gregom

iTrader: (3)

My diff is starting to slip again, i.e. not locking, causing one wheel to spin during autox/track/drift... I changed the gear oil about 6 months ago and it helped a ton... was working great until last week. It works fine for the first few turns or so then once it gets hot, it becomes useless.

I'm going to change the gear oil tomorrow with 75w140 synthetic and see if that helps again (probably will)... but after doing some research on Nissan's VLSD it seems maybe we can add a shim/washer inside the diff which will help it lock a lot sooner, and feel more like a 1.5 clutch-type LSD. Take a look at Nissan Silvia forum topic discussing this:
http://zilvia.net/f/s-chassis/200226...-j30-vlsd.html

This looks like its not too hard to do and may help a lot, assuming the 350Z's VLSD is the same or very similar. Has anyone had any experience doing this, or done any research on it? I searched the forums and didn't find a thing specific to this mod.

Any feedback helpful, especially from you mechanical guys who understand how diff's work.

Z_ology

iTrader: (44)

You can do this...BUT I WOULD NOT RECOMMEND IT!!!

What this does is bind the spider gear to achieve the "locking action". This will wear the spiders out and possibly cause some other issues. The reason that adding washer on both sides acts the same as a 2 way is that it binds the spiders so much that they can't move at all!

By the way...changing the gear lube in the rear end does not change anything having to do with the vlsd. The viscous fluid is sealed in its own housing inside the diff. It is completely seperate from the gear lube for the rest of the rear end. Hope this helps.

RandomHer0

iTrader: (9)

The only way I could see changing the gear fluid helping the VLSD would be keeping it cooler in some way with better fluids...

Get a real LSD.

gregom

iTrader: (3)

Thanks for the replies guys... I did see a couple posts on there saying that exact thing. There's also posts saying some have been running it for some time without issue. I'm trying to think of what problems this could cause other than slowly tearing the gears in the diff apart. At which point you'd have to get an entirely new diff. It doesn't appear one can buy a whole diff new, looks like you have to buy the parts and build it, and if you could get away with just the gears and a few other parts might be able to do it for less than $300. But how often would it have to be done?

BTW I know the gear oil and gears are completely separate from the viscous coupling unit... but when I changed the gear oil last in hope to fix the diff because it wasn't really locking anymore, it did help, it functioned flawlessly after that all up until recently. But as RandomHer0 said, the oil for sure will affect cooling of the diff, which could help the VC unit. I don't know much about this technology, so i'm just speculating here... but maybe if the VC fluid is getting too hot it has the opposite effect and stops binding abilities. But you'd think, since the VC fluid is supposed to work when it gets warm, that it would work better the hotter it is. But every liquid has its effective temp range. Does anyone really understand this? I've searched online but can't find any good articles explaining it.

Anyway getting a real, mechanical clutch-type LSD is always an option, but certainly not a budget-minded one. So I may have just deal with small, short-term fixes until I can get the money for a full on diff. Either way racing for cheap isn't easy... its hard on a car and stock OEM parts can only take abuse for so long, so if I continue tracking my car I see some future repairs in order. Maybe I should invest in another car so i'm not daily driving my track car. Ugh... gotta pay to play right...

gregom

iTrader: (3)

Well I changed the gear oil in my diff tonight... that stuff was nasty! See tiny little metal flakes perhaps, but they were so small its hard to tell. I put in some fresh new stuff, i'm glad I bought the fluid transfer hand pump it would have been incredibly difficult without it. I'll know in a couple days when I get a chance to drive it hard if it has helped.

BTW does anyone know why "Genuine Nissan" diff fluid is 75w140 and the FSM recommends 80w90? Would there be a noticeable difference between the two?

gregom

iTrader: (3)

So it's been almost a full week and the oil change definitely restored my VLSD to full function. I think I will just get in a pattern of changing the diff oil every 6 months.