ODOMETER testing OUTside the car?
11-22-2015, 11:51 PM
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84 300sd (w126) diesel
ODOMETER testing OUTside the car?
How can I TEST an ODOMETER (with new gears) , to confirm working, OUTside thecar, BEFORE reinstalling? Can I at least power the stepper motor, toconfirm it works?
84300sd (w126) diesel with a common problem: SPEEDometer still works,but ODOmeter stopped. Thanks.
84300sd (w126) diesel with a common problem: SPEEDometer still works,but ODOmeter stopped. Thanks.
11-23-2015, 05:33 PM
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84 300sd (w126) diesel
Again,the problem on my 84 300sd (w126) with 247k miles was that theSPEEDometer (126-542-5201) still worked, but the TRIPmeter and theODOmeter had stopped counting miles. The most likely cause of thisvery common problem is broken / missing teeth on the odometer gears. After removing the instrument cluster - a procedure well describedseveral internet documents and videos - I discovered that, sureenough...
Ihad odometer GEARS with broken teeth. I replaced three 3 gears (2big, 1 small) - ("12T-MERC-KIT-w126-DIESEL" $17 fromGaragistic.com). Now, with these new gears, the TRIPmeter and theODOmeter do count when I turn the gears manually (with my finger). So far so good.
Forgood measure, I replaced the two (2) 32-year old CAPACITORS (220ufand 47uF) on the PCB (printed circuit board: VDO 992-644-669). Thecapacitors are $1.50 ea. at RadioShack (The 220uF capacitor is272-1029. The 47uF capacitor is 272-1027.) NOTE: To access thecapacitors to replace them, you have to UNsolder the PCB from theodometer at five (5) points, DEsolder the two (2) originalcapacitors, solder in the two (2) new capacitors, and REsolder thePCB to the odometer at the five (5) points. There's a cleardescription with photos of this capacitor replacing procedure here:
http://www.e30tech.com/forum/showthread.php?t=119427
NOTE:Because these capacitors have very little "head room" oncethe PCB is REsoldered to the odometer, install the bigger (220uF)capacitor's bottom flush with the PCB, so that the capacitor is notstanding any "taller" than necessary on the PCB. Lay thesmaller (47uF) capacitor over "on its side" so it stands notaller than the bigger capacitor, again, not sticking up any tallerthan necessary on the PCB.
ThisDEsoldering /REsoldering is relatively easy if you have a decentsoldering iron with a pointed tip, and a fairly steady hand. BTW,removing the original solder when DEsoldering is fairly easy using aDEsoldering braid (like RadioShack 64-2090E)
BTW,when reconnecting the speedometer cable to the back of the instrumentcluster, I noticed that the plastic connector can appear fullyattached to the big pin, and screwed on, but still not making metalto metal contact INSIDE the plastic connector. Confirm that pin ismaking contact with that speedometer cable wire...that's what signalsthe car's speed to the speedometer / odometer.
Ihope these provided details save you time and aggravation. If fixingyour ODOmeter yourself is NOT for you, you can have it done for$100-200 by gentlemen like Rick Borth at Overseas Speedometer(SpeedoMeter.com).
So,at the end of all this, with now new gears and new capacitors, I'dlike to TEST the ODOmeter OUTside the car, so I can reinstall theinstrument cluster with confidence that the ODOmeter can and shouldwork in the car.
Fora bench test, I'd like to power the unit - is that, on the 8-pinconnector, 12vDC negative to pin 3 and positive to pin 7? - andduplicate the speedometer cable signal at, say, 60mph - is that 130Hz or so? - to the "big pin". Do I need to buy a squarewave signal generator to do this? (BTW, I specify 60mph because itwould be easy to confirm that the SPEEDometer is showing 60mph, andthat the ODOmeter is counting 1 mile per minute.)
I'msure this guidance would be helpful to a LOT of DIY ODOmeterrepairers out there, not just me. Thank you for your considerationand kind assistance.
Ihad odometer GEARS with broken teeth. I replaced three 3 gears (2big, 1 small) - ("12T-MERC-KIT-w126-DIESEL" $17 fromGaragistic.com). Now, with these new gears, the TRIPmeter and theODOmeter do count when I turn the gears manually (with my finger). So far so good.
Forgood measure, I replaced the two (2) 32-year old CAPACITORS (220ufand 47uF) on the PCB (printed circuit board: VDO 992-644-669). Thecapacitors are $1.50 ea. at RadioShack (The 220uF capacitor is272-1029. The 47uF capacitor is 272-1027.) NOTE: To access thecapacitors to replace them, you have to UNsolder the PCB from theodometer at five (5) points, DEsolder the two (2) originalcapacitors, solder in the two (2) new capacitors, and REsolder thePCB to the odometer at the five (5) points. There's a cleardescription with photos of this capacitor replacing procedure here:
http://www.e30tech.com/forum/showthread.php?t=119427
NOTE:Because these capacitors have very little "head room" oncethe PCB is REsoldered to the odometer, install the bigger (220uF)capacitor's bottom flush with the PCB, so that the capacitor is notstanding any "taller" than necessary on the PCB. Lay thesmaller (47uF) capacitor over "on its side" so it stands notaller than the bigger capacitor, again, not sticking up any tallerthan necessary on the PCB.
ThisDEsoldering /REsoldering is relatively easy if you have a decentsoldering iron with a pointed tip, and a fairly steady hand. BTW,removing the original solder when DEsoldering is fairly easy using aDEsoldering braid (like RadioShack 64-2090E)
BTW,when reconnecting the speedometer cable to the back of the instrumentcluster, I noticed that the plastic connector can appear fullyattached to the big pin, and screwed on, but still not making metalto metal contact INSIDE the plastic connector. Confirm that pin ismaking contact with that speedometer cable wire...that's what signalsthe car's speed to the speedometer / odometer.
Ihope these provided details save you time and aggravation. If fixingyour ODOmeter yourself is NOT for you, you can have it done for$100-200 by gentlemen like Rick Borth at Overseas Speedometer(SpeedoMeter.com).
So,at the end of all this, with now new gears and new capacitors, I'dlike to TEST the ODOmeter OUTside the car, so I can reinstall theinstrument cluster with confidence that the ODOmeter can and shouldwork in the car.
Fora bench test, I'd like to power the unit - is that, on the 8-pinconnector, 12vDC negative to pin 3 and positive to pin 7? - andduplicate the speedometer cable signal at, say, 60mph - is that 130Hz or so? - to the "big pin". Do I need to buy a squarewave signal generator to do this? (BTW, I specify 60mph because itwould be easy to confirm that the SPEEDometer is showing 60mph, andthat the ODOmeter is counting 1 mile per minute.)
I'msure this guidance would be helpful to a LOT of DIY ODOmeterrepairers out there, not just me. Thank you for your considerationand kind assistance.
