Low Ratio Valve Problems.

[andrew]

I think (think) my Daf 33's low ratio valve isn't functioning properly. There's an ominous sound of leaking air from around the valve and when I connect my vacuum valve to the "change up" pipe leading from the rotary valve to the pipe that runs to the rear of the car there's no vacuum being created, no matter how hard I rev the engine. The vacuum should come on when the engine reaches 2850 RPM, but I'm getting nothing! The change-down side is working fine, both when the green button is on and when the brakes are applied. I checked there's vacuum coming FROM the manifold (well, there's bound to be, isn't there?) but it seems to be lost inside the valve, as there's no vacuum in the other big pipe that runs from the low hold valve to the rotary one.

I do have a spare low ratio valve, but I don't know if it's a 6 or a 12 volt one! Is there a way of telling by visual examination or does anyone know if there are any numbers I can look at to determine its voltage? I DON'T want to burn it out if it's the wrong voltage. My car's a 12 volt one, by the way.

[gromsound]

Hi Andrew, Andre here ;-)

I just went through my stash of spare valves for you with a multimeter.

I found that all 12V ones (including 66 type) show a (dutch*) resistance of about 35 ohms, while the 6V ones give a reading of about 10 ohms.

(didnt see any numbers or voltage values on them by the way)

You may swap the coil from your obviously defective valve if the spare is found to be a 6V one. I suppose the rubber valve disc in your valve is broken. You can of course use half a 66 one if that is available to swap parts.

good luck!

(* i will oonli zay dis wans ;-) )

[andrew]

Thanks for the advice! The valve currently fitted to the car has a resistance of 31.2 ohms, which is near enough to the 35 ohms you suggested. this is the resistance measured with the wiring isolated from the car; with the green lead connected to its feed from the low hold switch, even with the ignition turned off, the resistance drops to 0.07 ohms. This could be caused by a dead short through the small bulb in the switch. The low ratio hold valve I have in my store gives a similar resistance of 37.8 ohms, which, again, is more or less the same, the small changes could be caused through dirt on the terminals.

So far so good.... Although probably inadvisable, given current Health and Safely diktats, I was able to draw air through the valve by sucking on the large pipe in the middle of the valve that's not on the car, which is horizontal when the valve's mounted in the car. The air is sucked in through the other large pipe, through the valve and out through the middle pipe, so I've deduced that the manifold feed should be connected to the horizontal pipe and the pipe connecting to the rotary valve should be attached to the other large pipe. I've checked the valve in the car and it does exactly the same, so I'm going to investigate further.....

[starider]

Hi,

Let us know how you get on, I'm sure you have checked, but are all the short rubber vacuum connections to the primary unit in place and not perished?................starider

[gromsound]

you should also check the flow through the valve when energised with 12V. this will show whether the rubber ''pedestal'' on the solenoid is defective. You should also try blowing through the pipes, there may be a one way valve included in it (later type).
it should NOT open both ways without power on it, so i am afraid your spare one is also RIP...

[bobdisk]

Dont know if these pics are any help, I took them before dismantling so I could put it all back. Now its back together it seems to be working ok with the engine running (I think). Revs increase with brakes and green button. I have just tried a "suck & blow test" I can suck, but not blow the big pipe from the inlet manifold (reverse true at the other big pipe to the valve controlled by the accelerator). The two small pipes nearest the rubber cone over the wires connectors will pass wind (!) both ways.There is no apparent connection between the big pipes and the small pipes.

[gromsound]

Let's see if this helps:

[just a moment while i try to upload the pics somewhere, the ''image with sunglasses'' for direct insertion here as Richard described it doesnt work.....]

stationary

normal driving

braking or hill retarder on

dark dots = atmosferic pressure, open dots = vacuum

upper tube = thin for upswitch

lower tube = thick for downswitch

Hope this is helpful!

[andrew]

Thank you all! I've found where the problem was (wait for it....) My vacuum pressure gauge pipe had a split in it, and I feel somewhat foolish as a result, putting it mildly! Nevertheless, I've learnt a good deal more about the Daf 33's vacuum set up, and Gronsound's diagrams & Bob's pictures of his 33's pipework were very helpful.

Having used a new piece of smaller diameter pipe to run from the lowest outlet on the rotary valve onto my vacuum gauge, I've now set the valve to open at 2850 R.P.M., as per Steve Bidwell's advice in an earlier magazine. I'm satisfied that the electric low ratio hold is working correctly, although the green light on the dashboard occasionally illuminating for no reason is a bit odd! I suspect it's a faulty earth in the switch, as the car doesn't spontaneously change down when this happens. As a result of my investigations I now understand more fully where that vacuum goes and how it's routed through the system, which can only be a good thing! Did anyone else know that the two vacuum pipes running to the primary unit at the rear of the car have slightly different diameters? No, neither did I, until I looked very carefully a the ones on my car. I suppose this is to prevent confusion when reconnecting them to the primary unit after a belt change.

Thanks once again, one and all, for your help!

EDIT AN HOUR LATER: I've just been out for a run in the car and the change up seems perfect and very smooth. The change down also works perfectly. I don't have a rev counter fitted in the car yet, but it seems to be changing up at just the right time.

[dafman50]

Have both metal and plastic vac valves in stock all new.