mysterious operation of the vacuum system...

[stefano64]

1 - engine running and idling:
the kickdown channel is closed
the overdrive channel is closed

2 - accelerating:
the kickdown channel is closed
the overdrive channel is opened (the valve clicks on the right side)
the car starts and accelerates regularly

3 - full throttle:
the kickdown channel is closed
the overdrive channel is closed (the valve clcks on the right side)
the car is at the max speed, what happens?

4 - braking and removing gas:
the kickdown channel is opened (the valve click on the left side)
the overdrive channel is closed (the valve clicks on the right side)
the car slows down with engine braking

5 - pressing the command low ratio with the engine running at minimum:
the kickdown channel is opened (the valve click on the left side)
he overdrive channel is closed

6 - pressing the command low ratio and then proceeding with a few of gas:
the kickdown channel is opened (the valve click on the left side)
the overdrive channel is opened (the valve clicks on the right side)
the car moves slowly with engine braking

I understand correctly?

[macplaxton]

DAF 66 Vacuum System Schematic by macplaxton, on Flickr

A = Overdrive solenoid
B = Kickdown solenoid

1 yes
2 yes - where throttle is 1/8 to 3/4 open - A is open
3 yes - near full throttle, carb switch contacts open again, A is closed. What happens? Nothing. Car is at top speed.
4 yes - effect is more noticeable at lower speeds.
5 yes
6 yes - keeps car is low ratio, usable range 0 - 50km/h

The degree of effect of having A or B side open is variable depending on the manifold vacuum at the time.

[stefano64]

Thanks mac!

But the clicks indicate that the solenoids work well?

It's possible that solenoids click but do not work properly? it is useful to open and go see the internal conditions? I have a kit from Danny (two diods and one or two gaskets)... I'ts difficult dismount and open the emv?

[macplaxton]

Clicks indicator the solenoid work, but the rubber valve seal may be defective. In the overhaul kit you have, you can disregard the diodes, these are for the Volvos with a tacho relay. (To protect the switching transistor inside the tacho relay from back EMF damaging it).

The unit can be taken apart, but only so far... I'll explain later. Typing on phone is difficult!

[stefano64]

I will wait patiently!

[macplaxton]

Find a good fitting screwdriver to avoid deforming the heads of the screws. Sometimes they can be quite rusty.


EMV screws by macplaxton, on Flickr

You can then remove each end and it should be straightforward to replace the rubber valve and the O-ring.

This is a 44 one, which differs from a 66, as it only has one solenoid, but the idea is the same.


EMV1 by macplaxton, on Flickr
EMV2 by macplaxton, on Flickr

That covers the main problem. Tearing of the rubber valve "mushrooms".

The other part that can cause issues in the spring loaded bit under the rear centre cap. It's glued together so it can be quite tricky to open the back of unit. The adjust screw is under the wax:

DAF_Vacuum_Valve_Screw.jpg by macplaxton, on Flickr

The round rear cover is on the opposite side. (You can see it above and to the left of "4" in the diagram above)

[macplaxton]

Oh yes and patience is required along with a small flat blade screwdrive to remove those 3 rubber mountings!