(bumping an old thread for completeness of info)... From GM Heritage Center do***entation 1966 C10 standard equipment is 3.73 hypoid, semi-floating Options include-- RPO Description G80 Positraction w/3.73, not available with overdrive transmission; or 4.11 w/overdrive transmission H01 3.07, not available with Powerglide or overdrive transmission H04 4.11, included with overdrive transmission Elsewhere in the do***entation, they list a 3.36, but it may be for C20/30 power teams or G-series ch***is (van)... it's unclear, and there is no RPO listed.
My 1964 C10 came stock with 4.10 ratio. They didn't deviate too far from the model for '64, '65, '66. The ratio was stamped right on the ring gear when the cover was removed. The thing about the C10 rearends is that they had a trailing arm suspension that was unique to the truck. So it's not as easy as finding some car rearend and stuffing it in with a perfect fit. They were pretty good rearends for the most part. If there is something wrong with yours, you'd probably just be better off having it repaired. If you want a different ratio, ring and pinion sets can be had. If you are just looking for a straight out swap for some reason.... you have a lot of fabrication in front of you. If you are planning on using a C10 rear in another vehicle, you should be able to take off all the perches and make it work.
Next time you have the lid off, count the teeth. You will find there are 9 on the pinion and 37 on the ring... = 4.111111111. That is the same as the 4.11 in the '66 rearend. It is unclear why GM so loosely interchanged "4.10" with "4.11" in their labeling (it's not unlike the mystery of calling both the 396 and 402 the "400"). BTW, GM Heritage Center do***entation for the '64 C10 lists the same 3 ratios and RPO codes as I posted earlier for '66 MY-- 3.07, 3.73, and 4.11.
I had a 66 C10 Suburban with the original 3.73 gears. I bought the 12 bolt rear out of a 70s van and swapped the 3.08 gears and diff carrier into the 66 and had a nice highway truck.
Probably rounding..... The a couple tenths of an inch of deviation in tire height due to under/over inflation of the tires would probably have more effect on output RPM than the .01 of ratio on the output....depending on mph. As I remember it, I think they had the tooth count stamped on the ring as well.
Jim-I do remember seeing that. Had to dig into my archives, see below scanned photos of my 66 Carryall sales lit. See rear susp. options highlighted in blue. Doug
Interesting stuff. Your chart does not show what combinations are available. But you could always swap in whatever you wanted, after you took delivery. My guess is the 3.07 gears were a rarely ordered option back then.
So was 3.08, my '65 had a 3.08 it was the standard gear for a 6 cylinder 3 speed trucks. What you have stock depends on how the truck was equipped, and what you can run gear wise depends on which carrier you have, for instance a 4.11 gear wouldn't bolt directly to my carrier and a 3.08 gear won't bolt directly to a carrier from a truck with a deep gear. make sense?
Yes, it's all there...but the list I posted shows that the optional 3.07 ratio was not available with Powerglide or Overdrive, and that the 4.11 ratio was standard with Overdrive. Your chart does not show that.
My 66 327 powerglide truck came with a 3.73 Posi. I found a 3.08 in the junkyard years ago, but every other one of the 15 I've owned from 64-66 were 3.73's.
Based on what I've seen over the years(GM), not only did the head not know what the tail was doing, the head didn't even know there was a tail.
Ok ive got a 66 LB big window with all the chrome. sold new in calif. Factory equipped with 327 & turbo 400 three speed trans and a 390 no spin rear end. not a posi with springs & clutches. But a genuine no spin with the overrunning ratchets and the popping sounds when cornering. had a sticker on the dash stating no spin differential. and a packet in the glove box containing the info about the no spin.
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