While space pre­cludes list­ing com­mon fail­ures for ev­ery au­to­matic gear­box pro­duced in the last 20 years, look out for five com­mon symp­toms that in­di­cate po­ten­tial prob­lems.

Car Mechanics (UK) - - Automatic Gearboxes -

1. Slip­ping gears and sud­den ris­ing en­gine revs be­tween shifts (‘flare’)

This tends to be caused by low oil pres­sure, or in­cor­rect or poor-qual­ity fluid be­ing used. Look for in­cor­rect fluid lev­els, as well as a blocked oil fil­ter.

2. No clutch lock-up from the torque con­verter

Usu­ally caused by an elec­tri­cal prob­lem and not the trans­mis­sion. Check the brake pedal switch, as lock-up should can­cel, when the pedal is de­pressed. As lock-up func­tions only at nor­mal op­er­at­ing tem­per­a­tures, a faulty coolant tem­per­a­ture sen­sor might be re­spon­si­ble, for ex­am­ple.

3. De­layed en­gage­ment af­ter se­lect­ing ‘Drive’ or ‘Re­verse’

Look for a worn, or dam­aged, gear se­lec­tor ca­ble and loose link­ages. Drop­ping food, or drink, into the gear se­lec­tor mech­a­nism can af­fect the elec­tri­cal con­tacts and may just need a de­gree of in­te­rior trim dis­man­tling and a good clean.

4. Miss­ing gears or no drive

Usu­ally caused by faulty gear-speed sen­sors mounted on the trans­mis­sion. With some gear­boxes, it is pos­si­ble to swap the con­nec­tors around by ac­ci­dent. Have a live di­ag­nos­tic check con­ducted to eval­u­ate the read­ings be­fore sus­pect­ing that the more ex­pen­sive gear­box in­ter­nals are the cause of your prob­lems.

5. Noise

Any new and un­usual sounds in­di­cate a prob­lem and should be in­ves­ti­gated im­me­di­ately, not only to en­sure safety, but also to pre­vent cat­a­strophic dam­age lead­ing to ex­pen­sive re­pairs.

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