1966 chevy gear ratio?

[joe1966]

I have a 1966 chevy truck with a 350 small block 4 bolt main, sm420 4 speed with granny. I am pretty sure it has 4:11 gears in it and it is terrible on the freeway. it has very high rpm's on the freeway. and i allready made my desicion to change the gears to 3.08's. i have a 4 speed so off the line it should be good and on the freeeway it should be great!, now, if i buy the ring and pinion do i need to change out the carrier to? since it is a way higher gear ratio? let me know. thank you, joe

[ozzyman]

Depends on what rear end you have.... If you have one like mine (Eaton) I'm stuck with a choice of 4.57 or 4.11..... Swapping in a GM 14 Bolt FF with 3.73s

[biscuit]

I was in the same boat 4.11's on a non posi 4 series carrier so i got a set 3.08's with the carrier from a 80 suburban . Richmond install kit with timken bearings and life was good

[joe1966]

Well i got a gm 12 bolt. with 4.11s., i am gonna go the junk yards or something to get a ring and pinion and hopefully a carrier. 4.11s are very low geared
great take off though but with my sm420 the take off will still be great and the high end will be awesome! with 3.08s

[Captainfab]

Yes you will definitely need a different carrier (3 series) for a set of 3.08 gears.

[joe1966]

U wouldnt happen to know how much a set of ring and pinions and a 3 series carrier go for would ya? like maybe brand new?
thanks

[DRTYRAT30]

Originally Posted by joe1966

U wouldnt happen to know how much a set of ring and pinions and a 3 series carrier go for would ya? like maybe brand new?
thanks

Well nobody makes a open 3 series carrier that i know of (i could be wrong) so you would have to find a used one or go to a new Posi style carrier like i just did. I ended up doing a full overhaul, because i had 17 spline axles and with the posi it needed 30 spline so i just went all new with 3.08 gears.

with the stock 3.73's i had, it was 3188 rpm's with a 27" tire at 65mph

Now with 3.08's at 65 it's 2,600 rpm's a lot better for freeway and it's still good for a cruiser in town with the short tire's i have...

Here is a link to the calculator and the place that rebuilt my rearend..

http://www.differentials.com/technic...tio-calculator

[shawno72]

So you are saying that the 3.08's with a four on the floor will still have plenty of take off and what kind of rpm's on the freeway?

[shawno72]

Thanks Jesse I'm going from 3.73's to a posi with 3.08's that I'm picking up tomorrow. Later on this year I will be doing a 700r4 conversion but for now I will still be rockin the manual gearbox.

[LT1 Burb]

Originally Posted by shawno72

Thanks Jesse I'm going from 3.73's to a posi with 3.08's that I'm picking up tomorrow. Later on this year I will be doing a 700r4 conversion but for now I will still be rockin the manual gearbox.

Shawno, you are going to hate the 3:08 with the 700R4, I have had this combo with a 26" tire for a few years and just bought a 3:73 carrier and gear set.I turn around 1500 rpm at 65 and it bogs down the motor just getting on the gas.If you had a 3 speed auto you would probably be fine but on my truck cruising speed is definately out of the motor powerband and my vacuum gauge confirms it. Also it is hard to put 350HP to use with this combo.

[purebred]

I have a type 3, 12 bolt with 307 gears, at 60 mph I am turning about 2600 rpm's.

[DRTYRAT30]

For sure man... The hot set-up now with $4.20 gas prices is a overdrive 200 4r or 700 R4 and 3.42's... the low first gear in those tranny's and the mid range gear make it good in town and cool on the hiway...with a 28" tire at 65mph you would be at 1865rpm's with the overdrive.. thats like 20+ mpg's

[LostMy65]

How do you guys think the 3.07 will work with the sm420 mostly city driving in an area of rolling hills?
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[Captainfab]

What diameter tires are you planning on running? What engine? The low end torque the engine puts out will make a difference. It sounds like it might be a little tall of a gear, but it might be okay. Of course you can always use 1st gear if need be.

Originally Posted by LostMy65

How do you guys think the 3.07 will work with the sm420 mostly city driving in an area of rolling hills?
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[LostMy65]

Originally Posted by Captainfab

What diameter tires are you planning on running? What engine? The low end torque the engine puts out will make a difference. It sounds like it might be a little tall of a gear, but it might be okay. Of course you can always use 1st gear if need be.

This is regarding my 65.
Right now it has a 3.90 rear from a 62.
The tires are only 26" tall.
I really don't think I'll benefit from an OD Tranny because I'll rarely get above 55 mph. And most of my driving will be 40. 45 tops.
Eventually I'm thinking of putting a th350.

The engine is a 327 that requires premium octane fuel.
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[Captainfab]

With short tires like that, you might be alright. Although that also depends on how 'radical' that 327 is. That engine may not like taking off with a somewhat tall gear. The 3.07 gear would likely be okay with the TH350, and maybe a small stall converter if the engine needs one.

IMO the 3.42 gears are a good comprimise. Here is a chart that gives you some rpm comparisons.

http://www.sierrabronco.com/TireGearRatio.htm

And here's another online rpm calculator.

http://www.csgnetwork.com/multirpmcalc.html

Originally Posted by LostMy65

This is regarding my 65.
Right now it has a 3.90 rear from a 62.
The tires are only 26" tall.
I really don't think I'll benefit from an OD Tranny because I'll rarely get above 55 mph. And most of my driving will be 40. 45 tops.
Eventually I'm thinking of putting a th350.

The engine is a 327 that requires premium octane fuel.
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[shawno72]

Should be ok
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[Fastest32]

I have this same transmission (sm420) and found a guy selling a 2.76 rear end. I have the inline 6 and its screaming on the highway. You think those gears will be ok or too tall?
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