cracked subframe

[select]

Yes, thats exactly what happens if you stay with stock bushings.

To use his analogy.

Using the BMW repair = Simply Replacing the coke can with a new one., it just delays the "cracking process" which will inevitably happen.

The point is, to drill and weld the cracks that are there and they will be on nearly all csl with 60.000 miles. Even 316i have this problem, so its not only affecting cars which are driven hard. And reinforce the structure with the plates, whichs point is, to distribute the induced load via a bigger area. But the key thing is, to replace the squishy stock bushings with delrin or even solid ones, to stop the load from even ocurring. Like BMW did with from factory with M3 GTS and F8X M4.

See this video of an Camaro, which has the same issues.

[Mike R]

Originally Posted by select

My Point is, a new floor pan from BMW is no fix at all.

YES IT IS. BMW don't just replace the floor plan, do your research .

If you JUST weld plates to the "coke can" floor plan (as you have pointed out) - it WILL just crack around the welds of the plates and rip out the ENTIRE floor section around the plates .

The BMW repair replaces the entire floor section with a new item, but the key part to their repair is to fill the void with a special resin that links the two floor parts together to create a honey-comb effect (which makes the boot floor and sub frame mount much stronger than the sum of their parts - in the same way it does for composite sheets).

The main problem is the holes for the subframe bolts are just too big and allow a yawing motion that causes the cracks. Spoon actually do some "Rigid Collars" for the E46 M3 that effectively plug the holes and allow the precise location of the bolts which will prevent the yawing motion. I don't really understand why more people haven't fitted these.

Here is a video that shows them on another car, but the principle is the same :

[select]

I know they inject foam too. Funny enough they didnt until they were faced with lawsuits they started to inject foam.

Still its a Bandaid.. as it doesnt fix the issue. It merely strengthens the chassis to be able to withstand it. For what amount of time? Nobody knows, i decided for myself that i didnt want my csl to be a testbed for BMW, so i used what is proven to fix the issue.

Regarding the rigid collars i think i have read about that solution in the past.
But its not very widespread this.

[MisterCorn]

Originally Posted by select

Yes, thats exactly what happens if you stay with stock bushings.

To use his analogy.

Using the BMW repair = Simply Replacing the coke can with a new one., it just delays the "cracking process" which will inevitably happen.

The point is, to drill and weld the cracks that are there and they will be on nearly all csl with 60.000 miles. Even 316i have this problem, so its not only affecting cars which are driven hard. And reinforce the structure with the plates, whichs point is, to distribute the induced load via a bigger area. But the key thing is, to replace the squishy stock bushings with delrin or even solid ones, to stop the load from even ocurring. Like BMW did with from factory with M3 GTS and F8X M4.

See this video of an Camaro, which has the same issues.

[Mike R]

Originally Posted by select

I know they inject foam too. Funny enough they didnt until they were faced with lawsuits they started to inject foam.

Still its a Bandaid.. as it doesnt fix the issue. It merely strengthens the chassis to be able to withstand it. For what amount of time? Nobody knows, i decided for myself that i didnt want my csl to be a testbed for BMW, so i used what is proven to fix the issue.

Regarding the rigid collars i think i have read about that solution in the past.
But its not very widespread this.

The correct permanent fix would be the BMW repair and the installation of the Rigid Collars.

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

[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]

Originally Posted by Mike R

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.

Originally Posted by Mike R

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.

Originally Posted by Mike R

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.

Originally Posted by 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.

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

[Mike R]

Originally Posted by 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

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 ). 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

[Alx]

Another question would be:

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