Help choosing new rear end gears

[Terence]

Hi,
I have a 67 C10 with a turbo400 transmission(3 speed) and I want to change the rear end gears so it will be a better highway cruiser and easier on gas. Right now, I max out at about 80kms (50mph) before it sounds like the rpms are too high on the highway. I have no idea where to start in choosing new gears for the rear end, and would appreciate any advice/help on what I need to be looking for.

Thanks,
Terry

[Texasdeere]

3.08 gears are pretty good for highway and mileage. Your truck probably has 3.73 gears in it now. Also you may need a new carrier for the 3.08 if you currently have 3.73s now. I did this to a 74 C10 350/TH350 that I used to own and was pleased with the results. What engine do you have in your truck?

Welcome to the board from Texas!

[Terence]

hi there,
Thanks for the info. I have a 283 V8. Does tire size matter?? I have 15" rims ???

[action]

I had a 79 with 3.42 and a 27" tire and it was a good combo. I think 3.08 would be a bit of a turd.Although I have a 4x4 with 33" tires and 3.08 now that is a dog.
Jack

[Texasdeere]

The tire size can change rpms but not quite as much as a gear ratio change.

Here is a link you can play with:

http://www.xse.com/leres/bin/gearrat...mference=91.11

You can plug in different gears and tires. Your tires are probably around 29 inches in diameter. (a 235/75/15 tire is about 29 inches) your 3rd or top gear is a 1.00:1 ratio.

[Texasdeere]

A 3.08 ratio is at the bottom of the performance scale. Just don't install big tall tires. You should be turning about 2500 - 2600 rpms going 70 mph.

[Terence]

Thanks Texas c10,
Thats a pretty cool tool.

[Longhorn Man]

I had 28 inch tall tires with 3.07 gears in my last truck, and it was still fairly quick off the line, and still VARY capible of making smoke shows... plus I cruised on the freeway with low-ish RPMs.

[cooter914]

Anybody know how this info could translate to a 3 on the tree?

My 68 is really buzzin at 60mph.

[Longhorn Man]

the exact same.
all the trannys that came in these trucks have the same final ratio in the tranny with the exceptoin of the hand full of overdrives that were built.

[chadvicki]

Hoping to chime in with a question.

I ended up getting a 72 c-20 with the 350 engine and 3 speed auto. How do you determine the gearing you have in it? It most likely is stock.

When I am on the freeway I am at 3000 rpm's going about 65mph.

My wheels are 16" however I need to get new rims and tires. What would be the best setup for freeway useage involving (tires, rims, and gearing)

thanks,

Chad

[RustyParts]

Just throwing this in as an option, how about putting in an overdrive transmission? Best of both worlds keep your current gear and cruise on the highway too.

[lilred67]

i would go with 3.42's...you get some performance and some milage.
i have a '97 1/2 ton 4x4 gmc with 3.42's with 31" tires.i pull trucks/cars regularly in drive(not o.d.) and it pulls good.. at 70mph in d it's turning around 2500rpm's.....
if i change the gears out in my '67 i'm going 3.42's..........

[Longhorn Man]

a 3/4 ton with a small blcok and an auto woulda been a 4.10 onles otherwise optioned. Your revs sound about right for that too.

[67chevemall]

I have 3:73 right now with 27.5" tires she takes 21hours to go 1200 km
the car takes 11hours/ Great around town but I like to travel in it.

I bought 3:08's from a member with the carrier for $80 and they are mint.
I'm going with 27" rim/tire combo and 3:08's (if I can find a good shop here to put them in/not easy)

you can get nice tires 26-27" on 17 and 18" rims

shop around
Just copy the Nascar truck series specs with the 67 frame and your good to go.