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Pelican Technical Article:

Brake Hose Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$14 to $40

Talent:

**

Tools:

11mm, 14mm flare wrenches

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

New brake hoses, brake cleaner

Hot Tip:

Spray penetrating lubricant on the hose threads, ideally a few days before replacing the hoses

Performance Gain:

More dependable braking

Complementary Modification:

Flushing brake fluid, changing brake pads

Most drivers don't realize that rubber brake hoses are like tires: Over time, they degrade and fail. Rubber is also porous and brake hoses can allow moisture to permeate and degrade fluid over time. Contaminated brake fluid can also rot hoses internally. Consequently, glycol-based brake fluid should be fully flushed about every two years.

Unfortunately, brake hose degradation is seldom obvious. Hoses rarely seep or burst, unless they're subjected to impact or constant abrasion. Should this happen while driving, all pressure is lost to the failed hose's axle. Modern vehicles have dual-reservoir master cylinders so that the other axle's brakes will still work should a hose burst.

More common is that a hose's inner ply flakes away. The resulting shrapnel can act as a check-valve, causing the caliper to stick -- fluid is blocked from returning to the master cylinder. Accumulated inner-ply debris can even plug the line. Pedal feel is still firm, but fluid can't get to the calipers' pistons. Ergo, the brakes don't work properly.

Further, age and heat can cause hoses to swell which can mean lost hydraulic energy and a spongy pedal feel.

These days, enthusiasts often have a choice of OE-style rubber brake hoses or race-inspired braided-steel ones. When originally introduced, braided-steel hoses weren't DOT-compliant for street use because they didn't pass the Federal Motor Vehicle Safety Standard "whip" test: not leaking under a shock load where the flexile hose is attached to the rigid leader ends.

Pelican Parts offers DOT-approved braided-steel hoses for many applications. Performance-wise, their inner plies are still rubber. Enthusiasts often report a firmer pedal feel when using braided steel hoses. This style is supposedly less susceptible to swelling, which would make fluid flow more consistent.

If nothing else, the steel over braid protects against external abrasion, weather and road debris.

Always replace your brake lines in pair; front or rear axles and since you have to flush the system either way it might be easier in the long run to do all four at the same time.

Note: after replacing the lines you MUST bleed the brake system. DO NOT attempt to drive the vehicle before properly bleeding the brake system. Please see our article on bleeding you brakes for help.

Liberally coat the hose fittings at both the chassis bracket and caliper with penetrant.
Figure 1

Liberally coat the hose fittings at both the chassis bracket and caliper with penetrant. Then let the penetrant penetrate for at least a day, if possible.

Ideally, the hard line's male nut unscrews from the hose's female fitting with a flare wrench (this rear hose uses an 11mm wrench), which helps prevent the nut's shoulders from rounding off.
Figure 2

Ideally, the hard line's male nut unscrews from the hose's female fitting with a flare wrench (this rear hose uses an 11mm wrench), which helps prevent the nut's shoulders from rounding off. OE-style hoses have two ribs ("stamped lugs" in manual jargon) that steady it in the bracket. If the existing hose lacks these or twists in the bracket, "back up" the hose with channel locks or locking pliers while turning the nut with the flare wrench.

With the retaining tower rotated a quarter turn, the line's flared end and nut's thread are visible.
Figure 3

With the retaining tower rotated a quarter turn, the line's flared end and nut's thread are visible. The bracket has two slots that correspond to ribs on the OE hose's female end.

We'd previously removed the caliper for a different article, but it can remain mounted for hose replacement.
Figure 4

We'd previously removed the caliper for a different article, but it can remain mounted for hose replacement. Once the hose is free from the hard line, it can be unscrewed from the caliper using a 14mm flare wrench.

Brake hoses can accumulate dust and condensation during storage and transit.
Figure 5

Brake hoses can accumulate dust and condensation during storage and transit. Blow out new lines (ideally with air that's run through a moisture-separator) prior to installation.

In addition to new hoses (which should really be replaced in pairs if not all four), 11mm and 14mm flare wrenches are also needed.
Figure 6

In addition to new hoses (which should really be replaced in pairs if not all four), 11mm and 14mm flare wrenches are also needed. (They're shown here with their combo-wrench counterparts). Plugs help keep grit out of the steel brake line and caliper while the hose is being changed. Penetrating spray, a pan for containing leaked brake fluid, brake cleaner and fresh brake fluid will also be needed.

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