Crunch going into 4th

[FarmerPug]

This is a problem the car had before the new clutch and DMF. But even after they got changed, along with the gearbox oil its still there.

If giving the car some boot and going quickly through the gears the shift from 3rd to 4th if done quickly gives a bit of a crunch, it doesn't happen going down from 5th to 4th. But it does happen going up the way even if the clutch pedal is pressed as far down as it will go.

Under slower driving conditions it doesn't really happen, in the real world its likely to occur when overtaking in 3rd which normally has a change up to 4th at some point and the crunch happens. The gear engages ok there is never any issue getting it just wondering what might be causing it.

[lozz]

Hi.
Try.. Giving the throttle a blip (double-de-clutch)before slotting it in to gear..
If it then goes in smoothly..then it'd be worn syncro,,,s.

Something you just live with.

[PeterN]

You can get to the 5th gear by taking the end cover off the gearbox as it was added as an afterthought and isn't driven directly by the layshaft. I had a CX with the same problem many years ago, in fact the synchro eventually failed completely and I was able to replace it.

Peter

[FarmerPug]

Is there much to changing a syncro on a gearbox?

Although being a 406 it's probably cheaper to buy a breaker and use its box.
Not a huge issue i can drive away at this until it stops, it hasnt really got any worse

[PeterN]

It might be cheaper to buy a secondhand box for the parts but it would probably be less work to change the synchro in situ. I can't remember exactly what I had to do with mine as it was about 25 years ago and I can't remember what I did five minutes ago, the only thing I do remember was having several goes to refit the synchro hub as I had ball bearings flying all over the place but I suspect the design has been changed now to make it simpler to reassemble.

I'm sure someone on here must have done it recently.

Peter

[lozz]

Perhaps adding some molyslip might help.

I'd just live with it tbh...

[steve_earwig]

Molibbidibbenumumum - viewtopic.php?f=1&t=6123&p=60127&hilit= ... num#p60127

This reminds me of something....

Meh, just something for your clutch change vid perhaps Frank - later ML5Cs don't have a filler/level plug, you have to put the right amount in via the breather (which is much bigger) or the reversing light switch (which is also available on the earlier box and beats trying to get oil into the gearbox through the filler).

[FarmerPug]

Two flushes with 10-40 then some Molibbidibbenumumum, is it still working for you steve? Or was this on your 406?

It's definitely the syncro, had to be Wikipedia double de clutching , heard it mentioned in one of the fast and furious films, never thought it would be relevant in a 406. however the technique does work.

No filler level plug? I was just following the haynes book it referred to the ML5t but servicebox said the car has an ML5C. Is there much difference internally. it also mentioned disconnecting the speedometer sensor plug, as far as i can recall there was no speedometer sensor on the gearbox. Must be done through the abs sensor?

[steve_earwig]

T'was the old 406, it went ok for another couple of years as far as I can remember.

Haynes only covers up to 2002 IIRC, the filler/level plug delete must be after that. It should have the transponder but I'm no longer sure if it runs the speedometer and/or the ecu or if the ABS does one, t'other or maybe even both.

[Doggy]

There is a speed sensor on the diff housing. On full mux cars it's not used for the speedo, (that works off the ABS sensors), but it is used for the satnav.

Never figured out which one's responsible for the standstill threshold, (or whatever it's called), that works the auto door locks / changes the idle speed / switches the wipers to intermittent.

I think the ML5C is just a bit smaller externally, but it could be that ML5T's have reverse beside 4th and ML5C's have it beside first.