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Race Car Brake Lines Do's and Don'ts - Motorsport Tech Session

American Government Special Collections Reference Desk

Race Car Brake Lines Do's and Don'ts - Motorsport Tech Session

Grant Loc
September 2, 2011


Hello, how are you today?

This article will give you the information you need to make sure you have the best race car and motorsport brake lines in you car you can.

The brake lines operate and function as a blood system does in the human body. As in the human body there are some very pertinent facts which should be adhered to that will enable the blood to flow correctly and deliver good blood circulation.

Never route the brake lines near to the exhaust or any other heat source. This will raise the brake fluid temperature which is the enemy in maintaining positive brakes. In Motorsport the brake fluid temperature level will be increased due to hard braking, the heat is created from the brake pads friction when they are forced against the rotors. This heat is transferred by the calipers into the fluid and will give you Brake Fade. Adding any extra heat sources is a very bad design fault you want to be aiming to cool the fluid as much as possible.

Never route the brake lines in a way that will trap air for example in a loop, kink or high points. If you install the brake lines with any of these faults you will increase the chance of air being trapped. Air will give a very spongy pedal and not transfer the pressure you are exerting via the pedal to the calipers. This is due to the air in the system compressing. When a solid brake fluid line has been created you will have no air to compress, giving you a nice solid brake pedal.

Always use top spec brake lines. A good material to use are Steel lines these will give you a strong and durable brake line with next to no expansion. The Steel brake lines can also be cost effective. I am aware there are St/St braided lines available, but my advice is to use these to a minimum. Unless you have paid for the best flexi lines you may experience line expansion problems. Steel has the highest modules of elasticity of any material you can source for brake lines, thus helping to prevent line expansion. St/St Braided Flexi lines are fine for the feed side and to connect the main lines to the calipers.

The rigidity of the brake lines is very important and I feel we need to talk about this in more detail. With the correct brake lines you will get the force you exert on the brake pedal plus the ratio increase (Ratio increase is typically 5:1 or 6:1) and impact that pressure directly to the brake caliper.

If you use that force you have created by the pedal and the ratio increase in an expanding brake line you will loose the force created and not apply the correct pressure to the caliper. If you have installed a system where this is taking place you will not have an affective braking system and will not stop the car correctly. In the worst case the driver will use all the available travel in the pedal so the Master Cylinder piston has bottomed out in the cylinder bore, and still not have the brakes required!

By making the brake lines as rigid as possible will give you very little expansion and constantly deliver a strong and reliable brake every time you need it.

There is a myth that states if you install larger lines to the front from the rear this will alter the proportion braking force from front to rear. This is fallacy. Pressure is independent of the volume or area, so a 3/16 " I.D line to the front wheels will deliver the same pressure (PSI) as a 1/8" I.D line to the rear wheels.

The very important and vital rigidity and non expansion brake lines as we have talked about needs to be carried into the Flexi lines to the calipers. Only high quality St/St Braided flex hose should be used to carry the brake fluid to the calipers. Using a quality flexi St/St braided will give you the positive assurance that little pedal travel, pressure or work effort will be lost through line expansion. This is imperative when you are using a disc brake system where line pressures are much higher than in drum brakes.

Hose Specification

Liner: PTFE according to "ISO 12086, Part 1 PTFE-EPDM 1, 6.1.CE.4.1.2"Braid: AISI 304S15 Hard Drawn Stainless Steel Wire Working Temperature Range: Minus 60 Degrees C to Plus 260 Degrees C Maximum Allowable Elongation At Working Pressure - 4 % to + 2 % Work pressure rating 1500 PSI

Please note there are many types of flexi hoses so make sure you get the correct specification for your requirements.

One final area I would like to discuss is never assume that the brake Lines / Flexi Hoses you purchase are clean. To be 100% sure that there is no dust, grit or any other impurities in the hoses pour clean brake fluid through them to be sure the smallest amount of moisture and dirt are removed.

Thank you for your time reading this article, I hope it has been useful to you.


Grant Loc has been involved with Motorsports for over 15 years and the Director of obp Ltd. obp Ltd is a major player in Manufacture and Supply of Quality Race Car Products and provides most of the leading Motorsport distributors all over the World. obp manufacture Race Car Pedal Boxes, Handbrakes, Alloy Dry Oil Sump Tanks, etc. www.obpltd.com



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