Speedometer failing?

Matt_aka_Dale

Matt_aka_Dale

SCCoA Member
When driving at 44 mph (gps) the speedometer shows 26 mph. I do have the correct speed sensor gear on. I changed it back when I changed the wheels on the vehicle about 7+ years ago and the speedometer worked correctly up until recently. The Odometer and Trip are both working. I popped out the speedometer assembly and inspected it, but didn't see anything immediately wrong with it.

I've removed the VSS and inspected it, but I have not tested it in or out of the trans(checking it's output). The connector and harness underneath looked fine. There was some ATF in the connector(likely from the trans pan gasket seeping over time), but I cleaned it out from both the connector and the sensor and test drove after that. No change. I have checked the ATF level multiple times now and it is at the correct level.

I then replaced the current VSS with another same style Ford NOS one. It was not the exact part number(it was off by two letters. #E45F-9E731-AA vs. my current one #E9LF-9E731-AA). Once again there was no change.

I will say, leading up to this, the speedometer would show these wrong readings at random. I'd drive to work with it acting up and park it, then hours later, drive it home and it would be working correctly. Now it's just always showing a wrong speed. Whether it's off by about 6mph or 20mph.

After reading through a few past posts in the forum, one so far has given me more of a clue...or maybe even an answer. "The VSS; if one works, the signal is getting to the speedometer module. So there's a problem inside the module if one works and the other does not." Which, to me, sounds like I might need another speedometer.

Any words of wisdom or have I potentially figured it out?
 
I'd replace the speedometer with a late model speedometer. You will also want to install new odometer gears in the speedometer while you are resetting the miles on the replacement speedometer. Bill Evanoff at Super Coupe Performance can supply the gears and may even have a used speedometer for sale. He can also install the odometer gears and reset the miles to match your current speedometer.
 
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. Check with Gene's Speedometer, Milford, Ohio. (513) 563-4280
 
SC-AL said:
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. Check with Gene's Speedometer, Milford, Ohio. (513) 563-4280
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What did you discover? My son wanted to take the bird out today after it's been sitting quite awhile (I had a bunch of large boxes behind it in the garage) & I looked over to see how fast he was going through town and it wasn't showing anything! Worked fine last time we had it out....
 
David Neibert said:
I'd replace the speedometer with a late model speedometer. You will also want to install new odometer gears in the speedometer while you are resetting the miles on the replacement speedometer. Bill Evanoff at Super Coupe Performance can supply the gears and may even have a used speedometer for sale. He can also install the odometer gears and reset the miles to match your current speedometer.
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Is anyone else selling the parts/services? I don't see them on the site anymore other then the gear for the trans.
 
You can get a cluster off Ebay, Bill, or the Thunderbird SC shop and just take the speedo out of it then you have other gauges for back stock. The gears from again Ebay or the manufacturer Odometer Gears. The price is about the same and Odometer Gears has a good instructional of how to handle the swap.
 
fstcoup said:
You can get a cluster off Ebay, Bill, or the Thunderbird SC shop and just take the speedo out of it then you have other gauges for back stock. The gears from again Ebay or the manufacturer Odometer Gears. The price is about the same and Odometer Gears has a good instructional of how to handle the swap.
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I'll check Odometer gears, I'd rather keep everything original if possible though I agree spares is a good thing to have also.
Thanks!
 
SC speedo-sm.jpg

I did some speedometer work today. I had a speedometer that I got at a pick-N-pull auto wrecker, a couple of weeks ago.. It was from a1990 SC, with 147,886 miles. I wanted to use the odometer/trip assembly from my 1989 SC, which has 115,838 miles on it. I did this by removing the needle. I twisted it past 120 mph to loosen it, then carefully removed it with a small fork. Came off easily. Then removing the face plate, gave me access to 3 screws that allowed the removal of the odometer assembly. I inspected, and cleaned the gears with a Q-tip, and alcohol. I reassembled the original odometer unit, and faceplate, to the replacement speedometer, that consisted of the circuit board, and motors. I reinstalled the needle, so it was right at the first hash mark,(5mph). I removed the screws, but never removed the cluster. I did a speed check before putting the lens, and everything back together. It matched my GPS perfectly, from 20, to 80 mph. You probably wonder why I didn't change the little gears? I have a theory that the gears get damaged from pushing the trip reset fast, and hard. I haven't been resetting my trip in the last 10K miles. I do take a picture of the mileage, when I get gas, instead. The complete one in the photo, is from my 1990 SC auto. I had been using it for diagnostic purposes.
 
My speedometer trips out at highway speeds, above 60 or so it starts skipping. Pretty sure my gears are worn out
 
The Needle bouncing is the either the DC motor failing or the clockspring/balance is off. I've just learned to drive by RPM, yes its a bit of a pain to go 30mph and trying to remember if in 3rd or 4th. If I'm cruising and blowing past traffic I must be in 4th gear ;)
 
bowez said:
The Needle bouncing is the either the DC motor failing or the clockspring/balance is off. I've just learned to drive by RPM, yes its a bit of a pain to go 30mph and trying to remember if in 3rd or 4th. If I'm cruising and blowing past traffic I must be in 4th gear ;)
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So I'm "assuming" the VSS output spins the DC motor so the speedo needle in in the proper place based on vehicle speed?
 
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