Free printableTroubleshootingTSP-TS-06
GY6 CVT slipping, juddering and squealing
Three different noises from the same case, and they mean different things. What to look at with the cover off, in order.
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TSP-TS-06 · version v1.0 · September 2026. Opens in your browser's PDF viewer, where you can print directly.
The problem it solves
A transmission that shudders pulling away, squeals under load or revs without driving is usually fixed by replacing everything inside the case at once. That works, and it means you never learn which part had failed — so when it happens again in eight months you replace everything again.
The scooter transmission has no gears and no dipstick, so it gets ignored until it makes a noise. By then the owner is choosing between a belt, a clutch, rollers and springs with nothing to go on but a symptom.
The symptoms do separate, though. Judder that pulses in time with engine speed is the clutch grabbing and releasing. A steady squeal under load is different. Revs flaring without speed is slip somewhere in the drive, and where depends on whether it happens from a standstill or at speed.
This sheet is built around the inspection you do once the cover is off, in the order that puts the most-likely and easiest-to-see first. Every item ends at something visible.
The mistakes this sheet exists to prevent
- Replacing the belt because the CVT is noisy, without looking at the clutch, which glazes and causes the same symptoms.
- Fitting a new belt into a case contaminated with oil, which will glaze the new one within weeks.
- Cleaning the friction faces with something oily, which is how a freshly serviced CVT ends up slipping worse than before.
- Ignoring elongated spring holes in the clutch shoes, which change engagement and are easy to see once you know to look.
- Replacing rollers without checking the ramp plate and sliders they run against.
Who it is for
- Anyone whose scooter shudders or squeals pulling away
- Owners whose revs flare without the machine accelerating
- Anyone about to order a full CVT kit on a guess
What is on it
- The symptom split: judder, squeal and flare mean different things
- The full with-the-cover-off inspection in order
- What oil inside a dry case tells you, and why a new belt will not fix it
- A findings record that feeds the CVT service log
How to use it
- 01Note exactly when the noise happens — from a standstill, under load, at speed — before opening anything.
- 02Work down the inspection in order and write down what you see, including what looked fine.
- 03If you find oil in the case, find the leak before fitting anything new.
- 04Transfer the findings to the CVT service record so wear rates build up over time.
Also in a pack
Use it with the registry
Other sheets you may want
- CVT service record for a GY6 or Chinese scooterThe transmission is the highest-wear system on a scooter and the least documented. One sheet for everything that goes in it, with the measurements taken each time.
- GY6 belt size chart and measuring sheetHow to read the three numbers printed on a scooter drive belt, how to measure a belt that has no readable markings left, and a record sheet for the one you have.
- Variator roller size chart and measuring sheetDiameter, width and weight are three separate things, and a roller set is only interchangeable on all three. A record sheet with true-size circles and a weighing block.
Free to print, copy, and share — including in forums, clubs and workshops. If you find a mistake on this sheet, tell us and it gets corrected. Quote TSP-TS-06 and the version so we know exactly which sheet you mean. All printables.