2008 XC90D5 Much beter fuel consumption with no propshaft

Hiltonindurbs · Post by **Hiltonindurbs** » 31 Aug 2015, 14:21

Hi
My 2008 D5 AWD ( 178000 km )has a noisy diff/ Haldex and while hunting for a good used replacement I have been driving in 2WD ( Propshaft removed) to avoid further damage. Apart from the fact that all the noise has gone and she is beautifully smooth, the fuel consumption has improved from an average of 20 mpg to 24.9 mpg. How is this possible ??

I have one theory. The front tyres were replaced about 6 months ago , the rear were still good so not replaced.( All 4 Pirelli Scorpions with same pattern). However this caused a slight difference in diameter. Is it possible that this slight difference has caused the front and back wheels to fight each other, damage the diff and / or Haldex and burn extra fuel ?
Has anybody else had a similar experience ? I would love to hear some expert opinion on this.
Thanks

Post by **gstallons** » 31 Aug 2015, 17:10

Did this noise come before or after you did this ?
It is a poor decision to not replace all 4 tires at the same time & keep a documented tire rotation . You can measure the circumference of the new/old tires ( off the ground ) and decide what is right .

Hiltonindurbs · Post by **Hiltonindurbs** » 01 Sep 2015, 09:20

The noise started some time after fitting the new tyres. It started as a slight whine, and slowly over months developed into a wheel bearing going type sound. At the last service I asked the agents to check it out. Wow !! Bad idea. They wanted to replace the diff and propshaft for stupid money. When asked why both, the w/s manager says ; because we can't quite tell where the noise is coming from. Volvo does'nt repair anything , we just replace.

I did look into whether it was advisable to replace only 2 tyres on this car, and the advise I was given was; no problem. In hind sight , not such good advise it seems. I have since discussed this with various people who have AWD vehicles and some say it does not matter, others say always replace all 4 at the same time.
The car now has 4 new tyres .
What really is puzzling is the drop in fuel consumption.

Post by **gstallons** » 02 Sep 2015, 02:59

You took poor advice . Period . Now that you replaced the tires , have you reinstalled the driveshaft ?
The result of the poor decision is the Haldex unit is now worn out .

Post by **Homebrand** » 02 Sep 2015, 18:00

Hiltonindurbs wrote: What really is puzzling is the drop in fuel consumption.

Sending power to all 4 wheels requires more energy, hence greater fuel consumption.

Post by **precopster** » 02 Sep 2015, 19:08

The later Haldex units are far more forgiving and tolerant to tyre circumference variance than 98-02 units (which are not made by Haldex at all, excluding 2002 AWD S60s)

Put it down to wear and tear and perhaps lack of fresh lubrication, disassembly of the coupler and greasing of the splines maintenance.

Make certain that the replacement Haldex has fresh correct spec oil and fresh grease on the coupling splines.

Hiltonindurbs · Post by **Hiltonindurbs** » 03 Sep 2015, 09:19

Thanks for the responses. The Propshaft is still off. I jacked up one rear wheel and spun it . The noise sounds like it is coming from the Haldex not the diff. There is a slight roughness at one point as the Haldex Propshaft Flange is turned by hand. The back wheels do not turn, so the roughness has to be in the clutch plates or front Haldex bearing.
So Next step, is pull the Haldex out and see what is going on inside.
With the propshaft off it looks like 4 bolts and the hole thing comes off the diff....I think ?
I found some really informative links . Interesting that the Ford Kuga has the same Haldex Gen 3.
http://www.kugaownersclub.co.uk/forum/h ... c9458.html