Rear subframe replacement

[Davemca8]

Good evening, I have just joined this forum after owning my a6 avant for 8 years. 

At the beginning of the year my MOT reviled that my rear subframe was heavily corroded so I took it upon myself to rub it down and give it a coat of paint. In doing this I knocked a fairly large hole in the right supporting arm of the subframe. Rather than give up on this car and rush to we by any car I have decided to replace the rear subframe. 
 

I found a replacement on eBay that appears to be in reasonable condition and I’d like to order replacement parts such as drop links, control arms if required and all the fasteners required. I am having difficulty finding part numbers especially for the fasteners. Are there any diagrams with part numbers available? I have found American ones but not exactly what I need. 
 

Has anyone tackled this job before ? I have a fair amount of experience working on cars but haven’t tackled anything like this. I’m worried about alignment of the subframe and haven’t worked out exactly where to start. I’d like to remove the entire subframe with all the arms, hubs, brakes etc then swap everything over on the drive before refitting. Any help would be greatly appreciated! 
 

2012 A6 avant C7 2.0tdi FWD 

[spartacus 68]

Don’t under-estimate the task at hand. Luckily this is a 2WD version, but you’re looking at 13 year old car, and everything will be seized on. Hat off to you for attempting.
 

Look at parts here: https://www.lllparts.co.uk/catalogs/audi/RDW/A6/717/5

If it were me, then absolute minimum tools would be air compressor with air hammer, axle stands, full socket set with 1/2” extension breaker bar, heat (blow-torch), plus gas penetrating fluid, impact driver, battery or power torque wrench, ceramic anti seize grease, coil spring compressors, scissor jack, 2-tonne jack, wire brush, preferable on drill attachment for exposed bolt threads. Put money on rear coil spring rubber seats. being corroded.

Given the work you’re going to, this had better not be your daily driver. Allow yourself a few days, ideally under cover. Brake lines, then flexible hoses, clamp where possible, you’ll need to bleed brakes afterwards. Suspension parts, Meyle HD or Lemforder, and only torque with full vehicle laden weight.

Prior to dropping subframe, mark position. At the end, you’re still going to need to do alignment. Also use new subframe bolts from Audi.

You will likely need VCDS for rear electro mechanical brake, or chance it just leaving handbrake off and refit pads. Put the car battery on trickle charge, during refit.

Given you’re going to hassle of replacing, then swap out rear bearings too. F.A.G., nothing else. Once done, spray everything with Lanoguard every year.

Edited Sunday at 10:52 PM by spartacus 68

[Davemca8]

Thanks very much for the detailed reply. You have, rightly so, put the fear into me. 
 

I have pretty much all the tools you mention with the exception of compressor and air hammer. I used to tinker with Landrovers so I have some experience with rusty stubborn bolts. 

The plan in my head was to remove the brake callipers but leave them attached to the line tying them out of the way. Disconnect the harness to head light levelling, disconnect the shocks from either top or bottom, remove rear section of exhaust and lower the entire subframe with everything attached initially using the subframe bolts then onto a trolley jack. From there swap everything over replacing components as required. Then refit in the opposite order. 
 

I had scheduled a week due to inevitable bolt from hell but after sleeping on it I think I could using my heart rather than my head. I love the car but maybe it’s time to trade in… 

I’m in two minds at the moment. If I go through with it I will try and document my pain and keep this thread updated. 
 

It might just be too much of a job on my own. 

[Davemca8]

Also thanks very much for the link to parts catalog you don’t know how long I spent last night looking for exactly that. 

[spartacus 68]

I bought a compressor and air hammer for the dreaded pinch bold on upper arms on front suspension. I’m sure it’s possible to do this rear subframe job without it, although I’d want a Milwaukee 1/2” impact wrench with a swivel head as payback, as you’re on axle stands and not always east to get a breaker bar on it. For exhaust, cut off the centre connection brackets which will be like cheese anyway and fit Mikalor stainless clamps. Basically fit and forget.

Yes, you can leave brake calipers and brake lines connected, but you’ll need to support somehow.

On 2012, then trade in isn’t what you think it will be. The car is probably worth more to you than what it’s worth financially, if subframe is an advisory. Ultimately this is down to time and resource. If you’ve worked on Land Rovers, this will be a walk in the park.

You have eccentric bolts that control camber. Typically these are seized. I’d get new Audi bolts for that and lightly grease with ceramic grease.

[Davemca8]

Yeah agreed I’d estimate between £3-4K on a trade in and a like for like replacement 2019 model would be between £20k-£25k. 
 

I’m more than familiar with the exhaust centre section having replaced it multiple times but good to know there’s a stainless equivalent. Cheers for that 
 

Where are the eccentric bolts located on the subframe ? Would I have to take note of the original position and try to best match it? It would be going for a full alignment on successful replacement.