Mercedez class a

Hi, I'm having problems with the gearbox in my A-Class. When the car is stopped, the gears shift fine, but when I'm driving, I can't get it into third gear. Can anyone help me and tell me what the problem might be? Thanks!

Is your Mercedes manual or automatic?

Hi, my Mercedes is a manual, not an automatic.

Hi, I hope the following information is helpful: (There's a clutch master cylinder under the transmission; you need to bleed the system.)
On the driver's side fender, there's a servo motor. Remove the motor cover and turn the armature by hand so that you have pressure at the master cylinder to bleed the system. You should use a 10mm wrench. Otherwise, check that the servo motor works automatically with the brake pedal pressed. If all of this is okay, the clutch disc is most likely worn. Remember, it's a very simple system (don't forget the scanner), but it's most likely a mechanical failure. Regards, and I hope this information is helpful.

If you have the motor supports in good condition the most caused thing is that it is the synchronizer ring, of the third speed, since it not only has one.