Page 1 of 2 12 LastLast
Results 1 to 15 of 19

Thread: Speedometer out by 7kph

  1. #1
    Join Date
    Jul 2016
    Posts
    64

    Speedometer out by 7kph

    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.

  2. #2
    Join Date
    Jun 2008
    Location
    Columbia,SC
    Posts
    610

    tire size?

    I find it rather humorous that you misspelled shift and it blanked it out. Do you have stock size tires?

  3. #3
    Join Date
    Apr 2002
    Location
    Greenville, IN
    Posts
    4,261
    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.
    Matt Haub
    Shootouts: '09 SS 1st | '10 Mod1 2nd | '11 Bracket 3rd | '12 Bracket 1st | 2013 | '14 Bracket 3rd | 2015 | '16 Bracket 1st & Mod2 2nd | 2017 |
    Black '89 5spd - 281K miles, MPx, E85, Alky-Inj RWHP: ? RWTQ: ? Best 1/4mi:12.521, MPH:107.23mph
    35th Anniversary Auto 46k miles | Red '93 Auto 186k miles
    My Garage

  4. #4
    Join Date
    Dec 2007
    Location
    PNW
    Posts
    6,376
    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.
    Last edited by KMT; 12-11-2017 at 09:29 PM.

  5. #5
    Join Date
    Jul 2016
    Posts
    64
    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.

  6. #6
    Join Date
    Dec 2007
    Location
    PNW
    Posts
    6,376
    When was the speedo replaced? Recently?

  7. #7
    Join Date
    Jul 2016
    Posts
    64
    Replacement odometer has 44000kms on it and was replaced about 15-16 years ago when the car had roughly 73k kms.

  8. #8
    Join Date
    Dec 2007
    Location
    PNW
    Posts
    6,376
    Quote Originally Posted by BossII View Post
    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
    Last edited by KMT; 12-11-2017 at 11:10 PM.

  9. #9
    Join Date
    Jul 2016
    Posts
    64
    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.

  10. #10
    Join Date
    Dec 2007
    Location
    PNW
    Posts
    6,376
    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.
    Last edited by KMT; 12-11-2017 at 11:55 PM.

  11. #11
    Join Date
    Jul 2016
    Posts
    64
    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
    Last edited by BossII; 12-12-2017 at 01:28 AM.

  12. #12
    Join Date
    Dec 2007
    Location
    PNW
    Posts
    6,376
    Around 110 real speed the car is right about 2-2200 rpms.
    Sounds like a stock diff to me.

    Might want to count the teeth/check the color on the speedo gear at the trans. Check here to see it it's still stock too: http://www.sccoa.com/faq/speedgr.html

  13. #13
    Join Date
    Jul 2016
    Posts
    64
    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

  14. #14
    Join Date
    Sep 2014
    Location
    Broken Arrow, Ok
    Posts
    193
    Mine will jump up to 100-120 while I sitting still, lol

  15. #15
    Join Date
    Aug 2004
    Location
    Latitude: 41.909147 Longitude: -72.450263
    Posts
    2,023

    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.


    Don't crash into a tree just to avoid a skunk!


Similar Threads

  1. Help!! im getting out smarted by a lug nut
    By nwnsc in forum Technical Forum
    Replies: 11
    Last Post: 01-10-2010, 12:37 AM
  2. What would make a shifter pop out of 1st gear by itself?
    By skydivr7673 in forum Technical Forum
    Replies: 3
    Last Post: 02-27-2006, 01:20 PM
  3. Bird got checked out by cops for first time..
    By stas in forum Super Coupe Club of Ontario
    Replies: 23
    Last Post: 06-06-2005, 04:25 PM
  4. Mark Martin breaks out of his slump
    By cary Jackson in forum Non Technical Forum
    Replies: 5
    Last Post: 05-29-2002, 12:17 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •