Learn me Viscous Couplers for full-time awd use...

Edit: viscous, but typo stands. 

I have recently stuck my toe in the awd pool and want a fulltime setup on my crv, as opposed to the 'on demand' dual-pump clutchy thingy installed as stock. 

The honda rt4wd system found in the wagovan uses this, but is unobtanium as everyone has swapped it into their civics. It is helpfully already the correct flange, and installs in-line with a shortened stock driveshaft.

What other cars use VCs that are not integral to the transmission/diff? I heard some subies, volvos, and land rovers use em too...

Any experince or advice adding a vc? 

02 and older Volvo.  

Pretty sure that some years of Ford Escapes use them.

Note that for the US market, Subaru never used a viscous coupler.  They used a viscous limited slip diff, in the transmission.  Very big difference but most of the same words.  

Out of curiosity, what issues are you having with the stock AWD setup?  Viscous couplers do have a kind of "AWD lag" effect where the full time driven wheels need to be slipping before the other axle can start to recieve torque, and the nature of them means that this slippage must be maintained.  Honda went to a pump driven clutch so that they COULD be "constant on" if desired.

Nugi said:

Edit: viscous, but typo stands. 

Fixed

In reply to Knurled. :

So, thats a good question and the answer is, its complicated. The reason most honda guys like it, its being able to lock/'pin' the dual-pump unit, as it is known for slipping when hot, worn, or pushed very hard. The VC allows some torque always to be applied, and tends to be more reliable, especially with elevated power levels, than the dual pump. The drag racers like the more reliable power split and shock-load elimination for the undersized rear ends, with less need for front wheel slippage to generate rear wheel torque.

Iirc honda went to the dual-pump for mpg reasons over the vc. The dp system uses barely more friction than fwd setups, thats the beauty imho. Later 08+ dual pump diffs have bigger clutch packs to mitigate the issues some and swap right in. But still have signifigant lag even compared to vcs. I have toyed with resizing the pump orifii (smaller outlet hole builds pressure faster, keeps it locked longer, bigger inlet spools pump faster) or even adding a 'hydro locker' setup with a spare brake cyl, but living on dirt roads I kinda just want an always-on thing, even if I end up with a slightly smaller torque split overall.

I am open to a totally new rear diff if I can use standardish axles, but that seems unlikely. Even a front or rear LSD (or diff locker) would be nice, bit seem unavailable. 

Re: streetwise

What is it about the early ones? I asked because I heard of people using v70 ones i think? 

For those wondering, the dual pump system ,housed in the rear diff of the crv, element, and awd xtour, is a pump that spins at the speed of the difference between the front and rear (open) diffs.  This means fwd is the usual drive mode, but with a constantly driven driveshaft. When the front diff spins, and the rear does not, the pump pushes a motorcycle-style wet clutchpack together, and engages the rear wheels. So even though a 50/50 f/r torque split is possible, it is unlikely in irl. Hence the poor traction test results in youtube videos. It does get you unstuck, and helps when spinning wheels up an icy highway, but thats about all, even if it is 90% of the average drivers use case. 

In reply to Nugi :

Okay, I was thinking of the VTC systems not that.  Yeah that sounds like a more complicated way to get what a viscous coupler does.

Intereting there is a limited slip differential that works on that principle, too.

Nugi said:

The drag racers like the more reliable power split and shock-load elimination for the undersized rear ends, with less need for front wheel slippage to generate rear wheel torque.

 

Wait- people drag race CR-Vs?

In reply to Brett_Murphy :

No but people are putting CR-V transmissions into Civics with turbos now.

Volvo used a viscous coupler in their stuff til 02, then went to the Haldex hydraulic stuff.  There is only one ratio, since it's driven off the trans output.  I want to say the transfer case is 1:3, and the diff 3:1, but I could be off by a few percentage points.

Streetwiseguy said:

Volvo used a viscous coupler in their stuff til 02, then went to the Haldex hydraulic stuff.  There is only one ratio, since it's driven off the trans output.  I want to say the transfer case is 1:3, and the diff 3:1, but I could be off by a few percentage points.

I would like to say the viscous had a 1.27:1 angle gear and the Haldex has  1.32:1 angle gear, but don't hold me to that.

AWD Caravans used a VC on the driveshaft. 

I don't know if this has been done but it seems like if you tapped a couple of fittings into a Honda dual pump diff you could run an electric pump and basically turn the AWD on and off with a switch. 

But, the overarching story of the Honda dual pump system (in my opinion..) is one of people trying to 'fix' it before they can specifically articulate why they even think it's broke. 

In reply to Vigo :

I agree. Its not 'broke' for 99% of drivers I am sure. It works fine to pull me out of a ditch. I just like to tinker, and have a spare awd crv to play with. 

I did mention above that I am pretty sure you could plumb a brake mc to activate the dual pump system. The issue is that the dp seems to slip a LOT when hot, and heat up quick under power. Making any prolonged use problematic. Also if I did get a good lockup, it would be much harder on the rather weak driveline and diff than the decoupling a VC would offer. I am hoping to swap or turbo the car in the future. Even if I went k-series I would maintain awd, and it uses the same driveline to the back. I already have a chipped ecu waiting for it once I finish the clutch. 

I digress, thank you for all those who have suggested sources for couplers, keep em coming!

In reply to Nugi :

Bumping this thread because it's relative to my interest and I want to know if the dual pump system has been working out for you. 

Does anyone make aftermarket upgrade clutches for the CRV diffs?  My engineer brain says if you shim the clutch piston or increase the pump pressure you should be able to use this system with success.  Heat is said to kill these but I think you could get around a lot of that with a good fluid that is meant for multi-plate clutches like VW DSG oil and a fluid cooler.  I'd like to get around using a viscous coupler, that's one more thing you have to buy that a CRV or Element donor car don't have.

The e30 BMW 325iX used a viscous coupling transfer case that is separate from the transmission, but they're rare and expensive if you can find one.

What are all the crazy 9 sec civics doing? 

Aren't some of the Hondas using a Landrover Freelander Viscious Coupler? 

The VC in my 01 Volvo didn't appear to lag in engagement.  Maybe hard to tell because the back end would step out all at the same time with as spooling turbo and or downshift.  

This was on snow and rain as they were intended.  

On a volvo the VC is seperate but bolted directly to the rear diff housing, IIRC.

In reply to Carbon (Forum Supporter) :

Those crazy AWD civics are running in the 7's now. 

Seems like a lot of those guys are using the Land Rover VC, those are growing in popularity and price.