel. With all corrosion being inside the spring mount and in the front off the leg, it wasn’t necessary to cut back right to the front crossmember.

Trim to suit: With the dumb iron cut off, I then marked out and cut the replacement section, allowing a little extra material in case the measurements were slightly off, and also allowing for the thickness of the cutting disc. You can always take more material off.

Inner strength: I will be grinding the face of the welds down when the repair section is finally welded into the chassis. For strength, this is not ideal, though it is necessary in order to make it look correct. So here, I am ‘sleeving’ the inside of the chassis rail, which is a good way of adding lots of strength into the join, and it helps with the alignment.

Weld penetration: Each side of the sleeve has been cut, and several holes have been drilled through the chassis in order to rosette-weld the sleeve pieces to the chassis leg. Make sure the welds are properly penetrating the sleeve material.

Geometry check: With all four faces sleeved, I then moved onto double-checking the fitment of the repair section onto the chassis rail. This is done using the jig I made at the start, and a piece of rod (the same size as the spring mount holes) passed through both dumb irons. This is not the final fitment, but I want to make sure that everything is dimensionally correct and parallel, all whilst having as little gap as possible between the new and old metal, in order to make the best weld possible.

Tightening the fit: With the fitment checked, I then removed the repair section to drill it for spot-welding. Here, I’m cutting a screw thread into the sleeve material, which works well to improve fitment. By drilling through the sleeve material in a couple of places at the spot weld holes and then tapping them for a bolt, this allows temporary bolts to be fixed through the repair section into the sleeve to pull the two layers together. This ensures there is no air gap between the layers which could cause issues with the rosette welding.

Fully welded: With the rosette welds completed, you can fully seam weld the dumb iron to the chassis. With the sleeve material inside the chassis leg and everything still securely clamped in place, I turned the welder up hot and completed a full seam weld on each face.

Paint finish: Once cooled, you can then grind the welds flush and prep the area for paint, in this case blue to match the original colour of the chassis.

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