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MG TD TF 1500 - Master Cylinder Stroke

Does anyone know what the length of the stroke might be for the TD/TF brake master cylinder? I am asking about the length of movement of the bottom of the brake pedal under normal braking conditions with fully operational brakes.
Jim Merz

Can't be certain about TD, but very similar MGA only has 1.1" stroke used (empty system). That's pretty typical. So your "fully operational" system should be moving less than 1/4" (= about 1/4 of pedal travel) at the MC cylinder, if all is adjusted correctly.

FRM
FR Millmore

Thanks FRM. I am really surprised that it is such a small amount of movement. I wonder if it is the same on the TDs and TFs? On our cars, that area is pretty well boxed in so it is very difficult to measure when the car is fully assembled.
Jim Merz

All brake parts are the same for TD/TF, so no difference.

The stroke is typical of all MC I have investigated while looking into conversions of various sorts. A clear case of convergent design; it's what you need to do what has to be done, and still keep the parts at reasonable dimensions/tolerances/performance.

FRM
FR Millmore

So, as I understand what you are saying is that most MC strokes are about the same as what you first indicated? At least on MG cars? My sentence asking (I wonder if it is the same on TDs and TFs) really was asking if these two T cars have about the same effective piston stroke to stop the car as an MGA.
Jim Merz

"...most MC strokes are about the same as what you first indicated? At least on MG cars?"
>> Yes, and in fact on most cars. It is all tailored to the human leg and the required and practical design parameters of braking systems. If you designed for a longer stroke, response time and seal wear would increase a lot, while shorter stroke would make wear and mechanical tolerances more critical. FI, the MGA is nearly identical to my Mazda 323/Protege, same size M/C and same travel. The MGA comes with either front drums or discs, with rear drums. The Mazda comes with front discs and either drums or discs in the back, and has a booster. Bigger vehicles, like older American cars or pickups, tend to have everything bigger, but it still needs to work out the same at the pedal. My leg is the same in any of these cars.

"My sentence asking (I wonder if it is the same on TDs and TFs) really was asking if these two T cars have about the same effective piston stroke to stop the car as an MGA."
>>>The rear cylinders on T & A are the same, and the fronts are either the same size (7/8") or one size off. There are the same number of each, and the same brake design, so the fluid displacement required is the same or very close. The MGA MC is 7/8" bore, and I think the T is as well, but not certain. It is not far from it though. All that means the hydraulic ratio is the same, so the pedal mechanical ratio needs to be the same to keep pedal force in human range.

FRM
FR Millmore

Many thanks for your explanations. I appreciate it.
Jim Merz

This thread was discussed between 09/03/2012 and 11/03/2012

MG TD TF 1500 index

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