We recently had our friends from CRP Industries drop in to our FCP office, and they showed us something that I thought was really important to point out. Like most other maintenance items on your vehicle you should always replace your brake hoses in matched pairs, left and right. This point was illustrated when we were shown cutaways of a new brake hose vs and old brake hose which suffered an internal collapse. More on that later though.
Many prefer to stick with OE
Rubber brake hoses are prone to dry rot and other types of wear. Many people don't replace brake hoses until they can see external problems such as cracking or dry rot. However, the failure of rubber brake hoses can occur well before signs are seen on the surface. Personally, I'm not a fan of rubber brake hoses and prefer to upgrade to braided stainless steel hoses due to their service life length and performance benefits. However, many out there prefer to stick with OE style rubber hoses because they are more affordable and they are not a common replacement item. One interesting thing to note about the construction of the inside of rubber brake hydraulic hoses is they are layered. Your average rubber brake hose has 3 layers of material which provide strength and protection.
The failure can occur with no external signs
If your brakes are feeling spongy and the entire brake system seems to be in good shape (no leaks) look at your brake hoses. Dry rot and/or cracking of the other layer is an easy problem to spot. What is not easy to determine is if the inside of the brake hoses are suffering from an internal collapse. What I mean by an internal collapse of a brake hose is when the internal diameter decreases significantly due to degradation of the inner most layer. This failure can occur or begin without showing signs of failure externally. There is no set interval for brake hose replacement so with that said I recommend replacing your brake hoses when the pedal feel becomes spongy despite the rest of the braking system being in great condition and bled properly. The spongy feeling is most likely contributed to the inner diameter of the brake hose collapsing. This point is well illustrated with the images below.
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The lesson here is simple: always replace your brake hoses in pairs. If you don't do so there is a really good chance that you will feel an uneven amount of braking force via brake dive in the direction of the corner that is not receiving the same amount of input pressure. Essentially a brake hoses that is collapsed internally cannot allow the same amount of brake fluid to travel to brake caliper. The force behind the brake fluid will also not be transferred to the brake caliper. Inspecting brake hoses and replacing them in cheap insurance and it's directly tied into your own personal safety. If you wouldn't replace a single control arm without replacing the adjacent side don't do it with something as simple as rubber brake hoses either.
About the Author
Gareth runs the BMW catalog at FCP Euro, he can be reached at gareth@fcpeuro.com
