Oil on rear brakes

[Nick Salmon]

I was reading a 1991 edition of The Bulletin and came across this, reproduced from The Austin Magazine of January 1932. As I have just this issue to deal with I wonder if anyone can shed light on the 'larger nut'?


Question: I find that there is a slight tendency - nothing to worry about in particular - for oil to penetrate from the back axle casing through the hub onto the lining on one of the rear brakes of my 1930 Austin Seven. Though only slight, as I say, I am afraid that this leakage may develop and prevent the brake from acting with its normal efficiency.I have reduced the replenishments of lubricant for the axle, but the oil still seems to get through. Is there any means I can adopt of overcoming this trouble without dismantling the hub or draining the axle?

Answer: Our Service Department can supply a special nut that is designed to act as a further means of stopping any oil that may pass the oil retaining washer in the Austin Seven rear hub. This nut is of a larger size than the axle nut formerly fitted as standard, and when tightened home, makes an oil tight seal with the end face of the hub. By fitting one of these axle nuts in place of that now used on your car, you will no doubt be able to overcome the trouble. When you have tightened this nut home, do not forget to secure it with the split pin.

[Zetomagneto]

It is the half shaft nut, so will only cure the leak if oil is finding its way along between the axle taper and rear hub.The larger nut covers a greater area of the outer face of the hub, in other words the larger nut is larger when measured across the flats.Will only cure the leak if that's where the oil is coming from!

[Derek Sheldon]

Modern oil seals available from Seven Workshop,a good fix

[Bob Culver]

On several other makes I have often been surprised how much oil finds its way past the keyway, and nut face and thread. The leak is external but oil can work its way behind the face of the brake drum. Daubing paint over the nut will often seal. Modern h.m.p bearing grease uncontaminated will likely not exit.

If the hub flange gasket or substituteis is inadequate grease will find its way into the brakes. (whateve the arrangement the wheel bearing ideally should not float endways in the assembled hub. The steel seal washer reduces the clearance.)

Period advice to fill the hub with grease is absurd unless wading is intended. Packing little more than the races will suffice for years. And it has been long established that filling the diff to the book level is unnecessary and overtaxes the original simple seals within the axle tubes. Once diff oil reaches  and adds to the bearing grease, little except  modern seals running on good surface will retain. Very many "modern" allow the diff oil to freely reach the wheel bearings and rely entirely upon the final seal. Sealed bearings assist but are not really intended to block the passage of oil.

[Steve Berg]

On several other makes I have often been surprised how much  oil finds its way past the keyway, and nut face and  thread. The leak is external but oil can work its way behind the face of the brake drum. Daubing paint over the nut will often seal. Modern h.m.p bearing grease uncontaminated will likely not exit.

If the hub flange gasket or substituteis is inadequate grease will find its way into the brakes. (whateve the arrangement the wheel bearing ideally should not float endways in the assembled hub. The steel seal washer reduces the clearance.)

Period advice to fill the hub with grease is absurd unless wading is intended. Packing little more than the races will suffice for years. And it has been long established that filling the diff to the book level is unnecessary and overtaxes the original simple seals within the axle tubes. Once diff oil reaches  and adds to the bearing grease, little except  modern seals running on good surface will retain. Very many "modern" allow the diff oil to freely reach the wheel bearings and rely entirely upon the final seal. Sealed bearings assist but are not really intended to block the passage of oil.

Bob, I understand the book level of oil in the back axle is 1 pint. I guess half of this, 200-250 ml, be sufficient. Do you agree?

[Bob Culver]

I am no authority on the ideal level. There have been very extensive posts on and someone can hopefully refer to. The main thing is that never allowed to run really low and dry.

For decades my RP was maintained full but not without problems. The first suggestion of a lower level I read in an old NZ VAR mag where it was recorded that Len Southward used to advise. Pre war Len ran a business specialising in Seven maintenance, but is now remembered mainly for the world renowned motor museum he later established.

[Parazine]

I am no authority on the ideal level. There have been very extensive posts on and someone can hopefully refer to. The main thing is that never allowed to run really low and dry.

For decades my RP was maintained full but not without problems. The first suggestion of a lower level I read in an old NZ VAR mag where it was recorded that Len Southward used to advise. Pre war Len ran a business specialising in Seven maintenance, but is now remembered mainly for the world renowned motor museum he later established.

I usually go for about 1/2" - 3/4" below the filler plug level. The exact level doesn't matter too much, the key point is that the oil level shouldn't be above the half shafts, otherwise it will leak down the tubes. All of the differential components get covered in oil film and that provides the lubrication necessary.
For regular servicing, just check that the level is maintained and as Bob says, the axle mustn't run too low.

[Ruairidh Dunford]

Adding to Tim’s comment above - I was taught to jack the car up by the rear cross member until the axle hangs down with the wheels off the ground and then fill until oil just starts to come out the hole. This most probably equates to it being 1/2-3/4” below the oil in normal operating position.