Visco vs. Haldex - discuss

[keeno]

Just to add a little, albeit slightly different experience with 4wd, I tested both my A4 tdi quattro and S4 quattro in 5 inches of snow last winter. The tdi was amazing, went straight, had amazin traction and was very predictable The S4 however, was tail-happy, oversteered like a bugger and was generally scary. I then found the reason: the tdi had a 50-50 drive split whereas the S4 had the 'sports' option of 60-40 rear torque bias. Amazing what diiference that made in tricky conditions. Drivin both cars was chalk and cheese.

[syncropaddy]

I then found the reason: the tdi had a 50-50 drive split whereas the S4 had the 'sports' option of 60-40 rear torque bias.

I wonder what the bias is on the Passat TDi 4motion

[silverbullet]

Depends on the installation. I don't know if the inline V6 models are 3-diff (proper quattro) or Haldex coupled like transverse engine quattro/4motion. Bias is probably to the front, so rear wheel assistance comes in progressively as fronts start to slip, as I understand it.

[Trundler]

A far as I'm aware, regardless of what badge VAG choose to put on the boot lid, all the in-line engine cars (Audi A4, A6, A8 and the Passat) are proper quattro and all the transverse engined cars (Golf, A3, TT etc) are Haldex clutch and not really full time 4WD. I am a bit confused when it comes to Transporter T4s and T5s but I presume they are all viscous coupled Syncros, even if wearing a 4Motion badge.

I am from an era when all quattros were either fixed 50-50 split or mechanically variable via Torsen diff (25/75 to 75/25) I had no idea they were now producing S4s etc with a 60/40 split.

The bottom line is that the Syncro system and the original quatto 50-50 system, although "simple" both work very well indeed. I have no direct experience of the Haldex but reading the theory (and various road tests) makes me think it is a seriously compromised arrangement.

[silverbullet]

T4 and T5 are Haldex coupled i.e. FWD with rear assist.
All manufacturers seem to have abandoned Viscos in favour of the Haldex system (or versions thereof), which is now up to 5th Generation and also twin couplers on the SAAB x-drive system. Viscos just don't give the service life that manufactureres now demand.
About the last Viscos used in a way that syncro owners would recognise (but reversed) were things like the Freelander 1, which used to eat the VC every 60k if you were lucky. But it did have different diff ratios front to rear, to achieve the torque bias. So the VC was being worked all the time...What a BL bodge!

[Trundler]

So, even the 'Syncro'-badged T4 had the Haldex system? I never knew that...

[Trundler]

...Viscos just don't give the service life that manufactureres now demand.

I believe the same issue saw the demise of the G-lader supercharger.

[silverbullet]

So, even the 'Syncro'-badged T4 had the Haldex system? I never knew that...

Yup. "quattro" and "syncro" became mere brand trademarks, rather than a description of the system fitted.

[torchy]

"""There is nothing like the FWD just kicking in after the rear end has already gone critical, it doesn't feel part time or half-arsed either. The 4WD is very much permanent and it very much works."""

Could'nt agree more, In the snow this year....I forced a back end skid and the way the front end pulled out was exceptional, regaining control in a blink. VW built an impresive peice of kit.