Brake Booster Vacuum Line. Porsche 997 / 987 Boxster / Cayman 2005–13  ›  99735557101

The Genuine Porsche Brake Booster Vacuum Line is an important part of the vacuum-assisted braking system used on selected Porsche 911 (997) models.

Fits:

• Porsche Boxster 987 2.7L 2005-08/08
• Porsche Boxster 987 S 3.2/3.4L 2005-08/08
• Porsche Boxster 987 MKII 2.9L 2009-12
• Porsche Boxster S 987 MKII 3.4L 2009-12
• Porsche 997 MK1 Carrera 2 3.6L 2005-08
• Porsche 997 MK1 Carrera 2S 3.8L 2005-08
• Porsche 997 MK1 Carrera 4 3.6L 2005-08
• Porsche 997 MK1 Carrera 4S 3.8L 2005-08
• Porsche 997 MK1 TURBO 2007-09
• Porsche 997 MK1 GT3 / GT3 RS 2007-09
• Porsche 997 MK1 GT2 2007-09
• Porsche 997 MKII Carrera C2 3.6L 2009-12
• Porsche 997 MKII Carrera C4 3.6L 2009-12
• Porsche 997 MKII Carrera C2S 3.8L 2009-12
• Porsche 997 MKII Carrera C4S 3.8L 2009-12
• Porsche 997 MKII GT3 / GT3 RS 2010-11
• Porsche 997 MKII Turbo 2010-13
• Porsche 997 MKII GT2 RS 2011-13
• Porsche Cayman 2.7L 987C 2006-08
• Porsche Cayman S 3.4L 987C 2005-08
• Porsche Cayman 2.9L 987C MKII 2009-12
• Porsche Cayman S / R 3.4L 987C MKII 2009-12  

The line carries vacuum through the vehicle to the brake servo / brake booster. This vacuum assistance reduces the amount of pedal effort required from the driver when applying the brakes, allowing the braking system to deliver strong and progressive braking with a normal pedal feel.

Because the line must remain airtight, cracks, damaged connections or leaks can reduce the amount of vacuum available to the brake booster. This can lead to a noticeably harder brake pedal and reduced power assistance, even though the hydraulic brakes may still operate mechanically.

What This Product Does:

• Carries vacuum to the brake booster.
• Supports power-assisted brake operation.
• Reduces the amount of pedal force required during braking.
• Helps maintain a consistent and predictable brake pedal feel.
• Forms part of the sealed brake-servo vacuum circuit.
• Transfers vacuum through the central/underbody section of the vehicle.
• Helps the brake booster provide additional braking assistance.
• Replaces a cracked, damaged, leaking or deteriorated original vacuum line.
• Restores vacuum-system integrity when a leak has been identified.

Porsche parts diagrams list 99735557101 directly within the brake-line and underbody vacuum system, identifying it as the central vacuum line in the brake system.

Symptoms Of Wear Or Failure:
Possible symptoms include:

• Brake pedal becoming unusually hard.
• Increased pedal effort required to slow the vehicle.
• Reduced brake-servo assistance.
• Brakes feeling normal initially but becoming harder after repeated pedal applications.
• Hissing noise when the brake pedal is pressed.
• Hissing or air-leak noise from underneath the vehicle.
• Vacuum-related noises after the engine is switched off.
• Inconsistent brake pedal assistance.
• Cracks or splits in the vacuum line.
• Damaged or loose line connections.
• Physical damage caused by road debris or underbody impact.
• Deteriorated seals or connecting pieces.
• Brake booster failing to retain vacuum.
• Vacuum-system faults found during diagnostic testing.

A hard brake pedal does not automatically mean the vacuum line itself has failed. The brake booster, vacuum pump, non-return valve, connections and other vacuum hoses should also be checked during diagnosis.

Why Replacement Matters:
The brake booster relies on vacuum to provide power assistance.

If the vacuum line develops a leak, the booster may receive insufficient vacuum to assist braking correctly. The hydraulic braking system can still apply the brakes, but substantially greater pedal force may be required.

Replacing a leaking or damaged vacuum line helps restore:

• Correct brake booster vacuum.
• Normal brake pedal effort.
• Consistent braking assistance.
• Predictable brake pedal feel.
• A sealed vacuum circuit.
• Reliable brake-servo operation.

Because this component directly affects brake assistance, confirmed vacuum leaks should be addressed promptly.