ratio adapter

[jdl71]

Not sure if this is exactly what it's called, but it bolts on the t-case between the speedo cable and the speedo cable socket on the case. It doesn't work. I took it off, cleaned it, spun it by hand, everything seemed fine. I put the speedo cable on without it and the speedometer works, although slow as expected. I put the cable on the adapter and turn it by hand, and the speedo works. Put the adapter on the t-case, nothing. This is driving me nuts. I found a similar thread about this, but don't think there was ever a solution. Assuming I have to find one of these from a boneyard, does anyone know what exactly it's called? Or any ideas why every scenario makes the speedo work except all of it together?

[heavychevy91]

Like this?

I had this on my 86 C10. I was told it was on there because I had the optional 2.73 rear ratio with the 3 speed and was to correct my speedo. i had my speedo cable break off in it, and i couldnt get the end out. i ended up just playing with speedo drive gears untill i found one close to my actual speed. A gps was helpful for this. I tried to find a replacement for it but with no avil. i found a few on ebay but they were all the wrong ratio. it seemed there wasnt much info on them.

ill post a picture of the side of mine when my phone corporates. it reads, "STEWART-WARNER 666 F F3 1:2500BT"

[RCCoors]

My 77 C20 had one on the TH350, however the PO had changed tire size and made the speedo read off by 12 mph. I ordered new drive and driven gear along with a new tail gasket/o-ring set. All problems gone along with stopping a nagging leak at the tranny. A very easy job in about 30 minutes of time.

[SNWBLL]

Lot of good info here.
http://www.transmissioncenter.net/speedometer_calibration_______va.htm#Speedometer_Cables

I found the part I needed at our local junk yard.