^^ The above problem was also faced by the notorious Shehzore owners, its brake prop valve is angle related, meaning it will release the rear brakes when the rear unloads (hard braking).
These chaps had installed heavier leaf springs in their trucks which raised it and then swayed with the smallest load, Similarly nearly all local corollas are lifted from the back due to CNG, which causes the rear beam axle to swing out of range sometimes.