[christi]

My understanding of the synchro trans as fitted to B3 and B4 (Europe) is that the front drive is much the same as the standard front wheel drive, but that there is a power take of on the back of the trans, to which a viscous couple drives a prop shaft for the rear wheels.
In other works there is no centre diff, and the front wheels are always fully driven and connected to the output of the gearbox.
So, when dumping the clutch on a slippery road, do you get a moment of front wheel slip before the viscous coupling locks up enough to drive the rear?
I guess that the front has to slip a bit before that coupling sees a speed difference from input to output and transfers any power.
What affect does this have on drivability?
What about when you stomp on the gas mid way around a slippery corner? Does the front break free for a second until the back end catches up?
Also how much power / economy do you loose due to the extra prop shafts and stuff?
Is this the same system basically as Audi Quattros?

 

[G60syncro]

Re: Question about synchro trans (christi)

Here is syncro 101, an introduction to AWD:
Front end and rear end both have conventionnal differentials, with front end equipped with the ABS traction control as discussed with Mike in another post. Contrary to Audi's torsen helicoidal gear differential (just like a Quaife) both ends are connected together by a center "differential" which consists of a viscous coupling and an overrunning clutch. The clutch is there to allow the font end to drive the rear end, but to prevent the rear to drive the font while braking... That would screw up with the ABS system. The VC is filled with a polymer fluid that reacts as a solid when subjected to shearing forces, such as those encountered when the input and output discs are rotating against eachother at different speeds.
The front transfer case and rear differential have different gear ratios, which creates a 10% mismatch in I/O speeds. This causes the VC to be partially active at all times, and allows smoother and quicker engagement.
As far as driving is concerned, on dry pavement the AWD is completely transparent. When the conditions deteriorate, it does engage very progressively, and makes the car very neutral through corners. Once I got the hang of it, I gave a few rides to some of my friends. I could enter snowy curves at mad speeds. They were amazed at how the car would start to understeer and plow through the corner, then with a blip on the throttle, the car would regain its stability and make it through the corner as if it were nothing.
In regular driving, it only makes the car extremely stable, and it feels just like a FWD. It's when you start getting near the limits that things become interesting.... It's way different, stomping on the gaz in the middle of a corner will cause the VC to lock up real quick, so you get instant traction on all four. So what was an understeering condition becomes oversteering and if you're not ready for it you can get surprised!! But the oversteer is very controllable by modulating the throttle, and soon you'll find yourself making perfect 4 wheel drifts every occasion you get!!
Though the extra drivetrain should cause a drop in power, you don't really feel it because you get a gain in traction... this is power that would have been wasted anyways. Fuel economy is another matter, I can't really compare because last winter was when the G60 started having vacuum leaks and it ran way too rich... I'll probsbly have more relevant data over the next months as snow here starts to accumulate. In the summer I do 600km of mixed city/highway on a 70L tank... I expect this number to fall by about 100km... This number does vary a lot whether you are easily tempted to "stomp on it" or not.
Whew! that was a lot of info crammed in one post!! If I left out anything, let me know!!

 

[christi]

Re: Question about synchro trans (G60syncro)

okay, I had a look at the parts database yesterday (I was bored and curious) and here is what I have found. It doesn't contradict you but maybe clarifys a little.
There is no centre differential.
The engine, through the gearbox, is firmly linked to the front wheels, just like a front wheel drive car. If the gearbox output shaft is turning, then the front differential has to turn too, it has no choice.
From the front diff there is a power take off. Basically they have attached this right angle take off arrangement onto the side of the front diff housing. One of the driveshafts passes through the centre of the unit, whilst it is driven by a tube (through which the driveshaft goes) that connects to the differential cage / output gear.
From the right angle power take off, there is a prop shaft that runs to the back of the car. This shaft is also firmly connected to the front diff, and if the gearbox output is turning, then it is turning.
The prop shaft arrives at the back of the car onto the viscous coupling. This is a simple in / out coupling, being driven by the front, and via the viscousness of it, driving the rear diff.
Haven't checked all of the gear ratios yet.
There are two versions of the front / rear diff and output take off, with different ratios depending on the engine. It looks like one for VR6 and the other for 2.0L. The year that I was looking at was 1996, so no G60s I guess.
The two versions also had a different viscous coupling, presumably of different viscousness.
I'm still dreaming of having a TDI syncro. If looks as though the wagon shell will take the rear syncro suspension. I think that the sedans do not though.
Next I have to see whether the TDI gears would fit in a syncro trans case to retain the TDI gearing.

 

[G60syncro]

Re: Question about synchro trans (christi)

Cool info.. I was wondering the same thing about wagon vs sedan setups... I know my trunk floor sits about 6" higher that a non syncro sedan, but on wagons I don't believe there is a difference in floor height between the two... Can someone confirm this??? Are the syncro and non-syncro wagons setup the same?? That would be too good to be true!!! Can you say instant syncro swap?? Besides, wagons are so cool!!!
There is a guy here in Quebec who blew his G60, so he swapped it for TDI reliability and fuel economy... He gutted the syncro gearbox and reinstalled the TDI gears... both the 02A and the 02C (syncro) gearboxes are basically the same, the differences are on the bellhousing itself and the differential... So you can swap all the shafts, gears and final drive ring gear from your TDI and install them in a syncro tranny case.


[Modified by G60syncro, 5:37 PM 12-7-2001]