Debate continues, and will doubtless never stop, about using copper slip on wheel bolts. The idea gives me the jitters, so I don't do it, but I know that others do, for their own reasons. Two things have reinforced my disinclination:
* The settings quoted in the official sources for my cars are for dry fixing.
* At this site
www.rockcrawler.com/techreports/fasteners_torque/i...#
it says "Notice that the torque required for a lubricated fastener is less than half that of an unlubricated fastener." The writer of this is not short of technical credibility: he's a rocket engineer.
Any other angles on this primary safety-critical issue?
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There are some schools of thought for both points of view.
Have no experience of a lubricated wheel bolt coming loose, but I have experiences of unlubricated wheel studs breaking!
That in itself isnt a problem/issue, but 1 step further. If a diy man changes his wheel and a bolt/stud breaks is he going to replace it before driving or drive it til he remembers to get 1 and then manages to fit it !
I am not qualified to say which is the correct way, but sometimes I do and sometimes I don't, depends on the vehicle, application and use !
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Working on my friends LeylandDAF 400 series the other day I spent 20 minutes getting one wheel nut off.These had been left dry,unless you count mud,for some time.So what do you do to prevent this situation without resorting to coppergrease?I have used it for years,always do the nuts/bolts up tight,judged by hand.and have not had any come loose yet.
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i agree with yorkiebar every car is different .
However sierraman i would never grease commercial wheelnuts as they will come off or hairline fracture the wheel rim due to slight undoing when the grease washes away.
Dont forget to tell friend these want checking after 40/50 miles its impersative
:-)
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Thread preparation obviously has a big impact on applied torque. Strictly speaking the wheel bolts should be installed 'dry'. Nowadays, though, wheels can stay on the car for literally years without being removed - hence problems with alloys 'welding' to hubs and wheel bolts siezing. What I do is put a little copper grease on the contacting surfaces and also a smidgeon on the threads. I don't lubricate the bevel that locates the bolt in the wheel. I then use a torque wrench and tighten them to the bottom end of the specified torque range. I've never had a problem doing this on numerous cars in the best part of 30 years.
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.......... problems with alloys 'welding' to hubs ...................... What I do is put a little copper grease on the contacting surfaces and also a smidgeon on the threads. I don't lubricate the bevel that locates the bolt in the wheel. I then use a torque wrench and tighten them to .......... the specified torque range.
Me too. In fact when I get a new car with alloys it's one of the first things I do. I never get any problems after doing that.
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L\'escargot.
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it says "Notice that the torque required for a lubricated fastener is less than half that of an unlubricated fastener." Any other angles on this primary safety-critical issue?
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I note it is one third the value for the smallest in his table.
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If using the supplied wrench, I doubt much damage, if any, could be done with lubricated bolts.
I always put a smear on having had a seized stud many, many years ago.
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I put a tiny smear and have never had a problem, except stuck bolts that crack when released. I think over or under torquing is a bigger issue. Always re-torque myself after any garage or tyre work.
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I've been using it for over 30 years now and never had a bolt or nut come loose or seize up. Like MW, I always redo the fixings after a garage has been at them. I usually do them up with whatever I'd have to undo them with if I had a puncture.
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I wouldn't trust that site too much.
He says for instance that once a fastener yields there is no preload.
This is just wrong! (rocket engineer or not - it's wrong!) Many specialist fasteners are designed to be torqued to yield - there are good reasons for doing so. At or beyond yield, you still have a preload equal to the yield stress multiplied by the stress area of the fastener, calling this significant level of preload zero is simply not correct. Bolt relaxation from a yielded state is back down a line parallel to the original elastic line on the stress strain curve, so the bolt will even behave OK if there is some embedding or gasket settling.
As the taper cone on a car wheel nut is at a larger radius than the thread, it changes the bolt preload/torque relationship more if you put grease here than if you put it on the threads themselves, and so, I am happier to put some grease on the threads, and leave the taper cone dry.
In a practical sense, wheel security on cars is nothing like the problem it is on trucks. Most loose car wheels are caused by negligent mechanics/DIYers simply forgetting to tighten them up rather than any systematic errors in the torquing or lubrication procedure.
The biggest improvement in truck wheel security came with the adoption of spigot wheels, and the riddance of taper cones from truck wheels and wheel nuts. How manufacturers ever thought that wheels ten taper nuts would ever go together and make proper contact all the way round each taper was an act of collective stupidity. It was so easy to end up with a situation where if only half of the taper was contacting, the stud would be loaded as much in bending as in tension. This significantly reduces the fatigue life of the stud, which in a non spigot application sees a stress cycle for every turn of the wheel.
Number_Cruncher
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Thanks for all these well informed responses.
Isn't it at the interface between taper cone and wheel that bonding/seizing is most likely, rather within the thread section?
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>>Isn't it at the interface between taper cone and wheel that bonding/seizing is most likely, rather within the thread section?
It's very easy to damage a bolt/stud which has seized on the threads, but quite unusual to cause damage un-seizing under the taper/cone or head of the nut or bolt.
For further info, I have found the following site to be a very useful source of information (among more official sources, like British and German Standards, and ESDU) when I have been called upon to look into fastener failures.
www.boltscience.com/
During one such investigation on a rial vehicle, I used a set of strain-gauged bolts. The idea was to see how the bolts took up preload during torque tightening, and then, to see what happened during a period of in-service running. The variation in the preload during the torquing process was quite surprising. The torque wrench was calibrated, and used by an experienced operator. The bolts were uniformly prepared and dried, as were the tapped holes in the bogie. Over 12 bolts, there was a variation of approximately 20% between the bolt with the highest preload, and the bolt with the lowest.
Although I didn't repeat the installation with lubricated fasteners, it is my understanding that while lubrication does change the torque/preload relationship, it also reduces the amount of scatter. This reduction in scatter is described in one of the excellent books by Shigley (Mechanical Engineering Design IIRC, but, by quoting sources, I am running the risk of being accused of being a librarian!)
Number_Cruncher
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If its on my own car then a slight bit of copper grease & the torque wrench is used & they get rechecked again after around 50 miles, never had a problem.
Anybody elses wheel bolts then its just FT with the breaker bar.
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Personally I always use copper grease on the mating surfaces of the hub/wheel and on the threads of the wheel bolts/studs. I have never had a problem with either a: breaking a bolt/stud, or b: one coming loose.
I have worked in garages where the mechanics have all had different views on the subject, some like it some don't, some will use it on brake components and some will fit brake pads/shoes completely dry. Each to their own but for me, I use it all the time.
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rial = rail
D'oh!
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When I fitted a towbar to my Sorrento i waxoiled everything before assembly. After pulling out two hefty threads whilst trying to torque to the specified settings I twigged that perhaps the waxoil was not the brightest of ideas!
Two helicoils and a good clean up produced less fraught fit. Enough said!
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Fullchat
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There might be a difference between bolts, and nuts on fixed studs.
Are bolts exposed or even projecting on the inside of the hub, and therefore vulnerable to wet and seizure? Nuts however are visible, and if greased one instinctively splodges any extrusion over the ends of the thread.
Are bolts more vulnerable to loosening? The strain would be directly and sideways on the threaded portion, whereas a nut merely has to resist longitudinal force.
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it says "Notice that the torque required for a lubricated fastener is less than half that of an unlubricated fastener."
I think the relevance of this is for when a fastener is tightened to its elastic limit. I doubt whether 81 Nm (60 lb.ft) on a wheel bolt comes anywhere near this condition. I think putting more axial load than is intended into a wheel bolt is more likely to damage the wheel (particularly an alloy) than damage the bolt thread.
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L\'escargot.
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