The motorcycles used by the "death squad" cops through most of the movie are Moto Guzzi police bikes. However, British motorcycles (probably Triumphs) were used during the chase scene at the end. These would have been favoured by the stunt riders as they are lighter and easier to handle than the Moto Guzzis.
Clint Eastwood declined the director's seat, and Ted Post stepped in, although interviews with Eastwood and books about him have indicated that he and second unit director Buddy Van Horn actually directed more of the film than Post did.
David Soul's performance as Officer John Davis, one of the vigilante cops, led to his being cast as Detective Ken Hutchinson in the classic cop series "Starsky and Hutch" (1975).
The SFPD range where Harry meets the four "rookies" is in reality the Oakland (California) Police Department's indoor range. It's now closed, partly due to the many "Dirty Harry" fans who kept trying to sneak into it, but mostly due to indoor inhaled lead problems.
Two deleted scenes help explain why Harry grows to suspect John Davis and his pals with the killings of Charlie McCoy and the mobsters. One occurs between the funeral flight for McCoy and the combat championship; after the flight Harry and Davis drive from the airport to a bowling alley for a few drinks; a black youth is suddenly chased outside and assaulted by four toughs; Davis attacks the toughs while Harry dispatches one with his beer mug. After subduing the robbers Davis harangues a group of eyewitnesses for letting such crimes take place; Harry witnesses Davis' harangue and sees in it his own approach to crime fighting, albeit far more severe. Later, after examining the bullet from Davis' gun at the combat championship range, Harry checks on old issues of a police magazine, in which are articles condemning the revolving door justice allowed by liberal politics - articles authored by the four rookie cops. These scenes were deleted presumably because they were judged to be "padding" and not necessary to establishing Harry's suspicion of the four rookie cops.
In the film, Carol McCoy hits on Harry after explaining the circumstances behind her divorce from Charlie. She pulls close to kiss Harry when her rambunctious children's play interrupts them both; a phone call from Earlington Smith to Harry (pertaining to their liquor store stakeout) then forces him to cut short their date and extricates him from a clearly awkward situation. However a publicity photo circulated overseas shows Harry and Carol relaxed and kissing - a different version of this scene where Harry succumbs to Carol's advances was reportedly filmed (and which would have changed the dynamic of Harry's relationship with Charlie) but discarded; it was from this discarded scene that the publicity photo came.
Directly after the scene in the garage where Callahan is threatened by the motorcycle cops, the cycles drove out and every single one of them crashed. Clint Eastwood said, "I've been threatened by the Keystone Kops."
According to writer John Milius, the reason the sex scene with the Asian woman is in the script is because Clint Eastwood received many fan letters from Asian women that contained sexual propositions.
Actor 'Mitch Ryan' plays a character who gets killed during the film. The day his death scene was scheduled to shoot, Ryan was ill. He brought a doctor's note that read Ryan was "too sick to die" that day.