1M Rear Subframe Rust

[sublimeguy]

I bought my 1M about a year ago. Had a look underneath while it is on a lift while swapping out all tires, and noticed the rear subframe is super rusted.

A mechanic told me it's not failing and ok, he sees the same for 10+ yr old BMWs, but it bugs me how crusty it is with the brake hoses all totally rusted.

I can keep driving it and/or swap it out for a brand new one. Was quoted for 8 hrs labor (need to check if that includes the brake hoses). I don't have a drive / garage unfortunately - so doing my own isn't an option.

At least I can defer the swap for probably a while, but just curious if anyone has any opinions or has seen something like this before. Does a full swap seem as necessary to others as it does to me? Or is this perhaps not as bad as it looks?

Attaching some nightmare photos. Any views appreciated!

[fast1eddy]

That looks pretty bad for a car of that age. I've driven my car through a few Canadian winters and my car doesn't look anywhere near that bad. I presume the previous owner drove it through winter as it had snow tires on when I bought it back in 2013.
The rust doesn't look terminal but you should do as much as you can to clean it up and mitigate further rust. I recently bought a very rusty E30 325ix and was able to clean up way worse chassis rust than that. I used wire brushes and wire wheels attached to my drill to remove as much loose rust as possible , then I coated everything with rust cure and let it sit for a few days before I did it again. Once I got it as clean as I could I coated it again. The stuff really does work as advertised.

[sublimeguy]

^ thanks for the reply and advice!

[Yeineken]

That seems pretty bad IMO. I've daily driven my car for 10 years in winters with salt and snow and my under carriage is no where remotely this bad, only minor surface rust.

Considering you are in LA, this is a red flag. Do you know the full history of the car and states its been in?

[WeryPert1]

Could be just that this car spent all of its life near the beach.... like beachfront. The damp salt air coming off the ocean can be worse than northern winters. (??)

[ShocknAwe]

Salt water.

Fing salt water.

I'm looking into treating mine too, not as bad as yours as it's >90% surface rust but I'm likely to have to replace my diff cover etc. Replaced every bolt in the suspension. In my case I was in a rush one morning and drove through our regular ocean floodwater, car then had a vanos failure and sat for 2mos but since out of my normal routine I didn't think to rinse out the undercarriage. Shit happens.

If you find something that works well put it here in a reply.

[brake-fade]

I think if you make changing every nut and bolt on the rear subframe a part of your scheduled preventative maintenance, along with brake hoses, you should be fine for a long while. It's the fasteners that rust and seize that are the issue. Seized bolts make an alignment a costly event due to seized adjuster bolts.