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Audi 90 Quattro Brake Master Cylinder Reservoirs

Audi 90 Quattro Brake master cylinder reservoirs

Starting at $35.95, AutoBuffy stocks 2 brake master cylinder reservoirs from SKP and Vaico. The reservoir is the translucent plastic tank that holds brake fluid and feeds the master cylinder. When it cracks, leaks, or its level sensor fails, your brake warning light triggers, fluid is lost, and braking performance degrades — a direct safety risk.

Signs your Audi 90 Quattro needs a new brake master cylinder reservoir

  • Brake warning light stays on even after fluid has been topped off
  • Visible brake fluid pooling or wet residue around the reservoir body or cap
  • Reservoir appears cracked, cloudy, or physically distorted when inspected
  • Fluid level drops repeatedly without any evidence of an external brake leak
  • Low-fluid warning activates intermittently due to a faulty float sensor inside the reservoir
  • Soft or spongy brake pedal caused by air entering the system through a compromised reservoir seal

Which brake master cylinder reservoir should you buy for your Audi 90 Quattro?

The most important decision is whether you need the reservoir alone or the reservoir pre-attached to a complete master cylinder assembly. Beyond that, consider whether the original level-sensor connector and cap style are retained, since a mismatched sensor will trigger a false warning light. OE-equivalent fit matters more here than performance upgrades — this is a sealed fluid container, not a friction component.

OE Replacement Reservoir (standalone)
Best for
Intact master cylinder with a cracked or leaking tank only
What you get
Direct-fit plastic tank with matching sensor port, cap, and grommets — lowest cost repair
Reservoir + Cap Assembly
Best for
Vehicles where the original cap seal is degraded or missing
What you get
Tank and sealing cap sold together, ensures no fluid evaporation or contamination at the opening
Reservoir with Integrated Level Sensor
Best for
Vehicles whose sensor is built into the tank and cannot be transferred
What you get
Pre-wired float sensor eliminates separate sensor sourcing and bench-testing before install
Complete Master Cylinder + Reservoir Assembly
Best for
High-mileage vehicles or those with internal master cylinder wear alongside reservoir damage
What you get
New piston, seals, and reservoir as one unit — higher upfront cost but single-job repair

Brake master cylinder reservoirs brands we stock for your Audi 90 Quattro

SKP
1 option · from $35.95
Vaico
1 option · from $97.95

Replacing a brake master cylinder reservoir on a Audi 90 Quattro

Moderate⏱ 1–2 hoursTurkey baster or fluid transfer pump (to empty old reservoir)Flathead screwdriver or trim pry tool (to release reservoir grommets)Pliers (for hose clamps if applicable)Brake fluid catch pan and shop ragsBrake bleeder kit or vacuum bleeder

Begin by suctioning out as much fluid as possible from the old reservoir to minimize spills, then unplug the fluid level sensor connector and carefully pry or twist the reservoir free from the master cylinder body — it is typically retained by press-fit rubber grommets. Transfer the grommets to the new reservoir if not supplied, seat it firmly onto the master cylinder ports, reconnect the sensor, refill with the correct fluid, and bleed the system to purge any air introduced during the swap.

Frequently asked questions

How much does it cost to replace brake master cylinder reservoirs on a Audi 90 Quattro?
Parts start at $35.95 for a standalone reservoir on a Audi 90 Quattro. A complete master cylinder and reservoir assembly costs more. Professional labor typically adds one to two hours of shop time. DIY replacement is achievable for most owners and keeps total cost close to the part price alone.
Can I drive my Audi 90 Quattro with a cracked brake master cylinder reservoir?
No. A cracked reservoir on a Audi 90 Quattro allows brake fluid to leak out and air to enter the hydraulic circuit. Even a partial fluid loss can reduce braking force significantly. If the reservoir is visibly damaged or fluid is actively seeping, do not drive the vehicle until the part is replaced and the system is bled.
Do I need to bleed the brakes after replacing the reservoir on my Audi 90 Quattro?
Yes, in most cases. Swapping the reservoir on a Audi 90 Quattro exposes the brake circuit to air, especially if the master cylinder is drained during the job. A full four-corner brake bleed is the safe standard. If the master cylinder is bench-bled before installation, you may limit bleeding to just the master cylinder ports.
Why does my Audi 90 Quattro brake warning light stay on after I refill the reservoir?
If the warning light stays on after refilling, the float sensor inside the reservoir may be stuck, corroded, or failed on your Audi 90 Quattro. The sensor triggers the light when it reads low fluid regardless of actual level. Replacing the reservoir — or the sensor if it is serviceable separately — typically resolves the fault.
Is a brake master cylinder reservoir the same as the master cylinder on a Audi 90 Quattro?
No. On a Audi 90 Quattro, the master cylinder is the hydraulic pump that converts pedal force into brake line pressure. The reservoir is the separate fluid tank that sits on top of it. They are often sold together but can fail independently. Always confirm which component is damaged before purchasing a replacement.
What brake fluid should I use when refilling the reservoir on my Audi 90 Quattro?
Use only the fluid specification listed on the reservoir cap or in the owner's manual for your Audi 90 Quattro. Most vehicles specify DOT 3, DOT 4, or DOT 5.1, which are glycol-based and compatible. Never mix fluid types, and never use DOT 5 silicone fluid in a system designed for glycol-based fluid, as it will damage seals.

Shop brake master cylinder reservoirs by year for the Audi 90 Quattro

19951994199319921991199019891988

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