940 1992 Speedometer intermittent

mikeanthony · Post by **mikeanthony** » 24 Jan 2009, 17:31

Turn on ignition Speedo jumps to 50
As soon as as vehicle moves speedo jumps to 25 mph.
speedo behaves normally once speed exceeds 25 mph and cruise control will work normally.
Speedo continues to work normally up to 50-60 mph and then starts to dither and fall off. Cruise control stops working.
Reduce speed to say 30-40 mph and speedo and cruise control will begin working once again. Stop car, run in and out of a shop, start and sequence repeats all over again. Sometimes speedo will hang in at freeway speeds for a few miles.

I have de-powered every unit that speedo feeds into then turned on ignition but 50 mph still comes up every time. So it appears to feeding from the ignition switch and/or is feeding through a faulty circuit in one of the connected units even though they are not powered.

Any ideas before I start digging deeper. I found a dry joint in the ECC unit and now the AC works again. Might get lucky with the speedo.

Mike

Post by **billofdurham** » 25 Jan 2009, 12:41

The speedo is driven by a sensor in the differential. Check the wires at the sensor are making good contact.

There have been cases recorded where dry joints in the speedo head are the cause of the problem, especially in damp weather.

Bill.

mikeanthony · Post by **mikeanthony** » 26 Jan 2009, 11:21

Reply to Bill,

Have had the sensor off, examined the leads and connectors. Looks in very good shape considering age. Do you know if the output can be monitored with a voltmeter and where I could get info on impedance and output voltage? It ran yesterday for about 12 freeway miles without any problems.

mikeanthony.

Post by **billofdurham** » 26 Jan 2009, 11:57

The impedance at the sender should be 1820 + or - 180 ohms.

I don't have the output voltage.

Bill.

mikeanthony · Post by **mikeanthony** » 27 Jan 2009, 12:31

Bill,

Thanks for the info will check it out. Any idea on how to remove the instrument bezel trim. my 940 is nothing like that presented in Haynes or Chilton. They show people happilly undoing screws at the side of removed vents and beneath removable screw plugs. From the drivers position all I can see is a rectangular hole at each side of the trim. Poke a screwdriver in there and you encounter "spring give" but nothing loosens. had the drivers side dash speaker off, both the head light and ECC covers off. Cant see a thing!The trim moves a little but I hesitate to force crispy 16 year old plastic. Had the center dash ventilator grills out, nothing, except the need now to epoxy a few things back together

ANY BODY, IDEAS PLEASE.

Mike

Post by **billofdurham** » 27 Jan 2009, 12:46

You are poking in the right place with your little screwdriver.

See: https://www.matthewsvolvosite.com/forums ... 3&start=36

Go to the second post on that page.

Bill.

mikeanthony · Post by **mikeanthony** » 27 Jan 2009, 18:39

Hi Bill,

looked at Sams bezel picture, its right on. Have depressed the clip and pulled, real hard, on the slot with a modified paint lid remover. Feels like its bolted in. Slid a hacksaw blade all around where possible, cant feel any screws or bolts. Have you ever had one of these out? The solution must be obvious to the designer but it beats both me and my son. Advice or commiseration are both appropriate. Incidentally, I didnt realise just how world wide this is. here is sam in Ozz, Me in southern California and you in Durham. We are in the cold season @ 70 F but I am of the age where one pullover is appropriate.

mike

Post by **billofdurham** » 28 Jan 2009, 12:08

Incidentally, I didnt realise just how world wide this is.

Matthew's site appeals to Volvo owners all over the world and all are welcome.

Yes, I have had more than one of these bezels off using the instructions I posted for Sam. There were no screws or bolts when the cars left the factory and I can't see that a previous owner would have needed to put any in. You may be unfortunate like Sam with her radio which had been glued in but, again, I can't see why anyone would do that with the cluster bezel.

There is one spring clip at each side of the bezel which you can feel as you push with the screwdriver. Working on one side only push the clip hard while pulling toward you with the shank of the screwdriver. You should only need to release one side with the screwdriver and the other should come out easily once you get it moving. The clips are robust and not easy to damage.

My wife has suggested that if you are really stuck we could pop over to help as our cold season temperature today reached 2C (36F) out of the wind, I don't know what it was in the wind, and we are both of an age where as many layers as possible are necessary.

Let us know how you get on.

Bill.

GrumpyOldMan · Post by **GrumpyOldMan** » 31 Jan 2009, 19:30

My moneys on the speedo its self.
My father has a 91 940, and I've repaired the speedo.
It had leaking electrolytic capacitors.
If you can solder it's not to hard a job, just time consuming to do right.

Pic shows what I'm talking about.
If you want more info etc, lemme know and I'll help out as best I can..

EDIT, had the same faults, speedo would read anything upto 80klms/hour while at traffic lights.
And anything from 0-100 while driving.....

mikeanthony · Post by **mikeanthony** » 02 Feb 2009, 16:12

Hi Grumpy,

Been elsewhere for a few days, like whale wathching down the beach. Waiting for a speedo cluster from E bay real cheap. I fixed a bad joint on the cap your talking about. The speedo runs all the time now but still has that silly offset voltage standing on it. The voltage does not show on the sensor input so it must be generated in the speedo. Sensor measures 1800 ohms on the money and puts out about 2.5 volts AC at 35 mph and about 4 volts at 70 mph. I guess its some kind of sawtooth voltage. Will be back to announce any cures.

Mike