DCi 6 speed crunch into third

[anonymous-user]

Yours thoughts, please.

2010 Megane DCi 106 6 speed. It crunches into third unless changing very slowly.






I’ve just changed the gearbox oil. This seems to have made the other gears even nicer, but no change to third.

I’m assuming this is a synchro that is going?

Thank you.

[Mr2Mike]

Unfortunately the fact that a single gear is affected means it's very likely worn synchromesh. Does it still crunch if you change gently/slowly?

[anonymous-user]

No. There is no noise at all if you gently bring it in.

That would be a shame. Although a second hand gearbox is £120 according to eBay...

Can’t find anything online to suggest this is common.

[Gary C]

Worn balking ring.

This is the bit that prevents the synchro hub from sliding together while the speed diff is too great.

Box out and strip.

[anonymous-user]

I’m not sure if it has changed, but it only crunches when up shifting. It seems fine when going from fourth to third. Wouldn’t it be more likely to crunch the other way around?

Thank you.

[Gary C]

MJ85 said:

I’m not sure if it has changed, but it only crunches when up shifting. It seems fine when going from fourth to third. Wouldn’t it be more likely to crunch the other way around?

Thank you.

The balking ring has two slopes on it for both directions, as you start to attempt to engage the splines, the rings cone presses on the gear and spins up or slows down the hub until the force from the speed diff is lower than the pressure from the ramp, the ring moves and the splines slip together. If the ring is worn on one side and letting the hub slide before the speed is matched its possible it will only crunch one way.

The balking teeth are there to stop the splines meeting until the speed diff is almost zero.

Some boxes I've had are a bit sensitive to the type of oil, but a mk1 mr2 I had behaved exactly as described and had to come out, stripped down and new ring/hub fitted.

Quite a fun job if your mechanically minded.

[anonymous-user]

Thank you for the info. Appreciated.