Tough Nuts

[Expatman]

When I put my summer wheels/tyres on in the Spring I carefully torqued the wheel nuts to 120 Nm. Changed to winters this weekend and the wheel nuts were very difficult to remove even using a "spider". I noticed that there seemed to be a white corrosion on the thread of the nuts which I removed with a wire brush. Then replaced the nuts and torqued to 120 Nm as specified. I did not grease or oil the wheel nuts at all because I remember reading that wheel nuts should not be lubricated in any way.

I fear that over the winter the nuts will corrode again and make then extremely difficult to remove next spring - or, even worse, I need to change a tyre by the roadside and without the 'spider' will be unable to loosen the nuts. Does anyone know if there are any permitted "lubricants" I could put on the wheel nut threads to prevent corrosion and ease removal?

[dcl5ad]

You've stumbled upon possibly the oldest debate in automotive history: "to grease, or not to grease, that is the question." Well, more accurately, "To copper slip or not to copper slip". as that's the only thing to consider applying.

 

Personally, having always owned Italian cars in the past, which all use a M12 fine pitch thread and are all copper-slipped from the factory and torqued to a much more elegant 80nm, I was a tad shocked not to see any on the yeti's bolts. VAG use a coarse metric thread, hence the 120nm tightening force. We've put copper slip on the Superb and not had any issues in 40k, though we do religiously re-torque both the winter steelies and the alloys after about 30 miles. 

Edited 4 November, 2013 by dcl5ad

[Expatman]

By copper slip do you mean high temperature copper grease? That is what I use on the wheel/hub cone to prevent the wheel welding itself to the hub - if so then I have some and could use it as you have.

[dcl5ad]

Yeah copper grease. Any anti-seize compound will do: just on the threads, none on the cone-shaped mating surfaces mind! I use an old toothbrush to make sure it goes where it's supposed to.

Edited 4 November, 2013 by dcl5ad

[briwy]

I always understood it to be a big nono to using any kind of grease on wheel nuts/bolts as it is then possible to overtorque them.

I agree they can be sods to get off but I carry an extendable wrench from the local motor factors for around a tenner whic works fine.

The other problem is the locking wheel nuts. The ones that came on the Yeti were crap and the tool just kept slipping off. In the end I nipped it down the local tyre place and they eventually managed it with the air gun. Now bought some more with a lot  deeper splines and problem solved.

[MarkBT]

How would grease make you over-torque the nuts? That's what a torque wrench is for.

Sent from my LT26i using Tapatalk

[briwy]

Because it alters the friction between the nut and threads which can make it possible to overtorque the bolt/nut which in turn may overstretch the bolt thus weakening it.

In practice it's unlilkely but it could happen. Hopefully the designed in safety factors on wheel connections is enough to take care of it.

Edited 5 November, 2013 by briwy

[dcl5ad]

Hmm :think: using a couple of online calculators, with a copper grease @ 120Nm you're looking at tensile load of about 73kN. The UTS of a hi-tensile M14 bolt should be about 140kN. 

 

With no lubrication & assuming the bolts are zinc plated then the clamping force could be around 37kN. Both are within 50% the UTS of the bolt, however, that is static load, so you got all the forces associated with driving to add on to that. 

 

I might be getting out the humble pie eating equipment.

[Yety]

Hmm :think: using a couple of online calculators, with a copper grease @ 120Nm you're looking at tensile load of about 73kN. The UTS of a hi-tensile M14 bolt should be about 140kN. 

 

With no lubrication & assuming the bolts are zinc plated then the clamping force could be around 37kN. Both are within 50% the UTS of the bolt, however, that is static load, so you got all the forces associated with driving to add on to that. 

 

I might be getting out the humble pie eating equipment.

 

Good open debate

 

You could well be right, I've seen other warning about lubing wheel nuts, but I've always stuck with anti-seizing everything in sight.

 

Over the years I've never had a fastener loosen, but they come undone when I want to remove them whatever the treatment they get

 

I guess we'd need a technical statement from a fastening maker with definitive evidence before assuming too much.

 

I think the answer might be a little in "delicate" places, and more heavy application in places where corrosion will probably cause problems down the line. 

[spottydog]

During my apprenticeship days it was always drilled into us that anything that had a critical torque setting should not be greased or lubricated in any way.

However, over the years I have never had a problem using copperslip on various nuts and bolts not deemed to need a critical torque setting. I would class wheel bolts in this category. Always check your bolts after 30/50 miles to make sure they are still tight. 

[briwy]

I contacted Skoda Uk re this grease/not to grease question and they have said that wheel bolts should not be greased. This obviously means that the quoted torque figures in the manual do not allow for greasing.

However, they haven't really  got an answer about getting stubborn locking bolts off so I suppose it still comes down to personal preference.

The only problem I can see is that if bolts that are greased did shear and an accident  ensued then the insurance companies could get stroppy as it doesn't appear to conform to Skoda's recommendation.

[nickguzzi]

Having had to get the "hot spanner" out to seized wheel nuts/bolts on too many occasions, I would never refit mine without.

I have never had a wheel nut/bolt come loose, I have never had one break.  Perhaps I lead a sheltered life, but never seen one either.  Seized bolts on the other hand....

 

There are "n" number of engineering table giving the comparative torque values with or without lube (not grease).  Most sites have in the preamble an explaination as to why a thread should be lubed,  mainly to prevent galling and hence unreliable and unpredictable stretch values in the fastener.  ie under torqued fasteners.

ARP who make a considerable % of the worlds threaded fasteners for motorsport applications always give their torque values on the basis of lubed threads. 

 

Its your car, to do with what you will.  If you have any reservations at all do as the manual says. 

You could also check out the number of threads on seized treads vs threads on seized threads due to corrosion. 

Perhaps even see if there is any evidence for correctly lubed bolts shearing or coming loose. 

 

The only logical reason I can think of for VAG to have a no lube policy, is that they use treated fasteners on the production line, which would make sense fro their point of view.  However, as we can see from all the queries and difficulties people put up here, it doesn't work long term.   Perhaps the bolt set should be replaced in its entirety at each wheel removal?