Friction Modifier in rear diff

[ralfnada]

Does anyone know if the full synthetic Castrol diff oil made now still requires the addition of a friction modifier for the LSD clutch packs please?
Just aquired a clean UX 03 XLT and it has the dreaded whine in the diff.
The TSB back in 04 said change to a 120 and add 4ozs of modifier as well.
The dealer will replace the oil but he says the new beaut Castrol synthetic already has a modifier in it so no need to add more.

 

[blueoval9erlifer]

I would just buy the friction modifier and then tell them to put it in since you have it. Its not like the extra modifier is going to hurt anything.

 

[IAmTodd]

I've heard the synthetics don't require the modifier. You could always try to run without it. If if makes noise then you can add a half bottle or so into it.

 

[delexploder]

If its whining then rebuild it just making it quiet with thicker oil and more grit will only make it worse down the road. Back in the day the Stealerships would put sawdust in them to make them quiet and its just a more expensive version to add the " better " fluids. I grew up in a shop that builds rears if it makes noise it needs parts

 

[ralfnada]

Hi blue oval, thanks for your thoughts with this.

 

[ralfnada]

I am Todd, At least we have some options here. Thank you

Delexploder, I would have thought that incorrect meshing of the heel and toe of the ring gear can cause this noise. I've screwed the dealer down to honouring the warranty for the replacement of the carrier bearings if this first plan doesnt work.