How to avoid breaking rusty bolts?

Question

Recently I've been dealing with some bolts that broke when I tried to disassemble part of the brakes on my car.

Soon I'll also have to do the same service on the other side, and I also need to change the front bearing assemblies. I'm concerned that I'll end up with more broken bolts and am looking for advice how to avoid breaking bolts.

The car is 9 years old, 115K miles, in a snowy northern climate with plenty of road salt.

I believe its still on the original front brake calipers & definitely has the original hubs. So the fasteners have had plenty of years exposure to the conditions.

I previously asked another question about dealing with broken bolts (How to remove broken bolt stubs from brake caliper bracket?) so I have good reason to think breaking more is likely.

I'm aware of general methods such as using penetrating oil, applying heat, rocking the fastener back & forth to gradually loosen it - but not really sure which of these methods are best to use vs. what to avoid, or if these could actually make things worse / cause unintended problems.

Answer 1

I've had some success with heat, usually with a propane torch, penetrating oil, and impact wrenches. But there is no solution that works 100% of the time. Some bolts are just seized so firmly that they break no matter what you do.

In that case the best approach is to drill out the bolt with as large a drill as you can. If you can get it thin enough the bolt may be able to be "peeled" out or you can use a thread chaser to get the rest out.

In extreme cases you just need to drill the entire thing out including the threads and use a bolt with a nut if possible.

Worst case your part is ruined and needs to be replaced. Hey, stuff happens!