3:07 gears best thing I could have done!

[Juspassinthru]

I picked up a stock 66 lwb a few weeks ago.It had a 4:10 rear end gear with a 250 6cyl and 3 speed on the column.I drive it round trip 62 miles daily and with the 4:10 gears 60 mph was really about as hard as I wanted to run the ol girl, and still only got 12 mpg.

I had a 3:07 rear end set up installed at a local hotrod shop owned by a friend of friends.
I just took it for a stroll around town and then hit the interstate and it runs and drives effortlessly !This is the best thing I could have done, she feels like a different truck.Im curious what my mpg will be but I bet it will be better than 12, I'll let you guys know.

[ChrisDollins]

I've been kicking around doing this to mine. Does it still feel peppy enough around town?

Chris
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[Juspassinthru]

Peppy enough for me Im very pleased. The Chevy 230 250 292 six bangers are some of the best motors ever made when used in the correct application.(lower rpm range) Keep in mind however, these trucks were not designed to run at todays current interstate speeds with factory gearing. In the era in which our trucks were made trucks were rarely used as a sole means of transportation for anything more than local driving, farm use, utility purposes and occasional trips into town.People didnt commute as much back then either and many trucks were more often confined to work use and rural purposes by design.

For me using my 66 as a daily driver, highway drivability is key.
Also the longevity of any motor is largely improved by lowering the rpm due to friction causing heat which leads to motor oil breakdown etc.
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[**grumpy**]

Yep.. Great swap.
Ive done it twice and have another 72 3.08 posi rear waiting for a new home.
best improvement Ive made to one of these trucks.

[Juspassinthru]

Grumpy what kind if mpg should I expect? The difference in drivability is amazing!
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[bk2life]

every thought of a gearvendors kit? im still kickin the idea around for my dually..

[CSGAS]

My current plan is to swap in an overdrive NV3500 trans. Changing the rear gears instead has the additional advantage of slowing down the long two-piece driveshaft though.

[61_FL_Apache]

Im happy with my 3.08 in town, but it could be better on the highway.. Im thinking of a taller tire next time for a little more highway gear.

[hd74]

thats the ratio i run with a 700r4 trans and i like it in town and hwy behind my 454

[ChrisDollins]

Yea, tire height will play a big role in it. What's your tire height justpassinthru? I've got a 4 speed granny that's about to go in, so I was thinking, go with a 3.07 gear and use granny as a first if I have to.

Chris
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[kieth]

If you guys want to see how your truck will perform before making the change send me your information and I will send you a spreadsheet showing all the variables and how the truck will run out and how much power it will have after the change. Here is what I will need:

1. Engine:

2. Transmission

3. Rear axle ratio

4. Tire diameter (ground to top of tire)

5. your email address

PM this info to me here on the board and I will figure it up for you.....

or just send it to tulsatruckcenter@sbcglobal.net Kieth

[**grumpy**]

Originally Posted by Juspassinthru

Grumpy what kind if mpg should I expect? The difference in drivability is amazing!
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The last truck I did a 3.08 swap was a 65 short fleet with a stock 305 sbc and granny 4spd.
before swap, it would scream at 60mph. After, it would run 75 easily all day

But, after the swap, I also added 255-70-15s on 5x5 15x8 steelies.
Those are a tall tire. So my final gear was more like a 2.90ish

It was a great highway driver. I got about 17mpg on trip to Columbus GGs. thats about 180 miles of highway driving each way.

[MikeN]

I bought a used set of 3.07 gears and plan to swap them in favor of my current 3.73's later this summer. I'm really looking forward to having a more relaxed ride on the freeway.

I have a stock 350 with a Q-jet carb, and I'm going to replace my 3-speed manual with a TH400. I'm also planning on doing some towing.

[kieth]

Originally Posted by MikeN

I bought a used set of 3.07 gears and plan to swap them in favor of my current 3.73's later this summer. I'm really looking forward to having a more relaxed ride on the freeway.

I have a stock 350 with a Q-jet carb, and I'm going to replace my 3-speed manual with a TH400. I'm also planning on doing some towing.

Might want to rethink that change, you could do a lot better with a 700r4 instead of the 400 and keep the 3:73 will be cheaper in the long run....

Kieth

[rockdogg2020]

only gear i could get without changing rear ends is 3.38. but it is still much better than the 3.90s i had. **Grumpy** how do you like those 255/70/15s. im about to buy two for my rear.

[**grumpy**]

I liked those tires on that truck. It was just a static lowered beater driver.
Im not sure Id run that big a tire on a bagged truck.
Maybe if ya trimmed inner bed and moved wheeltubs up some.

Heres the truck. We called it the Farm truck

[juanz1947]

Is there a rear end kit I can buy to change out my gears I have a 3.73 but want more speed on the freeway I have a 250 and 3 on the tree with tall tires
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[Juspassinthru]

Just buy a ring and pinion 307 and up to mid 3'syour existing carrier will work. It will give you an extra 10+ mph of freeway cruisabilty with only a small loss of power. Well worth it especially the part about lowering your rpms, good for longevity for sure.
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[Captainfab]

The 3.73 gears are on a 4 series carrier. If you want anything higher than 3.73's, you will need a 3 series carrier.

[PAPA KENT]

Originally Posted by Captainfab

The 3.73 gears are on a 4 series carrier. If you want anything higher than 3.73's, you will need a 3 series carrier.

hello captainfab,mine is a 62 with the old style rear end and a powerglide now does anyone make 308's for it? i have 373's now.

thanks!

[perro13]

Sorry if i'm hyjacking thread some. Never really cared about what gear ratio my rearend had in the past. i just new they where geared low because of the whininng , so i would adjust my driving speeds.How can i find out what i'm runinng in my rigs.

[wayno]

I think if you take the cover off it's stamped inside... I think you can also count the teeth and do some division but if you're like me I would to see if any of the stamping on the pumpkin itself sheds some light so I don't have to crack the pumpkin and drain it.

[MikeN]

There's two numbers stamped on the ring gear, like 41:11. They represent the number of teeth on the two gears. Divide one into the other and you get the ratio.

[Captainfab]

No, no one makes 3.07 gears for the Eaton HO32 differential. The only gears available are 3.38's. I believe Yukon makes them, which you can get from Randy's Ring and Pinion. You might also try Toms Differentials. They are located just North of CDA.

Your current gears should be 3.90's

Originally Posted by PAPA KENT

hello captainfab,mine is a 62 with the old style rear end and a powerglide now does anyone make 308's for it? i have 373's now.

thanks!

[Captainfab]

I always recommend pulling the rear cover and inspecting the gears, and finding the tooth count that is stamped into the edge of the ring gear. There will be 3 sets of numbers. One will be the part number, another will be the date( day,month and year) and the other will be the tooth count. The tooth count of 11 41 will be the 3.73 ratio. You can also physically count the teeth on the ring and pinion, and divide them.

Another good reason to pull the cover, is that the differential is one of the most neglected parts of a vehicle. It could likely stand a gear oil change. It'll cost you just a couple quarts of 80W90 gear oil and a cover gasket. If you happen to have a posi, you will need the friction modifier additive for the oil.

Originally Posted by perro13

Sorry if i'm hyjacking thread some. Never really cared about what gear ratio my rearend had in the past. i just new they where geared low because of the whininng , so i would adjust my driving speeds.How can i find out what i'm runinng in my rigs.