Mechanics

Brake Flex Hose

A brake flex hose is designed to transfer hydraulic force from the car frame to the brake caliper, wheel cylinder or junction block. Brake flex hoses are also used on some hydraulic clutch systems. The purpose of a flex hose is to allow movement of the suspension and steering systems of the car. These components move as the car is being driven over bumps and as steering action is performed. These brake flex hoses are constructed with specialized rubber, reinforced with nylon. Some brake hoses include a Teflon tube used as an inner liner for added strength. All brake flex hoses should be inspected whenever a car service is performed. 

If brake fluid is present at any part of the brake flex hose it should be replaced immediately. Once the brake hose been replaced follow normal brake system bleeding procedures. These hoses are connected at either by a double flare fitting and a copper sealing ring. It is recommenced that the copper sealing washer be replaced anytime you disconnect or reconnect a brake flex hose. The double flare does not need to be replaced when service is performed, but the flare does need to be clean before re-assembly. It is recommended using a semi boxed end wrench (flare nut/line wrench) when servicing the brake flex hose. This wrench is made to grab the fitting more efficiently to avoid stripping the hex fitting.

Brake Flex Hose
Brake Flex Hose

It is recommended using a flare nut/line wrench when servicing the brake flex hose. This wrench is made to grab the fitting more efficiently to avoid stripping the hex fitting.

Line Wrench
Line Wrench Used for Brake Lines

A brake hose can cause one of the hardest to find problems known to technicians everywhere. When a brake hose malfunctions internally it can cause a small part of the inner hose liner to become dislodged and act like a one way check valve that will either hold full brake pressure from getting a particular wheel or not allowing the brake pressure to bleed off. This condition with cause the brake to not work as hard as the other wheels or cause the wheel to drag and not fully release. Either of these conditions will cause a brake pull condition. If you suspect this problem use a pocket IR thermometer laser temperature reader. Drive the car for a short distance with repeated braking then park the car and use the pocket IR thermometer to test each wheel. 

You must test each wheel in the exact same place (I like to use one lug nut on each wheel). You are monitoring temperature differences from side to side, not from front to rear. Front to rear temperature differences are normal, side to side is not. (both front or both rear wheels) If a measurable amount of temperature differences exists replace both brake hoses involved. (Note: most brake pull problems of this nature are front brake related). Example: if both front wheels are tested and the right temperature reading is 190 degrees and the left side is 80 degrees, there is a problem with the 80 degree brake side.

Pocket IR Thermometer Laser Temperature Reader
Pocket IR Thermometer Laser Temperature Reader

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-18)