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The car is a 2005 Mini Cooper. The bolts that hold the exhaust mounts in place have rusted and snapped on both sides:

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I've taken up the floor of the boot and have located their heads on either side:

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If I took it to a garage for repair are they likely to just grind the rusted heads off and tac some new fixings to the underside?

Is it worth me even attempting to drill these out myself and put in new bolts for the rubber mounts? or is this a relatively common job that most garages could fix in 30 minutes?

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    Looks like you already have everything readily available to you ... I'd personally do it myself. If you have the mad skills, go for it. Use stainless steel hardware so you don't have this problem again. Use some type of sealant on both sides of the body so you don't have water bleed through when it rains (just don't get it on the threads of your bolts). – Pᴀᴜʟsᴛᴇʀ2 May 6 '14 at 18:24
  • @Paulster2 I have both drilling, and sealing skills, so I'll probably give it a go.. – StuR May 6 '14 at 18:46
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    Put the sealant around the holes, then put the new bolts in ... should seal it up just peachie. You may want to put flat washers on either side of body to support the bolt so it doesn't pull through. The head of the bolt will stick up a little bit more than what the stock bolts did, but you shouldn't notice it with the padding/carpet back in place. – Pᴀᴜʟsᴛᴇʀ2 May 6 '14 at 18:55
  • @Paulster2 Unless I grind the old heads off... sounds like a fire waiting to happen though. – StuR May 6 '14 at 19:01
  • If you hunt around, you might be able to get the same type of bolt again, which would save having the heads sticking up - They look like some variety of coachbolt. It's not a high-stress application, so stainless fixings ought to be fine... – Nick C May 7 '14 at 9:00
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The solution was to simply drill out the old bolts.

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I had the same it was easy. I differed in just using a 3mm and then 7.5mm drill bit, the stud (screw) is M8. So it just fell out during drilling.

  1. Strike center of circle with punch to guide drill
  2. Drill straight, cutting fluid helps, HSS drill or better (HSS is ok it is soft)
  3. Use an M8 tapper (from tap and dye set same pitch as your replacement bolt) cut new tread
  4. Screw in new bolt
  5. Put on bracket and new nut

Alternative: Had considered 8mm drill and locking nut eg without tap( drill bit and bolt under 2 pounds sterling!)

And new brackets I done this on convertible without taking of metal reinforcements under body.

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Also looking at the rusted bolt that is still place, many won't have confidence to drill car.

The tap and dye set may help you leave it in place. Consider penetrating oil tightening and un-tightening then cleaning bolt with dye and maybe even nut with tap, applying thread locking compound or something more permanent and consider the drill out solution if it fails.

The main challenge would be working area to turn the dye wheel.

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