Rear Axle Pinion Seal

Changing a leaking rear axle pinion seal
(from Ken Bridges)

I get asked this quite frequently, and normally I wouldn’t really recommend tampering with the differential. But as it is a very common complaint I will show you how I achieved changing a seal my own DIY way. It is important to stress that the pinion shaft is normally set to a specific pre-load when they leave the factory. This is important because, if the pre-load is incorrect it can shorten the life of the differential, or at least make it noisy in operation, possibly leading to bearing failure. I don’t own a pre-load gauge but I have changed the seals quite frequently this way and have got away with it. If you do not feel confident about this method then it is best to leave the job to a suitably qualified person.

Step one: Slacken wheel nuts on right hand side only. Jack up the rear end of the vehicle and place axle stands in position as support either on axle casing or rear jacking points.

Step two: Remove road wheel, it is not really necessary to remove both wheels.

Step three: Mark propshaft and pinion flange with either a centre dot or Tippex for re-alignment later. Remove all four propshaft bolts and lay prop to one side or cable tie it up out of the way. It is not necessary to remove from gearbox.

Step four: Mark pinion nut and pinion shaft with paint or Tippex to mark their relative positions. This is important. You will now also need to make a tool to stop pinion flange from turning whilst the nut is removed. It is unlikely that even the handbrake alone will stop the pinion turning. I used a long piece of 25mm diameter tube with two 8mm bolts welded 55mm apart. These bolts will sit in two of the holes in pinion flange. Note which holes I used, the tube can then be supported by the leaf spring. See photos 1&2.

Step five: You will need a suitable socket and breaker bar. Mark the socket with Tippex or marker pen at the bottom once it is on the pinion nut. Undo the nut counting exactly the number of turns it takes to remove the nut from the shaft. It is important you get this right. Make a note of the number so you don’t forget it.

Step six: Place a container under the diff to catch any oil. Mark the pinion flange in relation to pinion shaft with Tippex or similar. Then slide the pinion flange off the shaft. You can now remove the old seal with a screw driver or chisel. I just poked a hole in it and levered it out.

Step seven: In theory you are supposed to replace the crush spacer on the pinion shaft. So carefully lift out the front bearing then slide out the crush spacer. Replace the spacer with a new one, then, replace the bearing onto the shaft. You should now carefully tap the new pinion seal into position. I used a suitably sized nylon drift.

Step eight: Before replacing pinion flange check the surface of the flange where the pinion seal sits. If it is badly worn you may be able to polish it out. In my case I had to remove about 0.25mm on the lathe as the surface was badly pitted by rust and was not making a perfect seal. I would not recommend you remove anymore than this from the flange as the pinion seal will then be too big to make a good seal. I got away with this luckily. If yours is too badly worn or damaged you may have to source one in better condition. One you have done this slide the flange back into position noting the marks you made earlier.

Step nine: If like me, you have to re-use the same pinion nut, I recommend you using a locking compound on the threads before re-assembly. Don’t forget to put it back on by exactly the same number of turns by which it came off. As long as you re-align exactly the marks you made earlier, everything should be as it was before. The pinion shaft has a small groove cut into it, in which you should knock the edge of the nut with a chisel into it so to stop it coming undone. Should you be fortunate to own a pre-load gauge the setting according to the Ford Manual is 11lbs including pinion seal drag!!!!! I should also point out you can only set it this way if the differential is dismantled with the crown wheel removed. Hence, why I do it my way.

Step ten: Refill the axle with the correct grade of oil to the level of the filler hole. Replace the prop-shaft. Tighten the bolts to 15-18 lbs ft. Replace the road wheel(s).

Summary. I have to point out here that this is my DIY method of doing this. I have said it before, that differentials normally require specialist tools to dismantle and reset, and they also have a preload setting on the pinion. Few people have such a tool to measure this with. If you are not sure about tackling this or are unhappy with this method, then it is best that you take it to an axle specialist/re-conditioner.