I changed the diff seal on my 1972 4/4 a few months ago so can offer these tips from experience:
There are a number of different pinion seals, make sure you get the right one based on year. As bad luck would have it my 4/4 had the most expensive Timken seal!
As I was unsure about the torque figure, I made a tool up to lock the pinion flange, which was nothing more than a 5ft length of 2" x 1" box section, bolted to two opposing propshaft bolt holes and relieved to allow clearance for a socket on the pinion nut.
I marked the pinion and the nut with some Tippex with a volunteer holding the locking tool,I used my torque wrench going up in stages until I felt the nut move very slightly which was 139 ft lb
You will probably need some sort of puller to remove the flange, a three leg puller is the best with a small block of alloy or brass to protect the pinion shaft threads
Unless you are very very lucky the seal will come out in pieces. This is probably the most time consuming part of the job.
Check for wear to the part of the pinion flange where it engages with the seal, there should not be any. If there is, you are in trouble as the seal won't er seal! Give the flange a nice coating of gear oil.
Give the outside of the seal a nice coating of RTV compound and install it, make sure it goes in square, make a proper fitting mandrel up if possible.
Refit the pinion flange and replace the nut, a I used a bit of medium grade Locite on the nut but that is due to personal preference. Re-torque to the figure you obtained when removing the nut.
Check the breather hole on the axle is clear and refill with your favourite lubricant.
Hope this helps
Arwyn
