Why do my windscreen wipers smear and judder?
Why the glass is usually the problem rather than the blades, cleaning off the oily film properly, and the checks that identify a bent arm.
- Difficulty
- beginner
- Time
- 25 min
- Read
- 4 min
- Safety
- caution
Short answer
Clean the glass first — most smearing is an invisible film of road grime, wax and traffic film on the screen rather than a worn blade. Clean the blade edges with a damp cloth, and if it still smears after that, replace the blades and check the arms are pressing evenly.
New blades that smear straight out of the packet are the giveaway: the problem was never the blades. A windscreen collects an oily film from exhaust, road spray, screenwash residue and traffic that ordinary washing does not shift.
Safety
What you'll need
- Glass cleaner or a dedicated screen cleaner
- Microfibre cloths
- A clay bar or glass polish (optional)
Step by step
- Wet the screen and run a finger across it.If it drags and squeaks, the glass is clean. If it slides smoothly with a slight slippery feel, there is a film on it and that is your smear.
- Clean the glass properly with a dedicated cleaner.A car glass cleaner, or a little neat washing-up liquid on a cloth followed by a very thorough rinse. Ordinary car shampoo leaves gloss agents behind that make smearing worse.
- Do the outside and the inside.The inside collects a film from plastics and heating, which shows up as smear from a completely different direction. Two clean microfibre cloths, one damp and one dry.
- Clean the blade rubbers.Lift each arm and wipe the rubber edge with a damp cloth until it stops coming away black. It is astonishing how much grit a blade carries.
- Feel the blade edge with a fingernail.A good blade has a sharp square edge. A rounded, shiny, split or hardened edge cannot clear water and no amount of cleaning brings it back.
- Use a clay bar or glass polish for stubborn film.If cleaning has not fixed it, bonded contamination is the cause. A clay bar on wet, lubricated glass lifts it and takes ten minutes a screen.
- Check the arms sit square.Look along the blade with the arm resting on the screen. The rubber should meet the glass evenly along its whole length. A twisted arm leaves a strip untouched.
- Check the spring tension.Lift each arm a few centimetres and let it rest back. A weak arm that no longer presses firmly will smear and lift at speed however good the blade is.
- Replace the blades once the glass is clean.In this order, so you find out whether the blades were ever the problem. New blades on dirty glass smear immediately and waste the money.
- Avoid rain repellent until the glass is genuinely clean.Applied over a film it seals the film in and makes matters worse. On clean glass it works well and reduces wiper use considerably.
Tips
- Never run wipers on a dry screen. It tears the rubber edge in seconds and is the fastest way to ruin new blades.
- In frost, free the blades from the glass before switching the wipers on — pulling a frozen blade off strips the rubber.
- A rear screen smears for the same reasons and gets cleaned even less often.
Common mistakes
- Fitting new blades to a dirty screen — The film on the glass is what causes most smearing. New blades on top of it smear from the first use and get blamed for a problem they did not cause.
- Using household glass cleaner with added shine agents — Anything that leaves a residue leaves exactly the film you are trying to remove. Use a plain glass cleaner or a car-specific one.
If it doesn't work
Smearing only on the return stroke
Cause: The blade is not flipping over properly, usually a stiff or aged rubber — Fix: Clean the blade and check it hinges freely on the arm. If it is stiff, replace it.
Juddering and chattering across the screen
Cause: Dry or contaminated glass, or a bent arm holding the blade at the wrong angle — Fix: Clean the glass, use plenty of washer fluid, and if it persists have the arm checked.
A strip left unwiped along the blade
Cause: The arm is twisted or the blade is deformed — Fix: Sight along the blade on the glass. A visible gap means the arm needs straightening or replacing.
Perfect in the wet, awful with the washers
Cause: Screenwash reacting with a wax or polish on the glass — Fix: Clean the screen thoroughly with glass cleaner to strip the residue and stop applying wax to the windscreen.
Questions people ask
Why do new wipers still smear?
Because the glass is the problem. An invisible oily film of traffic residue survives ordinary washing and defeats any blade. Clean the screen properly and the same new blades usually work perfectly.
Does rain repellent help?
On genuinely clean glass, yes — water beads and blows off above about forty miles an hour and wipers are needed much less. Applied over a dirty screen it makes the smearing permanent.
Can a smeared windscreen fail an MOT?
Damage and obstruction in the driver's view are assessed, and the washers and wipers must work effectively. A screen that cannot be cleared properly is a real risk of failure as well as a hazard.