Hissing sound when braking = bad seal between brake booster and master cylinder
Thread Starter
Joined: Sep 2004
Posts: 8,631
Likes: 191
From: Las Vegas, NV, USA
Hissing sound when braking = bad seal between brake booster and master cylinder
Just an FYI for everyone. If you find your car suddenly making a hissing sound when the brakes are applied, it's most likely due to the failure of the rubber seal between the master cylinder and the booster. A VERY EASY FIX! I found this out in this thread in the EF/CRX forum...
Link----> https://honda-tech.com/forums/honda-...-hiss-1821190/
According to the near useless "Brake Booster Leak Test" in the helms manual, I had a bad brake booster ($80 to $150 to replace without core charge + several hours to change). Glad I found that thread cause it only cost me $6 for the seal at the local dealership and the install only took a couple minutes.
Steps I took in my 94 CX:
- Un-bolt the Master Cylinder and pull it forward off the booster (plenty of flex in the brake-lines)
- Dig out the rubber seal out of the booster and inspect it (mine had multiple chunks missing)
- Clean the pushrod and re-lube it's surface with a thin layer of silicone grease (I used sil-glyde brake caliper grease)
- Lightly lube the inner radius of the new seal
- Slide the seal over the MC's pushrod (seal is marked with "MP" on the side that faces the booster)
- Bolt the MC back in place
- Start the car and check for leaks.
Image of the part in question and where it goes (mine was part# 46185-SE0-003):
Link----> https://honda-tech.com/forums/honda-...-hiss-1821190/
According to the near useless "Brake Booster Leak Test" in the helms manual, I had a bad brake booster ($80 to $150 to replace without core charge + several hours to change). Glad I found that thread cause it only cost me $6 for the seal at the local dealership and the install only took a couple minutes.
Steps I took in my 94 CX:
- Un-bolt the Master Cylinder and pull it forward off the booster (plenty of flex in the brake-lines)
- Dig out the rubber seal out of the booster and inspect it (mine had multiple chunks missing)
- Clean the pushrod and re-lube it's surface with a thin layer of silicone grease (I used sil-glyde brake caliper grease)
- Lightly lube the inner radius of the new seal
- Slide the seal over the MC's pushrod (seal is marked with "MP" on the side that faces the booster)
- Bolt the MC back in place
- Start the car and check for leaks.
Image of the part in question and where it goes (mine was part# 46185-SE0-003):
Last edited by 94eg!; Aug 10, 2016 at 05:48 PM.
Trial User
Joined: Sep 2016
Posts: 1
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re: Hissing sound when braking = bad seal between brake booster and master cylinder
Just an FYI for everyone. If you find your car suddenly making a hissing sound when the brakes are applied, it's most likely due to the failure of the rubber seal between the master cylinder and the booster. A VERY EASY FIX! I found this out in this thread in the EF/CRX forum...
Link----> https://honda-tech.com/forums/honda-...-hiss-1821190/
According to the near useless "Brake Booster Leak Test" in the helms manual, I had a bad brake booster ($80 to $150 to replace without core charge + several hours to change). Glad I found that thread cause it only cost me $6 for the seal at the local dealership and the install only took a couple minutes.
Steps I took in my 94 CX:
- Un-bolt the Master Cylinder and pull it forward off the booster (plenty of flex in the brake-lines)
- Dig out the rubber seal out of the booster and inspect it (mine had multiple chunks missing)
- Clean the pushrod and re-lube it's surface with a thin layer of silicone grease (I used sil-glyde brake caliper grease)
- Lightly lube the inner radius of the new seal
- Slide the seal over the MC's pushrod (seal is marked with "MP" on the side that faces the booster)
- Bolt the MC back in place
- Start the car and check for leaks.
Image of the part in question and where it goes (mine was part# 46185-SE0-003):
Link----> https://honda-tech.com/forums/honda-...-hiss-1821190/
According to the near useless "Brake Booster Leak Test" in the helms manual, I had a bad brake booster ($80 to $150 to replace without core charge + several hours to change). Glad I found that thread cause it only cost me $6 for the seal at the local dealership and the install only took a couple minutes.
Steps I took in my 94 CX:
- Un-bolt the Master Cylinder and pull it forward off the booster (plenty of flex in the brake-lines)
- Dig out the rubber seal out of the booster and inspect it (mine had multiple chunks missing)
- Clean the pushrod and re-lube it's surface with a thin layer of silicone grease (I used sil-glyde brake caliper grease)
- Lightly lube the inner radius of the new seal
- Slide the seal over the MC's pushrod (seal is marked with "MP" on the side that faces the booster)
- Bolt the MC back in place
- Start the car and check for leaks.
Image of the part in question and where it goes (mine was part# 46185-SE0-003):
Thread Starter
Joined: Sep 2004
Posts: 8,631
Likes: 191
From: Las Vegas, NV, USA
re: Hissing sound when braking = bad seal between brake booster and master cylinder
The sound was coming from the engine bay. When I had my daughter apply the brakes with the engine running, I felt around the seam between the booster & master. I could feel the air rushing past my finger tips on the underside. If your leak is where the pushrod enters the booster (in the footwell), then the entire booster will have to be replaced. They are not serviceable. 
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