Rear subframe bolts

[gjm120]

Anyone know why the subframe fasteners were changed in length. I'm referring to the 4 bushing bolts and 4 bolts for the braces/pushrods highlighted in yellow on the attached.

The subframe, bushings and pushrods are the same parts regardless of year so I can only guess the point where the subframe and pushrods are attached to the body are different.

[bbnks2]

Originally Posted by gjm120

Anyone know why the subframe fasteners were changed in length. I'm referring to the 4 bushing bolts and 4 bolts for the braces/pushrods highlighted in yellow on the attached.

The subframe, bushings and pushrods are the same parts regardless of year so I can only guess the point where the subframe and pushrods are attached to the body are different.

Might've been done to save weight? They made them shorter 127mm-->110mm

[gjm120]

Originally Posted by bbnks2

Might've been done to save weight? They made them shorter 127mm-->110mm

Yea must save about 4 oz total.

I'm looking on realoem for the body part where this fastens to but can find it. I stumbled on this when ordering bolts to replace existing ones when doing subframe inserts.

Shorter bolts w/ same size holes (or shorter bolts and shallower holes for that matter) would be less holding strength. If the holes in the newer body are shallower it would be a problem to have bolts that didn't snug up completely. I know I'm overanalysing this.

[bbnks2]

Originally Posted by gjm120

Yea must save about 4 oz total.

I'm looking on realoem for the body part where this fastens to but can find it. I stumbled on this when ordering bolts to replace existing ones when doing subframe inserts.

Shorter bolts w/ same size holes (or shorter bolts and shallower holes for that matter) would be less holding strength. If the holes in the newer body are shallower it would be a problem to have bolts that didn't snug up completely. I know I'm overanalysing this.

Bolts don't generally bottom out in their holes so they will "snug up" fine.

[gjm120]

Originally Posted by bbnks2

Bolts don't generally bottom out in their holes so they will "snug up" fine.

I know. Just wish there was an explanation for the difference.

[Suprgnat]

Originally Posted by bbnks2

Might've been done to save weight? They made them shorter 127mm-->110mm

Strictly dollars and cents.

Look at it from the bean counter's point of view. Over the course of 100k vehicles, shortening those 8 bolts and dropping 4ish ounces means:

1. 12.5+ tons less steel to buy.
2. 8 kilometers less shaft on which to machine thread.
3. Some amount of labor time savings NOT having to fasten those 8 extra kilometers of thread.
4. Whatever environmental benefits there are from not mining, making, machining, and transporting an extra 12.5+ tons of steel.
5. Switching from a hex head to a torx head on one of the bolts = 1 less tool and more consistent torquing of the fastener at assembly.

[gjm120]

Originally Posted by Suprgnat

Strictly dollars and cents.

Look at it from the bean counter's point of view. Over the course of 100k vehicles, shortening those 8 bolts and dropping 4ish ounces means:

1. 12.5+ tons less steel to buy.
2. 8 kilometers less shaft on which to machine thread.
3. Some amount of labor time savings NOT having to fasten those 8 extra kilometers of thread.
4. Whatever environmental benefits there are from not mining, making, machining, and transporting an extra 12.5+ tons of steel.
5. Switching from a hex head to a torx head on one of the bolts = 1 less tool and more consistent torquing of the fastener at assembly.

That sort of penny pinching wouldn't surprise me but normally they supersede a part #. I'm only belaboring this because the Whiteline inserts add a slight bit of thickness and I bought the shorter (correct for my car) bolts.

[Suprgnat]

Originally Posted by gjm120

That sort of penny pinching wouldn't surprise me but normally they supersede a part #. I'm only belaboring this because the Whiteline inserts add a slight bit of thickness and I bought the shorter (correct for my car) bolts.

I see what you're saying, but they probably can't supersede the old P/N because the extra length is needed somewhere else.

How much thicker are the Whiteline inserts?

[gjm120]

Originally Posted by Suprgnat

I see what you're saying, but they probably can't supersede the old P/N because the extra length is needed somewhere else.

How much thicker are the Whiteline inserts?

Maybe ~1/8", 2-4mm. Probably not enough to worry about.

I feel there must be some reason for the length, likely a difference in the part of the body where the bolts go in. It's just doesn't make sense to recommend different bolts for different build dates without a reason.

I'm as much curious as concerned.

[Suprgnat]

Originally Posted by gjm120

Maybe ~1/8", 2-4mm. Probably not enough to worry about.

I feel there must be some reason for the length, likely a difference in the part of the body where the bolts go in. It's just doesn't make sense to recommend different bolts for different build dates without a reason.

I'm as much curious as concerned.

It is pretty weird. I looked at the RealOEM pages dealing with the bodywork, specifically the "Floor parts rear exterior" which includes all the "rear axle carrier" sheet metal, between a 1-2008 coupe and a 1-2013 coupe and they are identical.

It would be odd if BMW spec'd a bolt that was 17mm too long right from the get-go, so maybe I'm missing something.

You're not the first to notice, either: https://www.1addicts.com/forums/show...34&postcount=4 but an integrated washer won't account for an extra 17mm, nor do they look 17mm different in the picture.

[gjm120]

Originally Posted by Suprgnat

It is pretty weird. I looked at the RealOEM pages dealing with the bodywork, specifically the "Floor parts rear exterior" which includes all the "rear axle carrier" sheet metal, between a 1-2008 coupe and a 1-2013 coupe and they are identical.

It would be odd if BMW spec'd a bolt that was 17mm too long right from the get-go, so maybe I'm missing something.

You're not the first to notice, either: https://www.1addicts.com/forums/show...34&postcount=4 but an integrated washer won't account for an extra 17mm, nor do they look 17mm different in the picture.

At least I'm not the only one with OCD . That difference is next to nil though.

I saw the parts diagram you referenced but wasn't sure if that covered where the subframe mounts. There is a part that looks like the front subframe mounting point but it isn't specifically listed. It's the piece that looks like a dog bone. You can see the two holes where it appears the pushrods bolt on.

[bbnks2]

Maybe realOEM is showing incorrect data?

The 135i gets a rear brace which might explain why there are two bolts of different lengths... other cars like the 128i do not get the brace.

I can't recall if both cars use those "cup" things though...

[gjm120]

If brace is referring to the v-shape made up by the longish slats and the plate, yes that is on my car. (It's called a tension strut in RealOEM.)

I have a set of new subframe bolts - the 110mm ones - that I plan to install sometime soon. I may drop the subframe again to do a rear ARB so didn't use them. Didn't think to measure the existing ones when I did the inserts but will measure them when I replace. If the existing ones are 127mm then I'll order the correct ones.

My car also has the cups (stopper on RealOEM) on the 2 rearmost rear subframe bolts.

As far as I can tell, the subframe, bushings, stoppers, tension struts and push rods are the same across the years so this is a real mystery to me. Something had to change in the mounting points on the body itself. I wonder if anyone with a later car bought the longer bolts. It seems they could have bottomed out before clamping down. 17mm is a good bit of a difference.

[Traf]

Recently swapped my subframe, yes, new main subframe bolts are shorter.

[gjm120]

Originally Posted by Traf

Recently swapped my subframe, yes, new main subframe bolts are shorter.

The bolts that came off my car are exactly the same as the new ones. They are 110mm. This is the threaded part - there is an approx 7mm tapered tip.

I assume your car was built after Jun 2011?

[Traf]

Originally Posted by gjm120

The bolts that came off my car are exactly the same as the new ones. They are 110mm. This is the threaded part - there is an approx 7mm tapered tip.

I assume your car was built after Jun 2011?

Hm, no, but maybe they were changed before. So prior to 06/2011 the bolts are longer? I guess i didn't install the right ones...

07 Torx-bolt with washer M12X127-10.9 4 06/2011 33326760340
07 Torx screw with collar M12X1,5X110 4 06/2011 33306793892

[gjm120]

Originally Posted by Traf

Hm, no, but maybe they were changed before. So prior to 06/2011 the bolts are longer? I guess i didn't install the right ones...

07 Torx-bolt with washer M12X127-10.9 4 06/2011 33326760340
07 Torx screw with collar M12X1,5X110 4 06/2011 33306793892

Those part numbers are correct according to RealOEM. Also the pushrod bolts are 3mm longer up to 06/2011 (#8 on the pdf attached to the first post on this thread)

No one has any idea why the bolts lengths changed. Do you have or know the length of the bolts that were originally on your car? If they were 110mm, I'd think you have nothing to worry about if you used 110mm bolts when you replaced the subframe. If they were 127mm, you might want to do a little more digging into the issue. Since my original and the replacement bolts were the same size and the inserts don't add much thickness, I'm considering it ok.

I'd still like to understand why the change. There are a couple of BMW Technicians on this forum so maybe one of them will see this thread and shed some light on this.

[Traf]

Originally Posted by gjm120

Those part numbers are correct according to RealOEM. Also the pushrod bolts are 3mm longer up to 06/2011 (#8 on the pdf attached to the first post on this thread)

No one has any idea why the bolts lengths changed. Do you have or know the length of the bolts that were originally on your car? If they were 110mm, I'd think you have nothing to worry about if you used 110mm bolts when you replaced the subframe. If they were 127mm, you might want to do a little more digging into the issue. Since my original and the replacement bolts were the same size and the inserts don't add much thickness, I'm considering it ok.

I'd still like to understand why the change. There are a couple of BMW Technicians on this forum so maybe one of them will see this thread and shed some light on this.

The bolts on my car were definitely longer, i noticed it but didn't think much of it at the time.
The car is on stands atm so i will order the longer bolts and swap them, i ain't taking any chances for 30€ worth of bolts...

[gjm120]

Originally Posted by Traf

The bolts on my car were definitely longer, i noticed it but didn't think much of it at the time.
The car is on stands atm so i will order the longer bolts and swap them, i ain't taking any chances for 30€ worth of bolts...

I think that is the smart thing to do.

Just curious, why did you changeout your subframe?

[Traf]

Originally Posted by gjm120

I think that is the smart thing to do.

Just curious, why did you changeout your subframe?

Bent due to a crash so swapped it with an M3 subframe.

[gjm120]

Originally Posted by Traf

Bent due to a crash so swapped it with an M3 subframe.

Pretty big project!

I assume you checked that there is no difference in bolts for M subframes.

[Traf]

Originally Posted by gjm120

Pretty big project!

I assume you checked that there is no difference in bolts for M subframes.

Subframe bolts are the short ones.
Torx screw with collar M12X1,5X110 4 33306793892