Mk5 rust removal, new sills and subframe rebuild

[D2TPP]

Hi Folks,

After daily driving my mk5 for a few years, about a year ago I took it off the road to sort out a few spots of rust.. I started off thinking it’d probably be a new wing and a small patch repair on the sills.  A year later I’m getting ready to put it back on the road after a fair bit of work!  I’ll share some pics below…

It started with a few spots of rust on the surface of the sills and one wing.. but once I got the paint off the rust was far worse than it looked.



Once the sill covers and under-trays, arch liners were off I stripped back the paint with a wire wheel and the rust was way worse than expected.





There were several holes in the sills and the rear of the sills where dirt had gotten stuck behind the arch liner.

To get access and also to inspect the extent of the rust further I dropped the rear subframe, which looked like it had been sitting in a canal..



I also dropped the fuel tank to get better access and to avoid any accidents when welding!



Underneath was mainly surface rust.. but it still took a few long days with a knotty wheel on a grinder to shift it.  Once removed I covered in rust protection and some acid etch…



I decided because of a couple of holes and a fair bit of surface rust to cut the sills off and weld on new ones.  I decided to keep the top half and weld the new ones below the line of the sill covers.. only coming up at the very front and back edges where the rust was bad…


 
I’m glad I did as once cut off they were pretty crusty inside.. thankfully the inner sills were pretty solid and I only had to patch two small areas. Here is a photo mid weld…



The sills were fully welded and primed.. it’s worth noting, I decided to remove the interior during all of this to avoid any chance of it catching fire or being damaged by sparks etc.



With that done, I couldn’t exactly put on the old subframe.. so I set about finding a new (old) subframe and got a bit carried away buying alloy hub carriers and wishbones etc



…and brakes and suspension and a big bag of bolts from tps  (some out of necessity for the alloy hubs)…



With the subframes refurbed and fitt d with new bushes etc. it was time to clean the underside one last time and give it a few coats of Upol



I’ve now got the subframes back on and it looks like everything fits..



I’ve replaced pretty much everything so it is looking nice and shiny!



Last things below the car are finish fitting all these bungs and make up new brake lines.



Above the underside still have loads to do, finish sanding and filling paintwork, paint the whole car, fit the interior etc.

If you have any questions about anything above I have several hundred other photos and I think I can remember most of what I did.  I should also note, this was my first time taking on a project like this having never welded before and I had to teach myself as I went.. hence it taking about a year.  I also work full time and have a family, so I only get the odd evening to work on it.

I’m looking forward to driving it again in the near future.

[Clarkj93]

Awesome write up mate!

Wish I had a pit to use... not sure if I can sufficiently do my underside on an un-level driveway for weeks/months. I'm planning on doing the rear subframe though soon, what steps did you take to do the control arms and subframes? Looks like it would be difficult to get every aspect of surface rust in all the crevices. What did you use for paint/seal?

[D2TPP]

The subframe I got from eBay for £60 had practically zero rust! So that was a big bonus.  The downside was it was from an Audi a4 and didn’t have the rear bracket for the exhaust and the mounting point for the arb are about 10mm closer together that on the gti?!  I managed to cut off the exhaust hanger from my old subframe and weld it.  The arb, I’ve just moved the bracket along a little and filled in the gaps with 3D printed bushes.. but I’ll redrill new holes if I need to.

I bought new arms all around, which came powder coated.  I sprayed black stone chip on everything to give a bit of extra protection and to avoid scrapes when bolting it all back together.

As for the body work, the main bits were all done with a knotty wheel on a grinder and on a drill.  I took a fair bit of the seam sealer off to get all the rust away.. so it took a while to reapply all the seam sealer and prune the bare metal before using Upol.

Yeah really lucky to have access to a pit!

[Clarkj93]

Where did you buy the arms from? If aftermarket, which brand and was fitment OK? And are rhey identical? Like any difference in thickness or construction in anyway?

[D2TPP]

Got the arms off eBay, identical thickness and 10x stronger than my crusty old ones.  Digging through my eBay I got them for £100 from ‘parts for you’.  We’ll see how well the bushes fare, but I didn’t want to poly bush it all just yet. And again will be much better than the old subframe where every single bush was gubbed!

[Guy123]

Great write up! Where can I find a list of all the parts/part numbers needed?

[D2TPP]

Great write up! Where can I find a list of all the parts/part numbers needed?

I’ve got it all saved in my AUTODOC and eBay past purchases.  The only tricky bit was working out the longer bolts for the alloy hubs.. it wasn’t too tricky though and the guys at my local tps in Dundee were really helpful.

If there is anything you need to know the part number for let me know.

[D2TPP]

I managed to get the hard brake lines all made up and installed today.  The rears were a doddle, the front drivers side was a massive PITA.  I managed eventually though, it routes right along the ‘firewall’ / back of the engine bay, you have to remove a whole bunch of stuff if you want to keep to the original routing.



If you start at my red pipe cutter on the right of this photo and follow the copper coloured line.. you’ll see what I mean.

Anyway, managed to make them all up and finished fitting the braded lines to my refurbed calipers.



Didn’t get around to bleeding them.. but I’m guessing I’ll need to get the car running and use VAG com to activate the ABS to bleed them??

If so I might try and get the interior put back in next.

[D2TPP]

Finally got the car off the pits!  Going to try and remember how the interior goes together later this week 🤪

[Flyingscotsman]

Great thread!    Glad you said it took you a year.  When you post up the photos together it looks like it was last weekend's project.

[D2TPP]

Nah it took fecking ages 😂 I only got to it the odd weekend here and there.  But it certainly wasn’t a weekend task!

The trickiest part was welding the sills.  The originals are laser welded from the factory.  They are also made from pretty thin metal.. so experimenting with different techniques to make sure the continuous welds didn’t blow through and even just taking the galv off the new sills and priming and painting behind etc. took weeks and weeks to figure out and more weeks and weeks to execute!  .

[GilesWoodward59]

Good job on tackling that all yourself!!

[D2TPP]

Managed to get a bit more done this week, got the interior back in, got the back of the wings cleaned and covered in Upol.  One major PITA was the rear middle seat belt which was completely jammed.  After a bit of research.. smacking it with a rubber mallet and leaving it for a while managed to sort it.

The interior wasn’t too bad going back in… although I had forgotten about some of the trim I had broken when removing.. so another £60 or so on bits and bobs off eBay it was!

In preparation for putting ignition on to bleed the brakes, I had a look under the bonnet.. which reminded me I hadn’t put back the wiring loom to the power steering rack  I’ve watched a few vids on YouTube and it looks like it should be possible without dropping the steering rack *fingers crossed*. 
 

[Sean_ED30]

Great write up. I'm planning on doing something similar with the rear subframe on my car, In the picture it looks like you have used alloy hubs on the rear ?

[D2TPP]

Great write up. I'm planning on doing something similar with the rear subframe on my car, In the picture it looks like you have used alloy hubs on the rear ?

Yeah I’ve put on Alloy hubs all round.. not had the tracking set up yet.. but it all seems to fit!  I believe they are from a Passat.. the alloy wishbones on the front are from an s3.. but i understand you can also get these from a Passat