Diff lock issues ( possibly )

[RebelV8]

My recently acquired 2nd gen 3.0L has a diff lock in the back axle. Was out in it last night in the rain and it really doesn't like corners in the wet. Give it the slightest amount of power and your sideways before you know it without warning.
Huge amounts of fun but due to the lack of warning, a little dangerous, I would have thought.
Question is, is this behaviour normal, I know nothing about diff locks but assume they're the same or similar to the LSD that was in the back of my Mustang.
I could drive my Mustang in all weathers and it would only slide when I wanted it to or there would at least be a bit of warning before it stepped out. Which leads me to think something's wrong with the diff lock in the Surf.
Could it be something simple like needing new or better tyres?
Reducing the tyre pressure?
Or something wrong with the diff lock?
Is it a big, awkward or difficult job to return it to normal?
I was given two small gears ( cogs ) with it and told by previous owner that using them, I could return it to normal diff.
Need help as it's really undriveable in the wet

[tweak'e]

is it a little bit clunky especially on slow sharp turns ?
any clicking around long corners ?

i suspect they have fitted a lunchbox locker ie auto-locker, which replaces the spiders (the small gears they gave you).
they require a different driving style.
they are actually locked all the time. to get them to unlock for a corner you need to lift throttle and coast around the corner.
i never found it a problem in the wet if you drive correctly.
i removed my auto locker because i shifted into town and driving around at slow speed on tarseal is uncomfortable.

the other possibility is the locker is broken and its locked permanently. the give away is usually tire squeal on dry tarseal.

edit: i should add that throttle forces the locker to lock. if you do that while going around a corner, it forces the two different speed tires to go the same speed. that is very abrupt and can cause loss of traction on one wheel for a moment. thats probably whats causing your slide.
in the dry theres usually a bang and a tail end shake when they lock abruptly.

the other thing is because its locked you have more traction on the strights and can lead you to think you have more traction than you have and go faster than normal into a corner.
its a matter of taking it easy around corners.
even coming out of a turn you need to wait, wait and wait, until your fully straight before putting on the gas. ie no accelerating out of a corner.

[RebelV8]

Thanks for the explanation, really helps to understand it.

It doesn't seem to be clunky on sharp, slow turns.
I haven't noticed any clicking round long corners.

I haven't tried lifting off the throttle going round corners, I'll give it a shot.

The previous owner said it was supposed to disengage when it was on tarmac but it never had since he fitted it, so he just lived with it that way.

At parking speeds, or when reversing off my drive you can hear and feel the tyres scrubbing as you go turn. There's some tyre squeal on slow corners when the roads are dry.
If giving it some throttle on a corner makes it lock, then yeah, that would explain it sliding. I was going round a sharp ish corner that was also uphill so I had to put my foot down a little to get up the hill as it went round the corner, then it just went sideways, lol. No warning just started sliding very quickly.

I haven't heard any bangs on a dry corner, might have felt a little tail end shake though.

Sounds like I just need to learn how to drive it properly then.
If I lift off the throttle going round a corner, can it still slide?

Is it a big, difficult or awkward job to take it out and put the original spider gears back in?

[tweak'e]

uphill corners is the worse situation for using them.
with it unlocked, going around a corner you only have half traction for going forwards. so easy to overpower that one wheel thats been driven.
but being uphill it will often force it to lock and that can upset the grip if traction is border line.

not a huge job to change it back to stock. but you do need some gear.
i can find a link for you.
if you get a shop to do it look at fitting something else instead.

[tweak'e]

http://www.gearinstalls.com/v6lockrite.htm

good site to look through. most diesels use the v6 diff
i hope they gave you the washer for spiders to. should be 4 spiders by mem.

[tweak'e]

i forgot one thing.
you have to run identical tires with the same air pressure and tread depth.
when driving straight they need to rotate the same. if one is different (eg flat or worn) then it will try to unlock ever now a then. also the surf will be trying to turn all the time so the handling is going to feel a bit weird.

with open diffs you end up with one tire more worn than the other. then they put the locker in but forget to change the tires, and try driving with uneven tires.

[RebelV8]

Need to be careful on wet uphill corners until I get used to it then.

If I change it, I've probably got all the right gear. Only have two spiders in the box though, although there are some washers in there as well.

Thanks for the link, really helpful.

All four tyres are identical in make, tread pattern and pressure, they are worn but both seem to be worn by the same amount. I was thinking of reducing the tyre pressure a little, just incase they've been over inflated

Thanks again for all your help

[tweak'e]

Only have two spiders in the box though, although there are some washers in there as well.

that might be a problem. you should have 4 gears left over regardless of diff.
the typical diff has 4 spiders left over. the "4cyl" 2 spider diff you only have the two spiders but you also replace the two side gears as well. so you should have four gears left over.

easy way around it is to get another diff head of that ratio and swap them out.

[tweak'e]

I was thinking of reducing the tyre pressure a little, just incase they've been over inflated

Thanks again for all your help

that will help. by having some tire flex the tires will absorb some of the minor differences when driving.

[RebelV8]

Ok,
I'll try learning the right driving technique first as well as reducing the tyre pressures a little and see how that goes.
Thanks for all your help

Just a thought, but i suppose it could be possible that the previous owner only replaced two spiders and left the others as original?

[tweak'e]

Just a thought, but i suppose it could be possible that the previous owner only replaced two spiders and left the others as original?

no, there simply no room for spiders to be left inside the diff.

see how you go with it. i found open road to be fine, just around down was a bit of a pain.

[RebelV8]

Ok, will certainly give it a go