Transfer Case Viscous Clutch ?

Sean Krupa

Sean Krupa

Moderator
I have read all the stickies above but maybe someone can give me some additional advice. I removed the front propshaft yesterday and was going to Dyno it. On the way there the truck would barely move. So I went home and my buddy and I started checking everything and did alot of reading and a few phone calls. With the propshaft in, it is a animal and drives just fine but without the propshaft would barely move.

I replaced the viscous clutch last year along with the bearing being that it was locked. When I checked it yesterday according to the DaveP procedure it seemed OK. I had a spare new VC for a friend whom I will be rebuilding a spare transfer case and he said I can try his. Same thing would barely move. I heard that once there was a bad batch of VC but its hard to believe that it drives just fine with the propshaft installed.

Any additional ideas would be much appreciated.
 
Quickstop [UK]

Quickstop [UK]

Combating adversyty.
Re: Transfer Case Viscous Clutch ?

If the VC is not there, there is nothing to hold the planetary in place so the truck will just spin that planetary inside the ring gear. If the front prop is gone, the VC is not actually transmitting any torque - it is merely acting as a locking differential.

With the VC present, if the planetary tries to spin, there is a differential speed because the prop is out and the front output isn't driven. The VC sees a difference and then the force generated, albeit very small, catches up and the two shafts rotate at the same speed. (By acting as this locking diff component) But if the VC has failed and doesn't provide enough resistance, the planetary can spin freely.

You need that VC intact to lock the diff so power can get from the input shaft, through the locked planetary to the ring gear. No VC = spinning planetary = no drive.

Your VC is toast. Sorry man.
 
Sean Krupa

Sean Krupa

Moderator
Re: Transfer Case Viscous Clutch ?

Thanks Mark for the explanation. I'll have to call Cobra Transmission Tuesday and see what they can do. I sure am gettin good at rebuilding these Tcases ��
 
Brianawd

Brianawd

New member
Re: Transfer Case Viscous Clutch ?

Hey Sean. Are you headed to the dyno to do some tuning? If so I recommend finding
A awd dyno to do your tuning. Tuning in rwd the tune will be way off once your back to
Awd do to the difference in load. Any time you tune on a dyno your tune tends to need
Some adjusting when back on the street because of more load. But yours will end up
Being much more off. Just a FYI
 
Syclone#2960

Syclone#2960

What ever it takes!!
Re: Transfer Case Viscous Clutch ?

Im pretty sure the VC in my ty is on its way out too...this could explain the low dyno numbers it made. Makes we wonder how the high Hp/Tq guys are handling it.
 
Sean Krupa

Sean Krupa

Moderator
Re: Transfer Case Viscous Clutch ?

I'm wondering the same thing Bruce. These don't last forever, atleast I don't think so. I hope whoever makes these isn't building them different that now they are too loose.
 
0966Sy

0966Sy

Code what?
Re: Transfer Case Viscous Clutch ?

Sean Krupa said:
I'm wondering the same thing Bruce. These don't last forever, atleast I don't think so. I hope whoever makes these isn't building them different that now they are too loose.
Click to expand...

What was your source from the one installed, I rebuild a TC for a local guy with one he provided. I have not heard of anything bad with it. But I don't think it gets driven much. I know cobra has them, but his was from a cheaper source.
 
Sean Krupa

Sean Krupa

Moderator
Re: Transfer Case Viscous Clutch ?

The 1st one I installed was from Cobra. 2nd one a friend bought since I was guna rebuild a Tcase for him, it was from Allstate for a bit cheaper than Cobra. With the Propshaft installed it drives great and operates as it should. Most people wouldn't have a clue after they replaced the VC unless they removed the Prop and tested to see if it drove fine RWD. I have a feeling these aren't built to the same spec as they used to be.

FWIW, I'm basically just guna slap the Tcase back in the truck and drive it. Just take it to the track since it's operating as it should with the prop installed and that will give me my "Dyno" numbers.
 
Sean Krupa

Sean Krupa

Moderator
Re: Transfer Case Viscous Clutch ?

Thanks Hood! Im not on that Forum...yet. I talked with Dave again today as I spoke with STE Couplers in Cali. They both basically say the same thing. With these Aftermarket couplers, its a hit or miss. Basically, whoever is building them isn't building them to the specs like back in the day. They are essentially too loose.

With the 2 Couplers I have now, the Truck still drives great and it works perfectly fine like it should in AWD. Unless I decided to do a smokey burnout then it would be RWD. What I've decided is to use these Aftermarket Couplers and drive it AWD. I will be putting the Ty on a AWD Dyno. I don't "Need" to remove the Propshaft for any reason.

STE Couplers is the ONLY shop in the US that is dealing with these Couplers and Rebuilding them to GM Spec per say. They Cost $150 and a buddy is guna try it. Dave is also guna talk with STE and figure out a solution and also square up a explanation on exactly how these work and supposed to.
 
Brianawd

Brianawd

New member
Re: Transfer Case Viscous Clutch ?

From my experience with AWD cars. Doing a dyno in 2wd
Is a bad idea. Back in the day before AWD dyno we used to have to
Install a VC eliminator to dyno in FWD on a DSM. If you did not do
That it would burn up the VC or damage the center diff.
 
Sean Krupa

Sean Krupa

Moderator
Re: Transfer Case Viscous Clutch ?

Ya I would agree Brian. STE said the way my coupler is operating is "normal". Not supposed to be able to move just RWD. Removing the Prop will in sense try to drive the side with least resistance which would be the front. Dave kinda disagrees with that , obviously guys have driven without Propshaft and Dyno RWD.
 
Brianawd

Brianawd

New member
Re: Transfer Case Viscous Clutch ?

If the VC is tight then most likely one could drive in rwd. Or if he VC is seized it would alow one to run
In RWD as it would make the center diff act like it's welded.
 
skolman91

skolman91

Member
Re: Transfer Case Viscous Clutch ?

Sean Krupa said:
Ya I would agree Brian. STE said the way my coupler is operating is "normal". Not supposed to be able to move just RWD. Removing the Prop will in sense try to drive the side with least resistance which would be the front. Dave kinda disagrees with that , obviously guys have driven without Propshaft and Dyno RWD.
Click to expand...

I would also disagree, if that were the case then why did every oem 4472 application work rwd with the front out? Ive driven a very original sy with the front shaft out for a couple months back in the day, like many have said it makes them pretty worthless as the REAR wheels just go up in smoke.
With how loose the new aftermarket ones are, it would make me question how well they are splitting the tq with the front shaft in and awd compared to factory. If it was too loose wouldnt it send more than the stock 20-25% tq or whatever it is to the front? Or less?
 
Quickstop [UK]

Quickstop [UK]

Combating adversyty.
Re: Transfer Case Viscous Clutch ?

Think of the VC as a torque converter. If it is too weak, it won't transmit engine tq to the wheels. There isn't a direct link from the engine to the rear diff. It goes through the input shaft, the planetary carrier then to the wheels.

The planetary carrier is held in position by the VC. If the fronts lose traction, the outer planetary (RWD) will move in reference to the inner sun-shell (FWD). The VC will get hot and will try and lock up to split the tq in the same ratio. The ratio is fixed based on the relationship of the two gears.

However, the VC will not transmit as much power to both sets of wheels. If the engine tq overwhelms the tq capacity of the VC then it will just spin the VC, same as a converter that is too loose. Like a tq converter, excess power will get converted to heat, heat kills the VC.

They probably work fine on lower powered vehicles but one or two episodes of high power tq split and the VC is toasted.
 
skolman91

skolman91

Member
Re: Transfer Case Viscous Clutch ?

[QUOTE='Quickstop [UK]

However, the VC will not transmit as much power to both sets of wheels. If the engine tq overwhelms the tq capacity of the VC then it will just spin the VC, same as a converter that is too loose. Like a tq converter, excess power will get converted to heat, heat kills the VC.

They probably work fine on lower powered vehicles but one or two episodes of high power tq split and the VC is toasted.[/QUOTE]
This is what i was getting at, if the tq over powers the loose VC wouldnt the majorty of the power go to the least reaistance like a open differental.. The VC is just like the lsd clutch discs that lock up when slip happens.
Either way not good news, someone should find a reliable manufactuer of these, and the chains.
 
Sean Krupa

Sean Krupa

Moderator
Re: Transfer Case Viscous Clutch ?

Hey guys, I'm still learning about how this all works, but according to Dave who I just talked to.. with the Propshaft still in the VC does nothing unless you break the tires loose. I've had the Propshaft installed since last year and have given it all the power since then and been fine. Got on it today and pulls hard no sign of slippage.

My buddy ordered a couple of the Rebuilt GM VCs from STE in Cali and I'll be testing them within the next week. They should be the answer for a reliable replacement. I'll keep you guys updated. But for now, my truck is driving great like it should AWD, and Dave will be discussing to STE about how all these guys ran without a Prop and drove fine soon. He will also bring them a good known stock unit to compare since it's Tight.
 
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