Removal and Replacement
Removing and Installing Brake Booster
Removal
Note!
- To remove and install brake booster -C-, the brake master cylinder -B-, the hydraulic unit -D- and the booster pump -A- in vehicles with PSM must be removed.
- The assembly of the brake master cylinder -B- with the brake booster -C- must not be disconnected for removal and installation if both parts should be continued to be used!
1. Switch off ignition. Remove cover -A and B-.
2. Remove spare wheel (if present).
3. Drain brake fluid expansion tank. To do so, suck brake fluid out of the expansion tank or pump out the brake fluid using the brake pedal via a front and a rear brake caliper (use collecting bottle).
4. For vehicles with manual transmission, remove the clutch line at the reservoir.
- Press on the ring to do this (unlocking) and pull the line out of the reservoir at the same time.
5. Disconnect the electrical line (plug) on the reservoir.
6. Undo the brake lines on the brake master cylinder. Close the brake lines and the brake line connections with suitable plugs. Undo the fastening nuts -A- of the brake master cylinder. Pull out brake master cylinder.
- The brake master cylinder must be disconnected from the brake booster if both parts should continue to be used!
7. In vehicles with PSM, remove the booster pump -1- with the holder -1a-. For the removal of the booster pump, carry out the following removal steps:
- Remove suction line -2- for booster pump. Undo pressure pipe on the booster pump -3-. Close the lines and the pump connections with suitable plugs.
- Release plug -4- -arrows- and disconnect. Remove connector housing rearwards from out of the bracket -moving arrow-.
- Undo the three plastic fastening nuts -5- and remove the booster pump -1- with the holder -1a-.
Note!
- In the case of assembly work on the hydraulic connections, the electrical plug connections on the hydraulic unit must always be connected!
- This prevents the plug connections on the hydraulic unit or in the plugs inside from being splashed with brake fluid or water!
- Any damp plug must be wiped dry before being disconnected from the plug on the hydraulic unit!
- Brake fluid on electrical contacts (even thinned brake fluid) leads to corrosion and may cause faults in the system!
8. Remove hydraulic unit. To remove the hydraulic unit, carry out the following removal procedure:
- Undo the brake lines on the hydraulic unit.
- Close the brake lines and the brake line connections with suitable plugs.
- Pull the plug off the pressure sensor if present (vehicles with PSM 5.7).
- Unlock/disconnect the control module plug on the hydraulic unit. Cover the plug connector and the plug!
- Undo and guide out the hydraulic unit.
9. Remove holder of hydraulic unit (if still installed).
10. Separate the 2 push rods from each other (loosen). For this purpose, remove the fastening nut (fastening nut, as standard as of April 2001) -arrow-. To make the retainer or fastening nut accessible, adjust the bellows positioned above or undo on the body (according to bellow variant).
11. Disengage the vacuum line on the brake booster. Undo the fastening screws -arrows- of the brake booster (Torx T 45). Pull out brake booster.
Replacing brake booster
When replacing brake booster, pay attention to correct allocation of the bellows!
Bellows versions
2 bellows variants have been installed as standard in the 911 Carrera (996) since the production launch (first version and new/current version).
The first version -A- with 2 rubber bellows -1 and 2- has been installed up to the vehicle identification numbers listed in the following (Y-range / in the model year 2000).
F >>99YS6 00595
F >>99YS6 20336
F >>99YS6 40393
F >>99YS6 50545
The new/current bellows variant -B- is fitted with only one continuous bellow. Using the bellows version -B-, the following parts have been changed:
- Omission of bellows guide on the brake pedal push rod (No. 10 in the first version)
- The bellows connection is no longer directly to the body but to a sleeve (pipe) -7-.
In the case of replacement
Variant A: First version (spare parts not included)
The 2 rubber bellows -1 and 2- on the brake booster and on the body are no longer available for vehicles with bellows variant A (first version).
For assembly work in this area, the 2 rubber bellows -1 and 2 - and the grommet (rubber groove ring) -3- must be removed and the spare variant A1 must be installed in its place.
Variant A1: Spare version for A
With this variant -A1-, the new/current continuous bellows -B- is used instead of the 2 rubber bellows. A seal -7.2- is used together with an appropriate connection sleeve -7.1- for connection to the firewall! In addition, the 2 brake pushrods (on the brake booster and of brake pedal) must also be replaced!
The conversion is described in "Converting brake booster (bellows)".
Note!
- As a replacement part, the brake booster is delivered with the new/current continuous bellows -B-!
- In general, the following applies: The bellows -B- must be installed!
Installation
Note! Basic setting of the push rod -dimension X- is 138 mm (set in new brake boosters)! If necessary, correct during the relevant work!
1. Insert the brake booster with bellows -B-.
Note! Do not trap wiring harness!
2. Tighten fastening screws (Torx T 45) -arrow- to 23 Nm (17 ft. lbs.).
3. Connect the 2 push rods. For this purpose, fit the retainer or fastening nut (standard fastening nut as of April 2001) -arrow-.
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!
4. Check the position of the brake pedal -Dimension X = 45 + 5 mm- Perform measurement between the center of the brake pedal plate and the accelerator. Perform a fine adjustment of the brake pushrod if the correct position of the brake pedal is not given.
- Precise 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.
5. Fit the bellows onto the body or onto the connection sleeve and fasten with the clamps.
6. Check the setting of the brake light switch -(1)-.
The pedal must move a perceptible distance of approximately 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 brake-light setting.
7. Fit the vacuum hose for the brake booster.
8. 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.
9. Bleed the brakes.
Note!
- First bleed brakes as usual!
- Only after this (after the conventional bleeding) should the return pump actuation be performed (continue bleeding) with the Porsche System Tester 2 in vehicles with Traction Control (TC) or the booster pump control in the case of vehicles with PSM! If this is not observed, damage can occur to the return pump/booster pump!
- To bleed at rear on right with running return pump (TC) or at front right with running booster pump (PSM), the bleeding device remains connected (switched on)! Bleeding pressure approximately 2.0 bar!
10. Bleed the clutch in manual transmission vehicles.
11. When replacing the hydraulic unit in vehicles with ABS/TC or PSM (4-channel system), code the control module (manual transmission or Tiptronic).
12. 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.
13. Fit covers -A / B- and spare wheel (if available).