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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 Thu, Sep-29-2016, 01:53:52 PM   #1
VinceSE2
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Default "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

As I put quite some time into explaining this in my recent group buy thread, and just realized some of you who where not interested in the actual group buy (and thus did not read that thread), might be interested in my findings, I've pasted a part of the first post below.

EDIT: 04/13 2017

A few clarifications.

1. It's not the subframe that cracks, it's the floor panel (RACP) to which the subframe (rear axle) is attached.

2. There are actually two different main "subframe failures" that plague the E46 platform:

i. The subframe mount pulling out of the RACP.



BMW resolved this issue midst an updated RACP implemented on chassis' built feb 2000 and on. M3's are not affected by this issue.

"Plates" can resolve this issue. But this will eventually result in the second main failure described below.

ii. The RACP cracking and pulling away from the rest of the chassis. This issue is due to a bad load path resulting from a bad design.

This issue is thoroughly described below.

Neither "plates", nor "foam" address this underlying issue.

No cracks?

Often dealers or independent shops report no cracks following an inspection. As often, this is an incorrect finding/statement based on lack of knowledge and/or ignorance.

They have simply not found any evidence of FAILURE TYPE 1, the pre feb 2000, issue.

This extremely unfortunately leaves the owner of the vehicle unaware of a ticking bomb that could have been addressed at a reasonable cost, but will be VERY costly down the road.

And regarding the post feb 2000 issue, it's unfortunately very uncommon that there are no cracks present once the rear axle is removed, dirt is cleaned off, and the RACP is thoroughly examined.

It's also unfortunately very common that dealers and shops do not know where to look as they are really only aware of the very common issue on the pre feb 2000 built E46's.

The issue with the pre feb 2000 built E46's is that the rear left, or both rear mounts, is/are ripped out of the RACP as seen in the pictures below. And it's so obvious it's something you can't miss.







On E46's built post feb 2000 (all coupes and M3s included) the ripping out does not happen as BMW addressed this with the revised design shown below.

This picture (credit to James Redish) also shows where to look for the hairline crack which is typically one of the first indications of failure.



On these cars the cracks and failures are harder to spot if you don't know where to look. Especially for someone looking for the issue with the pre feb 2000 built E46's.

End EDIT: 04/13 2017

Happy reading and please let me know if you have any questions!





Quote:
Originally Posted by VinceSE2 View Post
What is this?



What's the VinceBar?



It's a solution that addresses the root cause to (not just the symptoms of) the dreaded "subframe" failures of the E46 chassis.



Why should I care?



Over the last couple of years it has become clear that the design of the rear axle subframe, or more specifically the way the rear axle subframe is attached to the rear of the E46 chassis, is not up to it's task. Especially in high power/torque models as the M3, 330i/d.



Here's a recent video of a single owner, low milage (60000 miles), non "tracked" M3 that Redish Motorsport recently posted on YouTube.



https://youtu.be/oQvEkYUNPOU



This is one of many great and informative videos James Redish has shared. Make sure to visit their YouTube channel.



Please note that it's actually not the subframe itself (which is a sturdy tubular frame) that fails, it's the chassis panel it is attached to. This panel is commonly referred to as the Rear Axle Carrier Panel, or abbreviated, the RACP.





Over the last couple of years there have also been a number of instances where new failures have occurred after the RACP has been reinforced using the common practice of welding, or epoxying, flat plates to the bottom side of the RACP (at the subframe mount locations).



The new failures have typically ranged from new cracks at other locations of the RACP, to very serious separation of the RACP from the rest of the chassis.

Here's one example. This car had TMS plates prior to this failure.



Underside of the RACP cracking despite TMS plates having been welded prior to this failure:





And here's another example. This car also has"d TMS plates prior to this failure.



(The pictures below are from the post from Jan 17th 19:43 in this thread)

In all three pictures it's clearly visible that TMS plates had been previously installed. Yet fatal failure occurred.











And here's the third repair that I did (I didn't do the first two). These pictures show additional popped spot weld not found/fixed during the second repair.

http://www.m3forum.net/m3forum/showp...68&postcount=2













EDIT 12/24 2016: Adding another example.

http://www.m3forum.net/m3forum/showthread.php?t=563955



Look to the right of the dust boot of the shock and you'll see how the RACP has cracked and been pulled loose/down.



EDIT 02/14 2017: Adding another example. This car also had TMS plates prior to this failure.

http://www.m3forum.net/m3forum/showt...p?p=1067583489

Top of RACP pulled down on both sides:





Underside of RACP cracking up and separating:





EDIT: 03/27 2017 Adding yet another example of failure despite TMS plates.
This one is REALLY bad!

In this picture the TMS plate is visible

http://www.m3forum.net/m3forum/showp...4&postcount=41








So what's wrong with the design of the E46 RACP?



The short story is that the panel itself is too weak, AND that the panel is inadequately attached to the rest of the chassis.



OR, the subframe mounts should have been positioned directly under/in the sturdy chassis legs (a wider subframe) instead of in the floor (which the RACP is). That way we wouldn't have needed to reinforce and/or relief the RACP from all, or parts of, the load.



This is what has been done to the E9X chassis, and to my surprise, is also the case on our VW Sharan minivan (which BTW is front wheel drive).



Let's first look at the subframe mounts of the VW Sharan.



In this picture, of the right rear suspension looking towards the front of the car, you can just barely notice that the front right mount is directly behind the coil spring. And both mounts are directly under/in the chassis leg.







In this picture, facing the right rear wheel well, you can clearly see how much further out to the side of the car (that's where the chassis leg is) the VW Sharan's subframe mounts are.







Here's another excellent example of how the subframe mounts are tied directly to the chassis legs. This is a E91 3-series Touring I happened to notice at a salvage yard.



Fortunately someone had cut out the rear right corner of the body and chassis, leaving the right side of the subframe exposed.







Notice the chassis leg to the left in the picture. In the picture it's the white "beam"running top/down (picture wise) just left of the center if the picture. It's running in the front/back direction and it has two clearly visible holes in it. The front one has a rubber plug/grommet in it. Notice how it starts to turn outwards (left in our viewing direction) just as it's getting covered by the harness of cables. It's taking this direction as it continues in the door sills.



Now look at the right side where the chassis leg has been removed. Can you see how the subframe mounts is sitting right below where the chassis leg used to be?



Also notice the cross section of the sill, how many layers it's made up with, and how sturdy it is.



Here's a picture of the side view that should help you understand how well the subframe mounts are placed in the E9X platform that followed the E46.







Now compare this to the positions of the subframe mounts of the E46 chassis (at the outside ends of the blue subframe where you can see the circular mounts and the shiny nuts)











Notice how the rear mounts are almost, but not quite, (and this is an important design flaw) all the way out to the chassis leg, but the fronts are very close to the center of the car.



However, both are attached to the "floor panel" (the RACP) rather than directly to the chassis leg itself.



The latter results in a, let's say, unfavorable and inefficient way of coupling/sending the rear axle torque load to the sturdy chassis legs (frame rails).



This is the culprit of the infamous so called "subframe issue" of the E46 ( and E36 AFAIK).



In technical terms this (the path the load needs to take) is referred to as the "load path".



The design of the E46 chassis forces the load to take a "detour" on it's way, from the subframe mount, to the chassis leg. And it's taking that detour via the flimsy, 0,75mm sheet metal of the RACP.



Here's a picture of the underside of the rear part of the E46 chassis. In this picture I've outlined the chassis leg in red.







Notice the dashed line directly outside of the rear mounts (with the blue oval surrounding it on the left side of the image), this is where the RACP is NOT connected to the chassis leg.



Here's a picture of the inside/topside where the gap is very obvious:







And this picture shows how the end plates of the VinceBar closes that gap:







In the gap area, without the VinceBar, the RACP is only attached to the outside perimeter of the chassis leg. And this is what makes the design even worse gas opposed to "just" applying the load to the floor/RACP) as the load now has to take a detour through most of the RACP on its way to the chassis leg.



Here are a few 2D sketches of the cross section of the area mentioned above. The gap between the RACP and the chassis leg is the area directly below where its says stitch weld in the first picture.



Quote:
Originally Posted by VinceSE2 View Post



First lets revisit my sketch.

Remember how I said that the cross section of the vertical plane going through the rear mount threaded receivers only connect to the outer most part of the chassis leg? And how this puts a lot of stress at the hotspots?









While the structural resin, aka "foam", does help relieve the stress at hotspot #1 (by stiffening the "beam" within the area enclosed by the cavity highlighted in grey)...







...it does nothing to improve the load path from the mount to the chassis, nor does it improve how the load is dissipated to other parts of the chassis leg.

Hence my idea of improving just that. In this image I have conceptually made that connection.







But in order to avoid bending the connection and/or the vertical wall of the chassis leg one should create something that is rather rigid such that it "cleanly" applies a vertical force to the chassis led. Something like this:







Apart from providing this rather "clean" vertical force, the bar also strengthens the factory "beam" and the bolt through design also relives the "beam". In addition the bolt through design relieves the spot welds, in the vertical plane as well as the bending, attaching the threaded receiver.



Very similar to the Mason Engineering rear strut bar with the cross brace. This design is however nearly completely hidden, and does not affect the luggage space, or the ability to load larger items with the rear back rests folded down. It doesn't negatively impact the usability of the car.

Just the way I like it!








You can find more detail about this in this thread: http://www.m3forum.net/m3forum/showp...63&postcount=2



What I've shown in the 2D sketches above is however just a cross section of the RACP where the rear mounts are. That does not explain the numerous cracks, and separation, that are formed in other places of the RACP.



Therefor I've created the image below.



Please note the thin red lines to the left of the image. Those thin red lines (in a simplified way) illustrate the "detour" the force is taking (because of the gap between the RACP and the chassis leg) from the mount to the chassis leg.







This is why the RACP starts cracking in the areas with the thin red lines, even after the addition of underside plates and/or the "foam"



And below you'll find another excellent video from Redish Automotive. It illustrates the effect of that unfavorable load path (from about 01:00 and on).






IMHO, this video (credit to James of Redish) clearly illustrates why the rear bar is needed. The rear bar relieves the RACP from most of the load which is causing the stress, that in turn, causes these popped spot welds and cracks.



The rear cross bar simply "sends" the load to the chassis legs without it having to pass through the RACP's areas of flimsy sheetmetal and spot welds. This is the load relief of the RACP.



OK, so what does the VinceBar solution actually do, and how does it work?



The VinceBar solution is actually made up of two major components:

1. The front "gusset cups" (formerly known as "pipe gussets")

2. The rear cross bar (the VinceBar itself)



1. The front gusset cups address the very common (but unfortunately not very commonly known) cracking of the top side of the front mounts.











These cracks stem from a combination of:

a. The lateral forces from the control arms (side to side forces from the rear wheels during cornering)

b. The vertical forces, mainly the upward compression force, from the subframe bushing area.



The front cups address these cracks by reinforcing the RACP, distributing the load to the rear seat floor (the next level of sheet metal above the RACP), and clamping the reinforcement to the RACP via a through bolt design.











2. The rear cross bar (the actual VinceBar.



As I believe it'sdesign, position and function is fairly well explained in the paragraphs above I will not repeat that here.

Last edited by VinceSE2; Thu, Apr-13-2017 at 10:30:04 PM.
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Old Mon, Oct-03-2016, 04:15:34 AM   #2
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

thats really good investigative work, Vince.

i agree with your identification of the 2 main design flaws: which the plates and epoxy alone do not overcome.
the key is to link the rear mounting points to a stronger part of the vehicle, like the chassis legs or the shock towers.

your Vincebar is a very neat solution that doesnt impede on luggage space yet addresses the issue. keep up the great work
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Old Mon, Oct-03-2016, 04:59:36 AM   #3
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

Great work Vince!
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Old Mon, Oct-03-2016, 07:39:42 AM   #4
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

Great work Vince. Im going to have to show this to my shop and see if they can do the weld in kit as i prefer that.
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Old Mon, Oct-03-2016, 11:44:34 AM   #5
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

Excellent explanation.
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Old Mon, Oct-03-2016, 05:05:30 PM   #6
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

proper work vince and nice composition in your explanation
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Old Mon, Oct-03-2016, 05:19:01 PM   #7
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

How much weight does this add to the car?

Side question: How much weight do Redish and/or Turner plates add?
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Old Mon, Oct-03-2016, 05:23:52 PM   #8
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

A pound or two who cares?
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Old Mon, Oct-03-2016, 08:48:25 PM   #9
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

This is super impressive, Vince. If you don't mind sharing, what is your background wrt this type of work?

Has anyone else installed one yet? If so, how many miles on it and what's been the report?

Can you recommend shops who have a proven track record installing this sort of reinforcement in e46 M3's?
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Old Tue, Oct-04-2016, 06:14:09 AM   #10
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Default Re: "Subframe" issue 101 - Why plates and/or foam is not a permanent fix

I think I am among the firsts who bought it from Vince.
Glad I did it, very happy.
Drove it a lot & hard for the last few months (mountain roads, no track).
I didn't cover the bar after the job so I could closely inspect & show people wondering about it.
Everything is nice and tight. Very happy with it.
I bought the epoxy version used the TMS plates I had on hand + 3 structural foam cartridge later. I did a thread about it and I there is also Vince's original thread where you can have a lot of detailed information.
FYI My car is the one with the blue subframe, arms & swaybars.
Have a good read!
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Discussing "Subframe" issue 101 - Why plates and/or foam is not a permanent fix 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)