Register now to get rid of these ads!

Speedo off

Discussion in 'The Hokey Ass Message Board' started by dan sutton, Jan 15, 2011.

  1. dan sutton
    Joined: Oct 21, 2008
    Posts: 196

    dan sutton
    Member

    Are speedometers capable of being calibrated for age and or different transmissions, or do I just bite the bullet and replace it?
    '48 Chevy to be exact. Mine is off 10 mph at 30.
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 47,959

    squirrel
    Member

    There are a couple different things to calibrate...and it depends on what transmission you have, as well as the rearend and tire size.

    What's in your truck?
     
  3. dan sutton
    Joined: Oct 21, 2008
    Posts: 196

    dan sutton
    Member

    Original 216, T5 trans (did not have ratio tag) 15" wheels,tall whitewalls, GM 10 bolt
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 47,959

    squirrel
    Member

    Did you check the odometer accuracy? like drive a mile (according to highway mile posts or GPS) and see how many miles or tenths of a mile the odometer reads. You can get more accuracy if you travel 5 or 10 miles.

    Once you do that, you can see how far off the gearing in the speedo drive of the transmission is off. It needs to be correct for the rearend gear and tire size you have. If the odo is 17% fast, you need a driven gear with 17% more teeth to slow it down. for example if it has 14 teeth now, you'd get one with 16 teeth to fix it if you had 17% error.

    Get that working right, then see if the speedo is accurate.
     

  5. flamed34
    Joined: Dec 30, 2009
    Posts: 733

    flamed34
    Member

    You can sometimes get lucky by changing the speedo driven gear in the trans - depends on the drive gear and if you can get a driven gear in the right range for tooth mesh. I've never messed with the set in a T5, but in an TH350/TH400 the gears are color coded. There's several links on the internet with calculators that require driven gear, drive gear, tire size if you do some searches.

    Also, if you do some searches in your area, there are companies that can make adapters to go between your trans and speedo cable.

    I've had to use both methods in the past. Good Luck
     
  6. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 26,149

    Jalopy Joker
    Member

    search poject33.com and click on calculators to help figure out things. some times just guessing with speedo gear changes or add on reducers can get expensive. do more research on figuring out type of transmission speedo sender,outside diam of your tires, rear gear ratio, etc
     
  7. NoSurf
    Joined: Jul 26, 2002
    Posts: 4,148

    NoSurf
    Member

    Or you could measure the angle of the speedo needle between 10 mph increments and print out a new gauge face... ;)
     
  8. dan sutton
    Joined: Oct 21, 2008
    Posts: 196

    dan sutton
    Member

    Not too many weeks after I started this thread the speedo gave up the ghost completely, and I just used a GPS to monitor the speed. Now that I have the trans out while changing the engine to a v8, I pulled the driven gear out of the tailshaft housing to see what the problem might be.
    Well....there is NO sign of anything...drive gear, shaft, nothing in view as you peer into the hole. Just some blue plastic debris on the red driven gear!
    Houston...we have a problem! How difficult is it to pull the housings apart??
    Or should I just keep using the GPS?
     
  9. If you want to slow it down get a gear with more teeth. If you want to speed it up get a gear with less teeth.
     
  10. Doesn't look like any of the clusters have to come off/apart, but I've never been in one...
    [​IMG]
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.