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Is there a way to disassemble a speedometer Driven Gear assembly?

'51 Special

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In order to match up my speeedometer to the 3.6 to 1 ratio rear end in my 51 Special, I need an 18 tooth driven gear. Problem is, I'm not finding an 18 tooth driven gear for a manual transmission. Can anyone tell me if the speedometer driven gear assembly can be disassembled. (The manual says: "The speedometer driven gear is furnished only as an assembly consisting of sleeve, shaft, retaining washer and gear.") My goal is to install an 18 tooth gear out of a dynaflow on the .5 inch shorter sleeve and shaft from a manual transmission driven gear assembly. But I cannot figure out how to get the lock ("retaining washer") off of the shaft.

Or, if someone knows of a source for an 18 tooth speedometer driven gear assembly for a manual transmission ...

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Old Tank posted this in the wrong thread:

[h=2]Re: 47 super exhaust manifold[/h]

The claim:

"We can slow your speedometer down as much as 58% or speed it up as much as 200%"

Even if this does not pan out there are other adapters out there that might. What you want is probably so rare that it is made of 'unobtainium'.

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Almost ANY speedometer shop can build a "ratio adapter" for speedometer calibration purposes. GM has LOTS of them as OEM equipment, back before the instrument clusters were "electronic" (as they are now). Many were there to do what you desire, to hit something "between" normal drive/driven gear ratio capabilities.

Take the ratio percentage between what you now have and what you want it to be, rather than just "add one tooth . . ." . Then find a speedometer shop that can build an adapter with the necessary ratio. This way you use and keep your existing gearset and also make the adjustment necessary to keep the "revs/mile" of the speedometer cable where they need to be.

Finding an operating speedometer shop can be a trick, though! Most went out of business when the owners retired, it seems. So, this leaves the salvage yard as your new shopping venue. The GM factory adapters had many shapes and configurations. Some put the speedometer cable at a right angle to the trans case, some didn't, but had the cable connection offset from the input side of the adapter. There were ALSO some formed plastic sleeves which fit the square end of the cable and then had a spline (ONE) which indexed with the output side of the adapter.

You might contact "the speedometer guy" in Michigan and see if he can help get you where you desire to be, regarding the speedometer drive/driven gear issue. Seems like he advertises in THE BUGLE?

Just some thoughts,


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  • 3 weeks later...

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