Lost drive in traffic, or a burning smell? Get off the road
If the car stops pulling, won't select a gear or smells hot and burnt, coast to the side if you can, pull over somewhere safe and switch off. Put your hazards on and get everyone away from the traffic if it's safe. Call roadside assistance if you have it, and don't try to nurse it home along a busy road. If anyone is hurt or in danger, call 000.
What slipping feels like on your gearbox
| What you'll notice | Usual causes | |
|---|---|---|
| Manual | Revs jump when you accelerate in a high gear or uphill. The pedal may bite higher than it used to, and there's a hot smell after hills | A worn clutch plate, or a fault in the clutch's hydraulics |
| Automatic | Revs flare during a gear change, a late or thumping shift, a delay when you select Drive | Low or worn fluid, worn internal clutches or bands, or the torque converter |
| CVT | Revs soar and the car lags or shudders as you take off | Slip in the belt or chain between its two pulleys, or tired fluid |
| Dual clutch | A jerk or shudder in slow traffic, hesitation off the mark | Wear in either of its two clutches, or the unit that controls them |
Why does a clutch slip?
A clutch is a friction plate clamped between the engine and the gearbox. A little slip is normal as you pull away. Once the plate wears thin, it can't hold the engine's power and slips when it shouldn't, and that extra heat speeds up the wear.
Hill starts, slow traffic and towing are the hard work. RACQ names hill starts and manoeuvring as causes of premature clutch wear, and resting a foot on the pedal does much the same. The friction material doesn't grow back, so the question is when, not if.
Why does an automatic slip?
An automatic changes gear by using fluid pressure to clamp internal clutches and bands, and the same fluid lubricates everything inside. When the fluid is low or worn out, gears can't be held properly and the friction parts start to wear.
NRMA says low transmission fluid could point to a bigger problem such as a leak, so look for spots on the driveway and read our page on transmission fluid leaks. Some gearboxes have a dipstick and some are sealed, so the owner's manual decides whether you can check it at all. Where you can, RACQ says the car should be parked with the engine running for an accurate reading.
Signs it's getting worse
- A burning smell, especially after a hill or a tow.
- A warning light, or the car drops into limp mode with low power.
- A delay before the car moves, or gears that won't select.
- Slipping in every gear, rather than only under hard acceleration.
What to do this week
Drive gently
Accelerate softly and avoid the steepest hills. Less load means less heat and less wear while you wait.
Leave the trailer at home
RACT says these faults can be more common when towing a trailer, boat or caravan. RACQ says heavy towing with an automatic can call for an extra or larger transmission cooler to prevent overheating, so don't tow until it's checked.
Note what it does
Which gear, hot or cold, uphill or on the flat, and whether it's getting more frequent. A mechanic can do a lot with that.
What will the mechanic check?
A road test comes first, then a scan for gearbox codes, because many automatics store a fault well before they fail. They'll check the fluid's level and condition, look for leaks, and on a manual check the clutch hydraulics and pedal travel.
The size of the job depends on what they find. On a manual, the clutch can only be reached by taking the gearbox out, so the mechanic should check the flywheel, pressure plate and release bearing while it's apart. On an automatic it can be anything from a fluid service to repairs inside the gearbox.
A clutch suits most general mechanics with a hoist. For automatic, CVT or dual-clutch faults, ask for a mechanic who works on transmissions regularly, because the test gear and the know-how are different. RACV warns that neglecting engine or transmission problems can lead to complete breakdowns.
Questions before you say yes
- Is it the clutch, the fluid or something inside the gearbox?
- What did the scan show?
- Does the estimate cover the flywheel and release bearing, or are those extra?
- If it's internal, do you do that work or send it out?
What you can do, and what's the mechanic's job
You can
- Note when it slips and which gear you're in.
- Check the fluid if your car has a dipstick, the way the owner's manual says.
- Look for fresh spots on the driveway.
Leave to the mechanic
- Scanning and road testing the gearbox.
- Removing the gearbox to replace a clutch.
- Changing transmission fluid to the maker's specification.
What we'd do
A clutch that only slips under hard acceleration: we'd send the job this week, go gently and skip the trailer. An automatic that flares between gears: we'd keep it to short, gentle trips, because damage inside builds quickly. If it isn't moving properly at all, we'd leave it parked and ask for a mobile mechanic or a tow. This is one problem that's a lot easier to deal with early.