Caliper Support Bolt Replacement (2004 X5 3.0i)
 

Hey gals & guys,
Appreciate any guidance. I have 3 options for these bolts once they are removed (to replace the rotors):
1- Replace with BMW bolts costing around $300 for all 4 wheels, 8 bolts
2-Replace with same grade bolts (10.9) from the local bolt supplier ($40 total)
3-Reuse. Bolts look fine with no sign of wear/rust at all.
Please help me choose a right option.
Thanks,

I've never replaced caliper support bolts (assume you're referring to caliper bracket bolts)... so I guess option 3 would be my vote. Clean and reuse.

Reuse unless there’s an issue. These aren’t special bolts, so there’s no real need to spend $300.

Yep, just reuse. No point of replacing them.

They are in a way special; they are grade 10.9 and are plated not plain. The washers are of hardened type.

Caliper Support Bolt Replacement (2004 X5 3.0i)
 

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.

There's nothing unusual about that. If you hadn't been aware of the specs, I'd have brought that up, but you already know to buy hardware of the correct spec.

Reuse the bolts for the bracket to hub. Replace the pins that hold the caliper to the bracket. Replace the caliper mounting boot as well. Reinstall the new pins DRY.

Note: At 100K I personally replace all bolts, boots, lines, rebuild the calipers etc at the brakes. The replacement bolts use a male TORX head, so you will in the future need a FEMALE Torx socket. The ability to torque and unbolt is improved moving forward at the socket self centers on twist.

?????
We are discussing #3 on Image below I looked up the costs from a local dealer.
Hex bolt M12X1,5X41 ZNS3 4 11/2005 34116767217
The cost is
Disc Brake Caliper Bracket Mounting Bolt - BMW (34-11-6-767-217)

MSRP: $17.98
Discount: $3.59 (20% off)
Sale Price: $14.39

I think to OP clicked on the assembly part (Bracket, bolts,etc) number #2

OP is Canadian. Much higher prices and a markup for the exchange rate on top.

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.

Would you please share the retailer info. Thanks

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

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.

https://uploads.tapatalk-cdn.com/202...86ae4b4c4a.jpg
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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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.

This is first class response! Thank you.

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.

That is not bad advice. I will add however that after remove and replace roughly 100-120 caliper bolts. 100% of the time it took more torque to remove them than the torque they were set with. E.g. I'm not concerned about adding thread lock though I certainly would not advise against it. Very good idea. Actually on a recent job where the bolts were so rusted I had to cut new faces on the bolt to remove: I added thread lock to ironically make it easier to remove next time.

(Nexuses the thread lock fills the gap that allows water/air ingress to cause the rust lock)

I've rarely added but after that last job from hell (took a couple hours to remove two caliper bolts after somebody else rounded off the bolt heads on some M14 bolts), just to keep out the rust is a good reason.

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

Ever since having a caliper bracket bolt back out on my Mom's Infiniti FX35 (was torqued to spec), I use a bit of red locktite every time I do a brake job. Didn't do any real damage, just gouging on wheel barrel, but could have been very bad. I've never had that happen on a BMW, but I take no chances now.

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?

You can definitely safely reuse those bolts if you don't see any signs of degradation.

Attached is a BMW spec on bolt torques, since you seem to be interested in drilling deeper into this than most.

Attachment 81532

Some complicating factors, just to point out how the mechanics / physics / metallurgy is not as simple as one might like (and why the "class 10.9", etc. exists to try to remove these complications from things people need to worry about every day):

• thread pitch matters;
• friction (and surface prep / lubrication) matters a lot;
• different parts of the fasteners will see different stress, so some level of yield at some locations may occur and be acceptable;
• when tightening a fastener, there is a stress due to torque resisted by friction, in addition to the stress due to elongation, and those combine, and they depend on friction, thread pitch, etc. at which point seemingly arbitrary parameters get introduced to the equations;
• that BMW spec (I think) has a disclaimer in there about re-using up to 3 times but no more;
• ... but re-using would surely logically depend on corrosion, age, mileage, etc. as well, but that is not given here;
• and this is BMW's spec, reminding us that anyone can make their own spec, which may be different.

If you're looking for more information and flames in a related topic, search on here for advice on whether to re-use the stiffener plate bolts (the 6-bolt aluminum or steel plate under the engine).

Great information thanks. Although my bolts look great & have no sign of rust, do you think I should still replace them with new ones, from the local bolt store, because of the age and mileage: 2004 model with over 160,000 miles? Thanks

I would definitely re-use them on my car. I recently did that actually, on my 2001 with 203k+ miles. I'm in CA with no rust issues.

An additional thing you can do to give yourself confidence that no plastic deformation has occurred is to see if you can easily thread things together with your fingers. Plastic deformation will be uneven, making that impossible over a long depth.

I was referring to your comment above:

"but re-using would surely logically depend on corrosion, age, mileage, etc. as well, but that is not given here"

and my high mileage and age of the car

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.

https://uploads.tapatalk-cdn.com/202...01c98110a7.jpg

That's a very good test. Especially when you can use a new nut on an old bolt.

Suspension bolts are usually on the order of 2x safety factor. A 12mm bolt has a clamping force of 5T. Two means 10T. Just shy of 8T@ sheer force each so the brake caliper can withstand 16T of sheer force that is a lot more than the tire can apply in perfect conditions.

https://www.bmwoffairfax.com/order-parts-online.htm

Just reuse the bolts as the next brake job will be end of life.

Yes, replace them. That's the answer you want to hear, right? :dunno:

Not necessarily. I have a 2006 with 265,000 miles. OP has 160,000. He's far from end of life. Properly cared for the M54 is practically bullet proof. Change the rest of the wear components as needed and properly care for the car and it will last a very long time. There have been people on here with over 350,000 miles on their X IIRC.

No question that a properly cared for X5 (or any BMW for that matter) will go a long long way. 89% will never get there as most drive 'em into the ground long before their time. As 4th and 5th owners seek the cheapest band aids as any preventative maintenance catch ups exceed the cost of ownership.

Personally I live on the fix it right the first time with quality parts and DIY skills island, but I also realize that our auto enthusiast island is quite a small fraction of the models left out there. My own X5 4.8is sits at 65K so it will outlive most of the daily drivers. No salt road, rain, or abuse. It sits nice and dry with a cover and a Battery tender humming away.

I agree. I'm of the same mind, fix it right the first time. If you don't you'll be fixing it again. Soon. Mine is a daily, but I live in California where rust and salt are not issues, so that part of it sort of takes care of itself. That said, BMW sure seems to use really cheap steel as, even in this climate, it sure rusts. I'm shooting to get 300,000 miles out of my X. I think I'll make it.

I decided to reuse. Thanks everyone for sharing your knowledge. It is much appreciated.
Have a great new year ahead!

Yea!

Multiple posts, metallurgy discussions, micro view discussions on pros and cons and we are completed!