half shaft bolts

[gms]

Safety wire is a good solution for those bolts, one step up from locktight!

[Timmer]

Interesting you mentioned this; I put on a half shaft for a '74 2002 I had in the later 1980's and within a few weeks it had worked itself loose enough to the point where one end dropped; luckily, I was just taking off from a red light that turned green. It's been mentioned before, check those bolts now and then for tightness.

Tim.

[jprocket]

I safety wired my half shafts also just because of these horror stories! I figured since i wont be pulling diffs or halfshafts every other weekend the effort would pay off. To that end, I blue loctite and safety wired both sides of the half shafts - the diff side and the wheel side. Of course this was after a rebuilt, repainted, and repacked/replaced the cv joints to make them go another 10 years.

[gms]

Actually, this was supposed to be a reply to Blunt's thread. But still applies!

[john_a]

Safety wire is a good solution for those bolts, one step up from locktight!

I've got a different take on this matter, hope no one takes offence..

It's fair to say virtually none of the factory installed fasteners here come loose, or BMW (and all the other manufacturers with half shafts) would have suffered serious warranty issues & recalls. My contention is that this is strictly a service installation problem. Have you ever heard of this happening where the axle was not previously R&R'd at some point? Often, we hear of it occuring shortly after an install.

It is a critical joint, and unfortunately it's in an awkward postion with the shaft angle & CV boot getting in the way of the bolts. It requires turning the axle to get access to all the fasteners, and it is very easy to skip a turn & end up getting the bolts tight without the joint clamped properly.

I'm going to suggest the problem occurs when the CV joint is not squarely clamped to the flange when the bolts get tightened, and as it rotates the cyclic rocking is quick to loosen things up further. Safety wire or loctite are not going to do anything to correct things if the root cause is uneven joint clamp. Especially with the M8 bolts and their low torque spec, the axle & CV are heavy and it is easy to have it installed just slightly off-square and still feel like all the bolts reached their torque.

I like to use a method that both improves the eveness of clamp, and provides a visual aid for future inspections. Of course, start with correct new or perfect threaded fasteners, and clean & chase the female threads in the flange (if you have the type without nuts.)

Get a torque wrench & a paint marker ready to "paint scribe" the fasteners.

Raise the corner of the car enough to be able to turn the axle you are working on (tire must clear the ground, vehicle in neutral.)

Here's the critical part to getting an evenly clamped joint: Use a cross star pattern to snug up the joint, and proceed in stages up to the final torque. Everyone knows they should tighten these parts evenly, but because of the awkward access and difficulty turning axle to follow the pattern, it gets missed more here than in other tasks, like tightening wheel lug bolts.

Install all the bolts for one CV joint just lightly "snug" tight.

Now on the next round, tighten them (either with torque wrench or your calibrated elbow) to something just under one-half of the final torque spec, and as you hit each bolt in turn use the paint marker to scribe a line on the CV joint body only (not over the bolt yet!) That paint mark will make it much more certain you are in fact following the appropriate cross star pattern in your tightening sequence. At this point, you may need to jam the wheel or brake rotor to hold the axle from turning as you turn the wrench. Watch your paint marks on the CV joint body, and you will be far more likely to hit the bolt pattern correctly, nothing missed, nothing hit twice.

Last tightening step, still following the cross-star pattern, as you hit the final torque on each bolt, use the marker to continue the paint scribe onto the bolt head. Again, this method ensures you don't get lost in the sequence. And every time you look at the axles in the future, you will be able to see if the fasteners have started to turn back out, as the paint scribes will no longer be aligned across the bolt heads/CV body.

Safety wire is described well in the great Carroll Smith book "Nuts, Bolts, Fasteners, and Plumbing Handbook" (which he originally titled "Screw to Win" to follow his earlier titles, "Engineer to Win", "Drive to Win". etc..)

Carrol dedicates about eight pages to safety wire, but prefaces that with an explanation that says "Contrary to popular belief, even the best job of safety wiring will contribute virtually nothing to the task of preventing a bolt from loosening..." "...all that safety wire can do is limit rotation of the bolt and prevent its departure" The benefit of safety wire is how it provides a visual confirmation that someone had paid some attention when it was tightened, and if won't fall completely out if it does get loose.

But typical .031" wire on an M8 bolt can just break with the force available from a turning axle that is rocking loose at the joint.

Finally, the tightening torque BMW listed for the 2002 is on the light side at 22 - 24 ft lbs.

The early E21 used the same part number M8 bolts & axle shaft, and BMW raised the torque spec to 29 - 31 ft lbs which is what I'd use on a stock 2002.

If you have the later E21 CV with the M10 bolts the torque goes up to 44 -49 ft lbs

My take on it is install with care, use paint scribe mark to aid keeping the pattern of tightening, and give those paint marks a look each time you're under the car to verify all is well. If you really want an extra measure of safety, Loctite is good and it also prevents the threads from getting corroded. This is definately one of those tasks where you 'make your own luck'.

[Bill_Riblett]

It's fair to say virtually none of the factory installed fasteners here come loose, or BMW (and all the other manufacturers with half shafts) would have suffered serious warranty issues & recalls. My contention is that this is strictly a service installation problem. Have you ever heard of this happening where the axle was not previously R&R'd at some point? Often, we hear of it occuring shortly after an install.

Actually I do know of one incident of factory installed fasteners coming loose. Early 77 320i (Dec 76 build) lost all the bolts on one halfshaft in the car's second year.

But you make a lot of good points about halfshaft installations.

[john_a]

Actually I do know of one incident of factory installed fasteners coming loose. Early 77 320i (Dec 76 build) lost all the bolts on one halfshaft in the car's second year.

Yeah, that would be one pissed off customer that drops a halfshaft on their new-ish BMW. I'm sure you know I said 'virtually' (instead of 'absolutely') in an attempt to relate how exceedingly rare it is, relative to how frequent we hear about it just in our small population of cars known on this board. BMW sold over one million E21, and there was not a high incidence of this failure (from the factory.) Contrast that with today, and the few thousand of remaining 2002 that are serviced by DIY method, and the alarming number of reports of axles coming loose. I'm no statistician, but there's a trend that's easy to spot.