I have several Quick-Grip clamps, and they're great! Unfortunately, some of mine are cheap knock-offs of the real IRWIN clamps, and aren't as durable.
After two failed in the exact same way, I thought I'd post this small Instructable about how I fixed and improved them.
Step 1: The Problem
In the middle of trying to hold something down for a big project, disaster! Squeeze the handle a bit too hard, and suddenly it no longer works.
The design flaw is that the handle pivots around a pin that is retained only by a ring moulded into each of the plastic sides. Even though the pin is quite solid, these rings are the weak point.
Stress them too often or too hard, and snap!