Brake Fluid Flush on Smart Fortwo and Roadster
Service interval: Every 2 years regardless of mileage
Tools you'll need
- Bleeder wrench (size varies — typically 7mm or 9mm)
- Clear bleed catch bottle and hose
- One-person bleed kit, helper, or pressure bleeder
- Turkey baster or syringe to draw old fluid from the reservoir
- Shop rags and water nearby (brake fluid eats paint)
Fluids & specs
| Fluid | Spec | Capacity |
|---|---|---|
| Brake fluid | DOT 4 — varies; check the workshop manual or the reservoir cap. Newer 453 ABS systems generally call for DOT 4 LV (low-viscosity). | Roughly 0.5-1.0 L for a full flush |
What this is and why it matters
Brake fluid is hygroscopic — it absorbs water out of the air over time, even with the cap on tight. Wet fluid boils at a lower temperature, which is how you get a soft pedal after a long downhill or a hard stop. It also corrodes the inside of the calipers, ABS modulator, and master cylinder. Two years is the standard interval for a reason.
On a Smart, the job is mechanically simple but the ABS modulator deserves respect. If you let the master cylinder reservoir run dry mid-flush, or if you crack open a line on the modulator itself, you can pull air into the modulator. Getting that air back out usually needs a Star Diagnosis or compatible scan tool to cycle the ABS pump while you bleed. Don't go there if you can avoid it.
What you'll need
A clear catch bottle so you can see fluid colour and bubbles. A bleeder wrench that fits properly — rounded bleeder screws are a real day-ruiner. Fresh fluid in a sealed bottle (once it's open, it starts absorbing water; don't reuse a half-used bottle from last year). For DOT 4 spec, look at the reservoir cap or the workshop manual on Manualslib. The 453 commonly calls for DOT 4 LV; the 450, 451, 452 generally take regular DOT 4. Confirm before you buy.
A pressure bleeder makes this a one-person job and keeps the reservoir topped up automatically. A vacuum bleeder also works. A helper pumping the pedal works fine if you have one.
Step by step
- Park on level ground, wheels chocked. Pop the wheels off if access is tight — on the 453 you can usually reach the bleeders with the wheels on, but it's easier without.
- Draw the old fluid out of the reservoir with a turkey baster down to the MIN line. Don't go below it or you pull air into the master cylinder. Refill with fresh fluid to the MAX line.
- Bleed sequence is generally furthest-from-master-cylinder first: rear right, then rear left, then front right, then front left. Some Smart variants vary — the workshop manual is the source of truth. If yours specifies a different order, follow it.
- At each wheel: clear hose onto the bleeder, other end into the catch bottle, crack the bleeder open. Helper pumps the pedal and holds it down. You close the bleeder. Helper releases. Repeat until fluid runs clear and bubble-free. Top up the reservoir between wheels — never let it run dry.
- With a pressure bleeder, you pressurize the reservoir to about 10-15 psi and just open each bleeder until clean fluid flows. No pedal pumping needed.
- After all four are done, top the reservoir to MAX. Pump the pedal a dozen times with the engine off. It should come up firm. If it's spongy, you have air somewhere — bleed again.
- Test drive at low speed first. Make sure the pedal feels right before you go anywhere serious.
Common gotchas
The reservoir running dry during the flush. This is the single most common way to turn a 90-minute job into a tow-truck call. Top up between wheels.
Cracking open the ABS modulator block. There's no reason to in a routine flush — stay at the wheel calipers. If you've already done it and the pedal won't come up, you probably need a scan tool to cycle the modulator pump. A Smart specialist or a shop with Star Diagnosis can do this.
Old fluid runs deep brown or black; healthy fluid is pale gold. If you've been running fluid that's near-black, do two flush cycles a week apart — the first one won't get all of it.
Brake fluid strips paint. Keep a wet rag and a bottle of water close. Wash any drips off the body, calipers, or your driveway right away.
When to skip DIY
If you've cracked an ABS line and the pedal won't firm up, stop and get a scan tool involved. If the bleeder screws are seized and rounding off, soak them in penetrating oil overnight or hand it to a shop with the right extractor — a snapped bleeder means caliper rebuild or replacement. If you've never bled brakes before and you're working alone without a pressure bleeder, find a helper or buy the bleeder kit. This isn't the place to wing it.
Parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| DOT 4 brake fluid (1L) | $10-20 | Search Google |
| DOT 4 LV brake fluid (1L) — 453 ABS | $15-25 | Search Google |
| One-person bleed kit | $10-25 | Search Google |
| Pressure bleeder (Motive-style) | $60-90 | Search Google |
Prices are rough community-reported ranges, not quotes. Aftermarket vs. genuine Mercedes parts swing the spread.
Manual references
- Browse Smart workshop manuals on smartcarmanuals.com — model-specific reference manuals on the home page; pick your chassis code section for torque specs and detailed procedures.
