Crack in caravan chassis

Pasley69 · Newbie

Crack in caravan chassis

Peter_n_Margaret · Senior Member

You don't like the advice offered elsewhere?
Pretty much the same people here :)
Cheers,
Peter

dorian · Guru

Drill a hole at the end of the crack to relieve the stress and prevent the crack from propagating.

-- Edited by dorian on Friday 26th of January 2024 02:35:30 PM

Possum3 · Guru

It appears that the crack may be caused by initial welding of cross member support.

I also note chassis is hot dip galvanised so grinding off gal is needed to weld.

As the cabin floor is resting on the cracked beam it will be a difficult home welding repair.

Dorian's suggested method is probably superior to DIY welding.

erad · Guru

If the crack is in the top flange of the chassis, this is serious. The top flange is the most critical part of the chassis, and the fact it has cracked means that it is under severe tension at times.

Ideally, the caravan body should be removed prior to doing any work on the chassis. Drilling a hole at the end of the crack should relieve the stress concentration which caused the crack in the first place. However it is difficult to determine where the crack ends. The crack can be propagating further at microscopic levels, but hopefully drilling a 5 mm hole should relieve the stresses at the end of the crack.

I would be inclined to drill the hole at the end of the crack and continue to monitor it. If possible, find the crack in the top flange and drill it as well. Assuming that you are not going to go seriously off-road, monitoring this will give you an idea if the crack is still active. Once you are certain that the crack is stabilised, then you can paint the area with zinc-rich paint to prevent further corrosion.

You dont say how old the caravan is, but if it is relatively new, I would be inclined to go back to the manufacturer and see if you can claim a warranty.

Greg 1 · Guru

If you do decide to weld the chassis it will need to have some properly designed doubler plates sandwiching the rail otherwise the crack will just propergate again. The doublers will need to be designed correctly and not just as a rectangular plate otherwise you will just shift the problem further along the rail. It is an issue that you should seek some professional engineering advice on in my opinion.

Steel Dog · Veteran Member

I have repaired a few cracked chassis similar to this one, check my attached 'dodgy' drawing, if you take it to a welder or get an 'On-Site' welder to come to you they should be able to oxy cut and make the plates on site, they just need to bring, I suggest an 8mm mild steel plate, enough to make one for each side of the chassis rail.

Drill an 8mm hole at the end of the crack, as suggested by others and tell the welder to use Austarc 16TC welding electrodes as they are 'Low Hydrogen' and are suitable to weld over galvanised steel, however it's best to grind off as much gal as possible before welding.

The drawing:
Red is the drill hole.
Yellow is the steel slotted and notched plate.
Blue are the welds (overhead welding).
Note: DO NOT WELD VERTICAL ONLY WELD HORIZONTAL (OVERHEAD) ALSO DO NOT WELD ACROSS THE CHASSIS RAIL as this weakens it.

Hope this helps.

Cassie63 · Senior Member

I had good experience with GP 6012 electrodes. Just grind the gal off back to metal and when finished a good coat of rust proofing.