Land Rover Repair: 4x4, spider gears, viscous coupling

Question
heres a link to explain spider gears or unit. http://www.infodotinc.com/machines/11d.htm
thanks john
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i just bought a 91 range rover and i seems that the 4x4 does not work. when in mud only the rear tires spin not either of the front. i jacked the hole truck up and put it on stands and tried it and once again only the rear tires spun. i took the fill pugs out of the diffs and manually turned the rear wheels. you could see all the gears turnig in the rear diff and both wheels would turn along with both front and rear drive shafts. in the front if you turned the passenger side tire the gears in the front diff would turn but if you did that on the drivers side nothing would tun in the front diff, and only one wheel would turn. At no point did the front drive shaft spin by tuning the front wheels. Do i have mutiple problems? Do i even have a problem? thanks for any help.
Answer -
Hi John:

All Rangies up to 1989 or thereabouts using the manual 4spd LT95 and 5spd LT77 gearboxes have a vacuum operated centre diff lock.  The automatics 3spd TF727 with LT230 transfer box and the 4spd ZF with LT230 transfer box have a linkage. Later models with the ZF and Borg Warner transfer box have a viscous coupling instead so there is no manual control of difflock.

All Range Rovers are full time 4x4, and have a centre diff in the transfer case. With a standard open diff you only need to lose one wheel and you've lost all traction. Very early 4sp vehicles had a limited slip centre diff, but most will have a vacumn operated centre diff lock. Later 5speeds and automatics also have this, but the transfer case is a different model, although functionally it's the same.

Late model and current Range Rovers have gone back to a limited slip centre diff, again a different model of transfer case.

So it would appear that your Rangie is ok from underneath!  To engage all four wheels, you lock the diff BEFORE you engage your gears...then away you go.

Does this help?

Let me know if you have any other Q's.

JohnMc

So your saying that eventhough no gears in the front diff turn when you turn the drivers side front tire that there is no problem and all i need to do is lock the diff before you engage the gears what do you mean if its full time 4wd what do you need to engage. and how do you do it. sorry if i sound stuip but this is all new to me.
thanks again
john
Answer -
Hi John,
++++++++++++++++++++++++  Follow up +++++++++++++

John,

it is possible that you have have an axle problem with the front differential.  A fellow Rangie owner told me that sometimes the 'spider unit' (not sure what this is) located in the front diff can fail.  It usually happens to Rangies used for off-roading and is rare for just city use.

IF (BIG IF) there is an axle problem, its more likely the CV joint or half axle is damaged.  The axle would have to be taken apart and examined for wear.   I had CV joint work done on my '95 Disco and its very expensive.  $2000 +

To determine differential or CV damage, check the diff fluid for metal fragments.  Swab out the axle area and look for fine metallic particles.

If you have never done axle work...take it to a specialist.  There are specialized tools and settings that only an experienced mechanic would have and understand.

I wish you well with this problem.  

JohnMc
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I'll be glad to help you out...let me contact some Rangie owners and see if there is anything specific to your '91 that might surprise me.

Meanwhile, here is a fantastic website the describes exactly how 4x4 work. It has great animated examples that assist in learning about 4 wheel drive, all-wheel drive, part and full time 4 wheel drive...

http://auto.howstuffworks.com/four-wheel-drive.htm


I'll follow-up with some more info soon.

Regards,

JohnMc

Answer
Hi John,

Thanks for the great URL on spider gears and shaft.  I've made a bookmark of this site and will certainly give it more reading.  So far on my 10 year old Disco, the only problems have been with the CV joint and a half-axle.  

Here in Quebec, Canada, there are not many shops that will even look at a LandRover drive train problem.  I am forced to travel 1.5 hours to Montreal and have the dealer service the vehicle.  The work is good, but the cost is shocking.

Thanks again,

JohnMc