Rear hub nuts?

#1
Hi
Having taken on a 66 2000 from my dad I have been going through the rear end and have found that what I would class as the rear hub nuts are loose. Normally on the aircooled VW's I am used to working on I would tighten them up to a specified torque. However what is this for a P6? I cannot find it anywhere in the workshop manual I have? Is there specific number or is it just tighten it up? Any help would be appreciated as I cannot seem to find anything on the forum or online. I can find things relating to a spring weight method but that seems to relate to rear hub bearing replacement which has not been done I just have loose nuts!!! :) cheers jamie
 

harveyp6

Well-Known Member
#2
There isn't a torque figure. The nuts tighten on to a collapsable spacer. The nuts have to crush the spacer such that you get a specific amount of pull needed to turn the hub on the shaft. This really needs to be done off the car. One of those things that it's probably best to have a squint in the WM before roaring in.
 
#3
Hi,
Thanks for the reply, so it looks like I am going to have to take the hub off the car then? Seems pretty involved just to tighten up a loose nut I must admit..
 

harveyp6

Well-Known Member
#4
Yes, but removing it isn't too much of a problem. Just the 4 bolts holding the halfshaft to the diff and the ring of 6 bolts holding the hub to the elbow. My only concern would be why the nut is loose. Maybe it went into the same garage that I took a similar assembly in to (Jag Main Stealer) on a S111 XJ6, to replace the bearings and set the preload. When it came back and I questioned why the hubnut didn't have a split pin in it I was told not to worry about it, fit the split pin, refit the assembly, and send the car back to the owner. Within days the rear hub collapsed because the preload hadn't been set, which is what it was sent there for in the first place. The car belonged to a director of Hawker Siddeley, and I can tell you, he wasn't impressed......
 
#5
Hi,

I think it was down to a garage carrying out work on the rear brakes for my dad years ago. it was pushed down to my garage about 5 years ago. So even though it doesn't need any bearings replacing and therefore a spacer, I set the preload using a spring balance whilst held in a vice. Is a different figure required if the spacer is already crushed so to speak? I am going to read the manual tonight to get my head around it.
 
#6
Hi

got the hub and drive shaft in the vice. Following the book I have tightened the hub nut until it takes a pull of around 4.5kg for the hub to start rotating. as I haven't had to crush the spacer does this sound about right or should it be more as I read that you need a big bar etc, I am assuming that is for the initial crushing of the spacer plus being an early hub I have the bolt screwed into it for adding grease i presume? does look a little dry in there as the grease i can see looks pretty old? should I add more or just leave as is and put it back on the car?? All advice greatly appreciated!! cheers Jamie
 

harveyp6

Well-Known Member
#7
IIRC (and I haven't read the WM on the subject for years) you have to take the reading once you have overcome the initial inertia, so the reading is a rolling pull, not the amout of force to get it moving in the first place. Once you get that reading within the limits then the spacer should be sufficiently collapsed to give the correct preload.
 

SydneyRoverP6B

Well-Known Member
Staff member
#9
got the hub and drive shaft in the vice. Following the book I have tightened the hub nut until it takes a pull of around 4.5kg for the hub to start rotating. as I haven't had to crush the spacer does this sound about right or should it be more as I read that you need a big bar etc, I am assuming that is for the initial crushing of the spacer plus being an early hub I have the bolt screwed into it for adding grease i presume? does look a little dry in there as the grease i can see looks pretty old? should I add more or just leave as is and put it back on the car?? All advice greatly appreciated!! cheers Jamie
When the spacer is new, to generate sufficient torque applied the central nut to compress the spacer takes considerable force, I dare say probably far more than you anticipate! Once the compressive force has been applied to the spacer in order to apply sufficient stress to the bearings to prevent premature failure, the spacer has suffered permanent deformation. In engineering terms it has suffered the Poission effect, named after the French mathematician and engineer Simeon Denis Poisson. What that means is that the overall length is now less that it was when new plus the cylindrical cross section has increased about the centroidal minor axis. In other words, it has a bulge around the centre. Having suffered permanent deformation means that the spacer has suffered plastic deformation. When you now apply a compressive stress to the spacer by tightening the nut, the strain will now increase in a non linear fashion relative to the applied stress. The stress will essentially remain constant but the spacer will shorten disproptionately preventing the bearings from receiving the correct preload. In short, they will wear rapidy and require replacing sooner rather than later. How long will they last, how long is a piece of string? For bearings, longevity is often a function of distance covered (assuming no other damaging interventions).

Ron.
 
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