Odometer Adjustment and Matching

I have decided to replace the original 1280 TPM trans with a later model 1000 TPM overdrive trans. After reading all the good information on this site about the different ways to make the speedometer match the new trans TPM (gear reducers and having my speedometer adjusted to turn correctly) I decided to go another route and thought I would share the experience here. I went on eBay and found a good 1000 TPM speedometer with about 42,000 miles showing. Since the miles on my 1972 MGB GT are original and I want the odometer portion to show the correct miles, I decided I would "adjust" the odometer on the new speedometer to match the current mileage.

Steps needed to dismantle and re-assemble the odometer:

1. Remove the chrome trim ring.
   
   
2. Loosen the retaining srcews on the rear of the unit.
3. Remove the speedometer from the case.
   
   
4. Remove the small plastic C-clip holding the odometer gears in place.
   
   
5. Remove the metal spring clip, gear and shaft alignment wheel - Be sure to note the order in which they come off.
6. Remove the second plastic c-clip from behind the plate where the shaft passes through to the odometer digit wheels.
7. Carefully pull the odometer shaft out of the odometer wheels.
   
   Note: Here is where I found a difference between the two odometers. One had a sleeve between the shaft and the wheels and the other did not. The sleeve made re-assembly much easier.
   
   
8. Carefully remove the digit wheels, washer, spring and metal retainer. Note the tabs that protude between each digit wheel and fits into the slot behind the wheels.
9. Separate the digit wheels but be sure to keep the small plastic spacer with the tab and the tiny yellow gear with each wheel. If these come apart they can still be put back together but it takes much more time and patience.
   
   
10. For the sleeve type wheels (easiest) - Place the 10,000's digit wheel on the shaft. Rotate the wheel so that the tab is opposite the digit you want to be displayed. (I used a piece of cardboard as a work surface so that I could make a groove in the cardboard for the tabs.) Place the 1,000 digit wheel on the shaft. Line up the tabs and the digit to be displayed before connecting to the previous wheel. Once the two wheels are touching you may need to rotate the first wheel for the second one to 'snap' in place. If once the wheels are 'snapped' together if the digits do not correctly align you will need to adjust the small yellow gear. Using a very small screwdriver, gently pry the spacer from is associated wheel, rotate the wheel into the corect position and push them back together. I only had this problem on the wheels that came apart from the spacers. Continue this process until all the digits are on the sleeve. Place the metal retainer, spring and washer on the sleeve and carefully place the entire assembly in place between the mounting plates. Be sure all of the tabs go back into the slot. Slide the shaft through the mounting plates and sleeve. Be sure the two small notches are on the end where the gears mount.
11. For the non-sleeve type wheels - Place the shaft through the mounting plate from the end that holds the gears. Be sure the two small notches are on the end where the gears mount. Place the washer, spring and metal retainer on the shaft. Place the 10,000's digit wheel on the shaft. Be sure the tab in the slot and rotate the wheel so that the desired digit is showing on the speedometer. Place the 1,000 digit wheel on the shaft. Line up the tabs and the digit to be displayed before connecting to the previous wheel. Once the two wheels are touching you may need to rotate the first wheel for the second one to 'snap' in place. If once the wheels are 'snapped' together if the digits do not correctly align you will need to adjust the small yellow gear. Using a very small screwdriver, gently pry the spacer from is associated wheel, rotate the wheel into the corect position and push them back together. I only had this problem on the wheels that came apart from the spacers. Continue this process until all the digits are on the shaft. The last wheel is very hard to squeeze in place and will take some work but it can be done.
    
    
12. Place the plastic C-clip on the shaft behind the mounting plate between the mounting plate and the metal washer (on the wheel side of the mounting plate). If this clip is not put back on, the shaft will be able to move and the assembly may come apart while in use. You may need to slide the shaft slightly until the c-clip snaps in place. Place the shaft alignment wheel on the shaft. Be sure the two tabs are toward the mounting plate and on either side of the top of the plate. Replace the gear, spring clip and plastic c-clip in the same order as originally installed.
13. Place the speedometer unit in the housing. Be sure the odometer reset pin lines up with the reset shaft in the rear of the case. Replace the mounting srews and faceplate.