Worst gear ratio EVER!!!!

[ElGracho]

As you may or may not know, I recently swapped a Goodwrench 350 and TH700R4 into my 1980 GMC Indy Hauler. I've only driven the truck about 300 miles since the first of June or so when I got it done and I've been annoyed since my speedo has been off.

I put a new drive and driven gear in the tranny to match up with my 255/70R15 tires (within .05" of the stock 235/75R15's, or probably closer than one brand to another of that same size...) and what I assumed were 3.07 gears. Ah yes, I used the assume word, and it bit me.

I've checked my speedo gear math but always used 3.07 for the rear end ratio since I knew it was higher than 3.42s but didn't think GM was using 2.73s much in 1980 (even though my 84 4WD and 86 2WD trucks BOTH had 2.73s...)

Anyhow, I know the only way to know my gear ratio for sure is to pull the cover and read the numbers off the ring gear, so tonight I did that.

I was shocked and very dissapointed to see a part number followed by:
16 41 3 80 which tells us my ratio is 2.56 to 1!!!

Holy crap! I was shocked when I pulled down 16mpg on my way back from California with a worn out 350 when i picked this thing up, but I gave most of the credit to the TH350C that used to be in the truck. I guess it was the gears. I'm sure they are original gears since the date code matches and there are no signs that the carrier has ever been out of the axle. GM sure made some bad choices in the late 70's and early 80's.

With those gears, at 70 mph in OD on the TH700, I'd be running 1450 RPM, thats pretty close to the converter stall speed and if it isn't locked up, it could even be slipping. No thanks, the 700R4 needs all the help it can get to keep from grenading and those terrible gears aren't the ticket.

Anyhow, I guess I'm looking for some 3.23 or 3.55 gears now!