2000-2001 Honda S2000 Power Brake Booster: Hissing Sounds, Hard Pedals, and Replacement Secrets
Your definitive guide to diagnosing, replacing, and finding the right used power brake booster for your AP1 Honda S2000.
- A hissing sound from the pedal or a suddenly hard pedal are the primary signs of a failing brake booster.
- A leaking master cylinder is the most common cause of booster failure; always inspect for paint bubbling and fluid stains on the booster before buying a used one.
- It is absolutely critical to adjust the pushrod clearance between the booster and master cylinder during installation to prevent brake drag or a spongy pedal.
- Driving with a failed brake booster is unsafe due to the increased pedal effort and stopping distance required.
- There are no recalls for the 2000-2001 S2000 brake booster; a recall for later models does not apply.
Symptoms of a Failing 2000-2001 S2000 Brake Booster
Brake booster failure on the early AP1 S2000 typically presents with distinct, hard-to-ignore symptoms. Because the booster operates on engine vacuum, failure involves air leaks and a loss of braking assistance.
1. Hissing Sound From the Brake Pedal
The most common and obvious sign of a failing brake booster is a hissing sound that occurs when you press the brake pedal. This sound is air being sucked through a tear or hole in the booster's internal rubber diaphragm. The sound will be noticeable inside the cabin, seemingly coming from under the dashboard near the pedal itself. It may stop once the pedal is fully depressed or released. Do not confuse this with a hiss from under the hood, which could be a simpler issue like a cracked vacuum hose.
2. Hard Brake Pedal
If the booster fails completely, you will lose all power assistance. This results in a brake pedal that is extremely firm and difficult to push. The car will still stop, but it will require significantly more leg strength, which can dramatically increase your stopping distance in an emergency. This symptom often follows a period of hissing noises as the internal leak worsens.
3. Stumbling or Rough Engine Idle
A failing brake booster creates a significant vacuum leak. This unmetered air entering the intake manifold can disrupt the engine's air-fuel ratio, leading to a rough idle, stumbling, or even stalling when you apply the brakes. This condition may also trigger a Check Engine Light with lean mixture codes, such as P0171.
Step-by-Step Diagnosis
You can confirm a failed brake booster with a simple test that requires no tools:
- With the vehicle's engine turned OFF, pump the brake pedal five or six times. This will bleed off any residual vacuum in the booster. The pedal should become firm and hard to press.
- Once the pedal is firm, hold it down with steady, moderate pressure.
- While still holding the pedal, start the engine.
- If the booster is working correctly, you will feel the pedal sink down an inch or two towards the floor as engine vacuum builds and the power assist kicks in.
- If the pedal does not sink or only moves very slightly, the booster is not holding a vacuum and has failed.
Warning: A leaking brake master cylinder is the number one killer of power brake boosters. Brake fluid is corrosive to the rubber diaphragm inside the booster. If you see paint bubbling or peeling on the booster directly below where the master cylinder mounts, your master cylinder is leaking and must be replaced along with the booster.
Buying a Used 2000-2001 S2000 Brake Booster
Given the high cost of new OEM units, a quality used brake booster is an excellent choice for most owners. OEM boosters are well-made and durable, often lasting the life of the vehicle unless damaged by external factors. Here's what to look for:
- Inspect for Brake Fluid Damage: This is the most important check. Closely examine the front of the booster where the master cylinder bolts on. Look for any signs of paint damage, bubbling, flaking, or rust. This indicates the donor car had a leaking master cylinder, which likely damaged the booster you're about to buy. A clean, dry front surface is a very good sign.
- Check the Vacuum Port: Ensure the plastic vacuum hose port is not cracked, broken, or brittle.
- Verify Part Numbers: The correct OEM part for the 2000-2001 S2000 is an assembly that includes the master cylinder, with part numbers like 01469-S2A-E01 or 01469-S2G-951. While aftermarket boosters are sold separately, used OEM parts are typically sold as the complete booster/master cylinder assembly.
- Mileage vs. Condition: While lower mileage is always a plus, the physical condition is more important. A high-mileage booster from a car with a healthy master cylinder is a better bet than a low-mileage one that has been soaked in brake fluid. The internal diaphragm can also fail from age-related dry rot, but fluid contamination is the more common killer.
Replacement Overview and Critical Procedures
Replacing the brake booster is a moderately difficult job that is feasible for an experienced DIY mechanic. The estimated shop labor time is between 2.5 and 3.5 hours.
The basic steps involve disconnecting the battery, removing the master cylinder, disconnecting the booster pushrod from the brake pedal inside the car, and unbolting the booster from the firewall.
Pro Tip: It is highly recommended to replace the master cylinder at the same time as the brake booster, especially if buying a used booster that doesn't come with one. A new master cylinder ensures you won't have a leak that destroys your replacement booster.
CRITICAL STEP: Pushrod Clearance Adjustment
You cannot simply bolt in a new or used booster. The clearance between the tip of the booster's pushrod and the piston inside the master cylinder is critical and must be adjusted.
- Too little clearance (preload): The brakes will drag constantly and may lock up as they heat up.
- Too much clearance: The brake pedal will have excessive free play and a spongy or delayed feel.
Honda specifies a special gauge (Part No. 07JAG-SD40100) for this procedure, but it can be done with careful measurement. The adjustment is made by loosening the star-shaped lock nut on the pushrod and turning the rod end in or out. This step is absolutely essential for brake safety and performance.
| Key Torque Specs | Value |
|---|---|
| Brake Booster Push Rod Lock Nut | 11 ft-lbs (15 N.m) |
| Brake Booster Push Rod Star Lock Nut | 16 ft-lbs (22 N.m) |
| Master Cylinder Mounting Nuts | 11 ft-lbs (15 N.m) |
After installation, the entire brake system must be bled to remove air from the hydraulic lines.
Cost Comparison for S2000 Brake Booster Replacement
| Part or Service | Estimated Cost | Notes |
|---|---|---|
| New OEM (Assembly) | $800 - $1100+ | Often includes master cylinder. Very expensive and may be hard to find. |
| New Aftermarket | $80 - $170 | Booster only. Quality can vary. |
| Used OEM (Assembly) | $125 - $250 | Good value, but inspect carefully for fluid damage. |
| Remanufactured | $150 - $250 | Often includes a core charge. A viable alternative to new. |
| Shop Labor Cost | $220 - $322 | For booster replacement only. |
Known Issues, Recalls, and TSBs
There are no specific recalls or Technical Service Bulletins (TSBs) for the power brake booster on 2000-2001 Honda S2000 models. A recall for a leaking brake booster was issued for 2006-2007 models, but the issue and parts are different and do not apply to the early AP1 cars.
Frequently Asked Questions (FAQ)
Can I use a brake booster from a later S2000 (AP2, 2004+)?
No, the brake systems are different, particularly on 2006+ models which feature Vehicle Stability Assist (VSA). The boosters and master cylinders are not directly interchangeable. You must use a booster specified for the 2000-2001 model years.
What about using a booster from a Civic or Integra?
While some Honda enthusiasts swap boosters from cars like the Integra Type R, this is a modification, not a direct replacement. It may alter the pedal feel and require modifications to fit. For a standard repair, it is best to stick with a direct-fit S2000 part.
Do I have to bleed the brakes after replacing just the booster?
Yes. Because you must remove the master cylinder to access the booster, the hydraulic lines are opened, allowing air to enter the system. You must perform a full brake bleed procedure, starting with the caliper furthest from the master cylinder, after the new booster and master cylinder are installed.
Is a hissing brake pedal always the booster?
If the hiss is loud inside the car and happens when you press the pedal, it is almost certainly the booster's internal diaphragm. A hiss from under the hood could be a less serious cracked vacuum supply hose. A simple diagnostic test can confirm the booster is the problem.
Technical Specifications
OEM Part Numbers: 01469-S2A-E01 01469-S2G-951 01469-S2A-000
System Type: Vacuum Assist. The booster and master cylinder are typically serviced as a single assembly under the OEM part numbers.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Honda S2000:
- Symptoms of a Failing 2000-2001 S2000 Brake Booster
- 1. Hissing Sound From the Brake Pedal
- 2. Hard Brake Pedal
- 3. Stumbling or Rough Engine Idle
- Step-by-Step Diagnosis
- Buying a Used 2000-2001 S2000 Brake Booster
- Replacement Overview and Critical Procedures
- CRITICAL STEP: Pushrod Clearance Adjustment
- Cost Comparison for S2000 Brake Booster Replacement
- Known Issues, Recalls, and TSBs
- Frequently Asked Questions (FAQ)
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