Speedometer out by 7kph

BossII

Registered User
Went past a speed reader doing 50kph and it said i was doing only 43kph, I turn around and go past it again only 43kph. I pick up my sister and she puts a gps speed reader on her phone and 50kph is only 43kph. Which explains why when i have my car in first gear it doesn't down ~~~~ until about 23kph compared to roughly 30kph for my old 89.

The odometer was replaced by the ford dealership for what ever reason. Are all SC speedometers out to lunch or is it just mine? Also would having a shift kit affect the speed at all? Which i don't think it does.
 
tire size?

I find it rather humorous that you misspelled shift and it blanked it out. Do you have stock size tires?
 
Our 35th reads about 5mph low...it's not unusual, I'd say.

If you're electronically savvy and it bugs you enough, it can be re-calibrated.

A different speedo gear might get you closer too....depends on what you have now though.
 
The speedo was off a few with my tire size choice on my Anny and I had a speedo shop look at the head...took him a few moments to change the spring and hand it back, no charge. Was dead on after that.
 
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Okay, my car only has roughly 120k kms on it with stock tires If i remember correctly the 89 was bang on for the speed and that car had around 250k kms. So not sure what was all replaced when they did the odometer. How would i re calibrate the speedo? If the car had rear gears done it would it through the speedo off, if they never replaced the speedo gears? Thanks for the info guys.
 
Replacement odometer has 44000kms on it and was replaced about 15-16 years ago when the car had roughly 73k kms.
 
Replacement odometer has 44000kms on it and was replaced about 15-16 years ago when the car had roughly 73k kms.

Your error is approx. 10% - I'd expect 5% to be normal.

You say you don't know why the speedo was replaced... Any idea if it was ever accurate? Is it the early style or late? What is the max indicated KPH?

I think we've covered the common issues that can contribute to a higher than normal error, such as diff has been changed, tires are not stock and hardware malfunction.

If you don't have reason to suspect tires or diff, I'd pull the cluster, then the speedo head and if the gears haven't started crumbling, I'd let a speedo shop tweak the spring a bit based on your actual vs. indicated data. If the gears are failing, new ones might be all you need. 15 years in them hasn't done them any favor in any case. The gears you get today are made with a different, more stable plastic compound, I think.

If the diff has been changed, you might get away with a different tooth drive gear at the trans.

A trans kit would have no effect, but...was the trans itself swapped out, do you know?

It would help trying to diagnose the error if you knew more about the car or when the error first started, tho
 
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I noticed it when i first bought the car. i noticed it didn't down shift into first gear until roughly 20kph, i was thinking it was just the shift kit or something. Not too many speed readers on the highway either so i always assumed since i owned the car the speedo was correct until the other day.

As for the transmission, it looks to be stock besides the deeper pan and trans cooler. I could be wrong, but it seems like the car does tach a little higher than the 89 did at roughly the same speed. I have tried doing some research to find what rpms SC run at in od to confirm anything with no such luck

Basically what i know is. It's Low kms, the odometer was replaced at roughly 73k kms, shift kit and deeper pan with cooler.

I need to do a history report to see what info i can find and maybe see if i can find the previous owner.
 
What is the max indicated KPH on that speedo face?

112 kph (70 mph) should be around 2,000 ~ 2,200 rpm I believe.

If you put the tach on 2,200, and if your speedo is off 10%, the indicated speed should read right near 100 kph...if your diff is stock.
 
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200 kph is the top speed on the face. At 100kph (93 real speed) in OD the car was tacking about 1490, then at 110 (103) It was closer to 1700-1750. Around 110 real speed the car is right about 2-2200 rpms.

I'll have to do another test drive in the daytime with cruise control on just ti verify my numbers
 
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Okay that rules out the rear diff. It's starting to get cold here, so not all that enthused to jack up and crawl under the car. I'll have to check that out though. At least with the car being 7kph out i can avoiding speeding tickets lol
 
Weak Spring

I got a 95SC 5speed. The Speedometer has always been 7mph fast on speeds below 40mph and 5-3mph on speeds above 45mps up until it hits 85mph. It's dead on at 95mph. Tested with GPS speedometer.
 
I noticed when going to my sisters place the speedo seemed to be reading a lot closer to what the speed sign was sign give or take a couple Kph.

I'll have to double check to see if it does it at higher speeds. With winter now hitting were i live i won't be able to do much until spring.

If it is a weak spring is it possible to fix? Thank you for all of the info so far guys.
 
If it is a weak spring is it possible to fix?

Very possible. They guy at the local speedometer shop took just a couple minutes and didn't even charge me. Took longer to find another spring that it did to change it. Of course that was with the cluster out of the dash and the head unit out of the cluster.

If I were you, I'd find a used speedo head, then replace the gears... unless you know they've been done, then swap it in. You might not even need to visit a shop.
 
Thanks everyone for the info. I'll look into maybe fixing the issue or just ignoring it. Depends on how bad the speedo bugs me :D
 
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