Clutch LSD rear?

[Stuffy]

Hey guys,
Anyone ever run a clutch style lsd in place of the the vc style one?
Just curious as I could possibly pick one up dirt cheap in 3.64.
Pros? Cons? Thoughts?

[spdracrm3]

Hey guys,
Anyone ever run a clutch style lsd in place of the the vc style one?
Just curious as I could possibly pick one up dirt cheap in 3.64.
Pros? Cons? Thoughts?

This ? Has come up before and I've never heard of it being done (must ask yourself why did BMW do what they did with a VC instead of an off the shelf plate diff).
Worth getting the diff and swapping the ring/pinion gear if you have a matching front already and price is right (then sell LSD) components to get money back...

Sent from my SM-G360V using Tapatalk

[iXguido]

I've been running 3.73 front and rear with a rear clutch lsd for more than a year without any issues for what it's worth. I just picked up a rear med case 3.64 clutch lsd that I'll be running with a front 3.64

[berlow94]

The reason BMW used a VC for the LSD in the rear diff instead of a clutch pack is because the IX was designed for low traction situations.
A clutch pack is a static split of power between L and R wheels. The VC will actively give more power to whichever wheel has more grip.
The same reason why clutch packs weren't used in transfer cases until they had the technology to electronically activate them and deactivate based on which wheels were slipping/gripping.


Sent from my iPhone using Tapatalk

[ForcedFirebird]

The reason BMW used a VC for the LSD in the rear diff instead of a clutch pack is because the IX was designed for low traction situations.
A clutch pack is a static split of power between L and R wheels. The VC will actively give more power to whichever wheel has more grip.
The same reason why clutch packs weren't used in transfer cases until they had the technology to electronically activate them and deactivate based on which wheels were slipping/gripping.


Sent from my iPhone using Tapatalk

Actively more power would only be in an electronically controlled, no? Viscous fluid heats up from the slip and semi-locks the carrier (partially) just like a clutch would.

It's more like it slowly locks the wheels together via the slip. They act like an open prior to the slip.

Would the lack of a single rear wheel spinning cause the center to not "lock" as intended and the reason a clutch pack is a bad idea in the rear? ie, the center diff wouldn't couple as easily?

[berlow94]

Actively more power would only be in an electronically controlled, no? Viscous fluid heats up from the slip and semi-locks the carrier (partially) just like a clutch would.

It's more like it slowly locks the wheels together via the slip. They act like an open prior to the slip.

Would the lack of a single rear wheel spinning cause the center to not "lock" as intended and the reason a clutch pack is a bad idea in the rear? ie, the center diff wouldn't couple as easily?

For electric control (to the best of my understanding) the car is all open differentials. The computer senses, via ABS wheels speed sensors, which wheels are spinning and applies brake to slow them down and shift power to the "gripping" wheels. I'm sure some newer cars do this using electronically controller locking diffs with clutch packs.

My understanding of the viscous unit in the diff and t-case of the E30 IX is that the quicker spinning wheel agitates the silicone fluid inside the unit which quickly spins the slowing moving wheels drawing power away from the slipping wheels.

After daily driving my '04 Nissan Titan and '03 e46 330XI (both use Bosch MK60 ABS and almost identical ASC systems) in VT winters, I feel that a fresh VC in an e30IX reacts much much quicker than the computers in the newer cars.
*By newer, I mean 10 years old. I haven't driven a new new and car.*

You bring up a good point about a clutch style rear diff affecting the factory VC in the t-case. I have no idea how it would be affected vs a viscous rear diff.


Sent from my iPhone using Tapatalk

[Kershaw]

I've been running 3.73 front and rear with a rear clutch lsd for more than a year without any issues for what it's worth. I just picked up a rear med case 3.64 clutch lsd that I'll be running with a front 3.64

How did you get a front 3.73?

[iXguido]

How did you get a front 3.73?

Found it in Germany a few years ago.

[ForcedFirebird]

For electric control (to the best of my understanding) the car is all open differentials. The computer senses, via ABS wheels speed sensors, which wheels are spinning and applies brake to slow them down and shift power to the "gripping" wheels. I'm sure some newer cars do this using electronically controller locking diffs with clutch packs.

My understanding of the viscous unit in the diff and t-case of the E30 IX is that the quicker spinning wheel agitates the silicone fluid inside the unit which quickly spins the slowing moving wheels drawing power away from the slipping wheels.

After daily driving my '04 Nissan Titan and '03 e46 330XI (both use Bosch MK60 ABS and almost identical ASC systems) in VT winters, I feel that a fresh VC in an e30IX reacts much much quicker than the computers in the newer cars.
*By newer, I mean 10 years old. I haven't driven a new new and car.*

You bring up a good point about a clutch style rear diff affecting the factory VC in the t-case. I have no idea how it would be affected vs a viscous rear diff.


Sent from my iPhone using Tapatalk

I have dealt with ASC style diffs in Benz, they haven't had many factory LSD's in years. I have used Quaife from them.

None of them truly "add" power to the gripping wheel, they simply lock the two together making the slipping wheel provide power to the more stationary wheel. Viscous does it with fluid like a torque converter, clutches work like a clutch in a car, more allowing a predetermined amount of slip and ramp rate. Since viscous uses the slip to create the mechanical connection, have to wonder how it affects power transfer to the front wheels. In my mind, it wouldn't affect it much, but it definitely would some since the rear drive shaft would be spinning slower in relation to the front shaft than if one wheel was spinning rapidly - it takes the spinning of a non-grip wheel to crate the mechanical lock. In a situation where a clutch pack was in a rear rear diff, you would think the rear shaft would be spinning slower than if the rear was open, or viscous. Not sure how the ramp rate of a viscous would compare to a clutch pack to know. IF the rear diff was 100% lock, I would think it would be detrimental to an AWD car, but the e30 clutch pack is only a 25% positive lock.

Anyone know how the VC diff would translate to lock % in conventional clutch?

[The Dark Side of Will]

A clutch type LSD has a static preload (65 ftlbs or more, IIRC). This preload on snow/ice would mean that both tires always spin; it essentially acts like a spool.

The VC has zero static preload and therefore does not act like a spool on snow/ice.

[nando]

Actively more power would only be in an electronically controlled, no? Viscous fluid heats up from the slip and semi-locks the carrier (partially) just like a clutch would.

It's more like it slowly locks the wheels together via the slip. They act like an open prior to the slip.

Would the lack of a single rear wheel spinning cause the center to not "lock" as intended and the reason a clutch pack is a bad idea in the rear? ie, the center diff wouldn't couple as easily?

no, the VC does NOT function by heating up the fluid!

This is something that has been argued many times - but the way it works is the *shear force* increases as the VC slips (due to the slotted/grooved plates inside the unit). This increase in shear force is what causes it to lock - any heat generated is simply a byproduct. There is a big difference in how a VC would function if it had to heat up the fluid to get any lock - it would be too slow when the car was cold, and also as the car slowly warmed up, the VC would slowly begin to lock all the wheels together.

The locking action is a lot faster than you think it is - the jack test for instance, a good VC will lock nearly instantly (as far as human perception) and the front/rear wheels will move at the same speed. A bad VC will let the front wheels spin faster than the rear. It doesn't matter if the VC is hot or cold, because the shear force is what makes it work - although the locking action is better when it's cooler. But you can't overheat it anyway because at 220c IIRC the seal melts and the fluid pukes out (and another reason why heat is a byproduct, and not the action that causes locking). :p

And no, the rear has no effect on the center VC.

[ACVC325ix]

So as all of our IX's cont to age and VC parts become more scare ( I assume this is the case...) does it makes sense to plan on running a clutch style lsd in place of the the vc style one at some point? I plan on running my IX until the end of time so I want to set it up for the long haul!

[berlow94]

So as all of our IX's cont to age and VC parts become more scare ( I assume this is the case...) does it makes sense to plan on running a clutch style lsd in place of the the vc style one at some point? I plan on running my IX until the end of time so I want to set it up for the long haul!

The VC is still available from BMW NA for the rear diff.
They are recently NLA for the t-case...


Sent from my iPhone using Tapatalk

[spdracrm3]

The can be rebuilt also

Sent from my SM-G360V using Tapatalk

[berlow94]

The can be rebuilt also

Sent from my SM-G360V using Tapatalk

They are welded shut by robots in a vacuum.

Curious to hear more about this...


Sent from my iPhone using Tapatalk