Boring motorway journey suddenly became quite exciting!
Discussion
So there I was, 90 minutes into a 200 mile motorway journey in my BMW E39 Touring, doing a steady 70mph with cruise control active, when suddenly and without warning, a large amount of rear-wheel steering got me quite excited. I managed to steer onto the hard shoulder and stopped, where I found the NSR wheel had about 3 inches toe out. Inspection revealed four wheel bolts were missing, only one bent one left keeping the wheel on the car.
Thought I'd take one bolt from each of the other wheels to put it back on, but then I found that all four missing bolts had in fact sheared, leaving the broken ends flush in the hub. So the journey was finished on various flatbeds instead.
So my question is, what is likely to have caused the bolts to shear?
Background
Original (2003) BMW wheels and bolts, all in apparently good condition. I had completed the outbound 200 mile journey two days earlier without incident. I'd taken all four wheels off the car a couple of days before the trip. The two rear wheels' bolts were somewhat tight to undo - but not outrageously so. On refitting the wheels, I torqued all wheel bolts in one session to the specified 120Nm. Bolts showed no sign of stretching or damage, and I've had the car for 9 years so no recent kerbing or other unknown events.
The only clue was that earlier in the day, driving about 20mph in a residential street, I could sometimes just hear what I thought was a very faint rumble indicating diff wear. Possibly one or more bolts had already sheared and the noise was actually from the wheel?
So, what theories do you have? Anyone had a similar experience?
Thought I'd take one bolt from each of the other wheels to put it back on, but then I found that all four missing bolts had in fact sheared, leaving the broken ends flush in the hub. So the journey was finished on various flatbeds instead.
So my question is, what is likely to have caused the bolts to shear?
Background
Original (2003) BMW wheels and bolts, all in apparently good condition. I had completed the outbound 200 mile journey two days earlier without incident. I'd taken all four wheels off the car a couple of days before the trip. The two rear wheels' bolts were somewhat tight to undo - but not outrageously so. On refitting the wheels, I torqued all wheel bolts in one session to the specified 120Nm. Bolts showed no sign of stretching or damage, and I've had the car for 9 years so no recent kerbing or other unknown events.
The only clue was that earlier in the day, driving about 20mph in a residential street, I could sometimes just hear what I thought was a very faint rumble indicating diff wear. Possibly one or more bolts had already sheared and the noise was actually from the wheel?
So, what theories do you have? Anyone had a similar experience?
What pattern did you tighten and torque the wheels in and did the wheels come off the hubs easily when you removed them? It could be that the wheels weren't seated properly
That said, far more likely that it's had the wheel nuts rattle gunned on and off by a particularly ham fisted garage before your ownership and your last removal of the wheels has sent them over the edge.
That said, far more likely that it's had the wheel nuts rattle gunned on and off by a particularly ham fisted garage before your ownership and your last removal of the wheels has sent them over the edge.
M4cruiser said:
Is (was) the wheel's central hole a snug fit on the central boss of the stub?
Sometimes incorrect wheels are fitted resulting in the bolts taking all the weight.
This is a mega complicated subject, and I'm not an expert, but the central boss is just there to centre the wheel. The bolts are there to clamp the wheel to the hub face, and it's the friction between the wheel and hub face that does the work.Sometimes incorrect wheels are fitted resulting in the bolts taking all the weight.
I agree with M_A_S. Check your torque wrench. I rujined a peectly good engine block I was rebuilding, by overtightening a stud that cracked the block.
A check is easy to do, if you have a bench vice or similar. GRip the drive shaft in the vice, handle horizontal, hang a weight off the handle and move it out until the wrench clicks. The weight divided by the distance from the drive shaft is the torque.
A check is easy to do, if you have a bench vice or similar. GRip the drive shaft in the vice, handle horizontal, hang a weight off the handle and move it out until the wrench clicks. The weight divided by the distance from the drive shaft is the torque.
Thank you all for your thoughts so far. To answer some of the points raised:
Bearings OK? - I believe so, will check to be sure
Torque wrench - not calibrated for a long time, will check as described by tapkaJohnD though it did not feel miles out.
Did you grease the bolts and/or the hub face? - No, neither of them, they went on dry
What pattern did you tighten and torque the wheels in? - I always start at the top and do 1,3,5,2,4 then round again 1,2,3,4,5,1 to check
Did the wheels come off the hubs easily when you removed them? - No! The rear two were stuck fast owing to corrosion between alloy wheel and steel hub centre boss. Had to wallop the tyres using the spare wheel to budge them. Cleaned corrosion and copper greased the centre boss when replacing.
Is (was) the wheel's central hole a snug fit on the central boss of the stub? - Yes, see above. The wheels are the originals for the car, style 66.
One point on the question of lubrication of the bolts. I subsequently checked the official BMW 'how to change a wheel' documentation and it said to install new bolts dry, but to put a thin smear of engine oil on both the threads and conical mating face when bolts were 'used'. I had not lubricated so it might have resulted in reduced preload. Even so, with 5 bolts at 120Nm torque and steady trundling up a motorway, I would not have expected bolt lubrication to make such a profound difference. Maybe if I was lapping the Nurburgring at 130mph . . .
Bearings OK? - I believe so, will check to be sure
Torque wrench - not calibrated for a long time, will check as described by tapkaJohnD though it did not feel miles out.
Did you grease the bolts and/or the hub face? - No, neither of them, they went on dry
What pattern did you tighten and torque the wheels in? - I always start at the top and do 1,3,5,2,4 then round again 1,2,3,4,5,1 to check
Did the wheels come off the hubs easily when you removed them? - No! The rear two were stuck fast owing to corrosion between alloy wheel and steel hub centre boss. Had to wallop the tyres using the spare wheel to budge them. Cleaned corrosion and copper greased the centre boss when replacing.
Is (was) the wheel's central hole a snug fit on the central boss of the stub? - Yes, see above. The wheels are the originals for the car, style 66.
One point on the question of lubrication of the bolts. I subsequently checked the official BMW 'how to change a wheel' documentation and it said to install new bolts dry, but to put a thin smear of engine oil on both the threads and conical mating face when bolts were 'used'. I had not lubricated so it might have resulted in reduced preload. Even so, with 5 bolts at 120Nm torque and steady trundling up a motorway, I would not have expected bolt lubrication to make such a profound difference. Maybe if I was lapping the Nurburgring at 130mph . . .
The fact they all had the issue....clearly points out to either overtightening, or not tightening enough.
Assuming they were good clean and also not freshly painted wheels where the flange was also coated.
Lots of people say not to lubricate nuts/bolts.....but I've seen far more problems from dry bolts, than I have with them with a light amount of copper grease over the years. ( and that precludes morons who plaster them with any sort of lubricant )
Assuming they were good clean and also not freshly painted wheels where the flange was also coated.
Lots of people say not to lubricate nuts/bolts.....but I've seen far more problems from dry bolts, than I have with them with a light amount of copper grease over the years. ( and that precludes morons who plaster them with any sort of lubricant )
The usual cause of a Sudden wheel "undoing" is because the wheel was not fully / squarely seated on the hub face before the fastenings were done up! It's quite possible, especially on older cars with corroded hubs / wheels for the wheel to sit and a slight angle, and still be torqued up. However, when the car is driven, the loads cause the wheels to suddenly snap back to square, which means at least 3 of the bolts are now very loose indeed!. Then the wheel starts to chaffe and vibrate, and soon, parts company from the hub....
If possible, always spin the wheel by hand after fitting to check it is indeed sqaure and true, snug all the bolts up first finger tight, then to say a low torque (15 Nm) and only then fully tighten in a criss-cross pattern. After any wheel removal i will recheck all the bolts for tightness after the first drive, especially if the brakes have been used heavily (the brakes heat the hub and wheel, which can cause it to seat on further and realse some of the clamp load)
(hint, a "click type" torque wrench is a comparitor between two lengths and a (adjustable) force......)
If possible, always spin the wheel by hand after fitting to check it is indeed sqaure and true, snug all the bolts up first finger tight, then to say a low torque (15 Nm) and only then fully tighten in a criss-cross pattern. After any wheel removal i will recheck all the bolts for tightness after the first drive, especially if the brakes have been used heavily (the brakes heat the hub and wheel, which can cause it to seat on further and realse some of the clamp load)
tapkaJohnD said:
Anyone notice the "whoops" moment in this ^^^ pic?(hint, a "click type" torque wrench is a comparitor between two lengths and a (adjustable) force......)
100% at some time in their life they have been over tightened & gone beyond their elastic limit, simply choosing that point to throw their hand in.
Possibly the only one left has been inadvertently swapped to another wheel at some time, so it could be worth a full new set of bolts as others on the car would most likely have been treated the same.
Possibly the only one left has been inadvertently swapped to another wheel at some time, so it could be worth a full new set of bolts as others on the car would most likely have been treated the same.
I've checked the calibration of my torque wrench using the method shown above. I used a bucket full of bricks and lump hammers for the weight, then weighed each item carefully.
With my wrench set exactly to 12kgfm (mine is calibrated in kilogram force metres not Nm) the actual torque applied as it just clicked was 12.1874 kgfm, which is 119.518 Nm. So I'm happy that it is accurate at this setting, and BMW specifies 120 Nm for these bolts.
So from the above discussion, the most likely explanations for the bolt failures are either that some of these bolts had been overtightened in the distant past, or that the wheel was somehow not fully seated on the hub when the bolts were torqued - and it later became fully seated and introduced a small amount of play, which continually hammered the bolts until first one, then the others in turn, sheared. This latter possibility would also explain the almost imperceptible rumble which I heard earlier that day at low speed, and mistakenly put down to diff wear.
I've already bought a new set of Febi Bilstein bolts for all the wheels. I will remove each wheel and make sure both wheel boss and hub are clean and flat, so hopefully there will be no repeat. I'll also be following Max_Torque's advice above when refitting.
As Tony1963 said, it could’ve ended very differently, so if you hear a new diff rumble, get out and check your wheel bolts!
With my wrench set exactly to 12kgfm (mine is calibrated in kilogram force metres not Nm) the actual torque applied as it just clicked was 12.1874 kgfm, which is 119.518 Nm. So I'm happy that it is accurate at this setting, and BMW specifies 120 Nm for these bolts.
So from the above discussion, the most likely explanations for the bolt failures are either that some of these bolts had been overtightened in the distant past, or that the wheel was somehow not fully seated on the hub when the bolts were torqued - and it later became fully seated and introduced a small amount of play, which continually hammered the bolts until first one, then the others in turn, sheared. This latter possibility would also explain the almost imperceptible rumble which I heard earlier that day at low speed, and mistakenly put down to diff wear.
I've already bought a new set of Febi Bilstein bolts for all the wheels. I will remove each wheel and make sure both wheel boss and hub are clean and flat, so hopefully there will be no repeat. I'll also be following Max_Torque's advice above when refitting.
As Tony1963 said, it could’ve ended very differently, so if you hear a new diff rumble, get out and check your wheel bolts!
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff