Smart Fortwo 451 Cabrio Convertible Top Maintenance

Tools you'll need

• Soft-bristle brush (NOT a stiff brush — it'll fluff the weave)
• Garden hose with a low-pressure nozzle
• Microfiber cloths
• Mild fabric soap or dedicated convertible top cleaner
• Fabric reproofer (303 High Tech Fabric Guard or equivalent)
• Silicone or PTFE-based lubricant (NOT lithium grease)
• Bucket

What this is and why it matters

The Smart Fortwo 451 Cabrio top is more than a piece of fabric stretched over a frame. It's a multi-piece assembly with motors, hinges, plastic sliders that ride in tracks, and a fabric skin that takes a beating from sun and weather. Routine care — the cheap, easy stuff — buys years before you end up in the harder repair territory.

The single most important thing this guide is not is the slider repair. If your top is already binding, sticking, or stopping mid-cycle, you don't need maintenance, you need the slider fix. Read the 451 Cabrio Roof Sliders page for that. This page is about keeping a working top working.

What you'll need

Tools and supplies are listed above. A few notes:

• Soft brush, not stiff. A stiff brush abrades the fabric and fluffs the weave. Once it's fluffed, water gets in. Use a soft brush like you'd use on a suede shoe.
• Mild soap, not detergent. Dish soap and laundry detergent strip the factory waterproofing faster than you'd think. Either get a dedicated top cleaner or use a very mild fabric wash.
• Silicone or PTFE lubricant for hinges, not lithium grease. Lithium grease is too thick for plastic-on-plastic contact and it attracts dirt, which then grinds into the surfaces. Silicone or PTFE (often sold as "dry lube") stays slick and doesn't gum up.

Step by step

Routine fabric clean

1. Open the top fully. Easier to reach all surfaces.
2. Rinse with the hose at low pressure. No pressure washer — pressure washers force water through the fabric and into the headliner. Soft stream only.
3. Brush gently with soapy water. Work in small sections, top to bottom. Don't scrub — let the soap do the work. Pay attention to the seams and the area around the rear window, which collects dirt fastest.
4. Rinse thoroughly. Soap residue attracts dirt and degrades the fabric over time. Rinse until the runoff is clear.
5. Let it dry fully before closing the top. A fabric top stored damp grows mildew. If you have to close it before it's dry, leave a window cracked.

Reproofing (every 2-3 years)

1. Start with a clean, dry top. The reproofer needs to penetrate the fabric. Dirt or soap residue blocks it.
2. Apply per the product's instructions. Most aerosol reproofers want a couple of light coats with 30 minutes between, applied at 6-8 inches from the surface. Mask the painted body and the rear plastic window with painter's tape and plastic sheet — overspray on glass dries cloudy.
3. Let it cure for 24 hours before driving in rain. The water-bead test is the easy check: if water sheets off in droplets, you're done. If it soaks in, do another coat.

Hinge and motor lubrication (once a year)

1. Open the top to its mid-position so the hinge points are exposed.
2. Wipe each hinge with a clean rag to remove old grease and dirt.
3. Apply a small amount of silicone or PTFE spray to each pivot point. A short pulse — you're not basting a turkey. Excess attracts grit.
4. Cycle the top a few times to work the lubricant in.

Slider inspection

1. Open the trunk and look at the roof bow tracks. The plastic sliders are visible — small white plastic blocks that ride in the tracks.
2. Look for warping, cracks, or visible wear. Healthy sliders are clean and smooth. Worn ones show flat spots, deformation, or stress marks. Per Richard Bowden — UK Smart cabrio specialist — these are a wear part that should be replaced approximately every 4 years regardless of visual condition.
3. If the top is starting to bind or stop part-way, sliders are the prime suspect. See the 451 Cabrio Roof Sliders page for the full diagnostic flow.

Common gotchas

• Don't operate the top below freezing. Fabric stiffens in cold weather and the seams take more stress every cycle. If you have to use the top in winter, warm the cabin first and let the fabric come up to temperature for a few minutes before cycling.
• Pressure washers ruin fabric tops. Even on a "low" setting, the pressure forces water through the weave and lifts the factory coating. Stick to a hose.
• Lithium grease on hinges is a slow poison. It grabs dust and turns into a grinding paste over a year or two. If a previous owner used lithium, clean it off thoroughly with brake cleaner or a degreaser before applying silicone.
• Detergent strips waterproofing. Dish soap is for dishes. Laundry detergent is for laundry. A convertible top is fabric-with-coating, and the coating is what keeps water out. Use a top-specific cleaner or a very mild fabric wash.
• The rear plastic window scratches easily. Don't use the brush on it. A clean microfiber and plain water for the window. There are dedicated plastic window cleaners (Plexus, Novus 1) that work well.
• Reproofer overspray on the body paint isn't fatal but it's annoying. Mask before you spray.
• Closing a wet top breeds mildew. Even a small damp spot in the corner becomes a black blotch in a few weeks. Always dry before closing.

When to skip DIY

The routine cleaning, reproofing, and hinge lube are owner-level jobs and the right thing to do at home.

The slider replacement is the line. It's not impossible — Richard Bowden has documented procedures and there are owners who've done it themselves — but you're working through cramped headliner space and parts availability isn't great through normal channels. In the US, Cosmic Cabrios is the canonical mobile specialist (262-341-4360). In the UK, Richard Bowden is the reference. If your top is already misbehaving, get the diagnosis right before you spend on parts that might not be the cause.

If your fabric is past saving — large tears, separated seams, a rear window so cloudy you can't see through it — that's a top replacement, not a maintenance job. Plan accordingly.

Parts & typical prices

Part	Typical price	Search
Convertible top cleaner	$10-20	Search Google
Fabric reproofer (303 or equivalent)	$15-25	Search Google
Silicone or PTFE lubricant spray	$8-15	Search Google
Replacement plastic roof sliders (set)	Cosmic Cabrios / Richard Bowden — call for current pricing	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.

Related fault codes

• 451 Cabrio Convertible Top Won't Close (Roof Slider Wear)
• Water Leak and Interior Moisture — Smart Fortwo and Roadster