300D OM606 auto gearbox question

[Creamy]

So, I have had this 300D Multivalve for nearly 3 years, and it has always had a bit of a gearbox issue, particularly when cold. 1st to 2nd is harsh, and 2nd to 3rd flares. From what I've read, this is common. It is possible to minimise the effects by adjusting throttle accordingly at the shifting points. Gearbox oil/filter has been changed which seemed to help a little, but I've learned to live with it. Also, when cold it seems to hold 1st gear for too long.

Anyway, I've just had the injectors/glow plugs replaced (that's another story altogether), and when it finally came back the shifting was greatly improved and it drove more like my other auto car with smooth up and down-shifting, and easy down-shifting under gentle acceleration.

In the month since then, the problem has gradually returned, and may even be worse than before. Having experienced smooth shifting for a brief time, I am optimistic about finally finding a solution, and I am assuming there is a vacuum system problem somewhere.

I have checked the vacuum coming off the pump is around 20mm/hg (I bought a guage specially for this) so this looks OK, and I have checked all the pipes/connections I can see, even under the intake manifold.

Any suggestions?

Where should I be checking vacuum readings, and what should I find?

Any help would be much appreciated!

Creamy

 

[Dieselman]

I suspect a vacuum leak at the pipe connections.

 

[Creamy]

Yes, that's what I thought - but what is the best way to seal the connectors -
grease/vaseline (but would make it easy to slip off)
RTV silicone (easy to inadvertently block the connection altogether)
something else?

 

[Creamy]

... an update

OK, it's been a while, so here's an update.

Decided to check the vacuum at a few different points today to see where there may be an issue.

Got a reading of around 22 direct from the vacuum pump, and around 11 on the feed to the auto box. This gradually drops over around 10 seconds so there is no major leak in the system. With the engine running, the auto box reading is pretty constant across the rev range, but drops if I open the throttle sharply. Opening to full throttle quickly drops vacuum down to around 1-2. But it quickly reverts back when I close the throttle.

How do these readings sound?

I've also been through all the vacuum connections I could get to (I removed the air intake to the manifold to reach the pipes underneath), checking if pushing/pulling the pipes/connectors affects the vacuum reading - it doesn't.

Any suggestions?

Thanks.

 

[carat 3.6]

I could be wrong here, but have you checked the vacuum conections at the egr valve, and the valves/flaps mounted under inlet manifold?

If I remember correctly one of the above is conected to the vent for the vacuum system. May have something to do with it.

 

[Creamy]

Thanks for the suggestion.

I'd like to know if these vacuum figures are within acceptable levels, or are they reading low?

If the vacuum is good, then I won't waste time on it. However, if the reading is lower than expected, then I'll investigate deeper.