Rear subframe replacement

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Manufactured from 2004 to 2013

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YLS
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Rear subframe replacement

Post by YLS »

I'm thinking ahead to keeping the car or moving it on. Everything is great on it and I'm really happy with it, but the rear subframe was picked up for rust on the last MOT. It will only get worse. I can either replace the subframe with a used one or move the car on before it's a problem. I would prefer to keep the car I think... e87 120d 2006 120k miles.

Used subframes are cheap. How big is the job to swap them? I've done the bush inserts so I know that bit. What else is involved? I'm happy removing springs/dampers. Do I need to disconnect brake lines, or can they stay in place and the calipers hang out the way? Handbrake too. Driveshafts come out ok. Diff looks straightforward once disconnected from the propshaft. Do I need to remove the control arms/knuckles before dropping the subframe or can they stay on and swap them off the car?

My big concern is that once the subframe is off then the main chassis is excessively rusty too. Some patches are slightly rusty/flaking paint already but I can't see the extent of it.

Basically is it all simple nuts and bolts or are there things that will catch me out like having to get new brake pipes made up, the handbrake cable taking two weeks to disconnect, etc. Is it possible as a one person DIY with a jack to support the weight of diff/subframe when removing?

Any idea how much a garge would charge to swap it over? 4 hours? 8 hours?

jonwilli
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Re: Rear subframe replacement

Post by jonwilli »

If you are going to keep the car I would strip a subframe back to metal and paint with POR15 before fitting to the car. Most of the ones on eBay are already pretty corroded as it is a common issue with the E series cars in this country. You could go to the effort of replacing and be back in the same situation in a few years time.

There are hard brake lines that run over the top of the subframe that need to be swapped. This is straight forward if the joints aren't corroded which they more often than not are. Rest of the swap is just bolt in, bolt out, then you need an alignment. You may find that some of the bolts need replacing as these get pretty corroded. Other thing to consider is the bushes on your donor subframe will probably be past their best and in order to paint more easily it is best to remove bushes and replace with new poly bushes. The poly bushes last longer than OEM ones and are easier to fit.

I think a garage would charge you about 5 to 6 hours labour for the subframe swap plus alignment so in the region £500 with VAT I would estimate.
BMW E81 130i
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YLS
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Re: Rear subframe replacement

Post by YLS »

Hi, thanks for the reply. The car is probably only worth £2500 so paying £500 labour for fitting isn't a great option. It'll probably be a DIY job if it needs doing.

Thanks for the tip about the brake lines, I was expecting them to be an issue somewhere along the way...good to know they will be!

I'd certainly be painting it first. I've got spray equipment so that's not an issue. And yes I plan on replacing the bushes when the frame is out. Although to be honest if they're not too bad I'd just swap the poly inserts in the current one over.

Thanks for the help.

jonwilli
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Re: Rear subframe replacement

Post by jonwilli »

YLS wrote:
Fri May 22, 2020 10:50 am
Thanks for the tip about the brake lines, I was expecting them to be an issue somewhere along the way...good to know they will be!
I paid for some one to fit my refurbed subframe and they made some new copper hard pipes. If I was fitting on my driveway I would have probably just bought a new pre bent hard pipe from BMW to have at hand during the install. I think they're about £30. Hand brake cable isn't an issue as it just clips to the subframe with a metal hook
BMW E81 130i
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BMW E82 135i N54

YLS
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Re: Rear subframe replacement

Post by YLS »

jonwilli wrote:
Fri May 22, 2020 11:36 am
If I was fitting on my driveway I would have probably just bought a new pre bent hard pipe from BMW to have at hand during the install. I think they're about £30.
Thanks, great suggestion.

Nyxeris
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Re: Rear subframe replacement

Post by Nyxeris »

I'd change the little 6" flexi hoses hoses that connect the four hard lines (part 7 on here) too, they're almost completely inaccessible with the subframe in place, might as well do them whilst you're there for the sake of £20.

I'd say the same for the rear guibo/flex disc (part 10 here), seem to be a common failure with age.

Also, can't hurt to give your diff a bit of a tidy up whilst it's off - 30mins with a wire wheel and POR15 just so it doesn't look like a huge hunk of rust next to your shiny restored subframe!

Give Redish Motorsport's youtube channel a look - videos like this where they fully restore the underside of an E9x M3 (90% the same underneath as our cars) will show you other places to look/parts to swap if you fancy it.
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M3AN
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Re: Rear subframe replacement

Post by M3AN »

Do E8x replacement hard lines come pre-bent? They don't for many other BMW models so worth keeping in mind if you have to bend them yourself and you don't have the proper kit.
Daily: E87 LCI 130iA Motorsport + LSD, Coilovers, Stainless 'Y Pipe' Exhaust & Backbox, NRW Shifters, 280hp Tune | Weekends: M3

Nyxeris
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Re: Rear subframe replacement

Post by Nyxeris »

M3AN wrote:
Sat May 23, 2020 12:20 am
Do E8x replacement hard lines come pre-bent? They don't for many other BMW models so worth keeping in mind if you have to bend them yourself and you don't have the proper kit.
The 4 shorter lines should be supplied pre-bent, but the long runs from the front of the car to the rear subframe won't be. When I asked Cotswold the chap said it's a bit of a gamble and depends on what's in stock in Germany - even for dealerships its impossible to know what you'll get until it arrives.
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