It helps to locate the mirror based on where you can get the bolts to from the inside. The OEM mount can get in the way. I located my mirror so the mounting bolts went through the door skin only. I located the first bolt as close to the OEM mount as possible and still be able to get a wrench on it, then made template for the mounting holes of the mirror to drill the other holes using the first hole for alignment.
Have someone hold the mirror where you want to put it and test the visual alignment from the drivers seat to ensure you can see where you want to see behind you before committing to holes.
Buying shorter bolts is always easier than modifying bolts. Especially in tight spots like this because getting the first thread to start is critical. If you need to cut the bolt, do it with a nut already on so the nut can chase the tread clean after cutting the bolt.
A ratcheting combo wrench works well. Finger contorsions and patience are also required...
|