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Brake master cylinder info - Ride/Handling/Suspension/Brakes/Wheels/Tyres - The Lotus Forums #ForTheOwners Jump to content


Brake master cylinder info


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I doubt if you would need to change the master cylinder.

However, the theory is to maintain enough fluid in the system and have a reasonable pedal pressure. Your new calipers will take much more fluid but it is only the amount of fluid required under braking that you need to contend with.

I am sure there must be a mathematical formular to work this out but I do not know it.

As a suck it and see I would fit the calipers with new pads and bleed the system.

Make up some spacers the thickness of the pad backing plates. Remove the pads and fit the spacers pump the system until the spacers are tight. Check the fluid reserve. If you still have plenty of fluid then the capacity is fine.

Refit your pads.

Next check your pedal pressure if you find this acceptable then your existing master cylinder is fine.

If too heavy then you need to look at a different bore size. For example if 3/4" go to 7/8" for a lighter pedal pressure or vice versa.

To save a lot of convertion work on the car there are specialists who can over bore and sleeve an master cylinder.

Having said all this perhaps you should contact AP Racing and ask what their advice would be.

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Great post dixi4uk. I didn't think  brake fluid capacity at all. Actually I know how to calculate master cylinder size but just wanted to know what is the stock diameter for Evora master cylinder to get into right ball park. It probably reads in casting. My current is 7/8 and there is also 15/16 available for my car. 
 
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In brake sizing you would normally start from finding out Center of Gravity and calculate weight transfer in braking. Then you would know how much braking force you need in each wheel. But lets not get into that because I can't use dual master cylinders. For hydraulic leverage ratio you'll need to calculate piston areas. Evora front calipers have 39mm and 35mm pistons. You need only calculate area from one side because opposing force is the same. Combined that's 2156mm^2 and master diameter is 22.22mm = 388mm^2. If you divide caliper area with master area you'll get ratio of 5.56. My stock brakes have single 51.5mm piston and area of 2083mm^2 and that would be ratio of 5.37 so there isn't big difference. Of course there is pedal leverage and brake booster in top of this.
 
If someone can check diameter from Evora master cylinder I would still appreciate it.
 
 
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You seem to be on top of the mathematical formulae. My post to you was just pure logic. The bit regarding capacity is just safety related. For instance if someone ran all the pads down to the backings would there still be enough fluid in the system. This I would think is a total impossibility in real life but the safety factor has to be considered.

I can not help regarding Evora cylinder sizes as I do not own one.

May I suggest a Lotus specialist for the original spec and to answer why there are two sizes.

My call would be PNM in Merseyside. The owner is Peter and very knowledgable. He is a man of few words, don't let that put you off. You will find his number on the internet.

Were AP racing any help?

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