05 ram 3500 srw diesel keeps losing speedometer.

Golf4llfe

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Joined
Jul 13, 2020
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4
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Make
Dodge
Model
Ram 3500
Year
05
Miles
190000
Engine
5.9
I've replaced the sensor and the wiring still have the taped loom around them. It'll act up when I idle for a period. I'm at a loss. Thanks for your help in advance
 

grcauto

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May 29, 2014
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Cluster?
 

NickD

wrench
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Aug 28, 2007
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Use to be a rotating permanent magnet, faster it rotated, the more the speedometer needle would rotate CW.

Now electrical pulses to an integrated circuit that converts these pulses to a proportional DC voltage, the speedometer is actually a volt meter. Usually fine poor electrical connector, particularly on the printed circuit where the cable connector is located. As this connector has more mass, when wave soldered, leaves some flux on the pins resulting in an erratic connection.

Typically its good when cold, heat expands the female for an erratic connection, and even with a tad of flux left on the pins that corrodes causing expansion. Hot soldering iron on each pin on the PCB cures this, you will see a puff of smoke.

On other Chrysler products I work on, poor contact for the power to the PCB, but here, everything goes black. Actually started in around 1985 or 6 when our wonderful EPA banned electroplating in the USA, we got better quality sending our parts to Thailand, Mexico was worse, China really sucked to borrow a teenage word.
 

Golf4llfe

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I'm taking it to a automotive electrical specialist Thursday. I'm hoping they can find the culprit.
 

NickD

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If you have any kind of GPS like a Garmin very accurately shows your speed.

Ha, use to go to an interstate and use a stop watch between mile post, driving at 60mph, should cover a mile in precisely 60 seconds. If say takes 65 seconds take the ratio of 60/65 times 60, speedometer 4.7 mph slower than 60.

With GPS just compare that number with your speedometer. These new cars are really quite accurate
 

NickD

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Worse one I worked on was a power inverter for a fluorescent display on a 94 Olds. Idiot selected the power rating based on a junction temperature of 25*C, but the actual power dissipation raised the junction temperature to 126*C. No wonder what the display kept on going black, and nothing, no speedometer, engine temperature, etc. nothing. Had to mount sizeable transistor on a heat sink wired to the same spot the original transistor were located.

I spoke to shops claiming to repair electronic dashes, maybe a capacitor, or a transistor, but if the microcontroller is bad, unrepairable, no way to purchase one from the OEM, but will sell a complete replacement panel for both arms and legs. But over the years, the major problem with these things were cold solder joints.

Another problem is ribbon cables, okay for a desk computer, but not for a vehicle that is suppose to work in a -40 to 125*C temperature environment with a humidity range of 0 to 100%. Ha, Lexus came out with a liquid Crystal Display, LCD for short, if the temperature dropped close to 0*F, liquid would freeze and that was the end of that display. Can sure find a bunch of idiot engineers. Ha, told some of them, company would be better off doubling their paycheck and make them stay home. Least they won't be in the plant doing damage.

Lot of them felt the company owed them a living for sleeping through a differential calculus class.
 

Golf4llfe

Newbie
Joined
Jul 13, 2020
Messages
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Points
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If you have any kind of GPS like a Garmin very accurately shows your speed.

Ha, use to go to an interstate and use a stop watch between mile post, driving at 60mph, should cover a mile in precisely 60 seconds. If say takes 65 seconds take the ratio of 60/65 times 60, speedometer 4.7 mph slower than 60.

With GPS just compare that number with your speedometer. These new cars are really quite accurate
I tried that today and it shows I'm going faster than I actually am. The truck has bigger than factory tires so that's backwards isn't it?
 

JackC

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Nov 14, 2006
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1,665
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Location
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Think about it-- The circumferance of your bigger than stock tires is more than stock. Therefore every time the wheel and tire assy goes around you travel farther down the road than the stock speedo thinks. That's faster. So, your truck is doing what it should and you are speeding when you think you are following the speed limit.
 

NickD

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Aug 28, 2007
Messages
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Have a 15 buck speedometer/odometer on my bicycle, since it works with anything from a 16 to 28" wheel, it can be adjusted quite accurately.

But can't make speedometer adjustments on say a $40,000.00 automobile.

Last time I received a speeding ticket, had my cruise control set, but my car creeped up to 57 mph at bottom of a steep hill where a cop was hiding, got fined a buck for each mile over the limit that was two dollars, and was told by the judge the law is like a pane of glass, once its broken, it broken. The court cost was 200 bucks.

Youngest daughter received two tickets in town in the same month, 27 and 28 mph in a 25 mph zone, fines weren't too bad, but our insurance company raised the rates $3,400.00 per year, this time changed insurance companies.

If I take my Supra out, can get a speeding ticket when parked.
 
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