The Stovebolt Site Forums The Shop Area Engine Shop Gear Ratio & Transmission Code

I was wondering what my rear end in my 66 Chevy C20 had for gearing. It had the 250 CID 6 banger and the 4 speed.
Is there a website or something out there that'd tell me what ratio the rear end has in it?

Also how do I know which 4 speed is in my pickup, there were different ones offered right?
It came from the factory with the #M20CL option which was the 4 speed tranny.

Or is there something on the pickup itself that'll tell me these things?
All I've found is the VIN Plate in the door and the plate on the drivers kick panel with the paint code & GVW.
Thanks.

I believe there was only one four speed offered for the 66 light duty trucks and that was the 22,500 pound SM420. I believe the SM420 ran from '47 thru '67. The SM465 debuted (I believe) in '68 weighing in at an even 40,000 lbs!

*tranny weights are obviously exaggerated.

-ftyler

Ftyler, I'm not so sure you're exaggerating...I have too many SM420s laying around...they're like trying to move blocks of lead.

Yeah, you've got an SM420 tranny. Final drive ratio is 1:1. It's one good sturdy tranny. A lot of 4 wheeler guys use 'em for off roading 'cause they're bulletproof and you can crawl with that granny low (not to mention pull a house down if you were so inclined).
Chances are you've got the great, big full floating Eaton H072 rear, 10 bolt cover with an enormous pumpkin. And chances are you've got a 4.57 gear.
If you're not planning on freeway driving and live where gas is not $2.50 a gallon, you got yourself one mean working machine.
If you do want freeway driving then do a search of posts. Many questions asked in the past. Especially by me!

Thanks everyone. Yea mugsy, I live in ND, no freeway driving, and you never know I might need to pull down a house someday!!
I think I'll keep it how the original owner got it.
These pickups weren't built to go 90mph down the interstate, they are still pickups...pickups were made to work, this one probably wont be worked too hard but it may as well be prepared.

I've had my '66 c10 cruising down the interstate doing at least 85 mph for many miles, keeping up with the fastest cruisers in the fast lane for long periods of time. Of course this is in open, rural interstate traffic, not congested urban/suburban traffic. The truck handles remarkably well at those speeds, even with the stock-style suspension.

I agree with your point, but it's nice to know that higher speed cruising with our later inline 6s are just a tranny swap away.

-ftyler

Sorry ftyler. I should've said these pickups were mainly built for work...speed wasn't a big concern back then for guys driving their pickups.
Although it would be nice to be able to take my pickup and keep up to the crowd on interstate....i'd much rather be able to pull a trailer or something and have power up the hills. I'm a full-blooded farmboy.
Thanks for all your advice this last week ftyler.