Speedo Gear Change

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Staff member
Sep 12, 2023
North Ridgeville, OH
Vehicle Details
1997 Thunderbird 4.6, 1998 Mark VIII LSC
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You are probably wondering how hard may this job be. Do you have to drop the tranny? What would the correct speedo gear be? Well, for all you guys that are so curious and would like to change the gear yourself, here is a little help on how to install it.

It's not hard at all. The speedo gear is located on the tail shaft of the tranny and you can get to it by jacking up the front end of your car. You don't have to drop the tranny.
  1. Look at the rear of the transmission where the driveshaft enters. Above that, on the driver's side, is a plate with a single bolt on it. It also has two wires coming out of it.
  2. Remove this bolt and the plug that has the wires coming out of it.
  3. Once you have done this, pull the plate straight off. It's a solid aluminum piece with a rubber O-ring seal at the base of it.
  4. On top is the plastic "speedo gear."
  5. The gear has a c-clip at the base of it. To remove the gear, just carefully pry out the C-clip so as not to break it; you have to reuse it to hold on the new gear.
  6. Put on the new gear on the end, and reattach the C-clip.
  7. Clean off any dirt or debris from the O-ring so it will seal properly and not leak. Lubricate the new gear with some fresh transmission fluid.
  8. Push the whole assembly back into the tail shaft of the tranny. You might have to jiggle it a little to get the gears to slide into place.
  9. Re-attach the plug for the wires and tighten down the bolt.
It might take a about a total of 15-20 minutes for an average person. It's not hard at all.


As to which gear you may need, there are more details about this in the Gears and Axles article. It's not quite as easy as saying "you have xx gears, so you'll need xx speedo gear". Tire size, transmission make/model/year and rear axle ratio all have a part to play in the correct speedo gear choice, and a handy calculator is provided to do the work for you.
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