Caliper Support Bolt Replacement (2004 X5 3.0i)

[2004bmwx53i]

Originally Posted by andrewwynn

They are not torqued near yield I reuse. Does BMW recommend non reuse? They often do for CYA legal reasons in suspension parts.

From TIS:

2AZ
Brake caliper to steering knuckle
(screws lightly oiled, contact surfaces between brake caliper and steering knuckle cleaned and grease-free)

110 N·m.

It states if self locking or microencapsulated replace them.

I'm not aware that E53 uses either.

I reuse them.

Thanks for the input. As for the yield point, how would we know that at 110 Nm the material would not be at or passed yield.
Also, would you please explain what is meant by microencapsulated.
BTW, my mileage is 167000 miles!
Thanks

[Fifty150hs]

Reuse them. There's nothing special about them besides the grade. As Andrew said, they're not torque to yield. If you are concerned, get proper grade bolts from a local supplier. No point in paying BMW's stupid mark up for a bolt you can get for a lot less.

[andrewwynn]

I'm not even sure what BMW means by microencapsulated but I think it's a special treatment that distresses the metal "one time" to lock it. These bolts aren't.

I use an app called iEngineer to look up bolt stress/yield etc.

I think those bolts are M12 front axle maybe M10 back.


Over 5 tons of force at normal torque.

The spec torque for 10.9 M12 is 122 N·m. That is 75% of yield 160 ish should be yield hence "nowhere near". You can stress a steel bolt effectively ∞ times if below 75% of yield. It acts just like a spring.


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[2004bmwx53i]

Originally Posted by andrewwynn

I'm not even sure what BMW means by microencapsulated but I think it's a special treatment that distresses the metal "one time" to lock it. These bolts aren't.

I use an app called iEngineer to look up bolt stress/yield etc.

I think those bolts are M12 front axle maybe M10 back.


Over 5 tons of force at normal torque.

The spec torque for 10.9 M12 is 122 N·m. That is 75% of yield 160 ish should be yield hence "nowhere near". You can stress a steel bolt effectively ∞ times if below 75% of yield. It acts just like a spring.

Sent from my iPhone using Tapatalk Pro

This is first class response! Thank you.

[2004bmwx53i]

Originally Posted by andrewwynn

I'm not even sure what BMW means by microencapsulated but I think it's a special treatment that distresses the metal "one time" to lock it. These bolts aren't.

I use an app called iEngineer to look up bolt stress/yield etc.

I think those bolts are M12 front axle maybe M10 back.


Over 5 tons of force at normal torque.

The spec torque for 10.9 M12 is 122 N·m. That is 75% of yield 160 ish should be yield hence "nowhere near". You can stress a steel bolt effectively ∞ times if below 75% of yield. It acts just like a spring.
Sent from my iPhone using Tapatalk Pro

Just to be nerdy, I found some info regarding the yield of 160. Yield is stress with units of pressure like psi, torque is of unit length x force. So they can't be compared. Please have a look at the link below (the tables) and let me know what you think (I get yield of 940 and proof load of 630 MPa). This has become an interesting discussion.Thanks

https://www.boltdepot.com/fastener-i...ade-Chart.aspx

[andrewwynn]

Originally Posted by 2004bmwx53i

Just to be nerdy, I found some info regarding the yield of 160. Yield is stress with units of pressure like psi, torque is of unit length x force. So they can't be compared. Please have a look at the link below (the tables) and let me know what you think (I get yield of 940 and proof load of 630 MPa). This has become an interesting discussion.Thanks

https://www.boltdepot.com/fastener-i...ade-Chart.aspx

You misunderstood me.

I was saying that you prob wouldn't reach yield until about 160 N·m where 122 is spec. (that could be off a fair amount it might not be a direct ratio).

Reality check;

M10 10.9 spec is 66 N·m and ratio to yield: 88 N·m. In testing, it was right about 90 N·m where the bolt went to plastic and the torque stopped climbing. BTW: a very very weird experience to turn a bolt 45° and no change in torque!

So: a 12mm should handle 140-150 N·m before damage. You should be able to torque to 122 limitless times.

So back my original stance: no problem at all to reuse, i would throw on thread lock if I had handy but wouldn't go out of my way if I didn't.

[2004bmwx53i]

Originally Posted by andrewwynn

You misunderstood me.

I was saying that you prob wouldn't reach yield until about 160 N·m where 122 is spec. (that could be off a fair amount it might not be a direct ratio).

Reality check;

M10 10.9 spec is 66 N·m and ratio to yield: 88 N·m. In testing, it was right about 90 N·m where the bolt went to plastic and the torque stopped climbing. BTW: a very very weird experience to turn a bolt 45° and no change in torque!

So: a 12mm should handle 140-150 N·m before damage. You should be able to torque to 122 limitless times.

So back my original stance: no problem at all to reuse, i would throw on thread lock if I had handy but wouldn't go out of my way if I didn't.

At anytime you're fed up with this thread, just stop responding.
As a matter of curiosity, how did you arrive at 88 N.m as the torque at yield. Shouldn't we consider Proof load rather than yield.
Proof load for 10.9 steel is 830 MPa. Effective tensile area (at the root of the thread) is about 50 mm2. So 830 x 50 is 41500 N (41.5 KN Clamping Force) Similarly for M12, it works out to be about 53 KN. Anything above this will cause permanent deformation. So we're at the limit already.
Agree?

[andrewwynn]

Originally Posted by 2004bmwx53i

At anytime you're fed up with this thread, just stop responding.
As a matter of curiosity, how did you arrive at 88 N.m as the torque at yield. Shouldn't we consider Proof load rather than yield.
Proof load for 10.9 steel is 830 MPa. Effective tensile area (at the root of the thread) is about 50 mm2. So 830 x 50 is 41500 N (41.5 KN Clamping Force) Similarly for M12, it works out to be about 53 KN. Anything above this will cause permanent deformation. So we're at the limit already.
Agree?

good catch I used tensile vs. yield.

The correct number would be 122*94/78=147 N·m for yield. (20% higher than proof).

The proof strength is 0.83 of yield not 0.75.

[bcredliner]

Micro-encapsulated bolts have Loctite or similar on them. That's why the bolts are special. I re-use them but apply blue Loctite before doing so. Calipers are subject to lots of vibration, shocks and heating and cooling cycles. I wouldn't reuse them without a new application of Loctite.

[2004bmwx53i]

Originally Posted by bcredliner

Micro-encapsulated bolts have Loctite or similar on them. That's why the bolts are special. I re-use them but apply blue Loctite before doing so. Calipers are subject to lots of vibration, shocks and heating and cooling cycles. I wouldn't reuse them without a new application of Loctite.

Just for the sake of technicalities, I would say that if bolts are torqued to specification they would not necessarily need extra locking measure. The torque supposedly has already taken vibration into account. This is my pure guess.
Adding thread lock does no harm at all. I'll do that. Thanks.