diffs and 4wd

[NeilT]

I promise i have searched before posting this!

There is something i can't understand about the 4WD system on my surf which I'm hoping someone can put to rest -

All agree that you shouldn't use 4wd on the road or you'll get transmission wind-up and snap a shaft etc. But most people seem to say that the Surfs don't come with locking diffs as standard. So if the diffs are not locked why would you get the transmission wind-up?

The way i understand it is the front diffs are always open (so same as 2wd car)
some Surfs have LSD rear (but even still they can slip so no transmission wind-up there....)
Is it the center diff that is locked?

In normal driving mode I've got 2wd at the rear, if one wheel spins i stop. I put it into 4wd, does that lock the rear? No? Then if one front wheel spins also will i still be sitting there like a pillock?

If the diffs are not locked why would there be transmission wind-up?

Sorry guys i know it's an old one but i just don't think i got it yet

Cheers
Neil

[Morr]

In order to prevent wind up a differential assembly is required between any 2 rotating assemblies recieving input from one source, ie driveshaft to rear splits to each wheel with a diff permitting different rotation speed between the wheels, same for the front.
When in 4wd you are splitting the gearbox output into 2, ie sending drive to both front and rear, however in the 2nd Gen Surf (and a great many other offroaders) there is no diff at this point, ie it will not permit front and rear systems to rotate at different speeds.

To allow use of 4wd on tarmac a total of 3 diffs are required, 1 in each axle plus in the transfer box

[NeilT]

Gotcha! So it's transmission wind-up in the shafts between front and rear not left and right on each axle. I think it was that i imagine going around corners effecting left and right more but it's to do with opposite corners instead.

Cheers for that, i think i got it now anyway....

[NeilT]

I've just noticed your picture and it looks like you have the same wind deflectors as i have. One of my clips is broken, do you know where to get spares? They are rivetted onto the plastic and clip into the window rubber. I can only find people selling the clip-less types on the web.
Cheers

[Morr]

Gotcha! So it's transmission wind-up in the shafts between front and rear not left and right on each axle. I think it was that i imagine going around corners effecting left and right more but it's to do with opposite corners instead.

Cheers for that, i think i got it now anyway....

Yep the windup is more or less in the shafts between front and rear sections, but if it builds up enough and has to release it will do it thru the weakest link it can find, which could be anywhere in the drivetrain, could be transfer box, CV joint, or theoretically anwhere else.


As for the deflectors, sorry came with the vehicle so I've no idea where you can get spare clips. Try your local breakers, or there are a few guys on here breaking Surfs from time to time, try asking in parts wanted.

[Chillitt]

ok so if wind up seeks the weakest link to er.. loose itself... surely that will be between the tyre and the wonderful english tarmac (ahem) meaning you just scrub the living bejesus out of your tyres.... doesnt it?

[Morr]

ok so if wind up seeks the weakest link to er.. loose itself... surely that will be between the tyre and the wonderful english tarmac (ahem) meaning you just scrub the living bejesus out of your tyres.... doesnt it?

Hopefully yes, that's all it should do, but when you are in a high continious (spell?) grip situation such as tarmac, it can take a lot to cause the tyre break traction, meanwhile the wind-up effect is putting strain on all other components involved. If something along the line is worn or already weaked for any reason, it could be the bit that lets go instead.

[NeilT]

In Chris Scott's Sahara Overland book he says even on wet roads he wouldn't want it in 4WD if it would wind up like our Surfs - he thinks the tyres, or a tyre i guess, suddenly letting go could cause a spin out on a corner, which makes good sense.

[JimL]

I doubt a wet road would be appropriate to have a 1st or 2nd gen in 4wd, hes right

[TonyN]

ok so if wind up seeks the weakest link to er.. loose itself... surely that will be between the tyre and the wonderful english tarmac (ahem) meaning you just scrub the living bejesus out of your tyres.... doesnt it?

On full lock your outer CV will lose with a few blips of throttle on dry tarmac.

The rest of the drive train is plenty strong.

[keithy]

transmission wind up

Just a point i have a 97 3.0 surf ssrg and can run in 4wd with no diff lock and no wind up is this just cos its a later model or am i missing something?

BY the way how do you tell if your rear diff is limited slip or not?

[TonyN]

Just a point i have a 97 3.0 surf ssrg and can run in 4wd with no diff lock and no wind up is this just cos its a later model or am i missing something?

BY the way how do you tell if your rear diff is limited slip or not?

No, 3rd gen are different, they are part time or perminant 4wd set up, its up to you, and can run happily in 4wd as they have a diff in the transfer case, when you lock the center diff, then it is just like a 2nd gen and shouldn't be used on the road.

AS for the LSD, either take the diff apart and see if its full of little clutch plates, or try and wheel spin it away from the traffic lights, open diff will only spin one wheel, if you have an LSD it should leave 2 rubber lines!

Seriously, LSD axles have a small while sticker on them saying 'LSD oil only' if you have a slipper.

[Gamedawn]

BY the way how do you tell if your rear diff is limited slip or not?

The other way is to look at the axle code on the Vin plate. If it ends in a 5 or (I think) a 3 then it's a lsd - if it ends in a 2 or a 4 then it's open. Mind you, some of Tony's methods are probably more fun

[Gizmo]

No, 3rd gen are different, they are part time or perminant 4wd set up, its up to you, and can run happily in 4wd as they have a diff in the transfer case, when you lock the center diff, then it is just like a 2nd gen and shouldn't be used on the road.

AS for the LSD, either take the diff apart and see if its full of little clutch plates, or try and wheel spin it away from the traffic lights, open diff will only spin one wheel, if you have an LSD it should leave 2 rubber lines!

Seriously, LSD axles have a small while sticker on them saying 'LSD oil only' if you have a slipper.

Thought mine was LSD due to sticker being present on rear diff casing [all text missing though], but after wheels off ground recently noticed they acted like open diff [wheels turn opposite when rotating] and the VIN code on bulkhead finishes off with a 4 against the Axle Code so must be open

[Linda]

The other way is to look at the axle code on the Vin plate. If it ends in a 5 or (I think) a 3 then it's a lsd - if it ends in a 2 or a 4 then it's open. Mind you, some of Tony's methods are probably more fun

Errr Sorry Roger.. Mine has an LSD but ends in a 2?????