How to remove and replace the Front Subframe

[decvalts]

How to…replace the front subframe on the Lupo - Most of this post was compiled from all the excellent advice in the many subframe threads in the forum and a lot of trial and error on my own Lupo SDI

The subframes on the Lupo seem prone to rusting pretty catastrophically… it is often missed at MOT because the undertray and other parts can hide the worst of it I suppose.

This guide is based on the SDI, the others are very similar but the positioning of certain components may be different (exhaust down pipe for example is at the back on the SDI…etc)  

In *theory* it's fairly straightforward, but seized bolts and broken captive nuts can add to your woes. Doing it on axle stands is also a bit more faffy than on a lift. (I did mine in the street on stands...) If I'd known all of this in advance I would guess I could probably have done it in a day or afternoon even. 

What replacement Subframe can I use?

(Feel free to correct this...I think this summarises the compatibility)

1.0, 1.4, 1.7 SDI: From a Lupo or Arosa these are interchangeable with each other. You can also use a Polo 6N subframe. (even a Polo GTI subframe I believe?)

TDI: Either a Lupo TDI, GTI or a Polo 6N2 TDI Subframe

GTI: You need a Lupo GTI subframe (or a TDI perhaps?)

Guide:

1. Jack up car and remove both front wheels
2. Remove under tray
3. Give the 4 subframe bolts a good soaking in penetrating spray
4. See if 4 subframe bolts can be cracked. Try more spray and leave overnight if necessary.
5. Turn the nuts very carefully, support the subframe underneath and then see if you can feel the captive nuts staying in place (or not) when giving them a few turns. They are prone to not staying captive and if the bolt(s) just spins you will need to cut into the chassis and weld in new nuts or drop bolts. I refer you to these excellent threads for pictures and guides on how to do this if needed:   - welding in drop bolts method - nice pics of the cut out parts in the chassis leg here
   
   You can also try applying downward pressure against the bolt with a pry bar inserted between the subframe and chassis, then attempting to turn the bolts again. 
   
   Next couple of steps might not be necessary, I did them on my SDI to make access easier. (The next few steps might vary by engine type)
6. Remove plastic inlet plenum box
7. Remove 4 inlet plenum trumpets 
8. Remove inlet manifold
9. Remove EGR valve (to give access to 1 bolt on the exhaust manifold!)
   
   Regardless of exactly how you get to it, you will need to drop the down pipe/front section of the exhaust from the exhaust manifold, as the subframe curves over the top of the exhaust below it. You do not necessarily need to remove it, lowering it a few inches will just about give you enough clearance to pass it over.
    
10. Remove exhaust manifold (8 nuts and washers) (You could also remove the 4 bolts on the flexi pipe junction, but I couldn’t reach these, and often they are seized. (Use heat if necessary))
11. Remove the 2 rubber exhaust mounts. Greasing them may help them come off but I ended up having to cut mine...
12. Drop the front pipe/flexi pipe down, support it on hangers or some chocks of wood. Obviously you want to avoid dropping the subframe on it and bending it/cracking a weak joint later…
13. Disconnect the ball joints on either side
14. Disconnect tie rod ends for more room if you like. (Optional)
15. Loosen Anti-roll bar bushes and bolts. (Optional)
16. Support the transmission if you are extra cautious like me (although it can be left to hang from the two engine mounts)
17. Remove dogbone/transmission/rear engine mount. Two 16mm spanners required for the bolt going through the gearbox. There is not a lot of room here, I couldn’t get a socket on either side of the nut or bolt head. (I suppose you could remove the gear linkage bit though) 
18. Remove the upper transmission mount, just above/behind where the down pipe was (1* 16mm hex bolt). You can’t actually see it from the top if you are working from above, you’ll need a short extension bar and feel around to find it. This is connected via a small flat bar to the top of the gearbox.
19. Support the weight of the steering rack on the passenger side with rope or ties. (Again, me being over cautious probably) The driver side is supported enough by the steering column union. 
20. Remove 4 steering rack bolts from beneath. (13mm hex). In theory the pair of mounting brackets should behave like “captive” nuts, but they often aren’t. (I had to cut/grind off the passenger side steering rack bolt heads as the nuts became free/spinning. At a glance it looks like you might be able to get a 13mm spanner in from the side to hold spinning nuts from above, but they are actually a weird octagonal shape so a socket/ring spanner won’t get any purchase.)
21. Support the subframe with a jack.
22. Remove 4 subframe big bolts. (18mm hex - 2* M12 x 1.5 x 80mm 2* M12 x 1.5 x 100mm)
23. Lower subframe with 2 people or use jack and wood blocks. (Don’t drop it on the exhaust.) As you are doing this ensure the steering rack separates, but try not to let it sag too much.
24. Manoeuver the subframe out by rotating and turning it towards front of car (It will come out in one piece with wishbones and anti-roll bar still attached with a bit of deft manoeuvring)
25. Installation is reversal of removal. (Ha!) (unless you are welding drop bolts in or new captive nuts…)
26. Squirting in some wax into the captive nut holes might be a good preventative measure to do here.
27. When offering up the new/refurbished subframe to the chassis and steering rack, you essentially have 8 bolts that you need to marry up and align. I started with the biggest M12 bolts that go into the front of the chassis, then the two slightly shorter ones that go through the control arms. Then finally the steering rack ones. If there are ‘dirt marks’ to help you align the subframe back up, try and stick to these if possible. Be careful pushing the bolts back into the captive nuts if you are using these, ensure they ‘take’ and avoid knocking them out of their channel…
28. Make sure everything removed is reinstalled and tightened. Use threadlock if reusing the bolts (yes, yes, you should use new ones ideally…)
    
    Have fun!

Torque settings:
(maybe forgo the extra quarter turns etc on the captive nut bolts if worried about further damage…)

4 main subframe bolts: 70 Nm (+ half a turn)
4 steering rack bolts: 30 Nm  (M8 x 80mm if you need to replace)

Refurbishing a salvage subframe:

• OEM part number is 6X0199315F
• Check for excessive corrosion, no point replacing an old one with similar problems
• Check for any missing captive nuts, or sheared off bolts present. Captive nuts should be present: 1) On the two control arm mount points, 2) On the dog bone/rear transmission mount - x3 - if any of them break, you can pre-attach a new engine mount using normal nuts, there's enough room to reach in with a long 13mm spanner. 4) Upper transmission mount (x2). Again not the end of the world if captive nuts missing or broken, can be replaced. 5) ARB mounts and the retaining metal clips.
• Check it isn't bent or warped!
• I didn't shot blast it, but just rubbed down with degreaser, wire brush, some coarse sand paper, then did couple of coats of red oxide primer, followed by Hammerite. Then spray Waxoyl in the insides thoroughly.

With the amount of stuff that has to come off it’s a good opportunity to overhaul or clean up a lot of parts, inlet plenum for example, new control arms/ball joints if needed, replace the exhaust manifold gasket as well if you have removed the old one etc.

 

 

 

Edited January 9, 2022 by decvalts
Some typos and refurb notes

[mk2]

Really excellent write up. Lots of fav points👍🏻