Offroad-Express

HELP PLEASE

Land Rover Diff.

Can someone advise me with regard diff ratios for my 109 workhorse ? Holden motor - high ratio diffs.

Rear diff is unserviceable, presume it is a 3.54 ( 13 to 46 teeth ).
Broke an axle carrying too much - all down hill from there !!
I have a replacement, but it is a 3.9 : 1 ratio ( 10 to 39 teeth ).
This diff appears to be in very good condition - the C.W. and P. seem to have wider and deeper teeth - it just looks heavier than the old one. All other parts of the unit and the casing appear identical.

I can find little information about a 3.9 ratio diff other than mention as being available as an after market option or maybe having come from an old Rover 90 CAR. The donor vehicle was an old worker, the diff housing has rover 219636 stamped on it and the pinion seal is a bolt in type.

Can someone set me straight on this ?

Also I am aware front and rear ratios should be matched, but given that 4 wheel drive is only used on the farm when ground conditions are soft and slippery, would I get away with 3.9 on the back and 3.54 on the front ?


Thanks,

John T.

I prefer to do a good job here. My truck is both a current restoration project and a full time worker in really rugged conditions. It is nearly 40 years old, but I have seen nothing newer that would do the work and take the hammering this machine gets.

Hi John,
as far as I'm aware your "40 year old 109" would have had 4.7:1 diffs when new.

I think that:

All leaf sprung were 4.7:1 (with exception of a few odd factory specials and stage 1 V8)

All coilers were 3.54:1 (including Defender, Disco and early Range Rover)

Up to about 93 the half-shafts had 10 splines on inner end, post 93 they were 24 spline. The 24 spline half-shafts are slightly stronger but the matching newer CV is weaker!

The 3.54 is the stronger diff of the two and there are 2 pin and 4 pin versions. The 2 pin has one pair of spider/planet gears and the 4 pin has 2 pairs. The 4 pin is stronger again but harder to find.

Wear of the hole in the nugget were the spider gear pin fits is the thing to watch for on a secondhand diff. On high k diffs the hole can get oval and causes lots of backlash/slop in the drive train.

I would strongly advise against fitting odd ratio diffs front and rear! If you managed to get away with it off road it would perform pretty badly as the front and rear wheels would be trying to turn at different speeds. If you forgot to disengage 4wd on tarseal for just a few meters the result would be real nasty.

A pre 93 disco diff would do ya, and probably be the most available. There are usually a few wrecking in trademe. Check a halfshaft and make sure the inner end has the same number of splines as you need (10 or 24) before stripping out the diff.

Cheers

L-andy

Pitangi wrote:
I have a replacement, but it is a 3.9 : 1 ratio ( 10 to 39 teeth ).
This diff appears to be in very good condition - the C.W. and P. seem to have wider and deeper teeth - it just looks heavier than the old one. All other parts of the unit and the casing appear identical.

I can find little information about a 3.9 ratio diff other than mention as being available as an after market option or maybe having come from an old Rover 90 CAR. The donor vehicle was an old worker, the diff housing has rover 219636 stamped on it and the pinion seal is a bolt in type.

Can someone set me straight on this ?

Also I am aware front and rear ratios should be matched, but given that 4 wheel drive is only used on the farm when ground conditions are soft and slippery, would I get away with 3.9 on the back and 3.54 on the front ?


Thanks,

John T.

I prefer to do a good job here. My truck is both a current restoration project and a full time worker in really rugged conditions. It is nearly 40 years old, but I have seen nothing newer that would do the work and take the hammering this machine gets.

From your description its sounds as though you do have a 3.9 diff head from an old Rover 90 car of the 50's.
These used to be sort after as replacements for the original LR diffs (4.7's) when holden engines or V8's were fitted.

You should not mix the ratios front and rear as even only been used off road in that state hard ground will take its toll sooner rather than later and you will be worse off.

If its a 3.5 diff with 10 spline axles you require then there should be a few around as they were used in the early classic Range Rovers and coil sprung Land Rovers up to 1993 when they changed to 24 spline axles.

If it's a 109" shouldn't the rear be a Salisbury?