Viscous Coupler Troubleshooting (1 Viewer)

[Stylo07]

After commuting on the highway in the Kansas City heat the past few weeks, I decided to lay under the truck and inspect things. I noticed the viscous coupler was very hot. The transfer case was quite hot, too. I've never performed this unscientific inspection before, so I have nothing with which I can compare.

I began troubleshooting... All four tires match, have about 6,000 miles, are within 2lbs of tire pressure and have been rotated once. I then put the transfer case in neutral, jacked up a front wheel and it spun with a little resistance. Then I took it to a gravel parking lot and did some lock-to-lock turns when I got off the highway. There was no skipping/hopping, the steering wheel turned fluidly. Then I locked the center diff in 4H and did some more turns. The center diff was clearly locking. Everything seems to be functioning perfectly, but the heat of the VC and TC is new to me.

Should the VC get too hot to touch for longer than two seconds?

 

[IBCRUSN]

Well, I can't really tell you whether you have any issues but everything else sounds in order. The guys that seem to have had issues with the VC seem to be where it locked up and the drive line binds. I can say under normal commuting around town in Wichita my tranny fluid temp is in the 140's at a minimum and the fluid is being cooled. That said the tranny itself will retain heat so I would suspect temps to be higher. Track down an IR thermometer and take some readings to find actual numbers.

 

[Stylo07]

Is an IR thermometer something I can loan from an auto parts store?

I've been reading, and found that the silicon fluid in the VC can degrade over time as it becomes contaminated with suspended metal particles. I'm wondering if that's the case -- it's still functioning, but is on its way out???

Any input is GREATLY appreciated. I just don't want this to affect the rest of the drivetrain, which I've spent lots of time/$$$ baselining.

 

[93yotasr5]

Have you recently/ever changed/ checked the t case fluid? Never hurts to flush it out and inspect it for anything out of the ordinary.

 

[Stylo07]

Yes, I did a drain/refill with Amsoil about 5k ago.

 

[jonheld]

After commuting on the highway in the Kansas City heat the past few weeks, I decided to lay under the truck and inspect things. I noticed the viscous coupler was very hot. The transfer case was quite hot, too. I've never performed this unscientific inspection before, so I have nothing with which I can compare.

Ummm...the VC is internal to the transfer case. You didn't have your hand on it.

 

[Stylo07]

You're right. I touched the portion of the case that houses the VC. It was very hot but seems to be functioning properly. I'm basically wondering if it's normal, or is it a sign of impending failure?

 

[jonheld]

The driveline and transmission tunnel get hot. The airflow from the front of the motor gets sucked through the transmission tunnel and out the rear of the truck. On a hot summer day after driving for a bit, it's going to get hot. The motor is hot, the transmission is hot and the transfer case is hot.

If your truck is driving normally and if the engine cooling system is functioning properly and if your fluids look good, then I wouldn't worry too much.

 

[Stylo07]

Thanks, Jon. That makes perfect sense to me. I'd read that a VC should only be warm to the touch. But in a full time 4WD vehicle it's seems unlikely that it wouldn't get hot.

 

[hawker7]

After installing my lift, and working on the rear drive line, I noticed the transfer case was really hot, so hot you didn't want to leave your hand there.

I have an IR thermometer and it read 160*. I called my friend, mag41snub up, and he came over and his measured the same or even a little hotter if I remember. I think these gear driven transfer cases just run pretty hot.

The fluid level was fine, and I had just changed it out last year using Valvoline 75-90.

I think you are fine.

 

[landtoy80]

Are you greasing the rear drive shaft yoke?
Is your yoke flinging grease?

If you are not flinging or seeing signs of grease working its way past the yoke and you are greasing it, then you are putting pressure on the output bearing of the t-case and thats where the extra heat could come from.

When I had a plugged yoke the t-case was super hot to the point where the viscus coupler locked up.

My VC would lock up after driving at hwy speed on hot day when making sharp turns.

 

[Stylo07]

Are you greasing the rear drive shaft yoke?
Is your yoke flinging grease?

If you are not flinging or seeing signs of grease working its way past the yoke and you are greasing it, then you are putting pressure on the output bearing of the t-case and thats where the extra heat could come from.

When I had a plugged yoke the t-case was super hot to the point where the viscus coupler locked up.

My VC would lock up after driving at hwy speed on hot day when making sharp turns.

I didn't think of that. The rear shaft was rebuilt about 6,000 miles ago, but I haven't greased it since then. I'll try that tonight and report back.

Thanks for the suggestion,
Matt

 

[Tools R Us]

... have an IR thermometer and it read 160*. ...

That is normal, I wouldn't worry about occasional 200F, so, no you can't hold your hand on it.

 

[bryson]

Are you greasing the rear drive shaft yoke?
Is your yoke flinging grease?

If you are not flinging or seeing signs of grease working its way past the yoke and you are greasing it, then you are putting pressure on the output bearing of the t-case and thats where the extra heat could come from.

When I had a plugged yoke the t-case was super hot to the point where the viscus coupler locked up.

My VC would lock up after driving at hwy speed on hot day when making sharp turns.

I don't understand how the driveshaft yoke being greased or not can have an effect on the t-case... Would you mind explaining?

 

[dansawyer]

I don't understand how the driveshaft yoke being greased or not can have an effect on the t-case... Would you mind explaining?

There have been reported cases where greasing the drive shaft splines has been associated with subsequent t/case bearing problems.

That said I would not jump to the conclusion not to grease the splines. The grease in the splines should work its way out just like the grease in the U joints. If that is not happening then something else is going on.

 

[Stylo07]

I went ahead and greased all zerks on both shafts. I won't know how if had an effect until I get home from work tomorrow.

I'm aware of the debate regarding how much grease should be in the splines, so I did about 5 pumps and left it at that for now. I didn't see movement while pumping. Regarding the concern of damaging the transfer case output by using too much grease on the splines, I thought it was provisioned for such an effect by using thrust bearings. I'm FAR from an expert on any of this - just trying to learn as I go along.

I'll report back regarding whether or not I notice any temp difference after getting home tomorrow.

 

[landtoy80]

A plugged yoke works as a hydrulic jack. You put pressure on the rear output bearing and rear diff. Pressure = heat.

 

[Stylo07]

REPORTING BACK:

I noticed no changes after getting home from work, so I pulled the zerk fitting and took it for a spin, compressing the rear axle over some curbs. No grease came out. I then installed the zerk fitting and pumped grease until I saw movement in the shaft. I can only assume it was extremely low, as I put approximately 25 pumps of grease in it.

Conclusion: The heat was/is normal. Perhaps some peculiar noises will go away now that the splines are filled with moly.

Comments/input are welcome. Thanks for everyone's help.

Matt

 

[doc W]

transfer case oil

Yes, I did a drain/refill with Amsoil about 5k ago.

When I first changed my transfer case oil I notices some metal particles. Immediately flushed it out twice again, ran it a few thousand miles then checked the oil. All clear. This was a year ago. Checked again recently and everything still clear.

Think is may have been some of the viscous coupling material. You may want to do drain your oil into a fine mesh screen and check on this.

 

[Pin_Head]

Think is may have been some of the viscous coupling material.

This does not seem likely. The moving parts in a VC are inside a welded, sealed assembly.