Modified de Dion axle in the UK

[Jacobsmess]

TLDR; has anyone modified their rear axle to be a de Dion axle in the UK and what legal implications did it have?

In planning my conversion I'm considering modifying my rear axle in order to use a transaxle setup (likely a leaf).

My vehicle is a large van and given size and lack of aerodynamics I really think going for the most efficient approach would be the best approach.

My plan is to buy an identical solid rear axle to what I already have, weld on a U-shape for the de Dion, cut the diff out from the axle and then add disc brakes in place of the original drums (potentially adding air assist bags to the leaf spring setup also).
The motor would then mount at the back in place of the diff, using modified drive shafts and CV joint to connect to the wheels, with half the drive shaft housed in the axle on bearings.

[tom91]

What is the age of the vehicle?

[Jacobsmess]

What is the age of the vehicle?

1993

[Aragorn]

My understanding, is that so long as you dont modify the chassis itself, your fine.

So fitting a different axle to the existing chassis hardpoints would be okay.

I dont think the regulations particularly care what you fit there. If you built a bolt in IRS subframe that attached to the existing hardpoints that would be totally fine for instance (assuming such a thing could be constructed). The difficult part might be constructing such an axle in a manner which is strong enough to take the loading of a large van.

The vagueness starts to creep in when you have to modify the chassis to fit the changes you've made. The DVLA recently have been responding in a somewhat combative manner to even very minor changes to the chassis. See the case of the Mini where they revoked its V5/identity due to some holes drilled in the boot floor for cable glands...

Previous guidance suggested that welding things to the chassis was fine, so long as you didnt weaken its structure. So for example welding in a chassis strengthening kit on a rally car was fine. As was welding in new engine mounts to accommodate a different engine. However with the recent attitude its somewhat of a crapshoot. Mix in their refusal to recategorise cars built between 2001 and 2017 makes things even more awkward.

So taking your example, I dont think they would really care about the De Dion axle itself so long as it was sat on the original leaf springs etc. However they could perhaps take offence to the fact you've welded mounts to the chassis to mount the motor under there.

[muehlpower]

I don't know anything about UK regulations, but I can imagine that you have better chances if you fit parts from another car. One possibility would be the axis of an Opel Diplomat!
I personally made a De Dion axle out of Mercedes trailing arms for my car. I also use the Mercedes brakes and drive shafts.

[Jacobsmess]

My understanding, is that so long as you dont modify the chassis itself, your fine.

So fitting a different axle to the existing chassis hardpoints would be okay.

I dont think the regulations particularly care what you fit there. If you built a bolt in IRS subframe that attached to the existing hardpoints that would be totally fine for instance (assuming such a thing could be constructed). The difficult part might be constructing such an axle in a manner which is strong enough to take the loading of a large van.

The vagueness starts to creep in when you have to modify the chassis to fit the changes you've made. The DVLA recently have been responding in a somewhat combative manner to even very minor changes to the chassis. See the case of the Mini where they revoked its V5/identity due to some holes drilled in the boot floor for cable glands...

Previous guidance suggested that welding things to the chassis was fine, so long as you didnt weaken its structure. So for example welding in a chassis strengthening kit on a rally car was fine. As was welding in new engine mounts to accommodate a different engine. However with the recent attitude its somewhat of a crapshoot. Mix in their refusal to recategorise cars built between 2001 and 2017 makes things even more awkward.

So taking your example, I dont think they would really care about the De Dion axle itself so long as it was sat on the original leaf springs etc. However they could perhaps take offence to the fact you've welded mounts to the chassis to mount the motor under there.

Ok, I'm away from the van but think I could probably add mounts to the unibody floor with spreader plates on the inner side alongside reusing old exhaust mounting and other bits. Fortunately my MOT station don't seem too fussed by my approaches so far....

[Jacobsmess]

I don't know anything about UK regulations, but I can imagine that you have better chances if you fit parts from another car. One possibility would be the axis of an Opel Diplomat!
I personally made a De Dion axle out of Mercedes trailing arms for my car. I also use the Mercedes brakes and drive shafts.

Diplo.png

I was thinking about that but it may be difficult to find something.

[muehlpower]

Mercedes is easy to find.

https://www.ebay.de/itm/285397074812?ep ... R6COzZy7Yg

I think cutting up a rigid axle is a bad idea. The semi-axles have bearings on the outside and are supported on the differential. Converting the wheel bearings so that it works and making a connection to the drive shaft is a huge effort.

[Aragorn]

Ok, I'm away from the van but think I could probably add mounts to the unibody floor with spreader plates on the inner side alongside reusing old exhaust mounting and other bits. Fortunately my MOT station don't seem too fussed by my approaches so far....

The MOT wont actually care even if you wildly modify the chassis. As long as everything looks properly attached and not obviously dangerous you'll pass an MOT.

The problem is that when you tell the DVLA you've converted it to electric, they will send out an inspector. Its them that can cause all the hassles.

[Jacobsmess]

The MOT wont actually care even if you wildly modify the chassis. As long as everything looks properly attached and not obviously dangerous you'll pass an MOT.

The problem is that when you tell the DVLA you've converted it to electric, they will send out an inspector. Its them that can cause all the hassles.

Ok that's good to know and interesting, I guess if you make it look OEM and/or take before and after pictures of any existing drain holes and their re-use as threaded points there wouldn't be an issue .... However that may be applying logic to a system devoid of it.

[Jacobsmess]

After looking for vehicles with matching PCDs and rear disc brakes with an axle that may be able to be swapped I've come across the VW Touareg (maybe the Audi Q8 also). An E-tron also seems to fit which might help with motor mounting....

Anyway, these are all rear subframes, would they be a suitable option for modification/swapping do you think?

I suspect not for a swap but modification potentially... Tracking width is also within 20mm which is nice.... I just need to work out how to add the leaf spring/dampener mounts.

They are also very cheap which is good.

Touareg

Etron rear axle (expensive)

[muehlpower]

I first fixed the two individual parts with a pipe and a threaded rod. This ensures that the wheels are straight afterwards and that the track width is correct. I also changed the attachment for the air spring, it would look different with a leaf spring. The welded tube has a diameter of 89mm and a wall thickness of 4mm.