Wikipedia describes Grand Funk Railroad as an "American rock band popular in the 70's. The band was formed in 1968 by Mark Farner (guitars, keyboards, lead vocals) and Don Brewer (drums, lead vocals) from Terry Knight and the Pack, and Mel Schacher (bass guitar) from Question Mark & the Mysterians. Terry Knight, a former band-mate of Farner and Brewer, soon became the band's manager. Knight named the band after the Grand Trunk Western Railroad, a well-known rail line in Michigan. First achieving recognition at the 1969 Atlanta Pop Festival, the band was signed by Capitol Records. After a raucous, well-received set on the first day of the festival, Grand Funk Railroad was asked back to play two additional days. Patterned after hard rock power trios such as Cream, Grand Funk Railroad, with Terry Knight's marketing savvy, developed its own popular style."
Under Terry Knights guidance in 1970, they sold more albums than any other American band. Their first album, released in that year went gold. Their second album "Closer To Home" went multiplatinum, and produced their first chart hit "I'm Your Captain" which, despite it's success, did not make number 1. Their early success was largely due to the money spent on advertising. Grand Funk Railroad might have been a very popular band, but the critics didn't like them so they received almost no airplay on the radio. In 1971 they broke a record held by the Beatles. They scheduled a concert in Shea Stadium and sold it out in 72 hours. Towards the end of that year they became dissatisfied with the managerial style and fiscal responsibility of their manager and fired Terry in early 1972 with just 3 months left on his contract. Terry sued for breach of contract which set off a protracted legal battle. At one point he repossessed the bands gear before a concert at Madison Square Garden. It seems to me that all they had to do to avoid that was let Terry's contract run out without renewing it.
In 1972 the band hired a keyboard player named Craig Frost to become a 4th member of the band. He was not their first choice. They had wanted Peter Frampton who had to decline due to contractual commitments with A&M records. The addition of keyboard to their sound changed their style from sort of a garage band based rock and roll to a critically acceptable rhythm & blues pop. With the hiring of Todd Rundgren as producer in 1973 they were finally able to produce 2 number one singles. "We're An American Band" went to number 1 in late 1973 and their second number 1 hit was a remake of Little Eva's "Loco-motion".
Although they were highly successful in the mid 1970's, personal issues, burn out and musical direction issues were taking it's toll on the band. Having learned from their experience with Terry Knight they forged on and completed their contractual commitment to Capitol Records. After the release of their last record with Capitol in 1976, the band went their separate ways. That same year they reunited and joined forces with Frank Zappa which resulted in a short lived renewal of spirit. By 1977 the stress became too much and they parted ways again.
Mark Farner went on to a solo career, Brewer, Schacher and Frost formed a band they named Flint. That didn't really go anywhere and Frost left to join Bob Segars Silver Bullet Band. In 1996 the three original members reunited and did various projects over the years. Again there seemed to be problems and Mark Farner acrimoniously left the band again in 1999. Brewer and Schacher have continued to perform as Grand Funk Railroad along with various other members of various other bands. Mark Farner is still recording and playing concerts with his own band. However, none of them have ever achieved the success they had in the 1970's. At least they're still rockin on.