Leaky rear wheel bearings ?

This is a Saga that keeps going round and rearing its ugly head. Rear wheel bearings can often leak all over your brakes. Old worn bearings can do it and sometimes new ones can. There are 3 routes that leaks can go. First is round the outside of the bearing case. There is supposed to be a raised lip on the seal that butts up against the inside of the axle case to control that. At least one make we see doesn't have that and is doomed to leak forever ! Second is between half-shaft and bearing. Rare, because the fit is so tight, but can happen if the shaft is hacked up by an angle grinder. 3rd is through the centre of the seal. When that happens it takes the bearing's grease with it, so is different to the other 2 in terms of the type of gunge you'll see everywhere. Here are some causes of leaks: 

1) Bearing fitted wrong way round on half-shaft

2) Bearing seal damaged during fitment to shaft (fitting press mistake)

3) Bent half-shaft

4) Bent axle case

5) Rear disc brake kit fitted

6) Half-shaft damaged by angle grinder

7) Faulty bearing or seal wrong (poor manufacturing)

Looking at the picture here and the above list we can carry out a few checks to rule some of these errors out. The side of the bearing shown is the inside. This faces inwards into the centre of the axle. Do not get this wrong - many have! If you look closely at the outside edge of the seal you will see it is raised slightly above the height of the outer metal edge of the bearing. This is crucial, make sure it is raised up, and make sure there are no nics out of it, before you put it on the shaft. If there is anything wrong get your supplier to change it. We check ours before we post them out. Some bearings out there do not have the raised seal - no names mentioned (Firstline).

Now a very important note on getting these pressed onto your half-shafts. The bearings are pressed down using a press tool, as the fit is very tight. It is absolutely essential that the press does not push against the seal during this process. This will crush the seal and it will not work properly. The reason the seal is raised like this is so it presses and seals against the smooth flat surface it meets inside the axle case when the shaft is bolted into the case.

One habbit that we have gotten into when fitting new rear bearings, is to raise the inner part of the seal gentle with a cocktail stick and smear a bit of grease on the surface of the seal, so it doesn't run dry when first drive. It might just stop the seal being damaged on the inner surface during the first few miles.

Next up make sure your shafts and the axle case are straight. Eyeball it all, check it all with straight edge ruler, do whatever it takes to be sure.

How did you remove the old bearing? Usually (99.9%) of the time you will not get this off with a puller and you (or your mechanic) will have to resort to using a grinder to chop the old bearing to pieces. This is fine but must be done extremely carefully. Any nics in the surface of the shaft are potential routes for oil to track its way under the bearing and out onto your brakes.

Now my favourite! The rear disc brake conversion. God I hate these things, but the biggest reason is that they are often a cause of rear bearing oil leaks. It's really simple this one. In most kits (well the bolt on types) you get a plate that replaces the original drum back plate. This is clamped in place by the half-shaft clamping plate. Well guess what! This new plate is thicker than the drum plate it replaces. What other job does the shaft clamp plate have to do? Apply enough pressure to the bearing to push it firmly into the case so the seal is pressed tightly up against the flat inside surface in the case - that's what. Suddenly we have a thicker piece of metal in the way stopping it from going all the way in - leak time !

So there we have it - a simple job that needs a lot of care - and can give bearings a false bad name.