340 auto valve connections

I`ve just got hold of a pristine 1988 340GL auto (22,000 miles only!)as a replacement for a recently deceased same model. On giving it a going over found that the vacumm control valve for the auto box has been disconnected (on both sides) I don`t know when this was done or why or indeed how long it has been like this.

Question is is there likely to be any damage to the engine /
transmission caused by running in this state - for example by prolonged over revving if the box didn`t change up properly?

The switch for the buzzer / warning light on the gear change was also
disconnected - but in this case it looks as if it may just have fallen off (very loose) Same question here.

Thanks

Will Plummer

I bought a 340cvt with a duff control valve in January!

In answer to your question: with only 22,000 on the clock the over revving is unlikely to have done any damage to your engine.
I guess there must be something wrong with the valve, gearbox or pipes though, or it would not be disconnected.

Check the valve:
Over 1800rpm there should be air going in through the left port (looking forward) and if you switch the low ratio hold it should go in the right port with quite loud hiss at any engine speed.
The rubber mushrooms inside the valves do perish and get stuck closed. They are near impossible to repair. I have tried using superglue but I got air leaks through the valve, which upset the mixture by adding air to the manifold. I got away with doing this to the low ratio hold side, but you couldn't with the change-up side as it is in use all the time, nearly.

If the valve does not give the correct airflows, check the electrical drives to it. DONT CONNECT 12 VOLTS across it!!! I have an expected voltage table which I can dig up if you want it.

Check the diaphragms in the gearbox:
Blow down each pipe in turn. A little air should go in but then stop with a pressure against your blow. When you stop blowing the air should blow back out of the pipe at you. Both sides should do this.
If the air blows out of the other pipe when you blow down one it may be blown diaphragms. If the air blows down contiuously but doesn't come back, suspect an air leak in the pipe.

Happy hunting
John

Thanks for the advice John

I have checked the valve and pipework as you suggested and blowing on the pipework suggested a leak which I tracked down to a disconnected vacumm pipe on the NS of the primary box. I now get a good "blowback" on each pipe

The valve works as your post suggests that it should, with a healthy vacumm as I increase the revs ( I can feel the valve actuating quite healthily ) and when I flick the low hold switch and a test run confirms that everything seems OK.

I am coming around to the idea that the diconnections were the result of cack handed fault finding attempts for a stiff and "graunchy" gear change - I have rectified this by reconnecting the microswitch in the gear change ( and thus the declutch servo valve) which was very loose and may have simply fallen off. Maybe this was the reason the car has such a low mileage - perhaps someone with a limited idea of how the system works checked a few connections sucked air through their teeth and suggested that "itsgonnacostyaguv"......

I`ll keep a close eye on things over the next few hundred miles and will be saving a few relevant items off the old car just in case..

Thanks again

Will Plummer

Yes. The motor trade outside Volvo specialists do regard these transmissions as a money-hole, mainly because they don't know what to do with them.
Good to hear you haven't any bad faults.

Regards
John

Hi, been reading this with interest ... I own a 1984 B 340 volvo auto which has done only 60,000 miles and has just passed it's mot with flying colours! :)

However I also have a problem with my auto box which I have had 4 a while now and haven't got round to solving...

It seems to me to be stuck in 'low gear hold' you can't go over about 30mph coz the engine screams. If you switch the low ratio switch it does not light up, occationally it does and when this happens it will change up, switch faulty? Vaccum unit faulty?

Really could do with this solved as my s40 is off the road and would be nice to potter round in the 340 for a while, any ideas would be much appreciated.

Craig Rigby

When I got mine it was doing 3300 rpm at 30 mph and 4000 at 45 mph. Beyond that the gearbox will not kill the engine as the centrifugal change-up comes in. But I had to fix mine.

Your description sounds like an open circuit in the low ratio hold electricals. I will get out my diagram tonight and post another message but if you have a voltmeter you can check, with the ignition on and the engine not running, whether you have 12 volts across the change-down side (points at road, not engine) of the 4-way vacuum valve. If so, you are electrically stuck in LR hold. (There are other ways you can be stuck in it).
DO NOT CONNECT 12 VOLTS ACCROSS ANY PART OF THIS VALVE as there are electronics involved!

If you find out where you are on the electrical side we'll take it from there...
:)

PS Have you checked the valve and pipework operation as in the previous post? The air going in through the right side of the valve at idle would indicate LR hold on without a voltmeter.

Excuse me for being really daft but the vacuum control is the white thing with 2 black mushroom shaped rubber bits either side with pipes going into the bulkhead?

Cheers
Will take the voltmeter from work home tonight and try it out over the weekend

--
Neo

Wow, you,ve even still got the rubber covers. I haven't.

I'll wait to hear about the results of your tests.

Tried some of the tests you were talking about, I seem to get a good blow back on each pipe, didn't get hold of a voltmeter so haven't really tested that... tried using a test bulb to see if it lit up and it didn't. Also visited my local 'scrappy' who had a rather dishevelled A reg CVT and tryed the valve control unit off that with no joy also noticed that the fuse for the valve control unit was blown replaced that and still no joy... and this black box thing which attaches to the valve control unit (am I right in thinking that that is the tachometric relay dodar) tried another one of those... still no joy...

One thing to note is that the low ratio hold switch doesn't light up (and it's not the blub!) it only stopped working when this stopped lighting up. I think that you were right when you said I was electronically stuck in low hold ... but I can't seem to get unstuck and now I'm running out of ideas!

Any ideas?

Much appreicated...

--
Craig Rigby

OK this is rather what I expected.

The low ratio hold control circuit contains three switches:

Brake pressure switch is between the LR hold switch and the relay.
It does not affect whether the LR hold switch light works.

The LR hold switch is in the middle of the circuit. The light works when the switch is switched because the LR switch is earthed through the kickdown switch.

The kickdown switch is on the throttle cable and is connected between the LR hold switch and earth. If this switch is open (in use) then the light on LR hold switch will not light up.

If you break the circuit anywhere, you get low ratio hold.

As your light is not working, suspect the kickdown switch (located on the throttle cable - probably inside the passenger compartment by the pedals) or the wiring from LR hold switch to kickdown switch to earth.

The tachometric relay switches the change-up side of the valve at 1800 rpm. However, it only does so if the change-down side is not energised.
Here is the truth table for this:
Engine speed---------LR hold-------Change-up----------Change-down
less than 1800rpm-----Off------------Off-----------------Off
more than 1800 rpm---Off------------On------------------Off
Any------------------------On-------------Off------------------On
So you won't get any change-up if the low ratio earth circuit, containing all three switches, is broken.
Happy hunting.