Get to grips with the studs
Page 44
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All seemed to be well and after two or three days of constant checking, I decided that it was just one of those things and carried on in my usual way, keeping an eye on the studs as a precaution.
Five days after that first incident, there they were again, two or three just beginning to show signs of working loose. I knew by now that I had a problem and back at base that weekend, I stripped off the two wheels that were held by the offenders. There was no damage to the wheel discs and a careful check on the studs which I had marked with some yellow crayon showed that they were still tight in the hub.
A bit puzzled, I checked the nuts, then the clamping rings that my spigot-mounted wheels are held tight by. All were sound. The next obvious move was to strip off the hub and have a look at the fixings where we used to have back-nuts. On my truck they are simply broad heads closing off a very slightly tapered spline which is a press fit in the hub flange. None of my visual inspections showed me anything at all and if I was completely honest, I would have to say that I did not really know what to do next. I wandered off to the local at lunchtime to have some wellearned refreshment and stumbled on a fitter from my local repairer.
Over a beer I told him what my problem was. He told me straight off that I should pop a feeler gauge down between the broad head at the back of the stud and the inner flange of the hub. It had been know, he said, for some studs not to be pressed fully home on assembly, so that when there was eventually some slackening of the fit on the spline, the stud started to pull through. It would, of course, only go through as far as the broad head and thereafter remain tight, and if I had just kept on tightening them up the symptom would have quickly disappeared.
After lunch I went back to the garage to find that he was absolutely right and half an hour with the heaviest piece of tube I could find, dogged the studs down firm.
With the whole unit made up again, I have not had any more slackening off while on the road, though if I do, I feel that I shall just keep pulling them up until they go solid.
Loose fixings are of course not the sort of thing one wants on any part of a vehicle. The inevitable result is that the loose unit will be damaged, particularly in the fixing holes, for you will find that it will be almost impossible to keep it tight thereafter. I find that the only way to avoid such problems is to keep a constant watch on all the suspect points and pay immediate attention to anything that begins to work so I manag to stay out of trouble.
One of the most frequer causes of wheel and hub failur is the over-zealous painter wh insists on giving the whole of th wheel assembly a very generoL coat of paint, with the laudabl intention of preventing rus Quite often one sees a truck thz has been pansied up a little ovE the weekend and in so doing th driver might have given th wheels a freshen-up.
That is of course very nice t see and any driver would d( serve a special pat on the badl you might think, for being s conscientious. But, comes th time when a wheel needs to b changed and the paint on th clamping face of the wheel b( comes an agent which prevent proper tightening and, in som cases, forms a lubricant whic allows the wheels to wor against each other until the fet thousandths of an inch of pair are worn away, leaving th assembly, if not loose, then ce tainly not completely tight.
Stretching of the wheel-stud by overtightening is anothE common cause of wheelstu failure. This is most ofte caused by the driver using a unnecessarily long tommy bar i the wheel brace. Most maker specify a torque figure to whic the wheel-studs should be tigf tened, and for the best result one should abide by these fic ures. And don't forget that i some instances the figur quoted refers to the stud bein lubricated first, whereas i others the figures refer to dr studs.
The extra effort required t produce overtightening on lubricated stud compared wit that on an unlubricated stud, i surprisingly small.
This article concludes th Driving for Profit series; reprint are available from CommerciE Motor on request at 15 pence.