Removing and installing brake booster: Installation

When replacing the brake booster, observe the correct allocation according to the Spare Parts catalogue! Different transmission ratio (boost ratio) of the 911 Turbo (996) compared to the 911 GT2.
Boost ratio 911 GT2 = 3.15 : 1. Boost ratio 911 Turbo (996) = 3.85 : 1.

Install new pushrod (push rod with fastening nut) -12.1- (if not already present) in place of -12- (push rod with retainer). When doing so, observe installation dimension X (138 mm).

Fig 1: Installing New Pushrods
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Basic setting of the push rod -dimension X- is 138 mm (set in new brake boosters)! If necessary, correct during the relevant work!

Fig 2: Identifying Push Rod Setting Dimension
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Insert brake booster with bellows -B- and tightened clamps -6- .

Fig 3: Inserting Brake Booster With Bellows And Clamps
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NOTE: Do not trap wiring harness!
Tighten fastening screws (Torx T 45) -arrow- to 23 Nm (17 ftlb.).

Fig 4: Tightening Fastening Screws
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Connect the 2 push rods. To do so, mount the fastening nuts -arrow-

Fig 5: Locating Push Rod Fastening Nuts
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NOTE:
- Adjusting the brake pushrod length changes the position of the brake pedal.
- Perform a fine adjustment of the brake pushrod if the correct position of the brake pedal is not given!
- After the brake pushrod is adjusted, check the brake light switch adjustment!
Check the position of the brake pedal -Dimension X = 45 + 5 mm- . Perform measurement between the centre of the brake pedal plate and the accelerator pedal. Perform a fine adjustment of the brake pushrod if the correct position of the brake pedal is not given.

Fig 6: Checking Position Of Brake Pedal
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- Fine adjustment of brake pushrods: Undo the lock nut for this purpose and the turn the push rod accordingly at the hexagon -arrow- until -dimension X = 45 + 5 mm- has been achieved. Subsequently re-tighten the lock nut.
Fig 7: Adjusting Brake Pushrods
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Fit the bellows onto the body and fasten with the clamps.
Check the setting of the brake light switch -1- .

Fig 8: Checking Setting Of Brake Light Switch
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The pedal must move a perceptible distance of approx. 5 to 10 mm before the brake light lights up. At the same time, check (make sure) that the brake light lights up before the pedal meets perceptible resistance or before brake pressure builds up. If necessary, set/re-adjust. Refer to CHECKING BRAKE LIGHT SWITCH SETTING .
Fit the vacuum hose for the brake booster.
Install hydraulic unit, boost pump (in vehicles with PSM) and brake master cylinder. Fit all brake lines.
NOTE: Ensure that the reservoir is engaged correctly on the brake master cylinder.
Bleed the brakes (see BLEEDING BRAKES (VEHICLE WITH PSM) or BLEEDING BRAKE - GT2 ).
NOTE:
- First bleed brakes as usual!
- Only afterwards (after the conventional bleeding) should the booster pump control be performed (continue bleeding) with the Porsche System Tester 2 in vehicles with PSM! If this is not observed, damage can occur to the booster pump!
  
  Fig 9: Identifying Porsche System Tester 2
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- To bleed at front on right with running booster pump (PSM), the bleeding device should remain connected (switched on)! Bleeding pressure approximately 2.0 bar!
When replacing the hydraulic unit in vehicles with PSM (4-channel system), code the control module (manual transmission or Tiptronic).
Carry out the following tests:
- Check the system (brake lines and connections) for leaks.
- Read out and erase the fault memory of the ABS or PSM control module with the Porsche System Tester 2 (PST 2). Additionally, perform the static test in the system.
- Check electrical and hydraulic lines (brake lines) for incorrect assignment using the PST 2.
NOTE: The exchange test checks that the brake lines/solenoid valves are assigned to the correct brake calipers (wheels)!
- Then start the engine. The ABS and if necessary also the PSM-related lights in the instrument cluster must go out when the engine is running.
- Carry out a function check of the brakes. Then perform a short test drive and perform at least one ABS control operation, taking the road conditions into consideration. Read out the ABS or PSM fault memory again. There must not be any stored faults.
Install covers -A / B- .

Fig 10: Installing Covers
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