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Old 20-03-2019   #1
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Rear wheel bearing pre load

OK so I have a 1967 Fiat 600D but I believe the 126 has the same rear bearing set up. The main dealer workshop manual says "bearing rotation torque should not exceed 0.4 ft/lbs (50 kgmm)" . This is set by first fitting a calibrated dynamometer. I have no chance in my workshop - so has anyone any advice as to what torque to set the castellated nut too on the end of the wheel shaft? Any advice would be most welcome. gpursh@sky.com
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Old 27-03-2019   #2
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Re: Rear wheel bearing pre load

Hello, I have same question. I believe the Fiat 600 WSM includes this information. Not sure how you get 0.36 ft lbs on a torque wrench.
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Old 01-04-2019   #3
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Re: Rear wheel bearing pre load

Never done one of these but it reminds me of when just about everything was rear wheel drive. I can't remember specifically which vehicles they were after all these years but the preload on the pinion bearings on some very common "every day" vehicles was done in the same way. Two taper races with a collapsible spacer between them. As you tighten the main pinion nut the spacer collapses and the bearings move closer together. You only get (as you will know) one shot at it, over tighten and you're stripping it out and fitting a new spacer, and explaining to the boss why you're wasting his money. On the ones I did preload was tested by wrapping some string around the drive flange (which the U/J bolts to) and using a spring balance to unwind the string. There was a max and min figure allowable on the spring balance. Because you couldn't test it whilst tightening the nut you got quite good at judging how tight to do it up. After doing a few you could get it right first time. It's on this experience I'm basing what is following.

When you look at what is actually trying to be achieved here with a wheel bearing (unlike a diff pinion bearing which is rotating maybe 3 times faster so probably a bit more critical) think about other wheel bearing setups. What you are invariably trying to achieve is the elimination of any play between the races and rollers (or maybe balls, depending on type of bearing) but without forcing the races so tightly together that friction will create so much heat that the bearing self destroys!

If I had to do this and had none of the special tooling recommended I would build the whole hub up and tighten the nut until very little play could be felt. then I'd fit the wheel - to give me greater leverage - and continue tightening the nut, slowly and carefully, whilst rocking the wheel (probably two people would be an easier way to do this so one could tighten and one rock the wheel) until all traces of play have disappeared. You may actually end up with very slightly less preload than the manufacturer specifies this way but you are not going to damage the bearings. Then, after a few hundred miles check it again as it may have settled a bit and need a slight tightening. I would then probably recheck again after maybe a couple of thousand miles just to be sure.

I offer this as an interesting, I hope, observation on your problem. I'm not intending it to be a prescriptive description of how you should proceed and if you do decide to try something along these lines then, of course, I wish you luck but would point out that as you have not done it the way the manufacturer recommends you are open to a lot of problems if something goes wrong (probably the least of which might be that your insurance could refuse to pay out!
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