1948 1 1/2 litre Mk IV rear wheel bearing

goodoldgrandad · October 12, 2018, 6:47am

I have noticed slight play on one of the rear wheels when I jacked the car up, which I suspect is due to the wheel bearing. Any recommended procedure or tips to correctly adjust or tighten the captive axle nut/ split pin, etc to reduce the unwanted movement? Thanks

Peter_Scott · October 12, 2018, 7:41am

Hi David,

You just have to fiddle about with a screwdriver and long nosed pliers to get the split pin out. There are holes in the sides of the splined hub for limited access. If it proves impossible to get the split pin out you can always just shear it by unscrewing the nut and then clear the remains of the pin with a pin punch.

If you are wanting to remove the hub you might be lucky but quite possibly you will find that without a dedicated puller it’s just impossible to remove. Leave the nut partially unscrewed on the half shaft so as to protect the end of the shaft from the puller and also to limit the movement if the hub releases violently.

(My understanding of the term “captive” regarding nuts is limited to those that are fixed to their surroundings rather than those retained by a pin.)

Peter

goodoldgrandad · October 12, 2018, 10:51am

I have actually had the hubs, etc off as part of the restoration work undertaken, and now put everything back - but I’m not sure if I tightened or adjusted everything correctly. Certainly a tricky job, and not a quick process as you say. One rear wheel now appears to have a little bit of play in it. When I was rebuilding I simply tightened the centre nut until the axle didn’t move freely, then slackened it off 1/2 turn before inserting the split pin. I did this with all the wheels front and back, and the bearings themselves are ok. Thought there may be a more engineered process or torque setting to get it to be more than guess work!! Thanks. David.

Ed_Nantes · October 12, 2018, 11:25am

Oh no , that is VERY much the wrong thing to do

Firstly it shouldn’t need 1/2 a turn to get the pin in, only say 1/ 12 of a turn [ half a flat] but if you can’t get the split pin in when the nut is very tight .{ and you should use a 3/4 " drive socket bar { NOT a tube spanner] the the nut should be put in a lathe and a few thou" taken off the back until you can get the holes lined up. But never slackened off
If the re is too much end float in the bearings you need to work with the shims, And there should be about the same amount of shims on each side, nOt all ormore on one side.

goodoldgrandad · October 12, 2018, 1:10pm

That sounds like my error. I cannot see anything in the Service Manual I have for the rear axel information, but the details for the front axel definitely says “slacken off 1/2 turn”, so I did the same on the rear. I will tighten up the rear before I drive it on the road, but from what you say there is no formal factory torque setting for this nut then? Thanks

Peter_Scott · October 12, 2018, 2:46pm

The fronts are totally different to the rears. In the front you are tightening the pressure on taper roller bearings, whereas at the rear you are simply wanting the tightest fit on the tapers of the half shaft and hub which should be rock solid unlike the front bearings.

Peter

goodoldgrandad · October 12, 2018, 6:42pm

OK. Thanks for the clarification Peter. I will carry out a re-fit.

In case anyone else is wanting to know what we are on about - here are a couple of pictures of the hub nut and access hole for the split pin.

Peter_Lloyd · October 28, 2018, 2:26am

I posted this on the related topic, ‘Rear Wheel Hub Problem’ so thought I would drop it in again. The hub nut on the back half shaft must be made very tight as it takes the full driving torque. It is not intended to slip such that the full torque force would be applied to the key. Any slippage here hammers the key and the keyways in the shaft and hub, ultimately writing them all off.

Rear wheel hub problem

I have just helped a colleague sort out similar problems and bad work done by a p.o. His hub flange was bent by over-stressing with a jaw puller. The studs had to be cut out and the flange face skimmed. It was also fitted with an incorrect bearing - and this is a trap for the unwary. The rear bearing is a tapered bearing with a tapered inner race design, i.e. the inner bore of the inner race is tapered to match the shaft taper. Make sure you have the right bearing - the Timken one has a suffix ‘T’ after the number. An equivalent race with the same number without the ‘T’ is available in the standard parallel design and will fit but it is dangerous. It has an edge contact only connecting the race and the axle, increasing the bending and fatigue breaking potential.

A break here allows the wheel, drum and stub axle to go their own way. The car drops to the road, the back plate wears away in a shower of sparks and you have no brakes to stop it. I hope his half shaft doesn’t suffer from this incorrect fitment.

The other alert with these rear axles is getting the correct setting for the bearings. The principle is that they must run with a fine clearance, but not zero clearance. The manual gives the details and a range of a few thou’ which can only be set with metal shims. The reason for not having zero clearance, is that there is no way of determining whether it is just in contact, or is under preload. If preload, it will lead to premature failure. Also, the bearing takes thrust only in the outward direction. This is enabled by the wheel on the opposite side. Under side thrust mode in cornering, the outboard wheel pushes the axle inward, which in turn pushes the differential cage spacer onto the end of the other shaft and loading its bearing.