Diagnose with the springs off

Detach all springs and push the carriage slowly through its full travel, listening and feeling. Spring noise masks everything else, and removing it makes the actual fault obvious.

A gritty feel throughout means debris. A tick at the same point each stroke means a wheel. A rattle only under load means loose hardware.

Symptom to cause
SymptomMost likely causeFix
Gritty feel throughout travelDebris on railsClean rails thoroughly
Tick at same point each strokeFlat spot on a wheelReplace wheel set
Rattle only under loadLoose frame boltsCheck and snug all bolts
Hard knock on returnCompressed carriage stoppersReplace stoppers
Resistance feels lighter than beforeFatigued springsMeasure free length; replace set
Carriage pulls to one sideUneven rope length or wheel wearReset ropes; check wheels
Squeak under loadDry pulley bearingSpin-test pulleys; replace if rough

Start with the free fixes

Clean the rails and check every bolt before buying anything. Between them they resolve most reported problems, and both cost nothing.

Only after those two should you start replacing parts, because a new wheel on a dirty rail behaves exactly like the old one.

When it is not the machine

A carriage that feels different is sometimes an uneven floor rather than a fault. Check the levelling feet and confirm all four are in contact — a machine rocking on three feet feels loose in a way that resembles worn wheels.

Equally, a machine moved to a new room can feel different simply because the floor is more or less compliant.

When to call a technician

Frame damage, a racked frame that measures out of square, or a scored rail. All three are structural, none are DIY repairs, and continuing to use the machine makes them worse.

Everything else on the list above is within reach of anyone with basic tools and half an hour.