...Straight-trucks rented to fleets by RYDER? Can someone tell me the difference between a push-rod and slack adjuster located on the brake drum? Plus what is there main objective? Is it the brake cylinder that is located on the axles? Plus, if you know where the Air Compressor is located at under the hood and what it looks like that would be tremendously helpful? If you could send me a link to a picture of them, that would be awesome?