Here´s from the Flyguitars site:
´Grabber
Sliding pickup Gibson part number 13691. The single coil pickup of the Gibson Grabber bass was mounted onto a plastic slide, allowing it to be positioned by the neck, by the bridge, or anywhere inbetween. The pickup was designed for a "dark tonality" and was a simple single coil wrapped around an Indox magnet core. Some Gibson price lists incorrectly suggest that this pickup is a humbucker. The design remained unchanged for the 10 years of production, 1973-83. In later years, this pickup was also used on the early eighties Gibson Explorer bass.´
I´m not really sure myself, i always thought it was quite ´crisp´for a humbucker.
I´ve repaired many a pickup in my life, though never examined a grabber pup.
Nice having some grabber contents here, like it!