Manual transmission car automatically dropping gears for a second

millsy

I'm driving a Mazda 6 with manual transmission. The dash displays the gear I'm in.

Lately when I'm driving, the gears seem to have a mind of its own. Take today for instance, I was driving at a constant speed in 6th gear. Every so often the revs ramped up for a second and the dash showing the gear in 5th, then ther revs dropped back and the dash showed 6th again. I didn't manually change gear. Sometimes it showed 5th gear, less often showed 4th, but always goes back to 6th.

Also when I'm revving up, it might briefly drop a gear and then ramp up as normal.

It sounds like something isn't working properly. Any idea what I need to get replaced?

antodeco

Do you find that the clutch is slipping at all?

millsy

https://www.boards.ie/discussion/comment/121271198#Comment_121271198

Not sure how that would feel. There does sort of feel like there is brief loss of acceleration

colm_mcm

The car guesses the gear based on the engine rpm vs road speed. So if it’s saying 5th on the dash then the clutch is slipping.

millsy

So is that a clutch replacement? There's only about 60k miles (100k km) up on it.

Miscreant

https://www.boards.ie/discussion/comment/121273554#Comment_121273554

If the clutch is slipping then yes, it requires replacement. Mileage is no measure of how long a clutch will last, I have seen them needing replacement with less than 30k Kms on them.

millsy

Ball park how much would I expect to pay for a clutch replacement?

I recall someone telling me before that it's a good idea to also replace the gearbox when replacing the clutch as a lot of the cost of replacing the clutch is the labour and you can save that labour cost when replacing both together. Is this a good idea?

Stallingrad

https://www.boards.ie/discussion/comment/121273846#Comment_121273846

I think you may be confusing the flywheel with gearbox. It can be worth replacing the flywheel while the clutch is being replaced, a visual inspection by the fitter will usually determine whether it needs replacing or not. If you plan on holding onto the car for awhile it could be well worth changing at the same time.

Miscreant

Ballpark figures are hard to judge these days with all the price increases that have happened in the past couple of years. Used to be a clutch and flywheel could be anywhere from €700 to €1000 in a decent garage. Nowadays, it is potentially more.

Bring the car to a reputable garage and have them assess the clutch (usually done by driving the car). They will be best placed in letting you know what is needed.