2000 Mazda MPV, Driver Side
The brake hose in question is the flex hose in the wheel well that connects the hard line to the brake caliper. It lives in a harsh environment (whatever the wheel throws at it) esp in upstate New York where salt is used every winter.
The hose is OEM original. It has been on car for almost 21 years. Car developed a condition in middle of 2020, in which the steering wheel jerked when the brake was sharply applied. The steering jerked to the right on the 1st sharp apply of the brakes, but then the jerk went away on subsequent braking.
The brake rotors are rusted due to lack of driving during COVID pandemic. So I put on new rotors and pads. Caliper pistons are easily pushed back (almost too easy with fingers, on both driver and passenger side) during the rotor/pad replacement. I suspected a minor leak inside the piston over the piston seals. New rotors/pads did not fix the steering jerk, so new calipers are in order. Current calipers were aftermarket reman units, being on car for many years.
New calipers (both sides) somehow reduced the steering jerk (condition mention above) but did not completely cure it. During the caliper replacement, I noticed that the driver side brake hose did not gravity bleed. One drop every minute or so. The passenger side hose has a constant dripping. There is obviously a clog somewhere. Brake fluid can still go thru under pressure (steady stream). Betting it’s in the flex hose and I replaced it. Indeed, the culprit was the flex hose and it fixed the steering jerk issue.
I am curious where and how the hose is clogged so I cut it open. I first cut the hose in segments and checked each segment. All was well except for the segment in the middle where the attachment fitting is (the fitting is clamped on the hose so the hose can be attached to the strut, indicated by the small screw driver in picture below). During the caliper replacement time, I tried to run a weed-whacker line thru the hose but could not pass this point. Now it is 100% confirmed.
I further cut the fitting in half longitudinally, exposing the inside of the fitting and hose. Upon cutting it open, the root cause lays bare. The rust that grew inside of the fitting squeezes the hose and caused the inner tube of the hose to collapse and surrounding fabric “grew” into the inner tube space. Fluid can still go thru under pressure, but it would delay the apply of the brake on driver side. This explains why the initial jerk is toward the right, and it also explains subsequent braking does not have severe jerk because the fluid has been forced out already. See pictures below. The second picture shows how thick the rust was on the inside of the fitting.
Food for thought… how do you prevent (or delay rather) this from happening? Shove some rubber friendly grease in the opening of the fitting? A better design – sure, but this setup seems to be the industry norm.
The brake hose in question is the flex hose in the wheel well that connects the hard line to the brake caliper. It lives in a harsh environment (whatever the wheel throws at it) esp in upstate New York where salt is used every winter.
The hose is OEM original. It has been on car for almost 21 years. Car developed a condition in middle of 2020, in which the steering wheel jerked when the brake was sharply applied. The steering jerked to the right on the 1st sharp apply of the brakes, but then the jerk went away on subsequent braking.
The brake rotors are rusted due to lack of driving during COVID pandemic. So I put on new rotors and pads. Caliper pistons are easily pushed back (almost too easy with fingers, on both driver and passenger side) during the rotor/pad replacement. I suspected a minor leak inside the piston over the piston seals. New rotors/pads did not fix the steering jerk, so new calipers are in order. Current calipers were aftermarket reman units, being on car for many years.
New calipers (both sides) somehow reduced the steering jerk (condition mention above) but did not completely cure it. During the caliper replacement, I noticed that the driver side brake hose did not gravity bleed. One drop every minute or so. The passenger side hose has a constant dripping. There is obviously a clog somewhere. Brake fluid can still go thru under pressure (steady stream). Betting it’s in the flex hose and I replaced it. Indeed, the culprit was the flex hose and it fixed the steering jerk issue.
I am curious where and how the hose is clogged so I cut it open. I first cut the hose in segments and checked each segment. All was well except for the segment in the middle where the attachment fitting is (the fitting is clamped on the hose so the hose can be attached to the strut, indicated by the small screw driver in picture below). During the caliper replacement time, I tried to run a weed-whacker line thru the hose but could not pass this point. Now it is 100% confirmed.
I further cut the fitting in half longitudinally, exposing the inside of the fitting and hose. Upon cutting it open, the root cause lays bare. The rust that grew inside of the fitting squeezes the hose and caused the inner tube of the hose to collapse and surrounding fabric “grew” into the inner tube space. Fluid can still go thru under pressure, but it would delay the apply of the brake on driver side. This explains why the initial jerk is toward the right, and it also explains subsequent braking does not have severe jerk because the fluid has been forced out already. See pictures below. The second picture shows how thick the rust was on the inside of the fitting.
Food for thought… how do you prevent (or delay rather) this from happening? Shove some rubber friendly grease in the opening of the fitting? A better design – sure, but this setup seems to be the industry norm.