The DaveP Viscous Clutch / Transfer Case Test

[DaveP]

I frequently see peeps refer to this test, or suggest that it be tried. I originally wrote it 3-4 years ago, but now can't find it either, although I think it still exists. Here it is again. Now it's in the title, so it should show up in searches easier.

This test can be run with the T-case installed in the truck, or loose on the ground. What is being checked is the torque required to make the V-Clutch slip. I have checked lots of properly-functioning T-cases over the years. While this test is not scientific, or even to a manufacturer's specification, it will identify whether a V-clutch is "Locked", or "Open".

Here are the conditions for the test:

• Input shaft free to turn. If installed, transmission in Neutral.
• Rear output shaft Locked. If installed, put a bar through the u-joint, and lodge it against the floor or frame.
• Front output shaft is where you will apply the torque for the test. Use a socket on a torque wrench on the front output flange nut. If installed you can guestimate applying 40 foot lbs to a bar to turn the front shaft. One front wheel must be free to turn. Work safely under the car.

The "DaveP Spec" is:

• 12-15 Seconds
• to turn the front output 90º,
• at 40 ft lbs torque applied.

Here are a couple of pics of how I set up a case on the floor of my shop. Note that I turn the nut in the CW direction, so as not to loosen the nut.





Remember: There should be resistance between the front and rear outputs. If it is very loose, or breaks away quickly after torque is applied, the V-Clutch has failed Open. If you can't budge the front output with the rear locked, be sure trans is in Neutral, and if it still won't budge, the V-Clutch has failed Locked.

The failure mode that results in broken front axles, split boots, exploded propshafts, busted front diffs, and low-speed "parking lot jumps" is a LOCKED V-clutch.

Hope this helps someone.

 

[atomicmecha]

Re: The DaveP Viscous Clutch / Transfer Case Test

If I'm understanding this correctly, this can be done with the transmission in neutral and the rear wheels on the ground and the front prop shaft removed?

 

[DaveP]

Re: The DaveP Viscous Clutch / Transfer Case Test

If I'm understanding this correctly, this can be done with the transmission in neutral and the rear wheels on the ground and the front prop shaft removed?

Yes, BUT be careful!

IF the V-clutch is locked, and you apply torque to the front output nut, you will "drive" the rear wheels. You can push the truck right off jack stands, etc.

Be VERY, VERY careful working under the truck, and turning driveshafts with wheels on the ground. Think about what can happen as you're working. :myclone:

 

[RealFastV6]

Re: The DaveP Viscous Clutch / Transfer Case Test

GM published a very similar test for the NVG149 transfer case in 2003. Is that what you based this test on Dave?

 

[RealFastV6]

Re: The DaveP Viscous Clutch / Transfer Case Test

If I'm understanding this correctly, this can be done with the transmission in neutral and the rear wheels on the ground and the front prop shaft removed?

Wouldn't it be safer to put all 4 up and use the parking brake to stop the rear wheels?

 

[DaveP]

Re: The DaveP Viscous Clutch / Transfer Case Test

GM published a very similar test for the NVG149 transfer case in 2003. Is that what you based this test on Dave?

Someone posted that test on here. I looked at it, and the specs for the 149 were much looser than what I felt a BW was going to be. But yes, that test inspired me to develop a similar procedure for a SyTy case that anyone could use.

The spec I came up with: 12-15 seconds, to rotate the front output 90°, at 40 ft lbs is based on testing numerous properly functioning T-cases over the years. While NOT scientific, it WILL identify a viscous clutch that is not functioning properly.

I didn't name the test after myself; others here began to refer to the test by the author's name.

 

[RealFastV6]

Re: The DaveP Viscous Clutch / Transfer Case Test

Someone posted that test on here. I looked at it, and the specs for the 149 were much looser than what I felt a BW was going to be. But yes, that test inspired me to develop a similar procedure for a SyTy case that anyone could use.

The spec I came up with: 12-15 seconds, to rotate the front output 90°, at 40 ft lbs is based on testing numerous properly functioning T-cases over the years. While NOT scientific, it WILL identify a viscous clutch that is not functioning properly.

I didn't name the test after myself; others here began to refer to the test by the author's name.

Yeah agree your spec for our case seems to be right-on. I've used it to test a few spares I had kicking around.

 

[fivetodrive]

Re: The DaveP Viscous Clutch / Transfer Case Test

Dave asked me to add this to the sticky!

I spent a little time this morning removing the viscous coupler and planetary out of my transfer case. while I was doing this I noticed that it felt like me viscous coupler was not tight enough. so what does any good side tire do he does the Dave P viscous test. this one failed open.

here is a video


http://youtu.be/REg0uT-xq5o

I also thought it was a good time to make a video of disassembly. and also show how easy it is to put the for a 4l80 input shaft in the transfer case.

http://youtu.be/IDzCeXWhAYI

 

[atomicmecha]

Re: The DaveP Viscous Clutch / Transfer Case Test

Just did this test on one of the spare cases I have. Steel rod through the yolk of the rear output. Stood on that and applied torque to the front output. Had smooth resistance and passed the test. Glad I had this. Saved me from guessing or spending money on parts I didn't need.


Also, noticed the input does not spin at all during this. Thinking that's normal? I would think it would spin but it might be sticking just enough because this case needs a cleaning and oil before being used.

 

[atomicmecha]

Re: The DaveP Viscous Clutch / Transfer Case Test

Dave asked me to add this to the sticky!

You said in the first video that it failed open? Isn't how that case responded the right way? Thought if it was failed open there would be no resistance or it would have soft spots in the torque while rotating it.

 

[fivetodrive]

Re: The DaveP Viscous Clutch / Transfer Case Test

There was only 20 lbs of force. It was easy to spin...

 

[atomicmecha]

Re: The DaveP Viscous Clutch / Transfer Case Test

There was only 20 lbs of force. It was easy to spin...

Ah, that makes sense. Mine was not easy to spin at all.

 

[Typhoonracer]

Glad I re-found this!!!

 

[Typhoonracer]

Just redid this test over the weekend and passed with flying colors.
Now to look at geometry... and figure out WHY I keep braking CV axles. (Too short is a possibility)

 

[sprinter]

My Sy#427 has a locked up viscous coupling, I ran without a front prop shaft for a fe weeks while I was building a new one, lesson learned. I have a spare tc but it also has a locked VC. I have it out of the TC but can’t seem to locate replacement packing “ lube”. Does anyone know where I can source some or if anyone rebuilds these things.
HELP PLEASE

 

[vinnieTy]

The time has come that I will need to rebuild mine as the testing has failed. Sport machines doesn't have the parts in stock however to plan ahead is there an actual full video of the steps to do a transfer case rebuild? Cant find any on line. thanks

 

[2500avalanche]

I remember buying from Cobra transmissions back in the day, but I am not sure anymore...

 

[Isthatthingstock99]

The time has come that I will need to rebuild mine as the testing has failed. Sport machines doesn't have the parts in stock however to plan ahead is there an actual full video of the steps to do a transfer case rebuild? Cant find any on line. thanks

Vinnie, I just wanted to tell you that I have never taken apart a transfercase before setting up my Sy's on the bench. I tore it apart and used the attached PDF file for reference. If I was able to do it, you can too. I believe, though I don't have it in front of me, the Sy/Ty manuals available online also have an image that is similar and indicate the re-assembly. Something important to note about this PDF, I have not verified the reliability of the indicated part numbers. So unless you can verify the part numbers, I wouldn't use them for what to purchase for your case. This is just a good visual reference for disassembly and re-assembly should you not have one.