I recently had a 411 rear in my car and I decided to change it to a 336. Now I have a problem with the speedo gear. The correct speedo gear is blue with 20 teeth and it is smaller than the 411 gear. I was told I have to take out the tail of the transmission and put in a new gear. Is this an easy or hard job? Does anyone have any tricks in doing this? I was told that taking off the steel gear is a real pain. Is there any suggestions?
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Re: Replace Speedo Gear & Trans
Jay-----
The speedometer DRIVE gear is the gear that is fully internal to the transmission and mounted on the transmission main shaft. To remove this gear, you have to remove the transmission from the car and partially or fully disassemble it. Fortunately, you don't need to replace the DRIVE gear. You need only replace the speedometer DRIVEN gear. This gear can be found on the side of the transmission tailshaft housing, where the speedometer cable connects. To change it you simply remove the speedometer cable, remove the screw and retainer which secures the adapter, and pull out the adapter. It will be a little tight since it is sealed by an o-ring. Pull the gear out of the adapter and replace it with the new one, then install a new o-ring seal. Reverse the procedure to re-install.
The "blue" 20 tooth DRIVEN gear is probably the one you require, but I can't tell for sure since you didn't mention the year of your car. If you do require this gear, it is GM # 3987920In Appreciation of John Hinckley
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