AWD Transmission: convert my xc90 to 2wd?

[RoyMacDonald]

Originally Posted by Tannaton

I've just re-read this thread. To the OP zakmuh - why do you want to convert your XC90 to 2WD anyway? I don't think you have ever said?

As we have covered this would compromise some of the safety features on the car. Although it may be the case that the chances of this causing an accident are small - these are the days when police can download data from airbag and other systems on cars to establish speed of impact etc. - a missing rear differential and a large hole where is used to be would be obvious. The risk may be small but the consequences could be life changing for you and others.

He ignored an oil leak thinking it was from the Haldex but in fact it was the diff it overheated and the rear axel seized and took out the rear axel and Haldex!!

[RoyMacDonald]

Originally Posted by Tannaton

I *think* he will get away with it on the MOT, it covers the ABS and/or ESC system warning lamps only - not any messages shown on the dash. Technically it could be failed as parts of the ESC system have been removed, but 99% of testers are not likely to pick that up.

Thanks. It made me wonder so I looked it up and the MOT web site says...

Reasons for failure....

Brakes – Warning indicators
Electronic parking Brake (EPB) warning device must not be indicating a malfunction
ESC warning lamp must be present, working and not indicating a fault
ESC Switch must not be insecure or faulty
A brake fluid warnimg lamp must not be inoperative or illuminated
Class (v): Electronic braking system (EBS) warning device must not be inoperative or indicating a fault
ABS and ESC components and associated wiring/switch checked for presence and condition



Anti-Lock Braking (ABS) and Electronic Stability Control (ESC) Systems – Warning Indicator


Warning Lamp
Missing
Does not illuminate
Indicates a fault
(For ABS) does not follow the correct sequence

18 Will expensive repairs force vehicles to be scrapped?
The new MOT test may identify defects in complex systems that will be expensive to repair (e.g. faulty electronic control units) to allow an MOT test pass. But it must be remembered that if a vehicle has a defect in a safety or environmental system then the law requires that it is rectified if it is to be used on the UK’s road network. The new MOT items do not change that requirement but obviously motorists will no longer be able to ignore defects that could compromise safety.

• Electronic Stability Control (ESC) components, including the switch (if fitted) and malfunction warning
• Brake fluid warning lamp illuminated or inoperative
• Tyre Pressure Monitoring Systems (TPMS)
• SRS components including airbags, seat belt pre-tensioners, seat belt load limiters and SRS malfunction warning lamp
• Engine mountings
• Speedometer
• Indirect vision devices (where they replace obligatory mirrors)

Even though it may not count towards an MOT failure it could still be an offence under other road laws and result in a fine and penalty points on your driving licence. It is unlawful to drive a vehicle knowing it to be faulty and it may create insurance issues in the event of an accident if any known defects are considered contributory to the cause or extent of the accident.

I'm inclined to think the car is not longer safe myself because it is not running the correct software for the car to run as an AWD and does not know it is now FWD as others have said. In theory it should be a fail as vital components for the cars electronic stability control (ESC) have been removed.

[SwissXC90]

Having read through all these posts here's my feedback from an engineering perspective:

FORGET IT

Reasons:
The vehicle was manufactured as an AWD vehicle
The Volvo database records it as AWD, all fitted hardware and software and configurations are for AWD

Disabling the rear axle drive and attempting to convert to FWD is fraught with problems

• The vehicle config will no longer be the same as manufactured, and comparisions with the central Volvo config database will be problematic
• Any connections to a Volvo software config and updating device will be problematic, as the Volvo software will consider the vehicle AWD and always load and configure for AWD. The Volvo software cannot load FWD software, as the vehicle is recorded as an AWD vehicle.- All part numbers and software numbers fitted are for AWD.
• Any future software updates may override and delete any custom configuration
• Any repair of the vehicle may cause any custom software changes to be overwritten as the standard config will be loaded if the repaired decides to update the software
• Safety features of the vehicle will be comprimsed. STC, DSTC, Rolloverprotection, ABS etc all are based on a normal functioning AWD vehicle, where all wheels rotate and all wheels can be driven.
• Deliberately incurring hardware faults such as removing rear drive and attempting to reconfigure vehicle and software as FWD will cause problems. What those problems will be can only be determined after attempting any such conversion
• In some countries (mine for instance) this would be an instant vehicle testing and compliance (MOT) failure, as the vehicle no longer complies with it's country specific homologation and it's critical safety systems are comprimised. This point alone should be sufficient to defer any backyard mechanic from attempting such changes.

In the long run it is better to fix the original problem and retain the AWD functionality.

The only place such a configuration change would be anywhere near acceptable is anywhere where the vehicle is being used off public roads and is not subject to homologation rules. This means rallying, racing, hill trials etc, stuff like this: https://www.youtube.com/watch?v=KCMtVawd_Vo (also known as the my turbo is bigger than yours beauty contest , and the right place to get the answer to which four wheel drive system is the most reliable when you throw 1000 hp at it? )

[RoyMacDonald]

Originally Posted by xc90fubar

There's no 'kit' involved - it's simply removal of mechanical items.

The ABS is certainly working, I have tried it. The stability control possibly is not, and the collective views on informing insurers are probably correct and I admit it's something I hadn't thought of - I will contact them.

On balance though, I can't see how the car is that far removed from the 2wd version they make in the States - it hasn't suddenly become some top heavy out of control death trap overnight..! I have driven it fairly hard in both it's previous 4wd state and also since it was made 2wd and I can't say I notice any difference other than as mentioned, pulling out of junctions.

I did get a value from WBAC and it was for £11K. The cost to repair the car to manufacture spec for me to be able to sell it was £7K. In effect I would have got £4K back for an otherwise immaculate 1 owner full volvo history car...!

For £700 conversion cost I have now a 100,000 mile non 4x4 big estate car, albeit as you guys point out some issues still to be resolved. I am in contact with some breakers and if I find the parts required to put it back to it's original spec at reasonable cost I may well do so - certainly before I need the car next Winter for the annual ski trip. Now the car is back on the road I will probably keep it and run it into the ground.

And yes Roy, you are right I have learned a major lesson as regards the oil leak, but if you read my original post pulling the Haldex fuse was done on main dealer advice..!

Going on the information supplied by the garage that carried out the conversion, it's not the first time an XC90 has been converted to 2wd in view of cost prohibitive/uneconomical repair to the 4wd system. In fact they are considering whether putting the 2wd USA spec map onto the ecu would restore the stability systems as the car would no longer be looking for the 4wd unit. It's not as if Volvo don't themselves market a 2wd system mainly in the States and knowing how litigious the Americans are Volvo must consider that 2wd is sufficiently safe in that application.

Cheers,

Fubar

Just to update on the thinking behind the conversion. Personally I think that the best course of action would have been to get the necessary parts from a breakers. There must be plenty of the correct parts around because they are ones that normally never go wrong and last longer than the vehicle. That should reduce the cost to a fraction of the £7k repair cost.

The other alternative is to source FWD parts from breakers on the continent and convert that way if it is possible. I think it is vital to be able to run the FWD software on the converted vehicle though. The biggest problem is that VIDA is set up not to allow parts to be transferred from vehicle to vehicle unless it is done officially for security reasons. I suspect that there is no software in VIDA that will allow it to be done. Volvo can remove and add modules from car to car but will they allow a AWD to FWD conversion bearing in mind all the pitfalls of type approval?

Easiest route in my mind is get the correct parts from a breaker and fix the car properly.

[zakmuh]

Originally Posted by Tannaton

To the OP zakmuh - why do you want to convert your XC90 to 2WD anyway? I don't think you have ever said?

The model Im looking at buying is a 2003/2004 one. As you all know the AWD system is pretty knackered in these models. So I was thinking about this conversion option to make things easy.

I appreciate your advice on this everyone. I think I should give up the idea of doing this conversion and buy a one which has a good repair history, including gearbox and transfer box repair.

Cheers

[Tannaton]

Originally Posted by zakmuh

The model Im looking at buying is a 2003/2004 one. As you all know the AWD system is pretty knackered in these models. So I was thinking about this conversion option to make things easy.

I appreciate your advice on this everyone. I think I should give up the idea of doing this conversion and buy a one which has a good repair history, including gearbox and transfer box repair.

Cheers

...but the AWD system isn't knackered on all these models. There is a vulnerability in the splined sleeve on the earlier cars, but once that's fixed you should be okay. When I looked for my XC90 I think 2 in 5 had failed AWD, the others were okay. Just keep looking until you find a suitable car that has working AWD and you should be fine. It's the same for XC70 owners too.

Fixing an XC90 with failed AWD is probably way cheaper and easier than trying to convert to 2WD.

[RoyMacDonald]

Originally Posted by zakmuh

The model Im looking at buying is a 2003/2004 one. As you all know the AWD system is pretty knackered in these models. So I was thinking about this conversion option to make things easy.

I appreciate your advice on this everyone. I think I should give up the idea of doing this conversion and buy a one which has a good repair history, including gearbox and transfer box repair.

Cheers

Well mine is still OK after over 13 years. There are XC90's of that date with over 250k on the clock on the forum with the AWD still working well. Just needs looking after like any other component.

[zakmuh]

Yup, I'll hunt for a one with a sound breabox + AWD