Removing and installing brake master cylinder, vehicles with high-voltage system — AUDI
Removing and installing brake master cylinder, vehicles with high-voltage system on Audi: 9 steps. What to remove, in what order, and what to check after.
This is the brake master cylinder on high-voltage cars across the platform codes listed below, and the first step is not a spanner: the high-voltage system must be de-energised by a qualified high-voltage technician before anyone works near it. After that, the job itself is short. The brake fluid reservoir comes off, the brake lines are disconnected from the master cylinder and every open port is plugged immediately with clean sealing plugs. The mounting nuts come off and the cylinder is lifted carefully away from the servo, without letting brake fluid run into the servo. On refit the push rod has to locate correctly in the servo; new nuts and a new seal are used and the threads cleaned. The system is then re-energised by the high-voltage technician.
🧭 Before you start
Have the high-voltage system de-energised, then remove the brake fluid reservoir. Disconnect the brake lines and plug the ports at once, remove the mounting nuts and lift the master cylinder off the servo. Fit the new cylinder with a new seal and new nuts, making sure the push rod engages correctly, refit the reservoir and have the high-voltage system re-energised.
Fits: Audi A3 (8V, 2012–2020); platform code 85
- Opens: brake fluid
- Renewed: nuts
Don't miss
- Only a qualified high-voltage technician may de-energise and re-energise the system.
- Plug the brake line ports immediately with clean sealing plugs.
- Keep brake fluid out of the brake servo; it can be damaged irreparably.
- Renew the mounting nuts and the seal between master cylinder and servo; clean the threaded holes.
- Bleed the brakes and confirm a firm pedal before road use; general practice after opening the hydraulics.
Written for this job from the workshop steps below · TorqFix editorial.
📋 Procedure
- ⚠ High voltage can cause fatal injury.Danger of severe or fatal injuries from electric shock.The high-voltage system must be de-energised by a "“high-voltage technician”".Work on the de-energised high-voltage system may only be performed by an "“electrically instructed person”". — De-energise high-voltage system 93De-energising high-voltage system.
- Remove brake fluid reservoir .
- Disconnect brake lines (2, 3, 4) from brake master cylinder (1).
- Seal open connections immediately using clean sealing plugs from assembly parts set5Q0 698 311.
- Remove bolts (arrows).
- Detach brake master cylinder (1) carefully from brake servo. [Note: Always renew nuts if removed.Renew seal between brake master cylinder and brake servo.Always clean threaded holes for bolts (using a thread tap or similar).]
- ⚠ Risk of irreparable damage to brake servoBrake fluid must not be allowed to enter the brake servo. — When fitting brake master cylinder, make sure that push rod is correctly positioned in brake servo.
- Install brake fluid reservoir .
- ⚠ High voltage can cause fatal injury.Danger of severe or fatal injuries from electric shock.The high-voltage system must be re-energised by a "“high-voltage technician”". — Re-energise high-voltage system 93Re-energising high-voltage system.
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- Removing camshaft timing chain from camshafts – Audi A6/A7 C7 · 38 torque figures
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Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.
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The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.