changing gear ratio.....

[draggin49]

Decided im going to keep the factory 3 on the tree on my 69 c10 but the trucks has really low gearing
(I believe 4.11)
How hard to change this out for some tall gears so itll cruise nicely on the freeway?
I was thinking maybe 3.08's?

Its gonna be airbagged and more show than go. Mainly just will be cruised around low off the ground.has the factory small block so im not trying to have low gears for performance.driveablility is way more important.where I live ill be jumping on the freeway regularly.

Thanks guys!!!
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[brad_man_72]

Easy cheap way. Find a guy who is building a hot rod 67-70 and swap rear ends.
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[SS Tim]

3.73 gears would have been stock. 4.11s were an option and would be on the SPID unless you actually have an overdrive trans.(RPO M10). At this point worry more about what size tire you will be turning and if you are switching it to a later 5-lug axle first.

[sapper4]

I recently did the same thing on my 71 with a 3 speed. SS Tim is correct about factory gearing. Find a parts truck with a factory 350 as they normally came with a 3.07 or a 307 with an automatic transmission. I love my 71 so much more with the higway gear and the better fuel mileage. Happy hunting!

[buckskins4ever]

You would be much happier with a 3.42 gear setup for all around driving with the 3 on the tree.

[draggin49]

Roughly what rpms would 3.42's turn at 65mph with an average sized tire? Ill be running 15"
Steel wheels.

I havent driven my truck yet to see how bad the factory 3.73s are on the freeway.its the the original motor so would turning less rpms be easier on the motor?
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[buckskins4ever]

Originally Posted by draggin49

Roughly what rpms would 3.42's turn at 65mph with an average sized tire? Ill be running 15"
Steel wheels.

I havent driven my truck yet to see how bad the factory 3.73s are on the freeway.its the the original motor so would turning less rpms be easier on the motor?
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The 3.42's arent common and you will have to order a setup from a performance shop. I run a Eaton Full posi 3.73 12 bolt on mine. I ran 3.42 on a camaro with a TH350 trans and it ran great on the hwy. My own opinion, i would say go with the 3.73 if you have them. Lowering the rpms at high speed will be alot easier on your engine.

[SS Tim]

3.42 gears were not a stock ratio 67-72 as far I can tell which means they are not common. There are 3.36 G10 van applications and 3.54 big block C10 axles as well. Like I said earlier plan out what you want use. Look up an RPM calculator and work your actual numbers. Just remember the higher you gear it for low freeway RPMs means the less off the line power you have affecting drivability and mileage to some extent. Climbing hills up around Ojai is not going to be fun if you under gear the truck. To generalize if you have a 350 (or is a 307?) you could use 3.07 gears with near stock diameter tires. Problem is from the few posts I have seen you don't seem to know what you have, much less how it will perform but you want to change it. Research and plan.

[draggin49]

If they are 3.73 freeway should be manageable.old owner thought it had 4.10s
Im just leaving the trucks original motor/trans and add full air ride.
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[SS Tim]

Post up a SPID (label inside the glovebox) picture and we will figure out how your truck was originally built.

[draggin49]

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[SS Tim]

As built 307 V-8, 3 speed (3OTT) trans. 3.73 gears stock. Rare color combo especially with the factory pinstripe.

[draggin49]

Thanks for decoding that tim. I didnt know that a 307 was offered on these pickups. Kinda hoped it had.a 350 . Its gonna be more show than go, driving it around extra low with the air ride so the 307 should do ok for just cruising.
I am gonna get the tow truck over to bring it home tomorrow. Its on the side of my godfathers yard so theres some stuff in the way.gonna have to get creative to get it where the tow truck can load it.
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[c10srule]

i got a set of 3.42s out of a mid to late 70s truck and put them in my wifes truck, they work really well for all around, it has a 350/350 combo and 28" tires, i ran the 3.07s in mine for a while with a muncie 3 sp and 454, that was a really good combo as well running 3.73s now with turbo 350 because it works really well with my motor but does tend to wind out on the highway

[oldspowered67C10]

Youll love the 3.07 rear gear on the freeway. I have them with a th400 and 29" tall tires and 80mph all day long is comfortable. But with a 307 its not gonna be very exciting off the line, I have a big block oldsmobile engine that makes a ton of low speed torque so it works OK for me. It just depends whats more important to you but i would personally give up acceleration to have a vehicle that is comfortable at modern freeway speeds. Also dont forget that the 3.73 ring gear carrier wont work with 3.07 gears.