Thread: Borg Warner viscous, Care & Feeding

This is related to other threads here, but I want to concentrate on what makes them work, or break, and how to extend the life to something financially bearable.

I cannot give you any "cut apart" advice as mine is still going well at 196KK.
However this is my experience.
I change the oil with Castrol synthetic ATF about every 20Kk now and I add some Moly or Teflon. I check my viscous at every 5K oil change. I recently changed the front seal on the box as it started to leak. I do not worry about slop in the front bearing as that is normal. Hopefully the above will reduce the operating temps in the TC. The oil discolours very quickly ( as I posted a while ago) so it seems to work hard.

I have a feeling that a lot of soft sand work will probably shorten the VC life as it has to heat up before it will lock and in sand the front and rear axles will turn at different speeds before the VC locks, so it will be constantly hot.

Regarding tyres, I have always run 40PSI rear and 28-32 front . Most of my work is done with a reasonable load and towing so I would imagine the tyre diameters would be similar. I have never used different tyres or tyres worn differently front to back.

Time will tell how long mine will last but I do think one key is good oil very often. This should help the rear output shaft but who knows?
Regards Philip A

Hi we used to rebuild/repack the viscous units but stopped when new became more economic. The silicon fluid in the coupling, when overheated, changes state and becomes solid, very like a solid lump of rubber. BE VERY CAREFUL if you attempt to split a unit, when the silicon changed state it expands and it often splits the weld, if it doesnt split the weld and you put it in your lathe to turn the weld off it will most likely EXPLODE blowing the end off, be warned.
Anyway assuming you split the coupling chances are a couple of plates are scrapped and will need replacing so you will need a second sacrificial unit, obtaining the silicon, with the correct viscosity and the anti oxident added is a nightmare (in the UK).
Hope this doesnt sound too negative but do be careful, I found out the hard way, ouch.
Regards Ian Ashcroft

The viscous coupling in my Rangie had done around 650,000 kms when I sold the car. it was functioning perfectly.
I changed the oil once a year using Nulon fully synthetic oil and half a litre of Lucas auto trans additive.
I was always careful with the tyre pressures running the standard tyres at the recommended pressures and my mud tyres a little lower but in a similar proportion of pressure front to back.
The car was a daily driver, always heavily loaded. As for 4wding, I did not spend too much time in mud if I could avoid it but used the usual High Country tracks winter and summer including a fair bit of snow driving.

Why would changing the transmission fluid make any difference to the life of the VC? They are separate items.

Well maybe no effect but I was talking about the entiire BW trans.
However I guess you could argue that the trans will run cooler and that will keep the VC cooler when not slipping.
Regards Philip A

Originally Posted by Ian Ashcroft

Hi we used to rebuild/repack the viscous units but stopped when new became more economic.

Hi Ian .... Thanks for weighing in the subject
Could you tell us if the RRC Viscous hub itself, is the same internal construction design as the P38?

Cheers
Mike

Hi Mike yes the couplings are physically identical and can for be interchanged, there may be a slightly different slip limit but for all practical purposes they are the same.
As a matter of interest these couplings transmit a fixed torque up to their design limit (then they slip and overheat), this is why you cannot spectacle tow a RR or a freelander ( freelander visc coupling is same principle but more plates as it is a direct drive not a visc controlled diff). Many people think th couplings slip up to a limit then start to lock up, not so, for exampile you can drive a RR without the front prop but if you drive it agressively the coupling will slip, overheat, and go solid.

Regards Ian Ashcroft

Originally Posted by PhilipA

However I guess you could argue that the trans will run cooler and that will keep the VC cooler when not slipping.

A bit of a stretch there, Philip! I'm not convinced.