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Car Forum / Mercedes-Benz Cars / November 2006wheel lug bolts ouch
Ouch $340.00 plus tax Just my final comment on my message to the group with my problem with lug bolts ,even when torque.properly ??? Visited my local Merc dealer today ,to remove broken wheel lug bolt. Front axle hub $145.00. Install 20 new style lug bolts $145.00-( guaranteed not to freeze up ??) Misc. chge10.00 Labor $40..00 Service mgr. said old style bolts are common problem freezing up. And he cautioned Never never use anti seize lug on wheel bolts.I still have my doubts about that though.Thanks to group for advise Ernie > Ouch $340.00 plus tax Just my final comment on my message to > the group with my problem with lug bolts ,even when torque.properly ??? [quoted text clipped - 7 lines] > my > doubts about that though.Thanks to group for advise Ernie You just have doubts? After spending $340, I'd sure as hell be putting either a small dab of grease or anti-seize on the new ones. trader4@optonline.net schrieb: >> Ouch $340.00 plus tax Just my final comment on my message to >> the group with my problem with lug bolts ,even when torque.properly ??? [quoted text clipped - 10 lines] > You just have doubts? After spending $340, I'd sure as hell be > putting either a small dab of grease or anti-seize on the new ones. The prescription says: No grease. Best procedure is to wash everything in fuel, apply the bolts with 100 N m and fix it after a week. Torques are given in N m (or lb ft) for dry seats and windigs. Greasing may result in up to ten times the desired strain. You may break the screw, destroy the alloy and after a year when grease is gone you dont get the bolts removed. For alloys the procedure is essential because the material will embrittle over the time under strain and temperature chanings over limits.  SignatureRoland Franzius > trader4@optonline.net schrieb: >>> Ouch $340.00 plus tax Just my final comment on my message [quoted text clipped - 24 lines] > will embrittle over the time under strain and temperature chanings over > limits. 100 Nm is a bit low, my current MB manual says 150 Nm, previous cars had lower figures but still higher than 100 Nm. I acknowledge the "prescription" but my experience is the opposite. No grease, bolts get easily under tightened and may even drop. Only a small amount of grease to the screw, never a problem to open the bolts afterwards, never a lost bolt. If however one did carefully wash and clean and dry the bolts, that could be what MB is after (but they don't give that advice in the manual) and could be quite OK. I've never seen anybody doing this, certainly no tire shop has time for this. > trader4@optonline.net schrieb: > >> Ouch $340.00 plus tax Just my final comment on my message to [quoted text clipped - 17 lines] > Torques are given in N m (or lb ft) for dry seats and windigs. Greasing > may result in up to ten times the desired strain. How exactly is grease on threads going to get a bolt that was torqued to 100 up to 1000? The maximum torque is determined by the twisting force as applied, not lubricant. If this were true, there would be a hell of a lot of broken bolts all over the place. I've never seen a bolt break cause it had lube on it. But, I've seen a lot of them break cause they are rusted. You may break the > screw, destroy the alloy and after a year when grease is gone you dont > get the bolts removed. For alloys the procedure is essential because the > material will embrittle over the time under strain and temperature > chanings over limits. >> Ouch $340.00 plus tax Just my final comment on my message to >> the group with my problem with lug bolts ,even when torque.properly ??? [quoted text clipped - 10 lines] >You just have doubts? After spending $340, I'd sure as hell be >putting either a small dab of grease or anti-seize on the new ones. Mercedes says not to. There's two failure modes: no anti seize and the wheel may not come off. Or use anti seize and it may come off when you don't want it to. Which would you prefer? There's really not many times when yo uknow better than MB about their cars. SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net >>> Ouch $340.00 plus tax Just my final comment on my message >>> to [quoted text clipped - 23 lines] > There's really not many times when yo uknow better than MB about their > cars. No I'm not claiming that I would know better than MB, I'm referring to what all professionals do as far as I know (I'm not saying you would not be professional car expert, I just don't count the one-way relation, only you being familiar through internet to me :-) Now that we come to MB knowledge, I think we had one item discussed here where I definitely feel MB is wrong. That is their manual telling to put better tires to the front in the case that one set is new/significantly better than the other one. Tire rack(?) and others were referred strongly giving the opposite advice. On the two failure modes, I still accept that MB can be right but myself I have experience about cars and trucks in my immediate family for about 10 million kilometres and no single bolt problem (too tight or lose) with my method. Further more, one previous comment was that using grease would make the bolt tighten too much. Why should that make the wheel come off? I leave you two argue this (and leave others do their tire job as they wish, nothing so far has made me change the way I will do it as my experience supports). > Now that we come to MB knowledge, I think we had one item discussed here > where I definitely feel MB is wrong. That is their manual telling to put > better tires to the front in the case that one set is new/significantly > better than the other one. Tire rack(?) and others were referred strongly > giving the opposite advice. It's California law that new tires be mounted in the back, if you buy only two new tires at a tire shop. > Further more, one previous comment was that using grease would make the bolt > tighten too much. Why should that make the wheel come off? I leave you two > argue this (and leave others do their tire job as they wish, nothing so far > has made me change the way I will do it as my experience supports). It's an interesting thing to consider, but then again I'm not typically a user of torque wrenches. The one notable exception to this was when I was putting the heads on my old Oldsmobile engine, the shop manual specifically said to coat the head bolts in oil before torquing them, and then I had to torque up to something ridiculous (and my torque wrench didn't go quite that far so I kinda had to guess anyway, but at least I had the deflection meter thingy there to give me some information). -tom! -- >> Now that we come to MB knowledge, I think we had one item discussed >> here [quoted text clipped - 9 lines] > buy > only two new tires at a tire shop. Wow! Talk about mommy and daddy government. I wonder who came up with that little gem? <deletia> > -tom! > > -- > >You just have doubts? After spending $340, I'd sure as hell be > >putting either a small dab of grease or anti-seize on the new ones. > > Mercedes says not to. They're compelled by law to say not to, to keep them out of liability's way. > There's two failure modes: no anti seize and the wheel may not come > off. Or use anti seize and it may come off when you don't want it to. There are two more: use no antiseize and the wheel still falls off, and use antisieze and the wheel stays on. I definitely prefer the last of these. ;) I know people who've encountered the former, and I've even had nuts fall off after a visit to the tire store (years ago, when I > There's really not many times when yo uknow better than MB about their > cars. Unfortunately the litigious society that (some of) we live in requires that people putting product on the market distance themselves as far as possible from things that idiots may blame for their own stupidity. ;) -tom! -- > >> Ouch $340.00 plus tax Just my final comment on my message to > >> the group with my problem with lug bolts ,even when torque.properly ??? [quoted text clipped - 15 lines] > There's two failure modes: no anti seize and the wheel may not come > off. Or use anti seize and it may come off when you don't want it to. Been doing it here for years and not only hasn't a wheel come off, I've never seen a single bolt come loose. Nor have I seen any bolts that I have lubed in any other application come loose. What about bolts that go into oil pumps, oil pans, internal locations, during repairs, etc, where they can be reasonably expected to be exposed to oil? By this logic they should all fall out. If there is a reason behind there recommending not to use a lubricant, I suspect it has more to do with fear of morons getting oil on brake pads and rotors. > Which would you prefer? I prefer logic or real data as opposed to hysterics. > There's really not many times when yo uknow better than MB about their > cars. Then always listen to them. This means you take your car only to MB for repairs, because that's what they recommend too. > -- > Need Mercedes parts? http://parts.mbz.org > Richard Sexton | Mercedes stuff: http://mbz.org > 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net > 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net Yet another anecdotal data point, which may or may not have any bearing on wheel lug nuts on automobiles: On drilling rigs, where there are sometimes hundreds of 9m long sections of drill pipe screwed together, and the strength of the individual connection and the entire kilometers-long string depends on a very exact torquing of all of the connections, the threads are _always_ lubricated. Without the lubrication, the torque measurements are unreliable. John M. Who has broken two factory-supplied lug nut wrenches, neither of them for his '94 E320 < > If there is a reason behind there recommending not to use a lubricant, > I suspect it has more to do with fear of morons getting oil on brake > pads and rotors. This could be at least one explanation why MB suggests not to use oil on bolts, dummies could use excessive amounts and MB would not want their brakes affected. > < > > [quoted text clipped - 4 lines] > bolts, dummies could use excessive amounts and MB would not want their > brakes affected. ========================================================= The reason that bolts are used to make mechanical joints is that they clamp two parts together. The clamp force is made my stretching the bolts. As the bolts are tightened, the bolts are slightly stretched........steel is elastic to a small degree.......this elasticity is what makes the clamping force to hold two parts together. If the bolt threads are lubricated, the torque values are not accurate. The bolts are stretched much more than the engineering specs allow........possibly making the bolts stretch more than the elastic limit......thus the bolts will fail.(break) If the specs do not call for lube, do not use it. Do not under torque bolts and do not over torque them...... ============================================================ > > < > > > [quoted text clipped - 18 lines] > torque them...... > ============================================================ Looking into this some more, here's what I found. Whether you use lube or not does affect the clamping force as described above. The highest accuracy of getting a bolt to the correct tightness is achieved by measuring the actual bolt stretch when it is tightened and there are actually instruments available to do that. Of course this is only practical where you can get to both ends of the bolts and is also very time consuming. This site talks about some of the issues: http://www.dansmc.com/bolts2.htm As a test, he tried torquing a bolt with and without lube and found that with lube the bolt was effectively over torqued by about 20%. It would be very interesting to see more real world test data on this. But one very apparent thing is that for wheel bolts, one would think that there would be a very wide range of actual clamping force, because you have bolts in all kinds of condition. For example, I would strongly suspect that a brand new unlubed bolt on a new car is going to have a big variation in clamping force from one that is old, has some rust, etc. The new bolt/car is going to have the bolt under a lot more clamping force than the old one, because with less friction, the bolt is going to be stretched more to get it to the same torque. I'd suspect it results in a lot more variation than the 20% noted in the lube experiment above. Yet, this apparently doesn't create all kinds of problems in practice. Another thing that immediately comes to mind is that if getting the correct clamping force within a tight range is so critical on wheels, then why don't they spec that the bolts be lubed? With lube, the actual variation in range of values that bolts get tightened to with a torque wrench is going to be smaller, because the effects of friction, rust, etc from one bolt to another are largely eliminated. And then from the practical side of things, I think we all know that in the real world, with hundreds of millions of vehicles, we have all kinds of things actually going on. Does anyone doubt that we have wheel bolts that are both lubed and unlubed? Bolts that are tightened with a torque wrench, bolts tightened with an impact wrench and torque stick, bolts tightened with just an impact wrench, bolts tightened with the car wrench, bolts tightened with a breaker bar, and God only knows what else. Yet, personally, I haven't heard of horror stories of bolts failing and wheels flying off. The main thing I always hear are problems with rusted, siezed bolts that won't come out. > > The reason that bolts are used to make mechanical joints is that they > > clamp two parts together. The clamp force is made my stretching the > > bolts. As the bolts are tightened, the bolts are slightly > > stretched........steel is elastic to a small degree.......this > > elasticity is what makes the clamping force to hold two parts together. Correct to this point. > > If the bolt threads are lubricated, the torque values are not > > accurate. Torque is a measure of the force being applied around a fixed axis. Torque is used as an estimate of the actual force between the bolt head and the surface that it's intended to hold. There is no reason to suspect that the torque readings are inaccurate since your torque wrench doesn't magically stop working when lube is on the threads, but the amount of "holding force" can be considerably different. Note that this holding force is directly proportional to the amount of stretch being exhibited by the bolt. Let's spin this the other way. Consider bolts that are corroded and/or rusty. We can torque 'em up "properly" but do we think that the holding force is correct? Most definitely not; as we know that torque is an estimate of what the actual force is going to be. The problem really comes in when you shear the bolt off, and that shearing often (in my experience) is due to excessive torque and not holding force. That is to say, when I experience it most, the head of the bolt shears right off before the bolt itself has even started to stretch. Where the bolt breaks can tell you what force caused its failure, and more often than not (again, in my experience) it's because the torque being applied to the bolt is too high, and /not/ because the bolt was too tight (i.e. the bolt had not stretched too far). > > The bolts are stretched much more than the engineering specs > > allow........possibly making the bolts stretch more than the elastic > > limit......thus the bolts will fail.(break) If the specs do not call > > for lube, do not use it. Sure, although there is the question of, "what condition of threads do these specs require?" Rationally I'd say that the specs in the manual are for brand-new, still-in-plastic hardware, that most likely has some light oil on it to keep it from rusting before making it into the consumer's hands. Most of the fasteners on my car are not in this state, though. > This site talks about some of the issues: > http://www.dansmc.com/bolts2.htm Interesting writeup. > As a test, he tried torquing a bolt with and without lube and found > that with lube the bolt was effectively over torqued by about 20%. Ah- he found that there was a 20% greater holding force with the lubed bolt, but did not state whether he felt that was over-tight or the non-lubed version was under-tight. ...at least, not on that page (I didn't read anything else on his site). In other words, maybe the unlubed state was 25% under-tight? > I'd suspect it results in a lot more variation than the 20% noted in the > lube experiment above. Yet, this apparently doesn't create all kinds > of problems in practice. Exactly. ;) > Another thing that immediately comes to mind is that if getting the > correct clamping force within a tight range is so critical on wheels, > then why don't they spec that the bolts be lubed? Here's a crazy answer: maybe the "correct" clamping force isn't actually all that narrow of a window? -tom! -- Tom Plunket schrieb: >>> The reason that bolts are used to make mechanical joints is that they >>> clamp two parts together. The clamp force is made my stretching the [quoted text clipped - 15 lines] > holding force is directly proportional to the amount of stretch being > exhibited by the bolt. Torque in bolt winding is the sum of the bolt's head elongation force converted to torque by winding pitch and bolt diameter plus the torque proportional to this stress torque given by the friction force in the seat and in the winding. Since wheel bolts are constructed to bite into their conical seats without lockwashers, the main force contributing to the torque has to be the frictional contribution. So its natural to define the pressing force by a given applied torque in this biting process. While for a small car of 2 tons the bolts with forces around 1 ton per bolt even may hold a wheel if three of five have gone the situation is quite different for trucks. SignatureRoland Franzius > > > The reason that bolts are used to make mechanical joints is that they > > > clamp two parts together. The clamp force is made my stretching the [quoted text clipped - 56 lines] > didn't read anything else on his site). In other words, maybe the > unlubed state was 25% under-tight? I think the essential point those that say the bolts shouldn't be lubed are making is that the spec called out in the service manual assumes an unlubed bolt is being used. If you use that value with a lubed bolt, the actual clamping force is going to be higher, per the above discussion and experiment. And it's going to be so much higher, that something bad can happen, like the bolt will fail. What really is the issue and what it seems we agree on, is it's not clear exactly what the service manual torque spec is based on. A brand new bolt that is perfectly clean? A brand new bolt with some kind of small lube or similar coating to prevent rust before it's used? A worse case old bolt with some rust? An average of the two? > > I'd suspect it results in a lot more variation than the 20% noted in the > > lube experiment above. Yet, this apparently doesn't create all kinds [quoted text clipped - 8 lines] > Here's a crazy answer: maybe the "correct" clamping force isn't actually > all that narrow of a window? I think that's highly likely. |
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