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With the advent of cooler weather, my speedometer has become intermittent. It refuses to work when the air temperature is below 55-60. After about 10 minutes with the heater on, it suddenly springs to life. After that, it will continue to work after stopping and restarting for the rest of the day unless the car sits long enough to cool down completely, then the warmup cycle repeats.
I suspect a bad solder joint on one of the connections at the rear of the cluster. Any suggestions on where to look, and how to identify which one is the problem?
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Hi Blue Horse.
You didn't mention any other guages being affected, so I don't if you have the same issue I fixed a couple years ago. This was the situation on my 87 744t as temps dropped below 45 F:
Headlights off, no problems.
Headlights on...
no instrument or panel switch lights
speedometer, fuel guage and clock did not work
voltmeter and coolant guages did not register correctly
both dash turnsignal indicators were lit
high beam indicator was lit (high beams were not on)
all was well once the cabin warmed up (usually took 7-10 minutes)
I don't recall how I traced the issue, but I deduced that the dimmer unit was at fault. I was considering just to bypass the unit altogether but decided to first open the unit up and take a look at it. All I did was take off the back metal cover and remove the circuit board from the unit. The solder looked fine but there were a couple spots of corrosion that I just scraped off. I then put the circuit board back in. I can't remember what, but the metal cover was sitting awfully close to some contact on the circuit board and I was thinking perhaps it may have been flexing against the circuit board in colder temps, causing a short somehow. So, I left the cover off.
That's all I did, nothing else. No problems for 2 winters now. Test things out with headlights on and off. Hopefully, you have the same issue I had.
Kevin
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posted by
someone claiming to be Volvoman
on
Tue Nov 28 08:05 CST 2006 [ RELATED]
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Hello Blue Horse!
I have the same problem with my speedo (VDO) and my best guess is that the needle sticks mechanically when cold. Why?
1. I have resoldered all joints on the speedo with no improvement.
2. A whack on the cluster makes it work when cold.
3. When working, it will continue to do so for the rest of the day. My opinion is that a bad joint would make the needle jump up and down continuously.
4. The odo keeps running even though the needle doesn't move (rules out a bad sender unit)
So, my next move is to lubricate the needle using some kind of high grade watch oil, alternatively some electro cleaner (not WD40). If that doesn't work, I have to open the unit to see what makes the needle stick.
Good luck! (to both of us) :-)
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Two differences in our problems---when my speedo quits, the odo quits too, and whacking the dash doesn't seem to help it wake up, though once in a while when it has started when I moved one of the heater controls, but only after everything was fully warmed up (usually when cutting back the temp from max., as it was getting too hot inside the car)
My theory with the bad solder joint is that a part of it contracts when cold, breaking the connection, which is restored when it expands with heat as the car warms up.
Your problem may well be gummy old oil causing the needle to stick. You are correct in your choice of clock and instrument oil for lubricating it. If possible, clean the pivots with lighter fluid (naptha) then apply the oil sparingly--a tiny drop from the point of a pin should be sufficient. Use extreme caution when working on the speedo as it is very delicate.
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posted by
someone claiming to be Volvoman
on
Thu Nov 30 05:43 CST 2006 [ RELATED]
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OK, many thanks for the tips!
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What model year 740?
--
john
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Look for the small fuse like wire on the printboard. Replacing it fixed my spedo problems. Do a search in messages I posted. Somebody decribed the fix to me!
Enough problems left though.
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I concur. Last spring my wife's '87 740 speedo began to be intermittant, temp wasn't a factor. Needle would jerk around and eventually quit altogether. I jacked the rear and yes, it's a cramped area. I found the wire to the connector had flexed enough that it finally broke. I placed the rear of the car on jack stands on the rear jack points at the rocker panels (lifting the car by the differential). Letting the jack down dropped the rear end down quite a bit exposing the cable and the differential and the speedo connection. I also removed one end of the stabilizer bar and swung it up (I think...) and out of the way making it way easier to butt-splice and tape the cable. I also readjusted the cable positioning taking some of the stress off of it. Been fine since...
Roger
Southern Colorado
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I have had similar problems: no speedo when cold, suddenly started working when warmed up. However, the temperature was only coincidental. The culprit is the wires at the sensor on the differential have deteriorated and are shorting out. It is a tight space to work under, but I'd bet you find some rotten insulation on the sensor wires near the plug. I'd still like to get my car up on a rack and do a thorough re-wire of that area.
Hope this helps.
--
'92 745 B230F
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Thank you both TK and Data, but that's not it. I've already been there and done that. The wire was in fact bad and I replaced it. I know it's good now because the ABS light doesn't come on anymore when I go around a hard right turn. The problem is definitely related to the temperature in the interior of the car, which says to me it is in the cluster.
I should have mentioned in the original post that it is a 90 cluster, in an 88 car, which has a set of problems all its own---speedometer has an error which increases with speed, it reads slow at speeds over about 25, and will not read beyond 55 or so, which is actually about 75-80. I am more concerned with having an odometer that works (it reads correctly) so I can keep an eye on my mileage and service intervals.
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If you think you need one I have one from a 89 740 turbo. ledfoot
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Godspeed, my friend. Don't know where to lead you in that dark forest of mixing dash parts. Might I suggest you buy a cheap handheld GPS w/12 volt adapter to track mileage?
--
'92 745 B230F
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I'm not that concerned about measuring distances point to point, just want a cumulative total of miles traveled, so I can check fuel consumption and keep track of maintenance.
I don't think the intermittent problem has to do with the cluster being a different year than the car. I believe it is in the unit itself, and is probably what killed the car it came out of. It was a 90 GLE with the 16V engine. The intermittent odometer caused the timing belt to exceed its life span, and that's when the valves met the pistons.
I suspect the problem is a bad solder joint, like the ones that afflict the fuel pump and radio suppression relays, causing them to work intermittently.
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posted by
someone claiming to be jpezie
on
Thu Nov 23 06:05 CST 2006 [ RELATED]
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Check the mass-connection on the printed circuitboard behind the dasboard clock-cluster first before you try anything else.
Regards,
John
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