Mending fences:
2 meanings:
1. Lit. to repair fences as part of one's chores. Tom is mending fences today at the south end of the ranch.
2. Fig. to restore good relations (with someone). I think I had better get home and mend my fences. I had an argument with my daughter this morning. Sally called up her uncle to apologize and try to mend fences.
Very commonly used in the second example, as an idiom.
I would never tell a mechanic to "mend" my car. It sounds ridiculous.
The word "mend" can be used in a number of different ways, I WOULD NEVER use it in the context of fixing/repairing a car.
mend (mnd)
v. mend·ed, mend·ing, mends
v.tr.
1. To make repairs or restoration to; fix.
2. To reform or correct: mend one's ways.
v.intr.
1.
a. To improve in health or condition: The patient is mending well.
b. To heal: The bone mended in a month.
2. To make repairs or corrections.
n.
1. The act of mending: did a neat mend on the sock.
2. A mended place: You can't tell where the mend is.
Idioms:
mend fences
To improve poor relations, especially in politics: "Whatever thoughts he may have entertained about mending some fences with [them] were banished" (Conor Cruise O'Brien).
on the mend
Improving, especially in health.