RangeRovers.net Forum banner

1 - 13 of 13 Posts

·
Registered
1995-2002 Range Rover P38A
Joined
·
41 Posts
Discussion Starter #1
Hi all,
I’m soon starting the build "proper" of a P38 six wheel camper conversion, and I need some technical ABS assistance if possible.

It’s a UK build from a UK car – we’re looking at petrol HSE or diesel DHSE as the base vehicle, age as yet undefined.

In the UK, I have to satisfy VOSA and the DVLA – these are the 2 primary governing bodies who have to be entirely happy for the end result to be road legal. It’s taken months of conversation with both parties, and progress has finally been made so I can commit to the build. This is not my 1[SUP]st[/SUP] 6 wheeler, but it’s the 1[SUP]st[/SUP] attempt with a P38. Critically, the build has to happen 1[SUP]st[/SUP], and only then will the vehicle be accepted or otherwise as fit for road use – consequently its essential to get everything right before I start!

The modifications are loosely based on the Land Rover conversion of the RR Classic (commonly known as the TACR2, but there were other variants)

The 3[SUP]rd[/SUP] axle will be a P38 standard rear axle, standard suspension linkage and retaining the EAS – the axle will not be driven, it’s there to partly take the extra weight, but primarily to take the extra length - the mechanics of the chassis stretch and axle fitment etc. are now set, with all parties happy.

The EAS for the 3[SUP]rd[/SUP] axle will be piggy backed off the middle axle, and rely on the middle axle ride height sensors for height setting – there will be an extra tank and independent pump to accommodate the extra bags….so far so good.

However, I would like advice on braking the axle – obviously the original 2 axles are braked through the ABS system, and I now need to work out how to tap into this system. I’m pretty certain that I cannot have this axle under ABS control. On my Range Rover Classic 6 wheel TACR2, this was done by tapping into the original rear axle line, and adding a pressure reducing valve. The master cylinder was also changed to a larger one so enough fluid could be pushed through the system. This was not my system, but how Carmichael did it for all TACR2 conversions, however, the entire system was simple, and there was no ABS in place.

When this conversion is finished, I will have to demonstrate “adequate braking efficiency” on the 3[SUP]rd[/SUP] axle via a rolling road test at a DVLA inspectorate, so I need to be sure if I tap into the ABS system and run it through un-measured wheels we don’t get problems, lock up, poor braking etc. I’ve also got to be sure there’s no detrimental effect on the 1[SUP]st[/SUP] and 2[SUP]nd[/SUP] axle…..

…..any ideas/advice appreciated!
 

·
Super Moderator
Joined
·
2,071 Posts
The rear brakes are fed from the ABS powered circuit and there is already a pressure reducing valve in the circuit. I would have thought that simply running the 3rd axle calipers in parallel with the 2nd axle should be acceptable. An oversized master cylinder or reservoir shouldn't be needed. Of course this is only theory but being well aware of how the standard braking system works I can't see it being a problem. What might be a problem however is the ABS and Traction Control. As the 3rd axle won't have the sensors (or if it does I've no idea how you would connect them into the system), if the ABS operates when needed on a wheel on the 2nd axle so the brake is released to stop the wheel from locking, it will also release on the 3rd axle. ABS won't work on the 3rd axle as there is nothing to show that a wheel has locked. The traction control applies a brake if it detects a wheel spinning faster than the other one on the same axle, so again, it will apply the brakes on both rear axles and not just the one that has lost traction. I suspect in practice, with the 3rd axle not being driven, this shouldn't cause a problem but worth mentioning.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
41 Posts
Discussion Starter #3
Cheers Richard, appreciated.
I'm with you regarding the braking and how it will impact the non-ABS 3rd axle. Interesting note regarding the pressure, thanks for that.
The traction on the other hand is more challenging - to my understanding the system interacts with the EAS and will inflate on the wheel without grip - what impact this will have in the real world I'm not sure.

Cheers
 

·
Super Moderator
Joined
·
2,071 Posts
No, the only time the EAS does anything is if the car gets beached on the diffs so the wheels are dangling, then it raises all four corners up to an extra high extended mode (that can't be selected manually) to lift it up and allow the wheels to gain traction again. So that scenario is still going to work as intended. The Traction control solely uses the brakes. If one wheel starts to spin faster than the other on the same axle (detected by the ABS system sensors) the brake on that wheel is applied gently to slow it to the same speed as the other. That's why the P38 is so good off road without the need for locking diffs, by braking the wheel without traction, all power is transferred to the other wheel.

Presumably you will need to take it for an IVA test once completed? For the purposes of the test the Traction Control isn't relevant, it is only the braking that they will be interested in. They won't be able to test the 1st and 2nd axles on the rolling road tester, only the 3rd, so as long as the brakes are being applied and the 3rd axle doesn't lock up before the other two, I can't see it being a problem. I've taken a couple of imported 4x4s into the Norwich IVA test centre and all they did was use the deccelerometer in the passenger footwell to check braking performance as they only have a two wheel rolling road brake tester (really nice guy at the Norwich test centre too).
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
41 Posts
Discussion Starter #6
Hi Richard,

The DVLA have informed me that the IVA test is not applicable here - this was the first bog point which threw me and stalled the project for quite a while, as an IVA would be fairly onerous on such an old vehicle.

However, the DVLA are quite specific as to what the IVA scheme applies to, and campers are not considered - I'm not sure if the same applies if the car wasn't being converted to a camper at the same time as having its extra axle (so a pick up for example) but they have made it quite clear - this is a modification of a vehicle to a camper, and is IVA exempt, despite the addition of the extra axle.

What I will have to do is provide documentation (receipts and a cover letter explaining the work) and photographs, and ensure the vehicle is road worthy.
The DVLA will inspect the vehicle to ensure the work is of adequate quality, and inspect the vehicle and receipts to ensure no parts sourced are from stolen or cat A scrapped vehicles - it's then submitted for an MOT test (based on the age of the original vehicle) and if all is well, the V5 will be changed to read "3 axle rigid body" and the taxation class changed to "camper"

I reckon we have it cracked now - thanks for the advice :thumb:
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
1,408 Posts
Some pictures would be nice as this project progresses.

`)
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
41 Posts
Discussion Starter #8
Hi Dave,

I'll pop some stuff on here of course, but you can also follow the project in detail on my blog at www.ois4x4.co.uk - hopefully we'll be on our way mid this year, look out for a new tab in due course ;-) - for now the blog is all about my off roader and its mods.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
359 Posts
Didn't read everything.

Wouldn't it be handy if you can take the pressure off the airbags of the non driven axle.
If you can do this you get more grip on non hard surface, if your non driven axle is on operating pressure it takes the load of the driven axle and you can loose a lot of grip.

Trucks with double rear axles can do this quite often too.
 

·
Super Moderator
Joined
·
2,071 Posts
Surely the idea of the third axle is to spread the load between the two on the rear and prevent the existing one being overloaded? Take the pressure off it and it may as well not be there. Trucks do it when they are towing an unladen trailer (mainly to stop the tyres from being scrubbed when turning) but a camper conversion is always going to have the same, or very similar, weight on it which is why it needs the third axle in the first place.
 

·
Premium Member
Joined
·
1,332 Posts
I agree with Reinhoud. When offroading, you could find yourself in a position where the non driven rear axle takes the bulk of the weight, for example when crossing a ditch. Possibly resulting in not enough load on the middle axle to provide sufficient traction. Low traction situations are also low speed, so there is little risk of overloading. Just like in trucks, a 6x2 will usually lift it's third axle when leaving the tarmac, regardless of load, to decrease rolling resistance and increase traction.
 

·
Super Moderator
Joined
·
2,071 Posts
I agree in the circumstances you mention but who would build a camper van then try offroading it? Driving over a grass campsite maybe, but it isn't the sort of thing you are going to start crossing ditches in. Even then, it's a P38 with 4 wheel drive so even if the rears start to lose traction, it's still got the fronts to do the business.
 
1 - 13 of 13 Posts
Top