Philo Beddoe is a truck driver living in the San Fernando Valley. He lives in a small house, with an orangutan named Clyde, behind that of his friend, Orville Boggs, and his mother. Philo makes money on the side as a bare-knuckle fighter; he is often compared to a legendary fighter named Tank Murdock.
One night Philo becomes smitten with Lynn Halsey-Taylor, an aspiring country music singer he meets at the Palomino Club, a local honky-tonk bar. His relationship with her seems to be going well until one day she and her camper disappear from the trailer park. Believing that he is falling for her, Philo decides to set off for Lynn's home in Denver, Colorado.
Along the way, he has a run-in with a motorcycle gang called "The Black Widows", who incur Philo's wrath after two gang members insult him and Clyde at a traffic light. Philo chases them down and takes their bikes (which he repaints, repairs, and resells), and every attempt they make to get even results in disaster. Philo also incurs the wrath of LAPD cop named Putnam, with whom he gets into a fight at the Palomino. Both the officer and the Widows learn of Philo's trip to Colorado and head off to find him.
Orville and Clyde accompany Philo to Denver, and on the way, they meet a woman named Echo who becomes Orville's girlfriend. They earn money along the way by booking fights for Philo. After a fight in a slaughterhouse, the man holding the money tries to stiff Philo. Echo fires two shots from a .38, and the man hands over the money.
Knowing that Philo has come to look for her, Lynn helps the Black Widows lure him into a trap. Philo sees Lynn and attempts to talk to her, but finds himself surrounded by the Widows. He manages to fight most of them until Orville intervenes. Using a garbage truck with a dumpster hoist, he dumps all the motorcycles into the back of the truck. The Widows charge the garbage truck, but Orville gets away. Philo, Echo, and Orville then escape.
Philo finally finds Lynn and she reveals her true nature to him. Hurt by her callousness, Philo says that he is the only one dumb enough to want to take her further than her bed. Lynn erupts in a fit of rage, striking him repeatedly until she collapses in tears.
Orville learns that Tank Murdock, based in the area, is ready to retire after one more fight. Orville makes the arrangements, and Philo faces his elderly nemesis. During the fight, the crowd, initially pro-Murdock, begins to insult him, with some murmurs that Philo is going to be the next Murdock. Philo lets his guard down, intentionally giving Murdock a clear shot, knocking Philo down for the count. Murdock, having regained the crowd's esteem, is allowed to retire undefeated. Clyde, Orville and Echo head home the next day.
The script, written by Jeremy Joe Kronsberg, had been turned down by many other big production companies in Hollywood. Most of Eastwood's production team and his agents thought it was ill-advised. Bob Hoyt, whom Eastwood had contacts with (through his Malpaso secretary Judy Hoyt and Eastwood's long-term friend Fritz Manes), thought it showed promise and eventually convinced Warner Brothers to buy it. An orangutan named Manis was brought in to play Clyde; also cast were Geoffrey Lewis as the dimwitted Orville, Beverly D'Angelo as his girlfriend, and Sondra Locke as Lynn Halsey-Taylor, the country and western barroom singer. Eastwood spoke about using the orangutan for the main role, "Clyde was one of the most natural actors I ever worked with! But you had to get him on the first take because his boredom level was very limited."
The film has a contemporary western theme, displaying the blue collar aspects of the western United States, with many scenes shot in rural locations, cheap motel rooms, industrial facilities, and honky tonk bars. The film was shot on location, including the California communities of Bakersfield, North Hollywood, San Fernando, Sun Valley, Ukiah, and Van Nuys. It was also filmed in Colorado, including parts of Denver, Aurora and historic Georgetown. A few scenes were also filmed in Albuquerque, Santa Fe and Taos, all in New Mexico.
The film's title refers to the eponymous Eddie Rabbitt song from the soundtrack, in which the singer complains that his girlfriend turns him "every which way but loose"; i.e., he cannot bring himself to leave her although he is more of a freewheeling character.
Upon its release, the film was a surprising success and became Eastwood's most commercially successful film at the time. It ranks high amongst those of his career, and was the second-highest-grossing film of 1978. It was panned by the critic David Ansen of Newsweek, who described the film as a "plotless junk heap of moronic gags, sour romance and fatuous fisticuffs." Ansen continued, "The only decent part is played by an orangutan. One can forgive [his] participation—he couldn't read the script—but what is Eastwood's excuse?" Variety commented that, "This film is so awful it's almost as if Eastwood is using it to find out how far he can go—how bad a film he can associate himself with."
The soundtrack has many popular country music hits, including the title track "Every Which Way But Loose", by Eddie Rabbitt, and several numbers by Charlie Rich. Songwriter Snuff Garrett was hired to write songs for the film, including three for Sondra Locke's character, something which proved problematic as Locke was not a professional singer. Locke, who appears as Eastwood's love interest, performs several musical numbers in the film as well. One song Charlie Rich performed in the film, "I'll Wake You Up When I Get Home", hit number three on the charts in 1979 and was Rich's last top-ten single. Mel Tillis sings his own song "Send Me Down to Tucson" in full.