Thread: So who's replaced a viscous coupling?

^ spot on

Has anyone driven a BW car without front shaft and a stuffed VC "not siezed "? I have always thought that there is a direct connection with the rear but now I am not so sure.
I researched for about 4 hours last night, trying to find a schematic of the BW transfer.
The nearest I found was a sideways diagram of the 38 A box.
And it looks llike there is a centre diff in there and the viscous is just a "limited slip" mechanism.
There certainly is a part number for centre diff , I recall it is STC 5606 or similar.
So it may be that , if the VC dies "not seized" , that it would be like an LT230 without the diff locked.IE front wheels spinning and no drive to the rear on a loose steep hill.
Come to think of it , I saw this once many years ago.
Regards Philip A

Originally Posted by PhilipA

Has anyone driven a BW car without front shaft and a stuffed VC "not siezed "? I have always thought that there is a direct connection with the rear but now I am not so sure.
I researched for about 4 hours last night, trying to find a schematic of the BW transfer.
The nearest I found was a sideways diagram of the 38 A box.
And it looks llike there is a centre diff in there and the viscous is just a "limited slip" mechanism.
There certainly is a part number for centre diff , I recall it is STC 5606 or similar.
So it may be that , if the VC dies "not seized" , that it would be like an LT230 without the diff locked.IE front wheels spinning and no drive to the rear on a loose steep hill.
Come to think of it , I saw this once many years ago.
Regards Philip A

If you are correct there would be a cdl activation mechanism of some sort in the car like most other RR/Discos.

Also when a cdl 'dies' it seizes, unless it has been physically cracked open and the fluid leaked out - in this case there would be no drive to the front even with a locked cdl.

Gazzz

Well yes, that is what I have always thought.IE that there is a solid drive to the rear and the viscous is the only thing between the transfer and the front axle.
I am too lazy to undo my front driveshaft and try to drive it. In the next couple of weeks I will be fitting a Quaife front diff , so maybe will drive it without the front connected, if I can be stuffed after bench pressing 33KG.
But there are now two people on the board who claim that they have lost rear drive/or have had wheelspin at the front. IMHO, the car will lose front drive and this should show up as no wheelspin at the front , but maybe wheelspin at the back on a steep hill.
There seems to be all sorts of different terms for the components of the BW case, But I think all that is there is an epicyclic gearbox, at the top behind the ZF, a BIG chain and a rear output shaft,which is connected to the viscous and then to the front driveshaft.
Regards Philip A

The viscous coupling is forward of the morse chain and transfers a 50/50 torque split between front and rear axles. As it is constantly "locked", taking either prop shaft out will still drive opposite axle.
There is more of a direct drive to the rear than the front as the front output shaft is on the hydraulic side of the coupling.
With an LT230 box, unless the centre diff lock is switched, it basically acts as an open centre diff and will provide drive to the output shaft with the least amount of resistance.

just off the top of my head.........!

Phillip, this is from factory workshop manual:
"remove either the front or rear propeller shaft from the vehicle to eliminate drive to one of the axles. If the viscous unit is operating effectively, drive will be transferred to the axle that is still connected via the propeller shaft connected to the gearbox and the vehicle should remain driveable.

if the viscous unit has failed drive will not be transmitted to the axle.

A partially failed unit will be identified by excessively high engine revs and little vehicle movement when attempting to drive the vehicle."

the viscous is basically a hydraulic diff lock constantly on providing a 50/50 split but will still allow slippage. Its same principle as a viscous fan hub but without the temperature based switch (the coil wound up at the front) and not unlike a torque converter.

Ryan,
Not wanting to get into the pro or cons for which T'fer case is better but I have a VC transfer case if you are interested in a SH. I also have LT230's. Giveme a call on 0407 627 206 if you are interested.

Regards,
Col

Originally Posted by LOVEMYRANGIE

Its same principle as a viscous fan hub but without the temperature based switch (the coil wound up at the front) and not unlike a torque converter.

Not sure i agree with this statement. Like a fan hub yes, about all a viscous coupling has in common with a torque convertor is the fact they are both round A viscous coupling uses the shear force of the fluid (like the clutches in an auto trans) whens it operating at 50/50 split and uses the increased viscousity of the fluid provide increase drive tansfer(ie lcked up.).


A torque convertor doesnt rely on fulid viscousity changes to provide increased drive it relies on angular distiction between the impellor and stator vanes to provide a torque mulitplication and drive transfer.

The difference in speed between the impellor and stator provide the angular distinction and the torque increase not the fluid viscousity.

cheers

Luke