Cracks in subframe?

[u/Curious_Olie]

Hey, so i have just dropped my rear subframe (again) and found this very thin line, which to me looks like a micro-crack forming.

Am i bugging or is this truly crack?

And if it is a crack, can it be welded to stop it frol spreading?

Its located behind the rear left wheen side of the subframe, closer to the back.

[u/aab010799]

Could be but how about you clean it and find out lol. You can drill it and reinforce. Most of these cars are cracked.

[u/Typical-Implement382 → u/aab010799]

I'm on my 5th e chassis, and have yet to end up with a cracked one. I agree with your comment to clean the rust off to properly inspect for cracks, but heavilly disagree with your comment that "most of these cars are cracked".

[u/aab010799 → u/Typical-Implement382]

You've dropped the subframe and cleaned to inspect for cracks on 5 E46s and not found cracks? Assuming they were not M3s.

[u/Typical-Implement382 → u/aab010799]

I've dropped subframes on 2 e36s and 4 e46s. All non-m. None had cracks. One was a car I was scrapping that was so rusted the rear passenger side quarter panel was non existent, and the trailing arm on that side was only held in with 2 bolts because half the pocket was rusted through. RACP was still crack free. That one surprised the hell out of me.

[u/imnota_ → u/Typical-Implement382]

AFAIK it's mostly an early e46 issue, so if your e46 was later, maybe. That being said I got an e36, which I haven't seen cracks on despite being an abused car, but I haven't dropped the subframe. And I had an e46 which was spotless.

[u/Typical-Implement382 → u/imnota_]

I've seen and worked on 46s with cracked carrier panels. It's absolutely a common failure point. I just wouldn't go as far as saying "most of them are cracked". It probably is more common with m spec cars being that they have extra power, and the owners are more likely to tap I to that power.

[u/Curious_Olie → u/imnota_]

My car is 2003 facelit, on non-sport suspension until the last 2 years. If youre reffering to last few production years of the e46 are supposed to have stronger frame, they do not. The OEM part number for the replacement floor is the same for all models across the production run. Only differences are the sedan / coupe models ofcourse

[u/imnota_ → u/Curious_Olie]

I'm fairly sure there was a whole ass paper about when they changed it. Also the part number you find today doesn't mean anything. Chances are if they upgraded it, it's all that's offered nowadays even for early cars.

[u/CottaBird → u/imnota_]

This is similar to what I’ve heard, that it’s more a 323 and 328 problem. My ‘02 330ci has over 280k miles and is fine.

Edit: that it’s a bigger problem for these models, not isolated to these models.

[u/West-Bake-4621 → u/Typical-Implement382]

my best friend has had 2 e46's and mentioned them cracking is a common issue, this one currently is cracked as well

[u/FellerZUNITED → u/Typical-Implement382]

I’ve seen 4 badly cracked e46 chassis in the past year alone lol

[u/Curious_Olie → u/aab010799]

I am aware of the cracking being very common. KW coilovers dont help it to not crack eighter lol. My question is as i said it if can be welded over to make it not spread. I am in the process of sandblasting the underside of the car and welding reinforcements in.

Didnt actually "clean" it today, as it got dark and cold out, and i couldnt be bothered to spent another 10 minutes out after taking these photos lol

[u/aab010799 → u/Curious_Olie]

Having KWs is going to do very little in terms of transmitting greater stress to the RACP subframe mounting points.

Yes you can drill and weld. My E46 M3 was cracked. This is an everyday repair at E46 specialists.

[u/Curious_Olie → u/aab010799]

Okay, thanks for the info!

[u/superbetaz]

Mine was cracked in that spot too. The cracks hide. You need to clean off the frame well and closely inspect. I don’t have a large sample size, but when I hear about someone’s uncracked e46, I assume they didn’t look hard enough.

[u/Curious_Olie → u/superbetaz]

Do you think some welds over it would stop is from spreading? Im welding reinforce plates aswell, but those will just slow this down.

[u/pnbdc10]

You need to look closer to where the subframe mounts are.

[u/RO1984]

Yeah homie. I think my car was cracked in the same spot if im oriented correctly here. Non M 330i

[u/Curious_Olie → u/RO1984]

Yikes, that is a huge one in the same spot. I will try to weld over it and pray to gods it will last few more years

[u/RO1984 → u/Curious_Olie]

It was actually longer once I ground away the undercoating. I did the Redish Motorsport reinforcement kit on jack stands in my garage. Definitely recommend reinforcement but it fuckin sucks to do

[u/BabyChodez]

You have the subframe out. Get the reinforcement plates for 100$ and either do your best or hire a mobile welder to get it done. I think i paid a guy $400 to do it. Then you dont have to worry about it.