Subframe Dropped and cracks found

[poss]

Yea I kind of figured this would be inevitable. I'm just trying to see if the old plates need to come off or if I can keep them and do the top bar. Aside from checking for bad spot welds in the wheel arches... What else?

If you stop the fundamental cause of the metal fatigue I can't see any reason to take the band aids off. My advice is to forget about wasting time and money checking for the start of what is likely an inevitable failure, but instead prevent it with top side reinforcement.

[Nate047]

Yea I kind of figured this would be inevitable. I'm just trying to see if the old plates need to come off or if I can keep them and do the top bar. Aside from checking for bad spot welds in the wheel arches... What else?

[Thoglan]

Hope he had a good reason lol.

Can I jump in and ask something related, my car has plates on the underside from the previous owner, they are on there with epoxy and the job looks like it was done alright as far as anyone can know from just looking. I have been considering a topside bar reinforcement, and I was just wondering if there's any reason to be concerned about cracks if there are none visible from the top? I just don't know how good a job the last guy did. I will not be tackling this as a DIY regardless but I'm just curious.

Underside plates are not enough unfortunately. I was in a similar situation and purchased my car with only underside plates. about a year into ownership of normal driving there was cracking on the wheel arches.

[poss]

Hope he had a good reason lol.

Can I jump in and ask something related, my car has plates on the underside from the previous owner, they are on there with epoxy and the job looks like it was done alright as far as anyone can know from just looking. I have been considering a topside bar reinforcement, and I was just wondering if there's any reason to be concerned about cracks if there are none visible from the top? I just don't know how good a job the last guy did. I will not be tackling this as a DIY regardless but I'm just curious.

The wheel arch spot welds typically fail before anything is visible in the boot. If the boot floor is coming apart the damage is probably extensive by that stage. As per my previous post I would not wait to see failures before doing topside reinforcement as its a matter of when not if.

[Nate047]

Waited for my welder to show for about a month

Hope he had a good reason lol.

Can I jump in and ask something related, my car has plates on the underside from the previous owner, they are on there with epoxy and the job looks like it was done alright as far as anyone can know from just looking. I have been considering a topside bar reinforcement, and I was just wondering if there's any reason to be concerned about cracks if there are none visible from the top? I just don't know how good a job the last guy did. I will not be tackling this as a DIY regardless but I'm just curious.

[poss]

makes sense. I am hoping what I did removed enough of the flex to not crack again.

You should be fine. You've addressed the fundamental cause of the problem. Only doing underside plates without any topside reinforcement can see the cracking migrate to the wheel arches

[scotty737]

The design flaw addressed by both solutions is that the RACP structure (a kind of gusseted box girder structure made out of sheet metal) is indirectly tied to the chassis rails via the wheel arches - i.e.: it's effectively sprung to the chassis rails rather than directly connected, introducing enough movement to induce metal fatigue in the sheet metal structure (usually starting around the gusset welds).

Simply tying the RACP directly to the chassis rails is likely going to eliminate the majority of the flexing and prevent catastrophic metal fatigue during the serviceable lifetime of the car. Adding a bar and bolting the rear subframe mounts to it is going to pretty-much eliminate any remaining flex in the RACP due to its sheet metal structure, and adding rigidity to the rear end. Is it necessary to eliminate RACP cracking? Probably not, but it absolutely guarantees it will never happen. Will it improve the car's feel? Yes.

makes sense. I am hoping what I did removed enough of the flex to not crack again.

[poss]

What does the bar really do differently than this in terms of racp movement? If you really wanted a bar you could easily weld a piece of metal to both of these plates.

The design flaw addressed by both solutions is that the RACP structure (a kind of gusseted box girder structure made out of sheet metal) is indirectly tied to the chassis rails via the wheel arches - i.e.: it's effectively sprung to the chassis rails rather than directly connected, introducing enough movement to induce metal fatigue in the sheet metal structure (usually starting around the gusset welds).

Simply tying the RACP directly to the chassis rails is likely going to eliminate the majority of the flexing and prevent catastrophic metal fatigue during the serviceable lifetime of the car. Adding a bar and bolting the rear subframe mounts to it is going to pretty-much eliminate any remaining flex in the RACP due to its sheet metal structure, and adding rigidity to the rear end. Is it necessary to eliminate RACP cracking? Probably not, but it absolutely guarantees it will never happen. Will it improve the car's feel? Yes.

PS: I wouldn't wait for signs of cracking before doing topside reinforcement. I'd be doing it immediately if you plan to keep the vehicle and can afford it, 'cos cracking is not a matter of if, but when.

[scotty737]

My bad. Yes, its a similar topside reinforcement concept to the CMP Rail Plates

Yeah, they are nearly identical to those.

[poss]

He welded plates from the chassis rail to the RACP in the boot floor. That is a reinforement. Not as hardcore as a bar then welded between the plates and tied into the RACP but it is definately an improvement.

My bad. Yes, its a similar topside reinforcement concept to the CMP Rail Plates

[heinzboehmer]

What does the bar really do differently than this in terms of racp movement? If you really wanted a bar you could easily weld a pice of metal to both of these plates.

Vincebar and CMP both require you to drill up through the rear subframe mounts and relace the subframe bolts with extended studs. These studs then bolts to the bar, so that the rear of the subframe is directly bolted to the bar.

Similar thing is done for the front mounts with the gusset cups.

[scotty737]

What does the bar really do differently than this in terms of racp movement? If you really wanted a bar you could easily weld a pice of metal to both of these plates.

[scotty737]

I wouldn't consider it reinforced - you simply patched where the cracks manifest themselves, not the actual cause of the metal fatigue.

I think you missed something. That would just be installing plates on the bottom…

[ClevoCapri]

I wouldn't consider it reinforced - you simply patched where the cracks manifest themselves, not the actual cause of the metal fatigue.

He welded plates from the chassis rail to the RACP in the boot floor. That is a reinforement. Not as hardcore as a bar then welded between the plates and tied into the RACP but it is definately an improvement.

[poss]

I think the Vincebar and cmp are a much stronger solution. Although the reddish instructions said that this reinforcement is essentially what the e9x platform has. I have faith in it, but time will tell. I’m sure everyone will say it isn’t the solution and Vincebar/cmp is the only way lol.

If it fails in the future, I will look into something else but for now I’m considering it reinforced.

I wouldn't consider it reinforced - you simply patched where the cracks manifest themselves, not the actual cause of the metal fatigue.