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Viscous Coupling: How aggressive is too aggressive?
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ALIKA T3
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PostPosted: Sun Apr 12, 2015 11:07 am    Post subject: Reply with quote

I found it sketchy too, if VC catches, the torque wrench is gonna let go and hit the bench.... but interesting to see peoples ideas out there, always enriching.


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Waldi
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PostPosted: Sun Apr 12, 2015 11:21 am    Post subject: Reply with quote

Maybe he just fixed it in the mashine because it looks more profesional Wink

If you do all by yourself, repair a vc and build and install a decoupler costs less than 150€.
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ALIKA T3
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PostPosted: Sun Apr 12, 2015 12:38 pm    Post subject: Reply with quote

I know all of that, we are talking about agressive set ups, you're off topic.
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jalan
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PostPosted: Sun Jan 29, 2017 11:50 am    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

The VC torques are listed in Van Cafe's web site. Just look at the rebuilt VC info. Not sure who they are getting their VC's from but I would bet on German Transaxle in Bend.

stock vc 35 nm or 25 ft/lb
sport 55 nm or 40 ft/lb
agressive 86 nm or 62 ft/lb

These are the torques to turn a cold VC. We all know they increase dramatically once they get hot if they are working correctly.

I picked up a syncro that turned out to have a broken front diff input shaft. It broke right where the shaft entered the VC. Bad bearing probably caused it to flex.

Anyway, I welded a nut to the broken stub, put the vc in my vise, put my torque wrench on the nut and can easily measure the torque needed to spin a cold VC. That one turned out to be 45 ft/lbs which shows it is a bit stiffer than the sport VC.

I can think of two ways to measure the torque required to spin your VC without removing it from the van. The simplest way two compare two different vans VC's would be to jack up one front wheel and turn the wheel using a torque wrench applied to the axle nut. Repeat on the other van and you can compare the numbers. Decouplers engaged and rear wheels on the ground or e-brake engaged

A true torque reading could be obtained by removing the driveshaft and turning the input shaft via the flange nut with your torque wrench. Either block the front wheels or have a buddy step on the brakes. You will need the dial style wrench with a tell tale needle or a buddy with a good eye.

If anybody is interested I am putting together some VC rebuilding kits which will include the Viton seals and the OEM 30k fluid. Will put them up on the classifieds once the seals come in.
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PostPosted: Sun Jan 29, 2017 12:14 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

Jalen,

Sounds like a great idea as a DIY kit. So the torque readings. I assume you are measuring "break away" torque? Simply put, its what it takes to move the VC at a fairly slow wrench movement. I ask because it is easy to move the wrench faster than the other guy and get a much higher reading. So I suggest for others that you establish some rough way of staying together in this measurement such as "the speed of a second hand on a clock" or "5 seconds to rotate 90 degrees" or other agreement.

This way you will all have an agreed upon standard so that someone who takes the time to disconnect the shaft, jack the vehicle, etc is getting an equivalent and therefore useful measurement. Otherwise you guys will not be on the same page.

Also, a stone cold VC that has not moved for perhaps overnight is a good idea or comparable readings. Anything else others can think of to standardize this across the miles?

Doug
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ALIKA T3
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PostPosted: Sun Jan 29, 2017 12:20 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

Interesting numbers for the torque.

Yes German Transaxle takes care of the rebuild VC ( Vicous couplings) for VC ( Van Café ).


http://www.van-cafe.com/home/van/page_109_1248/rebuilt-viscous-coupler-coupling.html

I've been selling the Vitton kit in the classifieds for a few years now, the problem is people are not equipped with a scale accurate enough to handle up to 10kg with a 1 gram resolution . Silicone fluid has a 6months shelf life ( from what I read here) so I point customers towards buying their own, much cheaper in shipping for them then back and forth with an extra intermediary.

Aren't the Germans like DieselKontor selling 100 Cst viscosity silicone fluid in their kits??
Aloha!
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IdahoDoug
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PostPosted: Sun Jan 29, 2017 7:14 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

Actually, the method posted above using the rear wheel nut on the Freelander, known weights and a stop watch is a great way for people with Syncros to compare "aggressiveness" without completely disassembling their front diff to get the VC out and measure it on a bench. What you'd need as a data point would be for someone with a brand new VC from Van Cafe with a stated torque amount on the bench to measure what it is at the back wheel. Then all the rest would know if their VC is more or less aggressive. You can simply do the math in reverse to arrive at what your vehicle's VC "bench torque" number is.

Doug
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PostPosted: Sun Jan 29, 2017 7:21 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

Another practical way to assess the degree of aggressiveness of a VC, is how much it binds when making progressively tighter turns in an empty parking lot.

Count how many rotations of the wheel cause the motor to bog down when idling forward Smile

example..
1. motor does not bog down, even at full lock = VC that has failed in the open, decoupled, position. Ive had 2 of these.

2. motor bogs down 1/4 turn of the steering wheel less than full lock. I bought one of these brand new from Derek Drew.

3. motor bogs down 1/2 turn away from full lock. I consider this slightly aggressive and recommend a decoupler.

etc

maybe some people can report their test results for comparison sake, with their own impressions of how difficult their VC makes a tight turn into a parking space.

Note that in some cases, the VC will bind more after it has been driven for a while, such as freeway time.. People often report that coming off the freeway, their VC tends to bind more.

Why could that be true?Smile
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PostPosted: Sun Jan 29, 2017 7:25 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

IdahoDoug wrote:
Actually, the method posted above using the rear wheel nut on the Freelander, known weights and a stop watch is a great way for people with Syncros to compare "aggressiveness" without completely disassembling their front diff to get the VC out and measure it on a bench. What you'd need as a data point would be for someone with a brand new VC from Van Cafe with a stated torque amount on the bench to measure what it is at the back wheel. Then all the rest would know if their VC is more or less aggressive. You can simply do the math in reverse to arrive at what your vehicle's VC "bench torque" number is.

Doug


Hi Doug!

That would be assuming the rebuilt ones from German transaxles are rebuilt like the new ones from SDP.
You cannot find new ones anymore ( not rebuilt).
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PostPosted: Tue Jan 31, 2017 4:34 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote


Link

Here is my test with the torque wrench set to 80 foot pounds. Obviously coupled and just this wheel off the ground.

It would also rotate at 60 pounds if I was more gentle with it. At 40 ft lbs and it moved so slowly it was like watching paint dry. I know this is aggressive, but I can still manage dry pavement driving, just not sharp parking lot maneuvers.

How does this compare to yours?
Dave
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PostPosted: Tue Jan 31, 2017 4:51 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

candyman wrote:
That said, does this current vc sound like it is too aggressive?

If I were to install a decoupler, would the vc continue to become more aggressive with time even though it is not getting used near as much?


yes, too aggressive to run without a decoupler

no I dont think you should buy another VC

yes I think you should buy a decoupler.

no I dont think your VC will become more aggressive unless you run it coupled all the time. That is how it got aggressive to begin with. Aggressive is good, offpavement. Decoupled is good, onpavement.

VCs create drag on dry pavement. It is better to decouple until you are not on dry pavement.

Those torque readings for the various types of VCs are minimum DRAG values, NOT minimum forward traction values.

as you can see in the video, the VC Resists turning. Therefore the back wheels have to push harder, to overcome the resistance of the VC.
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ALIKA T3
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PostPosted: Tue Jan 31, 2017 11:26 pm    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

Thank you for the video Razz

I have to say, the torque applied to the wheel hardware is not the same value as the torque that would be measured at the axle nut.
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PostPosted: Wed Feb 01, 2017 10:15 am    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

ALIKA T3 wrote:
I have to say, the torque applied to the wheel hardware is not the same value as the torque that would be measured at the axle nut.


Referring to the pic in the top frame of this video, the chosen lugnut is directly above the axle nut. The torque will be appx same because the distance from lugnut to hand, is appx same as from axle center to hand.

If he had chosen a lugnut level with the axle center (for example), then the torque numbers would not be correct. Perhaps 10% off.

Imagine a lugnut pattern of 5x10mm (instead of 5 x 112mm). The torque at the lugnut would be almost equal to the axle in every case.

Imagine a lugnut pattern of 5x350mm (out at the 14" rim edge) of course the lugnut torque COULD be much different than axle torque. But depending how you do it,,,, if you chose a lugnut such that your hand is same distance from the axle, it would read same as the axle torque.
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PostPosted: Wed Feb 01, 2017 10:27 am    Post subject: Re: Viscous Coupling: How aggressive is too aggressive? Reply with quote

ALIKA T3 wrote:
Thank you for the video Razz

I have to say, the torque applied to the wheel hardware is not the same value as the torque that would be measured at the axle nut.


It would be nice to see the same video of a non aggressive VC for comparison. You really need to see how fast or slow the wheel moves at a given force to really compare.

I was surprised myself at how much force mine took. Still I wouldn't call it too aggressive since I have a decoupler and prefer to drive in 2wd 90% of the time. But watching the video makes me more aware of drive line bind with our delicate transaxles.

[quote="davevickery"]
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