Originally Posted by michaeldch
Thanks Steve - very helpful! I'd really like to avoid removing the downpipes - and had tried drilling to no avail. The tungsten option sounds good - but can you provide some more detail (or a photo?) of the bit you used to grind out the hardened steel stud?
I have already ground off the studs flush with the flange, and even the back of the stud also flush so I am ready to drill
You could try something like a HSSCo Drill as in the pic.
As mill I bought a 6mm from top to tail,
I then worked in circular moves until the studs became loose.
But you need at least a hole of about 6mm to start,
then the tungsten mill takes it with ease.
You could even try to mill without completely drilling through,
but you'll need some centering.
Perhaps some shop owners/installers can chime in and tell us how they usually do it,
I think this happens pretty often on higher mileage cars.
If I had the possibility I would try the cutting torch.