Thread: Viscous Coupling

Hi BO00YA .... On a side track .... What symptoms have you been experiencing that lead up to all this in the first place??

Mike

Originally Posted by BO00YA

Hey Garry,

I did the test exactly how you described in your video. I gave as much steady pressure as i could. If i can take wheel nuts off, i'm pretty sure i would be able to turn the VCU if it wasn't seized. I'm just very confused at the moment.

If the dot test worked, would that indicate that the VCU is fine?

I can understand the confusion. My VCU is very tight and requires considerable effort to move the wheel - most other people can move theirs with considerably less effort. How long is your breaker bar that you are using on the socket? Mine is about 2' long.

Have you done the reversing test - it is this scenario that normally gives first indication that the VCU is suspect requires further investigation.

Garry

Hey,

My breaker bar isn't as long as yours Garry. The reason why i wanted to test it was because reversing out of my driveway at full lock it felt tight. I've noticed it only really happens when the car is cold, like in the morning when i go to work. If i get home and leave soon after it reverses out fine..

Ben

Originally Posted by BO00YA

why i wanted to test it was because reversing out of my driveway at full lock it felt tight. I've noticed it only really happens when the car is cold

Garry .. correct me if i'm wrong ..

Ben ....The Viscous unit goes "locked solid" when stuffed /// regardless of the temperature .... Start the car / Drive around the block / Jack up the wheel & then try your wheel test ......

Originally Posted by BO00YA

Hey,

My breaker bar isn't as long as yours Garry. The reason why i wanted to test it was because reversing out of my driveway at full lock it felt tight. I've noticed it only really happens when the car is cold, like in the morning when i go to work. If i get home and leave soon after it reverses out fine..

Ben

It will always get a little tight but not really tight. I was having the same issue when backing out on cold mornings - that was prompted me to check mine and the film what I was doing.

To be honest - it sounds as if your VCU is OK.

Garry

Originally Posted by mike 90 RR

Garry .. correct me if i'm wrong ..

Ben ....The Viscous unit goes "locked solid" when stuffed /// regardless of the temperature .... Start the car / Drive around the block / Jack up the wheel & then try your wheel test ......

Unlike cooling fan viscous units, the VCU is not temperature related and the fluid does not lock due a change in temperature. The fluid gets thicker as a result of shear forces - internally the VCU has a series of stators and rotors - when the housing with stators attached rotates at the same speed as the input shaft with the rotors attached there is not difference in speeds so the viscosity of the fluid does not change. As soon as there is a difference in speed like when off road (front wheels turning different to the rears) the shear forces in the fluid between the rotors and stators causes the fluid to thicken so the rotors start to drive the stators. Simply the drive is transferred to the rear wheels.

Clear as mud .

Garry

Originally Posted by garrycol

Clear as mud .

Understood every word written ....

Only giving some "input" to this subject, as my RRC has the viscous unit also ... and have had to perform tests on it to check that it's working

Mike

Originally Posted by garrycol

It will always get a little tight but not really tight. I was having the same issue when backing out on cold mornings - that was prompted me to check mine and the film what I was doing.

To be honest - it sounds as if your VCU is OK.

Garry

Yeh i think for now i'm not going to get to concerned about it. Although i'm going to keep a very close eye on it and check it regularly.

Thanks for your help guys.