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Forester: viscous coupling locking center differential ??????

An earlier post mentioned that the 5 speed Forester had no center diff, only the viscous coupling giving drive to the rear wheels. On the Subdriven web site,an article on the 06 Forester

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hasthe following:

In all Forester models equipped with the 5-speed manual transmission, a viscous coupling locking center differential built into the transmission case divides engine power 50 percent front / 50 percent rear. Wheel slippage at the front causes more power to shift to the rear, and slippage at the rear transfers power to the front, ensuring that the wheels with the best traction receive more power.

Anyone know if the Forester now has an actual center diff ? A viscous coupling does act like a differential, but to call it a locking center differential seems like marketing fluff.

From the wording. seems like it doesn't, since it would say it has a viscous COUPLED center diff, if there was an actual diff in addition to the VC.

Reply to
ed
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Probably confusion with the auto versions, which do not have a centre diff. Instead it is solid front wheel drive, with an electronically controlled 'viscous' clutch to the rear wheels.

The distribution front to rear varies according to circumstances.

Reply to
Orienteer

Reply to
Edward Hayes

Ed, here's a link to a scan of the innards:

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Study it and see if you can figure it out.

If you can, then please explain it to me, cause I can't make heads or tails of the drawing (there's inner and outer shafts). There IS an actual third (center) diff aside from the front and rear.

Reply to
Danny Russell

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Reply to
Edward Hayes

That's what I thought when I first studied it, but looking closer It looks like the output of the trans powers the input of the center diff via the outside housing structure, then the two outputs of the center diff power the respective front & rear shafts. The drawing is a little bit ambiguous.

But look closely, you'll notice that the output from the trans is actually a hollow tube (labeled "Driven Shaft") and it surrounds the front drive shaft (labeled "Drive Pinion Shaft").

Reply to
Danny Russell

The center differential and the viscous coupling are two completely independent things. The center differential distributes the power between front and rear (just like the rear differential on a rear-drive car). There are two more differentials, one at the front, one at the rear, for left-right distribution.

The visous coupling is a friction device between the front and rear shafts that attempts to dampen any large difference in speeds between the two.

The center differential and the viscous coupling are in parallel.

Reply to
Paul

Subaru MT use three differentials;

- one between the front wheels to balance torque so that the wheels can turn at different speeds

- one between the back wheels to balance torque so that the wheels can turn at different speeds

- and one between the front axle and rear axle (driving the above differentials), so that the front and rear axles can turn at different speeds.

Now because differentials balance torque, if one wheel should get spin freely on ice (zero torque) all the differentials will see that all the wheels get zero torque and you won't go anyway.

So between the two "driven" gears of the centre differential, they stick a VC unit which allows the two shafts to turn at different speeds, but provides resistance, and that resistance increases as difference in shaft speed increases.

Which is why after 5 hours on the highway on a hot hot day, I can bearly turn my Subaru into a parking spot!

Reply to
Dominic Richens

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