MTFCA Forum

Model T Braking

As part of our semi-annual mechanical inspection necessary to register the car and use it on the road, the inspector has to test the braking.

A modern version of the 'Tapley Meter' is used. It measures the forces when the brakes are applied using an accelerometer.

Anyway, the minimum reading to 'pass' is "50" (somethings!)

Yesterday my T Roadster locked up the rear wheel with a skid along the seal. Meter reading was "41". "Well.." said the inspector,"you can't rally get better brakes than locking up the wheels" - Result: "pass".

It is refreshing to see there are sensible folk out there!

Best braking is obtained just short of wheel lockup. Ideally, both wheels will lock up at the exactly the same degree of brake application, which will allow the driver to exploit the full available braking capability. Model Ts drivers have access to both the service brake and the parking brakes, and both can be used in emergency situations. Reverse can also be used in emergency situations. Tire condition and pressure affect braking ability, as does vehicle loading and load distribution and road surface characteristics. A T engine tuned to permit a slow idle speed setting prevents needless brake wear and improves overall braking control. It's unlikely that an inspector who is unfamiliar with the Model T, particularly your Model T, obtained maximum available braking on a first or second attempt.

Physics tells you that if you have 2 wheel brakes, 50/50 front/rear weight distribution and no weight transfer under braking (which is impossible), the best you can hope for is 0.5g or 50%.
0.41 is very good.

I think you'd have some "weight transfer" from rear to front.

Somewhere in the past...the late Ralph Ricks delved deeply into this subject as part of his Nash Rambler hydraulic brake project for his yellow pick-um-up truck that was originally in that Great American Race tribute recreation (pre brakes?) I have no luck at searching this forum, even using google search...but I believe that by the time he was done Ralph had disclosed everything anyone wanted to know about the kinematics of braking in a Model T???

(Hoping to jog someones memory)

Pat,
The weight transfer due to braking is a function of braking g's and the height from the road surface to the vehicle center of gravity.

Art Mirtes

... Also torque from braking applied to the rear engine mounts, and any fluids shifting forward. Unicyclists are keenly aware of the dynamic effects of braking, as are motorcyclists.

Or, just politely explain that braking/stopping is over rated, and gets you nowhere. Unfortunately, it may have failed an acceleration test also.

I have an idea Adrian may yet have further revelations from this day...

The initial inspection of my T when I first got it registered was a bit of a joke. The display on the brake tester blanked out because of the Model T's unique ignition system. A somewhat pedantic guy was doing the test and wouldn't give up - so we ended up letting the car roll down a hill with the engine off. The handbrake test easily passed (it's a 26), but the speed at which the car rolled down the hill was not enough for the foot brake test. Eventually he was forced to give up and just pass it, after several hours of trying!
The guy I've used for the annual inspection since then has a bit more common sense.

Unfortunately, it may have failed an acceleration test also.

No brakes never stopped me!

"Cars are meant to go - not stop !"
-Ettore Bugatti, 1922

JohnH wrote: ↑

Sat Oct 15, 2022 6:03 pm

... the speed at which the car rolled down the hill was not enough for the foot brake test...

I'm not surprised, your 'hills' are just an extremely gentle undulation over here!

Otherwise good to hear you've found someone more sensible - better still the WA or Tassie system where there is no annual inspection (or in our case 6-monthly ).

... so, since the originator of this thread won't 'fess up ... rumour has it that his Model T actually had better braking than another vehicle he has, despite it (the T) missing vital suspension and exhaust components

Also, Mr W, apropos our earlier discussion - it's not really how you spell 'really'