Volvo AWD questions

in article mPPub.189791$9E1.1011013@attbi_s52, John at snipped-for-privacy@nospamcomcast.net wrote on 11/19/03 2:49 PM:

I just recently [last week] picked up an S60 R, with the model year 2004 version of AWD. The owner's manual does say that flatbed towing is preferred, but doesn't prohibit towing with two wheels on the ground, the rear as I remember. There are no warnings in the manual about slight differences in tread depth among the tires, although I recall that it does say that all 4 tires should be of the same type. My prior sedan was a VW Passat with 4Motion, which is an AWD system featuring a Torsen center differential: purely mechanical system, and the power split can go from

50/50 to as much as 66/34 front bias or 34/66 rear bias. Exactly the same system that Audi was calling Quattro in MY 2001. Audi dealers were recommending replacing all 4 tires if any tire needed replacement; the VW manual said nothing special about tire selection and replacement. A local tire dealer told me that replacement of all 4 tires was desirable if tread variation among the tires exceeded 3/32 of an inch. My garage queen is a Honda S2000 with a Torsen rear differential, and Honda recommends that the temporary spare NEVER be used on the rear, to avoid diameter differences - if you get a rear flat you must swap front to rear and put the spare on the front. My plan for the S60 R AWD is to carefully monitor and rotate the original equipment tires, and replace them when there is a lot of wear, or if one tire is much different than its mates. The car did come with a big warning sticker which said that its high performance tires may not last as much as 20,000 miles, and that they are not suitable for driving in snow. My understanding is that the cost of the 235/40 x 18 Pirellis is about $225 plus a pint of blood each, so I will administer lots of TLC and check the pressures quite often. AWD systems can be very expensive to repair, i.e., many thousands of $$, and I am sure the Haldex system is no exception. For now, it is extremely transparent in usage, and I am thankful for the 48 month, 50,000 mile warranty. Any lesser warranty and I might have been scared away.

Hi, John - - -

My wife drives our 98 V70XC. I drive our 02 S60AWD. The older AWD has the viscous coupling and the newer the Haldex system.

The simplest description of the two is that the older is a "coupling" that is always connecting front and rear wheels, while the Haldex system is a "clutch" that is brought into action within milliseconds where there is a difference in rotation, front to rear, that the computer perceives to represent slippage. At this point the Haldex clutch is fully engaged within about 1/6 of a revolution of the rear wheels. Quick!

The difference in systems is obvious - the older being mechanical, the newer controlled electronically. While both of our cars have called the systems into operation, neither has "commented" at the time, just getting the job done without complaint. The reasons for change by Volvo would likely represent cost (a local Volvo independent told me that the rear propellor shaft, with coupling, was over US$2,500 several years ago) and the fact that the Haldex is designed for external, electronic control.

bob noble Reno, NV, USA

The Haldex system can cope with differently worn tires without problems, but you should alway use tires with the same dimension. If you have differently worn tires, you will get optimum performance (as well as optimum safety) putting the worn tires at the front. Rotating the tires in order to keep them equally worn will be fine as well.

The car can be towed on two wheels - preferably with ignition off.

The Haldex coupling is a very superior system compared to the old visco. Both traction and handling is improved significantly.

/Staffan

Joe and Ruth Levy wrote: