TD and TF Rear Axle Oil Seal

8 Mar

There has been some past debate concerning the above subject; it has been said that this is a never ending problem, but why?

The MGTD/TF does not have a flange gasket on its two mating surfaces, which also carries the oil seal in a bearing cap; this cap has to be machined to exact standards in order to control the oil flow, particularly at the two mating flanges which must be absolutely flat (and many are not) – so let us look at some of the reasons.

Firstly, the axle bearing must protrude when fully home exactly ½” from the axle flange; likewise the bearing cap recess for the bearing must also be the same measurement and the tolerance should be -0.000”+0.005”. I know this is technical to some, but it is to ensure minimum movement of the ball bearing race, hence less oil loss and also to the flange mating faces.

Now, the bearing and oil seal cap has a very thin flange and can easily become distorted and damaged on removal and on reassembly, so check before assembly that the flange surface is absolutely flat and free from surface damage; also check with a straight edge of a rule as the flange can be bowed due to the bolts being pulled up unevenly when the cap is tightened down over the bearing. If the cap is bowed then this has to be rectified by machining in a lathe, removing only the minimum amount of metal to achieve a perfectly flat surface. This is a difficult operation to set up in a lathe and is probably best left to a skilled engineer.

Using a dial indicator clock on the lathe to set the bearing cap up, the following format should be adopted; the clock has to be set up at the centre part of the flange, near the bearing recess as this is the only part of the bearing cap which is not damaged and is perfectly flat, so that the clock reads that the surface is truly flat as you turn over the lathe by hand (indicated by the clock hand being stationary on “0”).

The cutting tool used on the lathe should also be set at this point on the bearing cap with a feeler gauge size 2 thousands of an inch between bearing face and cutting tool. Again, turning the lathe by hand, wind out the cutting tool, start up the lathe to remove any metal (which will be very small), finish off by setting the cutting tool at the centre point of the bearing cap so that the cutting tool barely touches the surface; wind out the cutting tool, start the lathe, moving the cutting tool to the centre – you will only be taking off 2 thousandths of an inch of metal and nothing at the centre of the bearing cap. Now you end up with a bearing cap surface which is perfectly flat and the bearing race recess remains correct in depth; you have only machined away the imperfections of the cap surface.

Before you assemble the bearing cap in place you should check the axle collar, on which the oil seal runs, is also perfect (no ridges etc) and is a good fit to the axle shaft (no play). It will also pay you to check the collar angle against the angle on the brake drum (or wire wheel hub if fitting new components). There could be a very slight difference, which has to be rectified because these two angles have got to match and there is no room for error.

What I do is to apply a very small amount of engineer’s blue to one part of the taper cone the complete length of the taper, then insert the cone into the drum or wire wheel hub and rotate with a little pressure back and forwards; remove to see if the blue has transferred on to the drum or wheel hub in a uniform way and for the complete length of the taper.

If this is not the case then what you have to do is to apply a very small amount of fine grinding paste with grease to the cone taper and rotate the cone in the drum or wheel hub taper angle; you will see the dull finish it leaves on the cone angles, which again, must be uniform. Remove all traces of grinding paste from both components, including the slots on the cone body and try again with the engineer’s blue. If the results are good, then all is well. If not, you will need to get out the grinding paste and start all over again!

When you are satisfied that you have got it right you can fix the taper collar in place on the axle shaft, which must be tapped right up to the roller bearing face – this is important. Assembly of the bearing cap with a new oil seal, to which low melting point grease has been added (to the seal internally over the protruding bearing race) is best done with longer bolts, which will then line up all the axle holes correctly. At this point, put around the outer diameter of the ball bearing race an application of RTV sealant and also to the axle flange. Put on the brake back plate, insert the original bolts very tightly and you will see that the sealant is now showing on the bearing flanges, being squeezed out under pressure.

You put a very, very small amount of grease on the taper part of the cone – this is to create a sliding effect on the cone. Place the brake drum or wire wheel hub on the axle shaft and torque the central nut up to 125 to 150 ft lbs (a considerable torque, which will need and extension bar to achieve it). Finally insert the split pin in the castellated nut. Hopefully, it will line up, but more often than not it won’t and you’ll need some thin shims to help.

I have tried to write this technical article in layman’s language – I hope I have succeeded!

Alan Atkins
alan.atkins903(at)hotmail.co.uk


« Previous: “Dave’s Doughnuts” (Donuts) (No you can’t eat ‘em!) Next: MG TD “All Clear” – Redux »

Do you have a comment to make about this article, or a question for the author? Fill in the form below!

Comment publicly on this article