I have a friend who purchased a 1926 model T touring with a ruckstel. He has owned the car for about a year. This past Summer the car developed a problem in that when he applies the brake fairly hard and holds the pedal in, it seems like the band grabs hold real hard, then it loosens up than grabs then looses and just as the car is about to stop it feels like the band locked on the drum. I went to see the car and I removed the brake band. It has kevlar linings and looked perfect. There were no cracks in the drum that were visible and hardly any lint in the lint screen. I put the band back in but I suspect there must be something in the transmission. I jacked the car up and could turn the rear wheels and could not hear any noises coming from the rear. Do you have any idea what might cause the symptom described above?
With the band removed, jack up the rear end and turn over the engine with the crank and the car in gear. If you have a dial indicator, use it, if not just use something that will tell you if the drum is turning true. Have someone turn over the engine while you look at the drum. It could be warped or cracked internally where you can't see it.
Are the ring and pinion jumping teeth?