difference between "haldex" and "before haldex" generation

[alex_plovdiv]

Hi.
I try to read something more about first generation volvo's AWD but I cant find many in the net. The only thing I find is they use a GKN viscous coupling. So I want to know something more about it - is it better or worst than haldex. Does the first generation AWD use electronic or it is only mechanical.
Thanks.

[DanielOsterberg]

Hey

The first generation of AWD vehicles from Volvo is as you said a viscous coupling which can transfer torque to the rear wheels if the front wheels start slipping there is however a max for this and i think it is 80Nm max to rear wheels. When driving along the car works as a AWD vehicle but will transfer more torque to the rear wheels when necessary.

This is what VIDA says about the first AWD system fitted to V70 XC 1998-
The AW 50-42 is an electronically-controlled four-speed automatic transmission with torque converter lock-up of the three highest gears. Because the transmission is controlled by an electronic control module gear-shifting can be controlled to allow the correct gear to be selected for driving conditions, engine load, driver's wishes, speed, etc. This yields good fuel economy combined with top-class performance and increased comfort by ensuring smoother shifts and lower noise levels.
A control module receives information about the selected gear and driving mode setting required. Together with signals from a number of sensors describing the running conditions of the car, this information is processed by the control module, which calculates optimum shifting and lock-up engagement points, depending on the driving mode selected. The control module then controls shifting and lock-up engagement by acting on the transmission hydraulic system. The control module also affects the quality of gear-changing by instantaneously modifying the hydraulic line pressure when shift is made.
The transmission's electronic control system receives continuous information from a number of sensors, as well as from the engine control system. Unlike a transmission with just a hydraulic control system, this enables the control system to adapt to extremely small changes in operating conditions and to control the various transmission functions so that the correct gear is always selected in accordance with the driving mode selected by the driver.
To facilitate fault-tracing, the control module has a built-in on-board diagnostic system (OBD II system) which records any faults in the control system and transmission, these can be read off via the data link connector (DLC).

The gearbox itself is controlled with the TCM but the AWD and viscous coupling has no diagnose and is not electronically controlled.

Be very aware of not using wheels with more than 10% tyre circumference since this will wear the coupling severely ending up in a FWD vehicle in the end and a very expensive repair. The 1998 and 1999 had some problems with the rear differential and also the propshaft is prone to have bearing failure therefore alot of V70 XC is sold as front wheel drive only nowadays since the prop shaft must be bought as a complete part from Volvo. You can hand it in to a mechanical workshop and change only the support bearing in case it fails.

[DanielOsterberg]

This is what is mentioned of the electronically controlled Haldex coupling from 2003- and onwards (different generations can differ)

Differential electronic module (DEM) is mounted directly on the clutch unit and makes up a unit together with the pressure reducing valve.
Differential electronic module (DEM) communicates with, among others, Engine control module (ECM) and Brake control module (BCM) via the CAN-net. With guidance of the sensor signals, Differential Electronic Module (DEM) controls the oil pressure to the discs through the pressure reducing valve.
The pressure reducing valve is controlled endlessly by a pulse-width modulated (PWM)-signal.
The electric feed pump starts at ignition on and immediately works up a maximal hydraulic pressure in the accumulator. When max. pressure has been reached, the feed pump shuts off until the pressure has dropped below 50% again. Then the feed pump starts again and builds up the max. pressure.
This procedure is calculated by Differential electronic module (DEM) using various parameters. In the accumulator the pressurized oil is routed to the clutch via the pressure reducing valve. Differential electronic module (DEM) controls the valve so that correct working pressure is obtained, 0-27.5 bar. The oil pressure to the discs is decisive to how much torque can be transmitted to the rear wheels.

The transmission and bevel gear transfers engine torque to the propeller shaft. The input shaft is joined to the clutch's output shaft via the multi-plate clutch pack. The multi-plate clutch in the coupling must be engaged to transfer torque to the rear axle. The inner and outer wet multi-plate clutch are the transfer point between the input and output shafts.
The feed pump builds up an oil pressure which then Differential electronic module (DEM) controls via the pressure reducing valve, so that correct pressure is obtained. Then the working piston is applied against the disc pack so that the clearance is eliminated and the clutch is prepared to enable quick reaction and control. At 27.5 bar deployed pressure from the pressure reducing valve max. torque is reached, 1,500 Nm, through the clutch to the rear wheels already at start.

Please ask away if you have more questions. In my opinion a pure mechanical all wheel drive (eg Subaru) is the most reliable one but not fuel economy wise, then the Haldex is superior. The viscous coupling has been used by many manufacturers and work good when you are not offroading constantly but just want to get there safer, works good when everything is in order as with everything. I have driven both Volvo variants and i would say the viscous is the most fun to drive but the Haldex is the better one but more like a grown up. I do prefer a pure mechanical AWD in any way.

[alex_plovdiv]

Thanks. Great answer. The whole info I need.

[RCB99]

I have a 2005 XC90 D5 Geartronic, first Volvo 4x4 after many years with Subarus. Took the Volvo to the Subaru dealer for MoT, failed on worn front tyres as expected, rears are also worn but still legal. Subaru dealer advised me to replace all 4 tyres, not just fronts, as having new tyres on front and worn on rear would risk diff damage due to wind up. Is this right?

Have to say so far after one winter more impressed with Subaru 4x4 than Volvo... Current Subaru (2002 Outback with 207,000 miles) gets through deep snow no problem but Volvo struggles.

[60041]

Changing one pair of tyres is not a problem with the later (>2003) Haldex equipped XC's. I was repeatedly told this when I had an XC70, there seems to be a lot of duff information out there, it only applies to the earlier models. I had an XC70 for 6 years and only ever changed one pair of tyres at a time and never had any problems.
When I took my 2004 car for an MOT, I was surprised when the tester refused to put the car on the brake rollers; he said that there was an advisory from the DVLA about the risk of transmission wind-up, and he used an old Tapley meter instead - something I had not seen for about 20 years.
As for your problems in snow, what tyres do you have on? I used to stick to Pirelli Scorpions and found them to be excellent tyres in all conditions, we did not have much snow this year, but last winter we had over 2 ft and I never had any problem in getting about even though we live 1/2 mile up a steep gravel track.
The Subaru is a very good vehicle, I used to occasionally repair them for farmers, but the XC70 should be almost equal in the snow -although maybe not off road.

[RCB99]

Thanks for the advice, think I'll just replace one pair for now, too mean to throw away tyres when they still have some tread.

Tyres are Pirelli Scorpion all round; we live up a farm track too, lot of snow last two years and Subaru Outback would go through maybe 9 ins of snow like it wasn't there, my Saab 9-3 Convertible just sat outside the house spinning its wheels uselessly so wife insisted I get a 4x4 for this winter..

Not much snow this winter and XC90 didn't get stuck but would get significant slippage from front wheels before back wheels seem to connect up, never any wheelspin at all from Subaru.

Also realised initially that I had no 4WD at all due to ABS fault, wife got car stuck in mud, had to get farmer to push her out, fortunately got it fixed just before only snow of winter.

Generally delighted with XC90 though, extremely comfortable on long journeys unlike Subaru, averaging 38mpg.

[asjesus]

The AWD of the subaru it is the best system 4x4 ( Symmetrical All-Wheel Drive).

M daily car (SKoda Superb Break 170CR 4x4) have a Haldex system (4 generation).

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Only in havy rain I test the system. In Portugal don't snow too much. But it's vey smooth and quick.

But when I bought the Superb, another option in mind ti was the Subaru Outback. But subaru has very little expression on Portugal and I went to Skoda.

[alex_plovdiv]

The best system 4 x 4 is classic 3 differentials(with locks on some) used by many cars. Subaru is not inventors of the hot water. Subaru is fashion of time.

[4candles]

Originally Posted by DanielOsterberg

This is what is mentioned of the electronically controlled Haldex coupling from 2003- and onwards (different generations can differ)

Differential electronic module (DEM) is mounted directly on the clutch unit and makes up a unit together with the pressure reducing valve.
Differential electronic module (DEM) communicates with, among others, Engine control module (ECM) and Brake control module (BCM) via the CAN-net. With guidance of the sensor signals, Differential Electronic Module (DEM) controls the oil pressure to the discs through the pressure reducing valve.
The pressure reducing valve is controlled endlessly by a pulse-width modulated (PWM)-signal.
The electric feed pump starts at ignition on and immediately works up a maximal hydraulic pressure in the accumulator. When max. pressure has been reached, the feed pump shuts off until the pressure has dropped below 50% again. Then the feed pump starts again and builds up the max. pressure.
This procedure is calculated by Differential electronic module (DEM) using various parameters. In the accumulator the pressurized oil is routed to the clutch via the pressure reducing valve. Differential electronic module (DEM) controls the valve so that correct working pressure is obtained, 0-27.5 bar. The oil pressure to the discs is decisive to how much torque can be transmitted to the rear wheels.

The transmission and bevel gear transfers engine torque to the propeller shaft. The input shaft is joined to the clutch's output shaft via the multi-plate clutch pack. The multi-plate clutch in the coupling must be engaged to transfer torque to the rear axle. The inner and outer wet multi-plate clutch are the transfer point between the input and output shafts.
The feed pump builds up an oil pressure which then Differential electronic module (DEM) controls via the pressure reducing valve, so that correct pressure is obtained. Then the working piston is applied against the disc pack so that the clearance is eliminated and the clutch is prepared to enable quick reaction and control. At 27.5 bar deployed pressure from the pressure reducing valve max. torque is reached, 1,500 Nm, through the clutch to the rear wheels already at start.

Please ask away if you have more questions. In my opinion a pure mechanical all wheel drive (eg Subaru) is the most reliable one but not fuel economy wise, then the Haldex is superior. The viscous coupling has been used by many manufacturers and work good when you are not offroading constantly but just want to get there safer, works good when everything is in order as with everything. I have driven both Volvo variants and i would say the viscous is the most fun to drive but the Haldex is the better one but more like a grown up. I do prefer a pure mechanical AWD in any way.

and the poster is from Gothenburg, wherever that is??? ;-D