Automatic Gearbox Problems: Slipping, Juddering and Delayed Engagement

Slipping: revs go up, speed does not

A slipping automatic feels like a momentary loss of drive. The engine note rises as if you had dipped the clutch, then the car catches up with a bump. Inside a conventional automatic, this is typically worn friction plates or bands that can no longer hold the load, or low hydraulic pressure caused by a pump, valve body or seal problem.

Low or degraded fluid makes slipping worse and can be the entire story in an early case. That is why the first thing a sensible garage checks is the fluid level and condition, using the correct procedure for your particular gearbox.

Juddering and shuddering

A shudder when pulling away gently, or a vibration at a steady cruise in a particular gear, is often linked to the torque converter lock-up clutch or to worn clutch packs. On dual clutch gearboxes, judder at low speed is a well known complaint and may involve clutch wear, a sensor fault or software that needs updating.

It is worth ruling out the basics too. Engine misfires, worn engine mountings and driveshaft faults can all feel like transmission judder, so a good diagnosis looks at the whole driveline and not only the box.

• Shudder at light throttle: converter lock-up or fluid condition
• Judder pulling away on a dual clutch: clutch wear or adaptation
• Vibration under load: check mountings and driveshafts too
• Flare between gear changes: slipping clutches or low pressure

Delayed engagement and harsh shifts

If there is a noticeable pause before the car moves when you select Drive or Reverse, or the gearbox slams into gear, the cause may be low fluid, worn internal seals, a sticking valve body or a fault in the electronic control. Some cars also store learned shift settings, called adaptations, and these can drift after a battery disconnection, a fluid change or component replacement. Resetting or relearning them is sometimes part of the repair.

Warning lights, limp mode and being stuck in one gear tend to come from stored fault codes. Reading those codes is the start of the process, not the end. A code points at a circuit or a sensor, and you still need to test to find out whether the part, the wiring or the gearbox itself is at fault.

What transmission diagnostics involve

Proper transmission diagnostics combine a fault code scan, live data from the gearbox control unit, a fluid check, a road test and, when needed, pressure testing or inspection. We use that combination at Banks of the Tyne because codes alone can send you in the wrong direction. A solenoid fault code, for instance, could mean a failed solenoid, a wiring issue or low fluid pressure.

Diagnosis tells you which of three roads you are on: a simple fix such as fluid, a sensor or software, a repair to the existing gearbox, or replacement with another unit. We would rather you know that before spending on parts.

Repair or replacement?

When internal damage is found, the choice depends on how widespread the wear is, whether metal debris has contaminated the whole system, the availability of parts for that model and how the cost compares with a replacement unit. We can discuss manual and automatic gearbox repairs and gearbox replacement once we have seen what is inside, and cost is not something we can responsibly quote without inspection.

Driving a slipping automatic hard and hoping it will clear almost always makes the damage worse. If it is slipping, juddering badly or refusing to engage, get it looked at before it fails on a busy road.

Frequently asked questions