'89 SC speedo way off...?

MrHomz

SCCoA Member
Hello all, I have a 1989 SC and the speedometer is only readying about 60% of the actual speed. At 115 km/h the needle only goes to 60 km/h. The odometer works as it should and is accurate.

Is this a VSS issue? Or any other ideas as to how to correct it?
 
If the odometer is accurate, then I would think the head is getting the correct signal from the VSS & the wiring to instrument cluster is good.

Does the cruise work properly?
 
The speedometer head is most likely at fault. The capacitors, etc. change in value, or fail over time. Needs to be sent to a speedometer repair shop.
 
If the odometer is accurate, then I would think the head is getting the correct signal from the VSS & the wiring to instrument cluster is good.

Does the cruise work properly?
Yes it does, used it yesterday and no issues with the cruise.
 
The speedometer head is most likely at fault. The capacitors, etc. change in value, or fail over time. Needs to be sent to a speedometer repair shop.
Okay I'll look into that.

It will after an hour of driving pick up speed so to speak, for example if I start out doing 115 it will read about 60... An hour later it might get up to around 75.
 
My 89 SC acted the same, but had an opposite error. This was an earlier post I wrote.

"In my 1989 SC, the speedometer would read about 18 mph fast at 40-50 mph. The inaccuracy would lessen, the more I drove. After about an hour, or more, it would only be off 3 mph. I temporarily replaced it with the speedo from my 1990 sc. Works fine now. I am either going to try an repair 89 original, or send it to a local speedometer repair shop."
 
My 89 SC acted the same, but had an opposite error. This was an earlier post I wrote.

"In my 1989 SC, the speedometer would read about 18 mph fast at 40-50 mph. The inaccuracy would lessen, the more I drove. After about an hour, or more, it would only be off 3 mph. I temporarily replaced it with the speedo from my 1990 sc. Works fine now. I am either going to try an repair 89 original, or send it to a local speedometer repair shop."
I pissed around with it yesterday, using the speedo out of another SC. That one, the spoeedo worked fine but the odo gear must be broken, so I know the cluster housing itself is okay. Today I drove it 2.5 hours to gret a windshield installed, and after 2 hours it read correctly. After sitting for 3 hours, it dropped about 10 km/h when I started back out, then 30 mins later it was correct again. Obviously a diode or resistor or someting on the speedo itself.
 
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