In 1966, Eric Burdon, frontman for The Animals, put together a new Animals lineup when the original members departed (Eric Burdon and the New Animals, sometimes called Eric Burdon and the Animals), including Weider on guitar. The first album by the new ensemble was the 1967 effort Winds of Change, in which the Animals abandoned their old blues sound and went psychedelic. Weider stayed with the group through 1968, recording The Twain Shall Meet, Every One of Us, and Love Is, the latter being a soul-based psychedelic rock album. After bassist Danny McCulloch left, Weider and co-guitarist Andy Summers alternated between guitar and bass during the band's concerts. By 1969, Weider was in California playing in an obscure group called Stonehenge when Ric Grech abruptly left Family during that band's first, disastrous U.S. tour and the band needed a new bassist immediately.
Weider thus replaced Grech in Family. Like Grech he was both a bassist and a violinist, and many of Family's songs had incorporated violin in their arrangements. Weider joined midway through the tour, which ended prematurely owing to lead singer Roger Chapman's visa problems. The single "No Mule's Fool", Family's first single with Weider on board, took the band in a country rock direction.
Weider appears on Family's two 1970 albums, A Song for Me and Anyway released ten months apart.
Weider left Family in the summer of 1971. He joined Stud, a group that coincidentally featured guitarist-bassist Jim Cregan, who would become Family's final bass player in 1972. He served as a multi-instrumentalist in Stud, playing guitar, bass, piano, violin, and cello for the group. After Stud broke up Weider did some session work and released his self-titled debut solo album in 1976. In the mid 1970s, he was also a member of the band Moonrider with Keith West. His more recent albums (listed below) are more in a New Age vein than in a folk, rock, or country style.
In 1979 he was featured on Gullivers album "Ridin' the Wind".