why is my Speedometer is OFF by 20 MPH!!!!!!!!!!!!!wkumale 03-07-2012, 10:05 PM Please help i have a 96 ranger 2.3 liter 5 speed. I just bought it and so i dont know the history.. The speedometer says 90 and the GPS says 72... the speedometer says 50 and the GPS says 36.... It seems the faster i go the more its off. I checked the tire sizes first. It has 195/70/R14 these look small but i was told these are what stock for the 2wd. Then i was told to try to replaced the Speed sensor.. I was told there are 2. One on the tranny and one on the rear. I was told to replace the one on the tranny. I did and there was no change. I searched a lot of threads and the rear sensor seems to only get replaced when the speedometer stops working altogether. What is my next step? anyone.... FishFind 03-07-2012, 10:12 PM What are the rpm at
when this is going on>> I would guess speedo wither on dash or on tranny. mmerlinn 03-08-2012, 11:19 AM Your tire size looks correct, but you can check them against the size noted on the VIN plate on the driver's door or driver's door support. Even if the tire sizes are incorrect, there is no way your speedometer could be that far off just because of the tires. The rear end ratio could have been changed by a previous owner. You may need to call the dealer to find out the correct ratio for your truck then check that info against the tag on your rear end. Other than that, the only possibility would be something broken in the speedometer chain, like sensor or speedometer head. taglicious 01-13-2013, 09:03 PM I just purchased a ranger with the same characteristics. When it's warmer out I'll check it out and see what the problem is. Mine, as it stands, is at the 15 mph marker. I'll post up as soon as I figure out what the problem is. taglicious 10-07-2015, 09:13 AM I just purchased a ranger with the same characteristics. When it's warmer out I'll check it out and see what the problem is. Mine, as it stands, is at the 15 mph marker. I'll post up as soon as I figure out what the problem is. i forgot to ask... what does your gauge say when it's parked? Mine actually says 15 mph. :runaround: 65comet 10-07-2015, 01:56 PM Could be someone took the speedometer apart to mess with the odometer and roll back the miles. When they put it back together they didn't push the speed arm indicator back in to the correct position. Automotive Network, Inc., Copyright ©2022 C1 & C2 Corvettes General C1 Corvette & C2 Corvette Discussion, Technical Info, Performance Upgrades, Project Builds, Restorations Speedometer off by 20mph +/- Heel &
Toe Thread Starter
Member Since: Aug 2018 Location: Palm Springs, CA Posts: 18 Received 0 Likes on 0 Posts Hi, I have a '63 327/340 w/4spd that I just picked up. At low speeds 35mph the speedo is accurate, but the faster I go the more the variance. What's the best method for correcting - I'd rather not put more miles on the clock than necessary! Thanks. Race Director
Member Since: Jan 2003 Location: Central Arkansas Posts: 14,326 That's a pretty sizeable speedo error but I was guess that the speedometer gear just needs to be changed. First thing to do is climb under the car, take the speedometer cable loose at the transmission, remove the retainer bolt and remove the speedometer gear housing and plastic gear. They just pull out once the bolt and retainer are removed. But the o-ring will provide a little resistance so you will have to work it out a little. Count the teeth on the gear and report back with that information and the color of the plastic gear. Also, do you know for sure what your rear gearing is? If not you should try to determine that too. You will get some help then with selecting a new gear. There is a possibility the speedometer head up in the instrument panel is out of calibration - but try the easy stuff first with the speedometer gear. The following 3 users liked this post by DansYellow66: Melting Slicks
Member Since: May 2001 Location: Dadeville AL Posts: 2,615 If the speedo gear is wrong (possibly due to tire size or rear gear change), then the error will be proportional at all speeds. For example, if it is 5 MPH fast at true 30 MPH, then it will be 10 MPH fast at true 60 MPH. If the error is not proportional to speed, then I would suspect either a problem with the speedometer head or possibly some slippage somewhere in the gear/cable. ..... I drove my car for years with a known error of 10%. For example, I knew that when the speedometer showed 60 MPH I was really doing 66. The following users liked this post: Heel & Toe Thread Starter
Member Since: Aug 2018 Location: Palm Springs, CA Posts: 18 Received 0 Likes on 0 Posts Quote: Originally Posted by DansYellow66 That's a pretty sizeable speedo error but I was guess that the speedometer gear just needs to be changed. First thing to do is climb under the car, take the speedometer cable loose at the transmission, remove the retainer bolt and remove the speedometer gear housing and plastic gear. They just pull out once the bolt and retainer are removed. But the o-ring will provide a little resistance so you will have to work it out a little. Count the teeth on the gear and report back with that information and the color of the plastic gear. Also, do you know for sure what your rear gearing is? If not you should try to determine that too. You will get some help then with selecting a new gear. There is a possibility the speedometer head up in the instrument panel is out of calibration - but try the easy stuff first with the speedometer gear. DansYellow66 - thanks! I figured this was the place to start, but wanted to get a little feedback. I don't know the ratio, as the car was restored 20 years ago, and it seems to have other minor modifications - Cam, etc.. Will go through the paperwork to see if I can shed more light on that. Will pull the gear and report back. Cheers! Heel & Toe Thread Starter
Member Since: Aug 2018 Location: Palm Springs, CA Posts: 18 Received 0 Likes on 0 Posts Quote: Originally Posted by kellsdad If the speedo gear is wrong (possibly due to tire size or rear gear change), then the error will be proportional at all speeds. For example, if it is 5 MPH fast at true 30 MPH, then it will be 10 MPH fast at true 60 MPH. If the error is not proportional to speed, then I would suspect either a problem with the speedometer head or possibly some slippage somewhere in the gear/cable. ..... I drove my car for years with a known error of 10%. For example, I knew that when the speedometer showed 60 MPH I was really doing 66. kellsdad - thank you - I have to look closely at the margin of error at all speeds to verify. I think it's consistent, but way more that 10%. Pro
Member Since: Feb 2015 Location: Omaha NE Posts: 532 I think the original poster is asking if he should change the gear in the transmission. Will going to a larger gear correct the speedometer? Assuming he has a 27 inch or close to stock tire. Will the rearend gear make a difference if the tire is stock height? There are 2 links in the middle of the page that might help explain what gear you may use, 24 or 25 tooth. Last edited by 61corv; 09-23-2018 at 01:59 PM. The following 2 users liked this post by 61corv: Safety Car
Member Since: Aug 2011 Posts: 3,550 The original plastic gear is brown and has 18 teeth. If you want the speedometer to go slower you need the next size which is black and has 23 teeth. The following 2 users liked this post by MOXIE62: Burning Brakes
Member Since: Mar 2001 Location: dalton ma Posts: 1,132 It's unlikely the gear is the wrong one if the speedometer is accurate at one particular speed. I have the same problem with my '62. Waaaay off at low speeds but the faster I go the closer it gets to correct. My problem is some kind of imbalance inside the speedmeter due to some soldering inside the speedometer from a way back when "bubba" repair. Do not worry about the miles (if in fact you have the correct gear) as there is no direct relationship between the odometer and the speedometer. Odometer is gear driven, speedometer is magnetic driven. The following users liked this post: Race Director
Member Since: May 2000 Location: Redondo Beach USA Posts: 12,487 Quote: Originally Posted by dsafian Hi, I have a '63 327/340 w/4spd that I just picked up. At low speeds 35mph the speedo is accurate, but the faster I go the more the variance. What's the best method for correcting - I'd rather not put more miles on the clock than necessary! Thanks. There are two kinds of speedometer error - offset error and gain error. Gain error means that the percent error is constant at all speeds. Offset error means the speedometer is off by constant MPH at all speeds. The limited data you've provided indicates you could have a combination of both offset and gain error, but more data is needed. Take a set of readings in 5 or 10 MPH increments from 15 MPH to your highest freeway cruising speed and compare them to either a portable GPS in your Corvette or the readings of a modern car pacing your Corvette. Post the data. Gain error can be caused by incorrect speedo gearing for the installed axle or tires with significantly different revs/mile than OE, but your installed 205/75R15 tires are close enough to OE tires revs/mile that they will not introduce significant error. Gain error of more than 3-4 percent can usually be corrected by installing a different speedo driven gear, which will change the reading up or down by about five percent. Offset error can only be corrected by removing the speedo needle and reclocking it on the pin. In addition to the speedo/GPS data you should read the axle code that is visible between the strut rod bracket and spring, and you may have to do some cleaning to see it. Also, count the number of driveshaft revolutions for one axle revolution to verify the installed ring and pinion ratio. It may be different from the code that shows the original axle ratio. There's no way anyone can diagnose and recommend a solution to your problem until you provide a complete set of data as discussed above. Duke The following users liked this post: |
Why is my speedometer off by 20 mph
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