Results 1 to 13 of 13

Thread: Dana 20 speedo correction question

  1. #1
    Registered CJBilly's Avatar
    Join Date
    Jun 2006
    Location
    East Central Indiana
    Posts
    175

    Default Dana 20 speedo correction question

    Looking for some sort of gear reduction/multiplier unit that connects to my Dana 20 for the speedo cable. Has anyone seen one or knows where to buy one?
    I figured once I could find one, probably would need to find a speedo repair place to swap out the gear(s) to match my axle gearing and tire combo.

    Thanks!

  2. #2
    Registered Don Stephens's Avatar
    Join Date
    Aug 2009
    Location
    Yorba Linda,Ca.
    Posts
    1,253

    Default

    It sounds like you just need to install the right speedo gear. There are outfits that will tell you what speedo gear you need and can supply you with one. Replacing it yourself is very easy to do as it is located at the end of the speedo cable at the transfer case.
    http://www.jeep4x4center.com/jeep-speedometer-gears/
    A speedo shop will do it for you if you want to pay their price.

  3. #3

    Default

    For the Dana 20, there are two speedo gears that need changed. The primary gear rides on the output shaft. The secondary gear is a smaller one that hooks up to the speedo cable. Finding new ones is impossible. You will need to dig through old t-cases. Dana 18 speedo gears are the same set up as Dana 20 and interchange.

    The gear calculators on the www don't work for the Dana 20 but back calculating it to figure out what you need based on your modifications is relatively easy.

    Here is the basic calculation. You just need to know the number of teeth in the gear you have.



    Bigger tires are going to slow the speedometer reading. So the ratio of the tire change would be:

    Old tire size/new tire size = tire ratio

    Lower gears are going to speed up the speedometer reading. So the ratio of the gear change would be:

    New gears / old gears = gear ratio

    For the overall ratio effect, multiply the two ratios together:

    Tire ratio x gear ratio = over all ratio change

    Multiply by 100 and you will have the percentage the speedometer is off.

    You can also multiply the over all gear ratio by the number of teeth on your speedo gear and that should give you the number of teeth you will need on a new speedo gear to correct the reading.
    Last edited by John Brereton; 12-22-2010 at 08:48 AM.
    '79 CJ5 with not much '79 left to it

    SOA on Wagoneer Dana 44s locked
    T18/D18 with OD drive train
    258 with HO 4L head and OBD1 Fuel Injection
    Still fixing and building after almost 20 years

  4. #4
    Registered CJBilly's Avatar
    Join Date
    Jun 2006
    Location
    East Central Indiana
    Posts
    175

    Default

    Don- I knew there were replacement speedo gears but I never saw anything for the older CJ transfer cases. Those would be helpful for my MJ if I needed them.

    John- The way my CJ is set up, I'm off about 10-15 MPH when driving down the highway. Nice set of calculations that you posted.
    I was hoping that there was something that screwed on the Dana 20 output shaft. Either I need to come up with some old speedo gears from my Dana 20/ Dana 18 transfer cases or remember to go 40 MPH in a 55 MPH speed zone.

    Thanks guys!!!

  5. #5
    Registered Don Stephens's Avatar
    Join Date
    Aug 2009
    Location
    Yorba Linda,Ca.
    Posts
    1,253

    Default

    After doing some research, I see the situation that you are in, John's post was informative. I have 35" tires/4.10 gears and still use the oem speedo gear. That gear reduction box does sound like a neat project though.

  6. #6

    Default

    I have some 15 tooth speedo gear sets. I found a 20 tooth one out of an old Scout which is what I'm using now. 15 tooth gears seemed to have been the norm if I remember right. The Scout had 4.27 gearing from factory which is why it had the 20 tooth speedo gear set.
    '79 CJ5 with not much '79 left to it

    SOA on Wagoneer Dana 44s locked
    T18/D18 with OD drive train
    258 with HO 4L head and OBD1 Fuel Injection
    Still fixing and building after almost 20 years

  7. #7
    Registered CJBilly's Avatar
    Join Date
    Jun 2006
    Location
    East Central Indiana
    Posts
    175

    Default

    Quote Originally Posted by Don Stephens View Post
    After doing some research, I see the situation that you are in, John's post was informative. I have 35" tires/4.10 gears and still use the oem speedo gear. That gear reduction box does sound like a neat project though.
    Look at what I found- check these out.
    http://www.wildhorses4x4.com/product...nco_Dash_Parts

    Looks like John is already on top of it.

  8. #8
    Registered Don Stephens's Avatar
    Join Date
    Aug 2009
    Location
    Yorba Linda,Ca.
    Posts
    1,253

    Default

    CJBilly, So now instead of having to replace the speedometer gear and the speedometer driven gear, all that is needed is to find the correct speedometer drive gear from Wild Horses?

  9. #9
    Registered CJBilly's Avatar
    Join Date
    Jun 2006
    Location
    East Central Indiana
    Posts
    175

    Default

    Don,

    It appears that the solution would be is to replace the speedo drive gear inside the dana 20 transfer case with the correct speedometer drive gear from Wild Horses.
    The actual speedometer at the dash would be left alone. I was hoping that there was an adapter of some kind that would correct the problem that would screw onto the speedo connection. Doesn't appear so.
    JP magazine (Feb. 2009) did an article on this issue. This is what I copied from the JP website.

    "Older Jeeps with Spicer 18 or Dana 20 T-cases are the hardest to re-gear because parts aren't that plentiful and the output retainer requires some disassembly to get to the components. Here you see the speedometer drive gear indexes the speedometer-driven gear, which is captured in the rear ouput housing.(picture shown) The drive gear is a light-press fit on the output shaft."


    Scott
    Last edited by CJBilly; 12-23-2010 at 10:44 PM.

  10. #10
    Registered
    Join Date
    Nov 2003
    Location
    lexington,indiana
    Posts
    37

    Default

    A speedo gear is hard to find for the Dana 20, I have tried. A transmission shop told me years ago they had an adapter that hooked up to the tranny case, correcting the calibration. I was lucky enuf to have found one, my speedometer is within 2-4 mph now, running 33's tires. I have posted a picture of the adapter. Good luck, hope you'll find one. Wouldn't it be nice if they start making these again? Hope this helps.
    Attached Images Attached Images
    1976 CJ5- centech tilt column, Heatercraft heater, Blazer high-back
    buckets, 258 reman I6,T-150, 2 1/2" Rubicon Express Lift, new windshield & frame, MC 2100 carb

  11. #11

    Default Ratio adapter

    Quote Originally Posted by CJBilly View Post
    Looking for some sort of gear reduction/multiplier unit that connects to my Dana 20 for the speedo cable. Has anyone seen one or knows where to buy one?
    I figured once I could find one, probably would need to find a speedo repair place to swap out the gear(s) to match my axle gearing and tire combo.

    Thanks!
    What you are looking for is called a ratio adapter. There are several different ratios available. They are not cheap, but they are available new and used.

    http://www.transmissioncenter.net/sp...atio%20adapter

    They are also on eBay.

    http://cgi.ebay.com/ebaymotors/ws/eB...STRK:MESELX:IT

    http://cgi.ebay.com/ebaymotors/Gear-...item53e4dd1bca

  12. #12
    Registered
    Join Date
    Jul 2008
    Location
    Glendale, Arizona
    Posts
    26

    Default

    As said above I'm looking at the #54RA2 ratio adapter for mine. My speedo is off by about 11%. It's a litlle pricey but should be an easy fix.

    http://www.transmissioncenter.net/sp..._____va.htm#gm ratio adapter
    '78 CJ-7, 401 w/ headers, T-18, Dana 20, MSD ignition, locked diffs, 4" lift

  13. #13
    Registered
    Join Date
    Mar 2004
    Location
    Sonoma, CA
    Posts
    90

    Default

    Quote Originally Posted by Gunga View Post
    As said above I'm looking at the #54RA2 ratio adapter for mine. My speedo is off by about 11%. It's a litlle pricey but should be an easy fix.

    http://www.transmissioncenter.net/sp..._____va.htm#gm ratio adapter
    I have been running that one for a few years now.
    '79 CJ5, 360, T-18, D-20 T-Low, D30 w/alloy, M20 w/Warn Full Float, 33", WeldWright OB Welder, York OBA and OB Shower.
    ______________________
    Old school crawl and camp.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Jeep Parts | Jeep Accessories | Trektop NX | Jeep Seat Covers | Jeep Wrangler | Jeep Wrangler Parts | Jeep Wrangler Accessories | Bestop | Jeep Tires | Jeep Stuff | Jeep Wrangler Tires | Jeep Wheels