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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Tue, Oct-30-2012, 02:52:08 AM   #111
bmwJohhnyD
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by kaiv View Post
Don't think I posted these so here's some illustration of fail










hmmm.. that is an interesting photo of the thread imprint in the bolt hole of the carrier.

wouldnt that bold have to be moving around in there to cause that imprint, thus making the bolt too small for the hole?

i am no bolt engineer, so maybe someone will chime in on that.

my old school mechanic dad immediately called shenanigans on the old bolts saying that a fully threaded ( tap bolt ) should not be used to join to peices together when one side isnt threaded. he essentially described the new bolt design, as what should be in there.

but dang.. still breaking..
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Old Tue, Oct-30-2012, 03:20:07 AM   #112
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by terraphantm View Post
Just did this - clunk when shifting is pretty much gone. Kinda surprised that there was a difference in feel at all, the old bolts were in there pretty tight
Definitely helped with the clunk in my case but I didn't really think about and realize it until I saw your post. I started to think it was something worse, possibly the subframe. It's quite a lot easier to change the bolts when the subframe is out as well.
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Old Tue, Oct-30-2012, 04:40:23 AM   #113
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Default Re: Differential Bolts replacement DIY: updated bolts

Subframe plates, subframe bushings, diff mounts, diff bolts, csb, guibo, and a lot of other stuff getting done next week... Clunk better go away!
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Old Tue, Oct-30-2012, 01:38:10 PM   #114
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by bmwbob View Post
my old school mechanic dad immediately called shenanigans on the old bolts saying that a fully threaded ( tap bolt ) should not be used to join to peices together when one side isnt threaded. he essentially described the new bolt design, as what should be in there.
You're dad is correct. Fully vs. partially threaded is precisely the issue here.
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Old Tue, Oct-30-2012, 03:41:01 PM   #115
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by drunk hal View Post
You're dad is correct. Fully vs. partially threaded is precisely the issue here.
i figured as much. he is about 85 percent correct, 65 percent of the time.

only time he messes up is when he is dated by technology.. ie electronic issues.

although the vanos concept really threw him for a loop.

he works on strictly old chevrolet's specifically and only corvettes.
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Old Tue, Oct-30-2012, 03:53:47 PM   #116
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by drunk hal View Post
You're dad is correct. Fully vs. partially threaded is precisely the issue here.
Not really. While a partially threaded bolt will likely last longer until failure...

At the proper torque spec, there should be enough friction such that there is no movement, period.

The new bolts are somewhat of a bandaid for some more central design issue. The engineers didn't just accidentally pick a fully threaded bolt by mistake. It shouldn't matter. There should be no movement. Now they're left updating it with a bolt that will be marginally better, but the issue isn't really resolved.

You have a hole which is over-sized (actually a slot really IIRC) to allow the diff to bolt up with some play for alignment, etc. And your friction surfaces, fastener size, etc. isn't what it should be to keep then fixed together.

The shoulder of the new bolt still has slop relative to the center of the bushing. It will still move (a HAIR less). It's just a bit stronger in sheer.

C/N: the new bolt is BETTER for the application, but it was definitely not "the issue". There's still slop with either bolt when not tight enough.

Last edited by prematureapex; Tue, Oct-30-2012 at 04:03:44 PM.
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Old Tue, Oct-30-2012, 03:56:08 PM   #117
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by prematureapex View Post
Not really. While a partially threaded bolt will likely last longer until failure...

At the proper torque spec, there should be enough friction such that there is no movement, period.

The new bolts are somewhat of a bandaid for some more central design issue.
go on...
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Old Tue, Oct-30-2012, 04:12:56 PM   #118
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by prematureapex View Post
Not really. While a partially threaded bolt will likely last longer until failure...

At the proper torque spec, there should be enough friction such that there is no movement, period.

The new bolts are somewhat of a bandaid for some more central design issue. The engineers didn't just accidentally pick a fully threaded bolt by mistake. It shouldn't matter. There should be no movement. Now they're left updating it with a bolt that will be marginally better, but the issue isn't really resolved.

You have a hole which is over-sized (actually a slot really IIRC) to allow the diff to bolt up with some play for alignment, etc. And your friction surfaces, fastener size, etc. isn't what it should be to keep then fixed together.

The shoulder of the new bolt still has slop relative to the center of the bushing. It will still move (a HAIR less). It's just a bit stronger in sheer.

C/N: the new bolt is BETTER for the application, but it was definitely not "the issue". There's still slop with either bolt when not tight enough.
*Shear

Fully threaded bolt is sloppy detailing in this application. Would be nice to know if that slop is needed or not, if it's not then it sounds like a custom shouldered bolt is in order.

Last edited by m3 hal; Tue, Oct-30-2012 at 04:18:00 PM.
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Old Wed, Oct-31-2012, 08:47:43 PM   #119
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Default Re: Differential Bolts replacement DIY: updated bolts

Hey Bob!

The thread imprint on the mount is a tell tale sign that the bolt was loose before it broke.

If the bolt had been tight, there would've no diff movement that would've caused the thread to get imprinted on the mount.

This is just my theory of course but it is further backed up by the fact that the broken bolt was easy to back out of the subframe (wouldn't have been so easy if it was torqued down!)



Quote:
Originally Posted by bmwbob View Post
hmmm.. that is an interesting photo of the thread imprint in the bolt hole of the carrier.

wouldnt that bold have to be moving around in there to cause that imprint, thus making the bolt too small for the hole?

i am no bolt engineer, so maybe someone will chime in on that.

my old school mechanic dad immediately called shenanigans on the old bolts saying that a fully threaded ( tap bolt ) should not be used to join to peices together when one side isnt threaded. he essentially described the new bolt design, as what should be in there.

but dang.. still breaking..
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Old Thu, Nov-01-2012, 12:52:47 AM   #120
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Default Re: Differential Bolts replacement DIY: updated bolts

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Originally Posted by drunk hal View Post
*Shear

Fully threaded bolt is sloppy detailing in this application. Would be nice to know if that slop is needed or not, if it's not then it sounds like a custom shouldered bolt is in order.
shear

Sloppy detailing, maybe.

However, the bushing centers are a bit slotted IIRC, so it's well beyond slop. Not sure if the slots are provided as a matter of easing diff installation, or providing another means to allow for alignment of the drivetrain.

Point being, even a custom shoulder isn't going to do it, unless you elongate it to match the factory slots, eliminating the design element entirely. That would be but another patch.

Proper torque should prevent any issues.
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Discussing Differential Bolts replacement DIY: updated bolts in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)