subframe fixes

[DuncanR]

Discovered this crack last week, is this in the right area to be classified as the usual type of cracking. Bear in mind that my car is caged albeit the cage does NOT pick up onto the turrets, which is a shame.
The bottom pictures is taken from the Offside of a UK car, looking out and up towards the wheel , its on a seam, under normal circumatnces I would drill the end myself now to stop it going further, which it may have done after this week-end ! But as its under warranty still Im loathe to do so. Thoughts oh wise expereinced crack heads

[DuncanR]

Also, can someone clear up the confusion re subframe and/or floor pan, people seem to generalise and refer to "subframe cracks" whereas mine are clearly floor pan/body, is it the case that the actual subframe itself also gets cracks ?

[shimmy]

Originally Posted by DuncanR

Also, can someone clear up the confusion re subframe and/or floor pan, people seem to generalise and refer to "subframe cracks" whereas mine are clearly floor pan/body, is it the case that the actual subframe itself also gets cracks ?

No Dunc, they are cracks in the bottom floor pan mainly, not the subframe. They start near to the subframe mounting points typically

[DuncanR]

Originally Posted by shimmy

No Dunc, they are cracks in the bottom floor pan mainly, not the subframe. They start near to the subframe mounting points typically

Gareth ! do I need to "borrow" Shimmys stock suspension before I bring car into Elms ?

[The Gorilla]

Hi,

DuncanR- I think your Internal Scaffolding
might raise more than an eyebrow for
a structural claim.

Looking at your Pics, if you have
to self repair, then its not that bad
on the face of it.

Regards,

The Gorilla.

[Niel333]

I managed to get resin but its coming from Germany and its going to cost me to get it here, do I have to get 2 for just a left side crack or is one enough?

[s.mac]

looks like the suspension could do with cleaning, greasing and springs powder coating

Gareth how much do BMW charge to apply the resin to the correct places??
not sure I would DIY

[monkeycsl]

Originally Posted by NZ_M3

I voluntarily fitted the BMW official epoxy fix into my car - even though mine has no cracks - quite simply because if you've seen the way the rear floor is designed you will realise that having such a large void space in between the sheet metal that forms the rear floor exacerbates torque stress transfer - and overtime it will tear it out.

Personally I am not a fan of welding extra plates into the rear floor (rust proofing is a big issue as there are areas you simply can't get to) - I've seen failures even with the plates in place - this is because it is a band-aid fix versus a load transfer fix.

By filling the void within the floor space transfers the torque load to a much larger area and most importantly above the floor to the secondary sheet metal that forms the ridge carrier - further the epoxy used has a dampening effect as it is not completely solid. It is a proven product used in Formula 3 race car suspension repairs.

I also don't believe in having a larger subframe bushing footprint helps - as this is no different to having a larger washer in between the subrame and the floor.

The problem is more related to the floor having a void thus allowing it to flex more so than the foot print of the mounting.

I can tell you for a fact that having the epoxy in the floor makes a very noticeable difference to the rear floor rigidity - and that's in a car with KW race 2 ways and 14kg/mm springs. I am not the only CSL owner in NZ with this in the floor and all have noted how noticeably different the rear felt post the epoxy install.

I agree with the solid bushes not helping to damp the forces but the bmw bushes appear to have a raised lip around the edge which seems to put excess pressure in a small surface area,why are they not flat to mate upto chassis?Do you think if there is no crack then the resin both sides will stop further cracks appearing?
Also you said you did both sides is it a repeat of first step and do you have to drill a 10 mm hole on offside as there is not one there like on the nearside hope this makes sense cheers.

[NZ_M3]

Christ Duncan that doesn't look too good. The other car I spoke about earlier in the post where the whole floor came apart had exactly the same type of body fractures like yours - are you running solid rear subframe mounts?

Unforunately Duncan, your car is a good illustration of what I have been saying for a while - that the stress cracks aren't isolated to the mounting floor pan itself - i.e. it is to do with the load being carried incorrectly through the body structure, cause premature fatigue fractures (i.e. the void in the bottom floor sheet metal).

I'd get that welded up ASAP before it drops the whole floor out of the car (which it will).


Neil333 - one tube is enough to do both rear mounts - If you are doing the fronts, then you need two.

Originally Posted by monkeycsl

I agree with the solid bushes not helping to damp the forces but the bmw bushes appear to have a raised lip around the edge which seems to put excess pressure in a small surface area,why are they not flat to mate upto chassis?Do you think if there is no crack then the resin both sides will stop further cracks appearing?
Also you said you did both sides is it a repeat of first step and do you have to drill a 10 mm hole on offside as there is not one there like on the nearside hope this makes sense cheers.

I honestly don't believe the raised lip has anything to do with the fractures - this is not an impact failure where the bushes are moving around so much that they are pulling out of the chassis - but rather a torque load transfer being carried incorrectly through the car causing premature fatigue stress fractures. Like I said, if the lip had anything to do with it, then a quick and easy fix by BMW would have been to simply wack a couple of 3mm washers in between the subframe and the chassis floor - they haven't done that because it is not related to it. Just look at the way Duncan's car is coming apart.


You only drill one hole - in the middle of the floor ridge - the resin is injected into pre-existing holes on the left and right side of that (not the first layer, but the second layer skin - lot of people get this wrong and inject it into the incorrect cavity space).

The link you posted where the guy cut open the sound proofing is incorrect - he was trying to get to the front mounts also - you actually get to those through the front seatbelt mounts - the rear mounts are done through existing holes in the chassis floor (covered by plastic bungs).

[monkeycsl]

Originally Posted by NZ_M3

Christ Duncan that doesn't look too good. The other car I spoke about earlier in the post where the whole floor came apart had exactly the same type of body fractures like yours - are you running solid rear subframe mounts?

Unforunately Duncan, your car is a good illustration of what I have been saying for a while - that the stress cracks aren't isolated to the mounting floor pan itself - i.e. it is to do with the load being carried incorrectly through the body structure, cause premature fatigue fractures (i.e. the void in the bottom floor sheet metal).

I'd get that welded up ASAP before it drops the whole floor out of the car (which it will).


Neil333 - one tube is enough to do both rear mounts - If you are doing the fronts, then you need two.




I honestly don't believe the raised lip has anything to do with the fractures - this is not an impact failure where the bushes are moving around so much that they are pulling out of the chassis - but rather a torque load transfer being carried incorrectly through the car causing premature fatigue stress fractures. Like I said, if the lip had anything to do with it, then a quick and easy fix by BMW would have been to simply wack a couple of 3mm washers in between the subframe and the chassis floor - they haven't done that because it is not related to it. Just look at the way Duncan's car is coming apart.


You only drill one hole - in the middle of the floor ridge - the resin is injected into pre-existing holes on the left and right side of that (not the first layer, but the second layer skin - lot of people get this wrong and inject it into the incorrect cavity space).

The link you posted where the guy cut open the sound proofing is incorrect - he was trying to get to the front mounts also - you actually get to those through the front seatbelt mounts - the rear mounts are done through existing holes in the chassis floor (covered by plastic bungs).

Thanks for that will do both sides. did you do front part too.I also heard the audi rs4 battery tray gets same treatment with the two part epoxy and its half the cost of the bmw stuff but prob a different type so wont risk it cheers again.