As my car approaches 70 000 miles (and I've started driving it again in the wheelspinny wet) I think it is time to treat my diff. I have changed the gearbox oil to mt90 and the engine oil is changed all the time. But as far as I know it's 24 year old diff oil. Is it similar to doing the gearbox oil (not too hard) shoud it increase the limited slip effect and is there anything more to it than that?

 

Could someone point me to the good stuff on opie oils?

 

Thanks guys.

Diff unit is quite unstressed on the zed and just draining and refilling with the regular gear oil will be fine, in fact you will most likely find what comes out quite clean as unlike engine oil it does not get subject to combustion gases etc.

 

One tip, undo the fill plug before the drain, saves a whole lot of grief if you have trouble with the fill plug! as they can be particularly tight.

 

 

Jeff TT

I know, I have had that scare before, not something you do twice!

 

Thanks jeff :thumbup1:

shoud it increase the limited slip effect

The LSD unit is a sealed unit inside the crownwheel cage so changing the oil has no effect on its action.

 

Other than that Jeff has covered everything else you need to know.

A nice how to Tom

 

http://zhome.com/ZCMnL/PICS/diffoilchange/diffoilchange.html

Thats a good how to, thanks Gary. And Pete, if the limited slip effect cannot be preserved, does it wear out? I have no experience of a proper mechanical one, but can tell that the zed with its (viscous/torsen????) Diff handles in a totally different way to my open mx5s and capri. I thulought with it being fluid based that it would lose performance in a similar way to a badly maintained auto box.

Thats a good how to, thanks Gary. And Pete, if the limited slip effect cannot be preserved, does it wear out? I have no experience of a proper mechanical one, but can tell that the zed with its (viscous/torsen????) Diff handles in a totally different way to my open mx5s and capri. I thulought with it being fluid based that it would lose performance in a similar way to a badly maintained auto box.

The viscous seled unit in the Z32 diff appears to be a long lived unit. I have limited knowledge of how it works but it is relatively mild in its action although as you say you can feel it work. If it stops working then you will know and then its probably not fixable.

The conventional salisbury/ Kaz/Cusco style is different. you can vary the amount of slip/ no slip by altering the plates both the direction they fit and the number employed. these do run in the whole diff oil and the correct type of oil is required . Kaz do one as to several other firms. This will become contaminated over time due to frictional wear on the plates and will need to be changed.

A well torqued up plate diff is not a road friendly item in reality as it clunks and clicks as it works. They also have a tendency to send the car "straight on" at roundabouts... not good.

Some Nissan models do have a softer road going plate type diff which is more user friendly but ultimately not so effective in the heat of competition.

Im my opinion and based on my experience and that of colleagues is that for tarmac/circuit use a Quaife torque biasing type diff is preffered but for off road gravel/forest rally use a well torqued plate diff is the way to go.

I spose the roundabout issue with a racey diff like ones you named above, would be that you get a lot of 'thrust' or traction as both wheels work as a good team and push you forward. Whereas with ours you can spin one wheel without too much difficulty, then that picks up the other one and you have both wheels slipping and oversteer? Good to know we have a good compromise. As long as I can do square corners out of junctions and accelerate in the damp with it scrabbling a bit rather than spinning one wheel then I am happy.

 

I have been in a car that had a unsprung clutch and I assume all the other hardcore tranny stuff, and, yeah, it whined like a touring car and clattered and chattered. I swear I could hear the propshaft banging off the bottom of the car. It was a stripped out wannabe drift, R32 GTST. Harsh!

 

Thanks for all the good advice I will let you know how I get on :-)

Here is the simple explanation on the VC LSD from the book "300ZX Enthusiast's Companion":

 

300ZX enthusiast p43_44.pdf