940 auto overdrive fault.

John Davies · Sep 4th, 2005, 00:58

Oh dear.

My wife 1991 940 automatic is playing up. The overdrive has a life of its own - it sometimes won't switch off after it has been operated; one clicks the switch without success and then a few miles down the road - or a few days later - it will switch off again.

On other occasions it will switch itself on - light comes on and everything - and then - and have to be switched off - if it will. Sometimes varying speed and changing up and down help it to disengage. I think.

As far as I can see the possible faults are -

1. Weak internal spring on selenoid - presumably this would cause the selenoid to operate and light to come on (as far as I can see) if there was a surge iof pressure within the box. Question - can one dismantle the selenoid and change the spring or does one have to change the entire selenoid? - If so does one have to drain the oild from the box first? The Haynes book is useless as far as the auto box goes.

2. Faulty switch/relay - switch appears fine. Relay 'clicks' when fuse removed, but haven't removed and bench tested it yet.

3. Faulty earth - can cause selenoid problems, but I can't see how it would cause this particular set of problems though.

All suggestions welcome!!

Thanks

John Davies

PS Anyone got a working selenoid for sale? Is it the same as a 240/740 unit?

nedah · Sep 4th, 2005, 12:30

I have a 1992 940 Manual which recently displayed similar symptoms in the overdrive mode. The problem was traced to a corroded terminal at the solenoid. The condition of the terminal allowed the voltage to vary between 0.3v and 12v which explained the intermittent nature of the fault. Cost of replacement part 20p, cost of labour £40.

Not sure if this helps with your auto box but hope the solution proves to be as simple.

Sep 6th, 2005, 16:15

About 13 years ago on a 240GLE I had a problem with the overdrive disengaging itself when I was cruising at 70MPH.
I eventually traced the fault to a faulty INHIBITOR SWITCH on the outside of the gearbox casing. This was a simple cylindrical switch which was activated when 4th gear was engaged. The purpose of this switch is to prevent the overdrive being engaged in all gears except 4th.
I fitted a new switch (£10.00 in 1992) and it worked perfectly.
I am not sure if 940s have this inhibitor switch but it is worth a look.

Mike Walker
London
020-8656-3383

dustyv · Sep 7th, 2005, 11:24

Hi,
I have a 1991 940 SE estate Auto.
I am confused re this "Overdrive" issue. I have the normal 4 speed auto box BUT at just over 60 mph a 5th gear seems to come into being - is this the 'overdrive'?Also, if this is so, is it totally automatic, as I haven't any other switchgear to either operate it or stop it's operation.
I also cannot find any documentation relating to any overdrive on the 4 autobox.
Obliged for your observations and advice.
dustyv

John Davies · Sep 9th, 2005, 01:11

Sorry - my sloppy terminology - comes of years with manual overdrive boxes.

Correctly speaking, our 940 has a switch which operates a selenoid to lock out fourth gear on the auto box, thus enabling you to stay in third when towing etc. - useful for hills etc.

Regards

John Davies

Sep 4th, 2005, 00:58	#1
John Davies VOC Member Last Online: Sep 26th, 2015 22:56 Join Date: Dec 2002 Location: Walsall	940 auto overdrive fault. Oh dear. My wife 1991 940 automatic is playing up. The overdrive has a life of its own - it sometimes won't switch off after it has been operated; one clicks the switch without success and then a few miles down the road - or a few days later - it will switch off again. On other occasions it will switch itself on - light comes on and everything - and then - and have to be switched off - if it will. Sometimes varying speed and changing up and down help it to disengage. I think. As far as I can see the possible faults are - 1. Weak internal spring on selenoid - presumably this would cause the selenoid to operate and light to come on (as far as I can see) if there was a surge iof pressure within the box. Question - can one dismantle the selenoid and change the spring or does one have to change the entire selenoid? - If so does one have to drain the oild from the box first? The Haynes book is useless as far as the auto box goes. 2. Faulty switch/relay - switch appears fine. Relay 'clicks' when fuse removed, but haven't removed and bench tested it yet. 3. Faulty earth - can cause selenoid problems, but I can't see how it would cause this particular set of problems though. All suggestions welcome!! Thanks John Davies PS Anyone got a working selenoid for sale? Is it the same as a 240/740 unit?

Sep 4th, 2005, 12:30	#2
nedah New Member Last Online: May 13th, 2007 23:12 Join Date: Dec 2004 Location: Witham Essex	RE: 940 auto overdrive fault. I have a 1992 940 Manual which recently displayed similar symptoms in the overdrive mode. The problem was traced to a corroded terminal at the solenoid. The condition of the terminal allowed the voltage to vary between 0.3v and 12v which explained the intermittent nature of the fault. Cost of replacement part 20p, cost of labour £40. Not sure if this helps with your auto box but hope the solution proves to be as simple.

Sep 6th, 2005, 16:15	#3
MIKE WALKER Guest Location:	RE: 940 auto overdrive fault. About 13 years ago on a 240GLE I had a problem with the overdrive disengaging itself when I was cruising at 70MPH. I eventually traced the fault to a faulty INHIBITOR SWITCH on the outside of the gearbox casing. This was a simple cylindrical switch which was activated when 4th gear was engaged. The purpose of this switch is to prevent the overdrive being engaged in all gears except 4th. I fitted a new switch (£10.00 in 1992) and it worked perfectly. I am not sure if 940s have this inhibitor switch but it is worth a look. Mike Walker London 020-8656-3383

Sep 7th, 2005, 11:24	#4
dustyv New Member Last Online: Jan 18th, 2014 10:49 Join Date: Dec 2003 Location: Wenvoe	RE: 940 auto overdrive fault. - Question Hi, I have a 1991 940 SE estate Auto. I am confused re this "Overdrive" issue. I have the normal 4 speed auto box BUT at just over 60 mph a 5th gear seems to come into being - is this the 'overdrive'?Also, if this is so, is it totally automatic, as I haven't any other switchgear to either operate it or stop it's operation. I also cannot find any documentation relating to any overdrive on the 4 autobox. Obliged for your observations and advice. dustyv

Sep 9th, 2005, 01:11	#5
John Davies VOC Member Last Online: Sep 26th, 2015 22:56 Join Date: Dec 2002 Location: Walsall	RE: 940 auto overdrive fault. - Question Sorry - my sloppy terminology - comes of years with manual overdrive boxes. Correctly speaking, our 940 has a switch which operates a selenoid to lock out fourth gear on the auto box, thus enabling you to stay in third when towing etc. - useful for hills etc. Regards John Davies

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