Cut open a clogged brake hose

Joined
Feb 26, 2009
Messages
342
Location
Upstate NY
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.

20201201_203239.jpg


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.
20201201_204542.jpg

20201201_204819.jpg
 
Perhaps swapping to upgraded performance broke hose would benefit...maybe stainless fittings? The region you're in, I'm sure rust is an absolute nightmare for repair shops.
 
Never cut one open before all the ones I’ve replaced I’m guessing fell apart on the inside. My truck still has the original 31 almost 32 year old brake hoses on it I have replacement ones but the others are seized on there.
 
I'd say this is precisely the reason that Mercedes Benz calls for "Brake Fluid Replacement" every 20,000 miles.
(Rolls Royce calls for brake hose replacement every 100,000 miles)
Another option would be to switch to silicone brake fluid early on, but that's not normally called for by the manufacturer.
 
Thanks for the cut & post.
Could be a common problem for vehicles driven in the snow for 20 years.

I think most of this problem could be solved by;
1) Changing the Brake Fluid every two years
2) Oil undercoat the vehicle

My Rubber Brake Lines will be 19 yo this Summer and I was already planning on changing them.
 
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.

View attachment 35727

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.
View attachment 35729
View attachment 35730
Wow thanks for posting pics. Incredible evidence for replacing brake lines due to age and condition.
 
Fluid film is supposedly safe for rubber parts. I get the important cavities of my undercarriage, including the backside of my brakes, mostly to keep the bleeders free, but to protect all the hardware. I get the hose-end doing this.
 
Thanks for posting. All I can say is WOW I flush my brake fluid on a regular basis; and I use plastic hose pliers to temporarily squeeze the rubber lines while opening the bleeder valve and forcing the wheel cylinder to seat. I want the old fluid to come out the bleeder valve, not return to the master cylinder. I've never even fantasized lines corroding like this. Nice documentation. Thanks for pics.
 
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