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MG MG Y Type - WHEEL STUDS

I have just broken a wheel stud when changing a wheel on the rear axle of my 1947 'Y' Type. What is worrying is that this happened without using too much force. The stud and all the others do not show any sign of necking or any other sign of an impending failure. I have now been given a second hand stud but I was wondering if any one else has had this experience. The YA have 3/8"BSF studs where the YB changed to ½"UNF studs, was this due to problems or to commonise with another model?
Should I use the second hand stud or replace them with new, after all they are 57 years old?
Steve Randle

Steve, the size changed because the axle itself changed when a Morris derived axle was replaced with a (better) Austin derived one. I would use the replacement stud but find out what is a reasonable torque setting for the stud's material and size and torque it up to that. If it shears it was no good and if it doesn't then use it! Let us know how you get on.

Ian Thomson
ian thomson

Steve: Drawing on my metallurgy from long ago, the break was probably caused by a crack in the stud which has been developing for a long time; these components were never really expected to last over 50 years! You don't need to have physical wear on the item, such as necking, to have cracks starting: it is usually a form of localised fatigue.

I know that TC owners now consider it sensible to have the front stub-axles crack-tested when rebuilding: ultrasound or dye-based testing can locate incipient cracking before failure, and can spot problems long before they are detectable by the naked eye. It seems a bit exotic to check all the wheel studs on the car this way, but if the studs hold the correct torque for the wheel nut you are very unlikely to have one break in use.
Tim Griggs

Being no metalurgist either there are two problems that spring to my mind as having a possible bearing on these things.

Over tightening can lead to stress fractures and exacerbation of latent defect.

Under tightening will cause necking as the wheel wears on the stud when the drum rotates and takes up the slack against the pin.

Wheel nuts are often over tightened by modern tyre bays using "windy" guns and after visiting such places my usual practice when I get home is to slacken the nuts off using a T bar and retighten to afirm bite and then a securing flat turn, if you know what I mean. I have never lost a wheel, or wheel stud, nor have I never been able not to remove a road wheel in the event of a puncture by the roadside either.

Happy motoring,

Paul
Paul Barrow

The YA nor the YB do not use an Austin derived rear axle. The YB has a Nuffield axle of a more modern design, ( BMC/Austin 'banjo' axles were not used on MGs until the ZA and MGA came along after 1953.) The threads were changed from the pre-war BSF to the USA based UNF ( ANF in the USA,) as that thread type was used in many UK factories when they were producing USA based designs for war machinery. UNF and UNC were the common UK threads of the 1950s to the mid 1970s, then the European based metric threads were used by the motor industry.

Morris, therefore MG, were using a right mixture of threads, the XPAG engine has ancient french metric threads in it, the body of the YA has BSF threads in it, the gearbox and rear axle had BSF, some brought out components had UNF threads. So it was logical to change to one common thread.

The rear axle of the YB, taken from the TD, was the improved post-war hypoid axle used on all Morris, MG, Wolseley and Riley cars until 1956. That used in the YA and YT was an ancient spiral-bevel design from pre-war Morris side-valve cars.

The simple reason that old studs shear off is, that they are old. The main problem is that tyre fitting firms used air-powered torque guns that slam the nuts up too tight, the operators to lazy to check it is set at the correct torque for the car. This is a serious problem on cars like Morris Minors, Minis, Austin A30-35 and A40s, as their studs are tiny. Also, over the years many different owners of doubtful techincal sympathy have used huge spider wrenches to pull up the nuts, often over tightening them. No wheel stud was designed to last over 50 years. Such items of primary safety fitted to aircraft would be 'lifed', and changed for new items every so-many flying hours. Like big end bolts in engines, some things are only supposed to be used once. A wheel stud might last say, five years, or even ten. But if the wheel has hardly even been removed, they might last fifty years.

Wnat we need to be aware of, is one day the Mot is going to demand we supply X-ray evidence of primary safety items on the annual Mot. I quote the problems that TA and TBs are having with cracking of their front stub-axles, early Morris Minors are having with their wheel centres cracking.

If in doubt, renew it.

Neil.
Neil Cairns

After visiting Silverstone at the weekend and talking with people, it would seem that know one makes replacement wheel studs for the YA! so I will have to use the second hand one, unless some one knows differently. Thanks for all your comments!
Steve Randle

When I broke Y 4099 I kept all the studs from the wheels for that express reason Steve - so that I have a good stock to draw from in case I need them! If you see or hear of a Y being broken you should do the same - provided the car really is beyond economic restoration.

Paul
Paul Barrow

This thread was discussed between 19/07/2004 and 27/07/2004

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