Auto gearbox's usually never get their gear oil changed as per the general 60,000miles service intervals so its best to keep an eye on the level and condition yourself. Leaving the oil to dergade or allowing the oil level to drop will result in the gearbox starting to behave strangely, some of the of the following are common symptoms;
- gears are held for longer before changing up
- gear changes are not as smooth
- the gear box is not as responsive to minor throttle adjustments
- kickdown is not consistent, may not kick down to a low enough gear
- strange rattle noises on modest acceleration and revs
Generally its best to check the gearbox oil level when the car is warm, take it for a short steady drive simoply to get the car upto temperature then;
- pull up and park and leave the engine running
- select each of the gears in turn one at a time (repeat this approximately 6 times)
- check the gearbox oil level in relation to the 'HOT' mark on the dipstick
- if the oil is not at the right level (at the top of the 'HOT' marking) then top it up (only use the correct specified gearbox oil!)
- select each of the gears in turn once again (repeat this a few times)
- re-check gearbox oil level
Once the oil level is correct, take the car for a short drive to see what difference has been made.
A friend with a 1996 Mercedes AMG C36 automatic contacted me asking if I could take a look at his car as suddenly he's noticing a rattling noise under acceleration which he thought was his engine going and that the kickdown only went up by around 500-1,000rpm rather than whipping itself round to more higher revs. I took the car for a drive and thought this feels like a crude 4spd auto box rather than a slick n smooth 4spd. The throttle itself seemed fine with the correct tension, the gearbox oil (checked with engine initially off) indicated an 'OK' reading. So I thought I'd check it properly with the engine on, now the reading was off the scale! So a gentle drive to Halfords and then threw some Castrol ATF in bit by bit to ensure it went to the correct level (with the engine on).
Once I was happy with the oil level, I asked my mate to drive the car now and see how it felt and I'll try and see where this rattle noise is comming from....... the box instantly operated like a more modern 5spd box, very responsive to all throttle inputs, kickdown was accurate and consistent every time, shifting to the right gear for maximum attack mode. Also the rattle on acceleration had been eliminated! I also asked him to head towards faster roads where the revs can be kept around 2,500/3,000rpm and then to floor it a few times. The box now kicks down as it should each and every time.