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MG Midget and Sprite Technical - Servo and 4 discs

I recently fitted rear discs to my midget to assist with on-track melting of rear shoes, along with a general rear axle update with LSD etc

I've just finished fitting a servo to my Midget. What a difference. It now stops better than anything else I've ever driven. The extra braking power has come from the fact that I am able to lock the wheels, which I couldn't before the servo. This is due to the bigger master cylinder needed to shift enough fluid for 4x disc calipers. It did work (and was thoroughly tested at a track day at Anglesey) but was putting a massive amount of stress into the pedal box and surroundings. It was only a matter of time before I bent something. This is better. And easier to drive.

I got it from Minispares - their single line servo kit - and it's fitted under the driver's side wing.

Probably unnecessary for a standard car but it's transformed mine from having enormous pedal effort required to not.
Rob Armstrong

I think you will find that you could have reduced the pedal effort by fitting a master cylinder with a different size bore that would have got the job done with less pedal effort. However, that would not have matched the difference that servo assistance can provide. I also think it's preferable to be able to brake hard without pushing your whole body back in the seat as you stand on the pedal! While a lot of people decry the servo, I suggest they have to consider there's a reason they were invented and reason they have stood the test of time. I also think a stab on the brakes with a servo is more effective than a stab on the brakes without as your leg muscle doesn't give it full stab as instantly as the servo does.

I'am assuming you have some sort of adjustable brake bias.

Not least if you get chance to roller brake test the brakes (an MOT station will do this for a non road car for a small fee) I'd be interested in the results (though I see from my records you have shared data before - MOT tester was a big chap). My car was tested yesterday and was 200 on each of the fronts and 150 on each of the rears = 700. I've see more than this before before interestingly when the car also weighed more.
Daniel

Hi Daniel. Yep, I could have reduced pedal effort with a smaller mc. In fact the first version with 4 discs used the original mc. Pedal travel was very long, it just couldn't shift enough fluid to apply the brakes fully. It would lock up, but wouldn't with carpet behind the brake pedal - a bit too close for comfort.

Hence the bigger mc to shift more fluid, with the downside of fairly mega pedal effort.

I think with 4 disc calipers there is a real need for a servo, or for messing about with the pedal pivots to get the standard mc to work. That'll still result in a harder pedal though.

I didn't manage to get brake readings this last MOT, but the mgf calipers pulled 35% handbrake efficiency on whatever the book weight is.

There's a proportioning valve in there too. It doesn't need much, and did a whole track day without one without incident.
Rob Armstrong

This thread was discussed between 14/04/2017 and 15/04/2017

MG Midget and Sprite Technical index

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