Brake Servo = Better Brakes?

[Tom Brearley]

I've often read that "a servo doesn't improve the brakes - it just lowers the pedal pressure."

But if I apply (say) 50lb of force on the brake pedal with my leg, then without a servo fitted there will be (say) 100lb of pressure at the brakes. With a servo, my 50lb of pressure would get assistance of (say) 20lb making total pedal pressure 70lb. That would then give 140lb at the brakes.

To me, that seems like an improvement.

What am I missing?

[Mnripley]

Tom don’t think you are really missing anything. If at the 100Ib pressure without servo you can lock up the wheels, then with the servo you would apply less leg pressure. Have tried mine with and without the servo and it doesn’t make a massive difference just less leg pressure for old things like me.

If you want to use your 140Ib then you need to take into consideration tyre’s and road conditions

[Tom Brearley]

Thanks, that makes sense. I'm not sure I can lock up the wheels with just my leg but I'll do some experiments on a suitable empty road.

[Vic Butler]

Unservoed disc brakes need more pedal pressure than unservoed drums because with drums there is a " self servo" by virtue of the rotation of the drum pulling the shoes.
However, I've got a front disc brake conversion on my Series 3 Land Rover and don't find the brakes heavy.