The brief
The CLA was due for its transmission fluid service, Mercedes calls for it at the 60,000 and 120,000 km marks, and the owner wanted it done on time. That's the right call, the fluid does the lubricating, cooling and clutch-engagement work in there, and keeping it fresh is what keeps the shifts crisp and the transmission healthy. This gearbox is a seven-speed dual-clutch, not a traditional torque-converter automatic, so the service is specific: drain the old fluid, replace the transmission fluid filter, refill with the exact Mercedes-spec dual-clutch fluid, and then set the level with the transmission at the right temperature, because it's a fill-to-temperature procedure, not a dipstick. Done right, it's the cheapest insurance there is on a dual-clutch box.
The diagnosis
A check confirmed the transmission was shifting fine, no jerkiness, no slipping, no fault codes, just fluid that had reached its service interval. The filter was due with it. So it was a straight fluid-and-filter service: drain the old fluid, fit the new filter, refill with the correct dual-clutch fluid, and set the level properly at temperature.
The work
The old transmission fluid was drained, the transmission fluid filter replaced with a new genuine Mercedes unit, and the gearbox refilled with the exact dual-clutch-spec fluid. It was then brought up to the specified temperature and the level set precisely the way the procedure calls for, with the fill plug torqued to spec, and the adaptations reset so the clutches relearned their engagement points on fresh fluid. A road test confirmed clean, crisp shifts through the range with smooth pull-away and no jerk.
The outcome
Crisp, smooth shifts, clean pull-away, no jerkiness, and the transmission running cooler on fresh fluid. The CLA went home with the transmission serviced on schedule. Dual-clutch fluid that's done its interval loses its edge and lets the clutches and the box work harder, so changing it, the filter and setting the level right is the proactive job that keeps a good dual-clutch a good dual-clutch.
