Would there be any concern if you had to go down a 6%-7% grade that was 7 miles long in your T? Would the car hold back enough to keep from using the brakes up?
The truck driver rule is use the same gear going down that you use going up!!!
Les is right. What's important is to not get going too fast. As long as you use the engine to maintain an appropriate speed you should be fine.
On the tour in Kingman earlier this year, we drove over to Laughlin by the Colorado River. There is a long, long grade down to the river with traffic lights at the bottom. All the Ts managed it with no drama by running down on compression and no allowing the speed to build up. You just have to be careful and not go too fast.
Guess you are not talking about the TT in your profile. I have gone down roads that I am sure were more then 7% with curves but not as long in high. I know in my gut I was borderline on going too fast. Things to take into consideration; how slow can you go to be safe with the amount of traffic and what is your passenger load? The T engine is low compression so the amount of engine braking is not great. If you are crawling down that road in low with a line of cars behind you and no place to turn out..I think you get the picture.
Also, retarding the spark helps.
Does the car have outside brakes or Ruckstell/Warford/other transmission? Which ever brakes it has, you don't want to keep pressing the pedal the whole time. On/off so they have time to cool/get oil. What condition is the front end in?
What Les and Henry said; keep speed and control and you should be fine.
Depends on where you are, the speed limit, and the amount of traffic. There is a mile downgrade between here and El Cajon. I can go up about 25 MPH in high gear. I go down in high and go about 40 MPH. I give it enough gas to go about 40. It would only go about 25 if I didn't give it any gas. It is a country road. I also have Rocky Mountain brakes. There is no signal or stop sign along the way and the only possible need to stop would be something unexpected. The road parallels the interstate highway which has signs posted 6% grade. Don't retard the spark unless you want to blow the muffler. Maybe you could retard just before coming to a stop, but if you have a smooth slow idle, just push the throttle all the way up.