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I recently had a clutch change on my hyundai coupe '06. The mechanic told me he also changed the gearbox oil as it was the right thing to do.

  1. When changing the clutch, is changing the gearbox oil also necessary?

  2. I asked him what would happen if he didn't do gearbox oil as I planned to sell the car, and he said it could breakdown or develop some other fault. Is this true?

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  • how much miles did it have? – Daniel May 7 '18 at 14:06
  • it was about 89000 but mechanic didn't even know that, without checking when i handed in car he just asked if gear box oil had been changed, though from age of car he may have assumed it's old. Also thats the first time I even went to that garage. – James Wilson May 8 '18 at 0:06
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Typically, the gear oil does not need to be changed when the clutch is. Transmission oil is internal and not related to the clutch. So, it is likely your mechanic simply checked the oil and determined it would be a good idea to change it. It is possible it was part of routine maintenance that was undone.

Can it cause faults? It is possible. Gear oil breaks down over time and gets contaminated. This reduces its effective ability to lubricate. In that case, excessive wear and premature failure can occur.

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  • Can it cause faults to the point it will the car will break down or you won't be able to drive it? – James Wilson May 8 '18 at 0:47
  • @JamesWilson if left long enough to wear to failure, yes. When the gearbox fails, it completely prevents power from being delivered to the wheels. – Leliel May 9 '18 at 5:44
  • Anything is possible if not maintained properly. – CharlieRB May 9 '18 at 11:26
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Some cars are specified that the transmission oil does not need to be changed in the life of the vehicle, but some owners have found that ignoring that and changing the oil at 60k miles does improve the "slickness" or quality of the gear change...

So, he may just be doing you a good job as it may have been low anyway, cynics may also say that he was doing it to line his pocket just to charge you for the oil.

If he is a mech that you trust then he was just looking after you.

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If the clutch is used up (not prematurely) the car and thus the gearbox probably has a lot of miles on it. If you then choose to change the clutch, a small investment, it'd be dumb not to also change the gearbox oil right away. The oil quality does degrade over miles, and to preserve your gearbox and smooth shifting, it's wise to change the oil. It's mostly less than 2 litres, and hence inexpensive to do.

At the same time, while draining the oil, the mechanic will observe the magnetic plug and the oil coming out of the gearbox. Sometimes a lot of metal debris is present in the oil and on the plug, and then you know the gearbox isn't going to live much longer. That's good to know, and may likely greatly influence your investments in reparations.

All in all, a small but wise investment in your car. It's common practice in most garages.

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