cracked subframe

[MisterCorn]

Unless somebody can provide evidence that a correctly torque subframe bolt is not stopping the subframe from moving, and that the subframe is held in place by the bolts being effectively used as dowels rather than clamps then I'm afraid I'm calling bullsh!t on the collars.

MC

[select]

Welding of plates will NOT fix the issue any more than doing just the BMW repair, it is the exact same band-aid.

Could you please stop suggesting that i ever said that plates only will fix it? I didn't, i said plates are for restrengthening the chassis, incase its been cracked, to former levels and the real fix to the issue are the solid bushings.

The yawing motion of the bolts (more prevalent in SMG equipped cars due to the shockloading the automated gear changes in the faster modes transfer to the diff and hence the subframe mounts) is the issue and so you have to remove this.

If you believe that some magical foam is able to stop any force induced by the brutal transmission shifts into the chassis, that is fine. I do not, or better said.. i don't trust that it will withstand this over time. Its a gamble... and if it fails its game over, because you will never get the foam out and any welding with the foam in place on the subframe is a serious fire hazard.

Obviously anything else that helps lesson this movement is going to increase the amount of time it takes to re-occur, but not prevent it (so still a band-aid).

Yes, but that is exactly what solid subframe bushings do. They tie the rear axle carrier to the subframe.. so there is ZERO movement. Thats the definition of solid.

Just look at what BMW did for the E92 M3. It has rubber subframe bushings from factory, just like the E46 M3. What have they done on the GTS? They used solid bushings.


@MisterCorn I don't know if the stock bushings allow YAW(Vertical) movement of the carrier but i don't think so. But its not the big problem for the subframe, its the lateral movement that the sheet metal can't handle.

Unless somebody can provide evidence that a correctly torque subframe bolt is not stopping the subframe from moving, and that the subframe is held in place by the bolts being effectively used as dowels rather than clamps then I'm afraid I'm calling bullsh!t on the collars.

I think thats the big question mark on these things, and probably the reason they are not very commonly known.

[Mike RT4]

Unless somebody can provide evidence that a correctly torque subframe bolt is not stopping the subframe from moving, and that the subframe is held in place by the bolts being effectively used as dowels rather than clamps then I'm afraid I'm calling bullsh!t on the collars.

MC

The subframe isn't moving, but because the bolt has so much tolerance, it allows the subframe and floor-pan to flex as one piece.

This yawing motion causes the cracking. By joining the two pieces together and fitting the collars, you eliminate the ability of the floor to flex.

Tom did a great analogy with a Coke can. Drink the contents and then drill a hole through it and stick a bolt through the hole and then try moving it, you will see how badly it flexes the two separate pieces (that's our standard floor pan :bigcry. Now fill the can with resin and try the experiment - it makes it much more rigid and less prone to flex - that's the BMW repair.

Do the same with just a washer either side and see what happens (that is the equivalent of just welding plates on without the resin). All it does is move the fracture point from around the hole to around the washer (plates).

Fitting more rigid bushes isn't going to stop the (E46) floor-pan from flexing...

[MisterCorn]

I understand the coke can analogy, it is the collars which I can't see how they fit in to the equation. Whether the collars are in place or not, when the subframe is bolted on to the car there is no relative movement between the subframe and the chassis, the clamping forces of the bots see to this. I can see that the collars would allow a more precise initial alignment of the subframe on the chassis by taking out the slop in the holes, but once it is clamped together I can't see how it has any impact at all. Sure the chassis around the mounting can and does flex, but I can't see any way in which the collars would affect this.

For the coke can analogy would it not be like drilling a more snug hole in the can so that the bolt can be fitted more accurately in the first place?

I really feel like I am fundamentally missing the point of what the collars are supposed to do here, I'm not being deliberately thick, honest!!

MC

[Alx007]

Another question would be:

Has any subframe cracked after the foam injections? (Even if it was still the standard subframe)

[Mike RT4]

I understand the coke can analogy, it is the collars which I can't see how they fit in to the equation. Whether the collars are in place or not, when the subframe is bolted on to the car there is no relative movement between the subframe and the chassis, the clamping forces of the bots see to this. I can see that the collars would allow a more precise initial alignment of the subframe on the chassis by taking out the slop in the holes, but once it is clamped together I can't see how it has any impact at all. Sure the chassis around the mounting can and does flex, but I can't see any way in which the collars would affect this.

For the coke can analogy would it not be like drilling a more snug hole in the can so that the bolt can be fitted more accurately in the first place?

I really feel like I am fundamentally missing the point of what the collars are supposed to do here, I'm not being deliberately thick, honest!!

MC

I just feel the collars do a belt and braces job. I have them on my S2000 and noticed an immediate improvement, so will be fitting them to the CSL as well.

I just think the elimination of any movement in this area is going to improve things and off the improvements that are stated in the above clip regarding geometry.

At the end of the day it is your car, but for the sake of £200 fitted, it seems a bit of a no-brainer to me (even if it only gives the geometry improvements) .

[select]

@Alx
Yes, unfortunately m3forum.net is currently offline, else i could give you the link.

Fitting more rigid bushes isn't going to stop the (E46) floor-pan from flexing...

I am sure you can back up your claims? Every E46 that races in VLN uses plates and solid bushings. And they never had any issues again, despite hammering the car for 24h on the Nordschleife.

Mike, why did you chose to largely ignore my post?

[Mike RT4]

Another question would be:

Has any subframe cracked after the foam injections? (Even if it was still the standard subframe)

Given that the original cracks took 10 years (one week before the warranty expired) and 50k miles to manifest themselves (on my car), I would guess that we have to wait even longer (as this is "supposed" to be a fix) before we know if it is truly the cure BMW state it is.

Come back to this thread in another 12 years time to see :bigcry::blalalala:

[Alx007]

:hahaha:

Given that the original cracks took 10 years (one week before the warranty expired) and 50k miles to manifest themselves (on my car), I would guess that we have to wait even longer (as this is "supposed" to be a fix) before we know if it is truly the cure BMW state it is.

Come back to this thread in another 12 years time to see :bigcry::blalalala:

[Mike RT4]

@Alx
Yes, unfortunately m3forum.net is currently offline, else i could give you the link.


I am sure you can back up your claims? Every E46 that races in VLN uses plates and solid bushings. And they never had any issues again, despite hammering the car for 24h on the Nordschleife.

Mike, why did you chose to largely ignore my post?

They are not road cars, they have fully welded cages that greatly change the strength of the car (subframe is often bolted into the cage in the boot) and they also don't do the big miles that road cars do. In addition, very few are SMG (which seem to be the worst suffers of subframe failure).

I personally think that a lot of this cumulative damage occurs in the lower gears (when you feel the diff thump in S6 going from 1st to 2nd and 2nd to 3rd). Race cars don't do this very often either, once they are away from the line the lower gears are used infrequently.

Like I said, it's your car, you do what you like :blalalala:.

[select]

Given that the original cracks took 10 years (one week before the warranty expired) and 50k miles to manifest themselves (on my car):bigcry::blalalala:

In case of CSLs.. you might have to wait another 12 years. But luckily there are regular E46's which get driven alot more.

First time BMW acknowledged that there is an issue with the subframe was in 2004. Click me.

And that is in Germany, where Manufacturers only acknowledge faults if they have to. I.E. the federal car agency is pushing them to start working on a fix or else they will force them to a recall.

[select]

Mike, surely its my car i can do what i like. But when someone asks for advice and you are spreading false claims, i feel the urge to voice my opinion.

If you have cracks then get them drilled and welded up and reinforce the structure with plates. Also replace bushings with stiffer ones, preferably solids. Thats exactly what BMW did on the E92 GTS and F8X M3/M4.
They didnt choose to inject foam...:whistle:

You can also inject the foam if you feel the need to, and that is the big plus.. you can always go back and foam it. But vice versa? Good Luck.
However there is no need for the foam once you've done the above.

• Contrary to what mike said, there are documented examples that only doing the Foam Injection isn't enough. Thats a fact.

• Every E46 thats used as trackcar/racecar on the Nürburgring and elsewhere (and that not only includes professional teams with a full cage) uses plates & solid bushings. Without any issue, since years.

• Be aware of the fact that any welding on the rear of your car will be difficult if not impossible with the foam injected. Because it will melt and catch fire.

I think everybody now can make himself an opinion on the matter. I however will rest my case.

[Mike RT4]

Mike, surely its my car i can do what i like. But when someone asks for advice and you are spreading false claims, i feel the urge to voice my opinion.

If you have cracks then get them drilled and welded up and reinforce the structure with plates. Also replace bushings with stiffer ones, preferably solids. Thats exactly what BMW did on the E92 GTS and F8X M3/M4.
They didnt choose to inject foam...:whistle:

You can also inject the foam if you feel the need to, and that is the big plus.. you can always go back and foam it. But vice versa? Good Luck.
However there is no need for the foam once you've done the above.

• Contrary to what mike said, there are documented examples that only doing the Foam Injection isn't enough. Thats a fact.

• Every E46 thats used as trackcar/racecar on the Nürburgring and elsewhere (and that not only includes professional teams with a full cage) uses plates & solid bushings. Without any issue, since years.

• Be aware of the fact that any welding on the rear of your car will be difficult if not impossible with the foam injected. Because it will melt and catch fire.

I think everybody now can make himself an opinion on the matter. I however will rest my case.

You can't compare the floor plan of a different car which has obviously had changes made based on the issues they had with the earlier model :clown:.

Or are you trying to say that following the millions BMW had to pay out on the issues with the E46, they decided to use the exact same design for subsequent models :bigcry: :blalalala: :hahaha: ?

Just reinforcing the sub-frame structure with plates is NOT a cure for the E46, hence why I am pulling you up on it. You only have to search Google for images of people in the USA who have done JUST that, to see the catastophic damage that then does to the floor pan, where the plates and all are ripped from the floor pan. There is little point in welding something of greater thickness to something that is paper thin (an exaggeration, but you get the point), you just move the failure point further out.

Obviously the best solution would be a much stronger floor plan (which was done on subsequent models). However, that isn't financially viable on an out-going model, so BMW came up with a "best fix" that will (hopefully) last a lot longer than the original arrangement. From an engineering and design point of view, it is certainly several times stronger than welding plates to an already weak structure :whistle:.

Which is why all of the (well known) companies in the UK do the welding of the plates in CONJUNCTION with the resin injection, it's just a cheaper way of doing the same repair without having to unpick all the spot welds and completely replace the floor plan with a new item (which is what BMW do).

[Chad]

Another question would be:

Has any subframe cracked after the foam injections? (Even if it was still the standard subframe)

yes my lad csl did. But then so did his cylinder head, then so did his engine, so on and so on, BMW then refused to fit another new floor, just welded it , but then he does rag the thing to death ,all good fun that's what they were made for ,:thumbs: ps from memory first boot we had done on his car was about 2010,

[JBird]

I don't buy the talk of solid bushings for a second. Ill try to explain why:

First of all terminology. Subframes do not crack, boot floor skins do. Below is a picture of the E46 rear end.

The OEM subframe bushings are there to isolate/soften/dampen the subframe movement/loads. Subframe loads are arise from road reaction forces & movements which pass through the tires, into the rim, into the upright, along suspension arms, into the (small & quite hard) suspension arm bushings, into the subframe, into the (large & soft) subframe bushings, then finally from the aluminum bushing core into the boot floor via the central bushing bolt/pin). Additional subframe loads arise from the diff/driveline - torque, likely to be higher in an SMG equipped car such as the CSL.

You can not avoid suspension & driveline loads, so you must 1) reduce peak load with a bushing, 2) ensure the floor is strong & rigid enough to dissipate the bushing pin load (on a road car, BMW foam resin injection).

By installing solid bushes, you will amplify the peak load that the boot floor sees, by, thumb in the wind, about 3x. Solid Bushes make sense for a track car with proper braced mounting points - e.g., M3 GTR or e46 track slag modified in a similar way, where a stiff, almost rigid rear end is wanted, and thing like a cage and bracing are viable.

Regarding plates VS OEM repair, we can probably argue all day long if 'Plates + Drilled cracks + Foam Injection' is as good as 'BMW new Floor + Foam Injection'. Probably if done properly they will be similar in how long they hold. Certaily, plates with no foam injection makes zero sense.

Personally, I think the plates are a mess, and there is that much welding involved the chance of a bad weld that causes a stress raisers and eventual cracking at the edge of the plates is high.

I would lean out the window and say a properly carried out BMW repair foam injection repair with OEM bushings will not crack again. All depends how well it is done.