Subframe mounting bolts

[5cylinderman]

Could someone explain to me why it is necessary to replace the mounting bolts when undergoing subframe removal/re-installation?
After taking delivery a full set of new bolts for my coupe I noticed that the they are only regular 10.9 high tensile bolts and not anything funky or "specialised".

Also, the new solid alloy subframe bushes I got have no coating on them. What is the best way of preventing them oxidising/corroding?

[Monkeymagic]

i reckon a lot of it is audi making sure that bolts are torqued properly. its most likely to be over cautious. when you look at elsawin nearly every bolt you remote should be replaced. however mention this to vag techs and they don.t. i can understand it for delicate matters but huge hardened steel bolts i fail to see the point. different if heavily rusted though.

[Mikes2]

They're supposedly stretch bolts

[re2500]

Get the bushes hard anodised somewhere.

[mcandmar]

No harm in having nice new shiny bolts but i usually dont bother unless there badly rusty or visibly damaged. Only ones i'm fussy about are the big CV joint bolts and balljoint pinch bolts, but they almost always come with CV joint boots or new balljoints. Inside the engine is a different story, replace everything.

[bambridge]

Get the bushes hard anodised somewhere.

Problem is that anodisers usually have a minimum charge £30/£50

I took a load of parts for hard black anodising, and also 4 wheel centres for silver anodising.

Got charged for the hard black and then extra £30-00 for the 4off discs(60mm dia)

And im a regular customer

[Error404]

The place we use at work for recoating boat window frames charge by whatever they can fit in the crate that goes in the bath, you'd think they could chuck some small bits in with other jobs etc, TBH I've never needed to so haven't asked them.
Depends what they are set up for I guess?

RE: subframe bolts, I use off-the-shelf 10.9s on mine, torqued to 80nm which is more than the factory setting and the angle setting combined. I find they come loose on track otherwise and didn't want to overtorque a "stretch" bolt.

[caterpillar]

i will use the wood tare oon the bolts; they dont loose, the dont get stucked, and the bolts dont rust.... i use this in all of the steering link, and all the bolts under the car...( the tare arent expencive....)

[UrS4boy]

They're supposedly stretch bolts

Correct. Anytime the manuals, e.g. the Bentley, gives a certain torque and then "a 90 deg turn", etc. the bolt is a stretch bolt that is only supposed to be used once and then replaced. Here are some example front suspension and subframe torques and stretches (in this case for a C4 UrS):

http://12v.org/urs/FrontSuspensionTorqueValues.PDF

[jamie9048]

I`ve built mine up using rubber grease between the alloy bush and frame just to help against corrosion, even though the frame is painted and the bush anodised