Speedo reducer what's it for
 

Anybody know what this reducer is for ?
666F V8
.9444W

Thanks for your help
Ken

Low Rear Gear cars.

My Guess later model Truck after 1970 with 4.10 gear ratio.
Checked eBay completed items and one sold for $64 but had no info at all for what it was for.

There are charts from GM that show when a particular combination of trans and wheel-tire size got a particular part number reducer. The part number is not one of the numbers you listed. you have to do a bit of google searching to cross reference the GM part number to the reduction number, in your case the .9444.

Here's an example for a 1970 Camaro,Chevelle, Nova 4 speed cars:

http://www.gmpartswiki.com/getpage?pageid=12662

If you plan on actually using it, you would be advised to open it up and clean out and re-pack the grease. It dries out over time.

I found one guy selling a reducer
and claiming it's for LS6 410 rear
666F V8
.8241C
maybe mine is for 456 rear ?

A friend here in Calgary gave me one that I used in the green 4:10 gear car I recently finished. They work well if you know what gear conversion they were intended for.

If you repack it with grease use a light grease. Otherwise the load can snap the tab on the drive gear clip inside the tail housing.

Are these also used on the automatic cars, mine came with 4:10 gears but someone put in 3:73 gears. If I return to the factory gears I will have to get a reducer.Thanks

I have a box full of those, there was two different kinds. Mostly for trucks.

Speedo Reducer...
 

Yes auto cars got these as well.