Rear gears

[Bass66C10]

I have a 66 straight 6 250. As far as I know everything is original in it including the transmission. I was to keep everything original but I wAnt to know what would be best to get speed of 70/75mph on the interstate. I don't drive it on there much, but would like to know when I did I could keep up with traffic. I have no problems now with running 60mph, but the closer I get to 65mph it sounds like my truck is doing everything it before blowing up

[LVPhotos]

Overdrive!

http://67-72chevytrucks.com/vboard/s...d.php?t=689851

[63burban]

Which would you rather change? The rear axle or the transmission? A 700r4 trans would make a lot of difference. Three speed overdrive trans is a good option as well.

[Bass66C10]

I would prefer the cheapest way. I have the three on the tree. What would be best gears to be able to run 65 mph with no problems like a new vehicle.

[joedoh]

figure out what rpm you want to run, I think I have heard 2200 on a 250, then enter your tire size and top gear of your 3 on the tree (1:1) into this calculator.

http://www.unixnerd.demon.co.uk/revs.html

with a 235/70/15, 67mph at 2200 rpm is a 2.73 rear gear.

a few things:

tire size affects this quite a bit so be aware of the effect of size changes

a really low numerical gear does not multiply torque like a high numerical gear, you may find your truck is sluggish to accelerate with a really low numerical gear and that granny first isnt so granny any longer.

wind drag is exponential as speed increases, you may numerically be able to achieve the desired speed but the frontal area of your flat 60s truck may not know how to do math. you might top out before the gear does owing to not having enough power/torque to keep going.

inline 6s dont really like higher rpm cruising, they sometimes puke oil out of the breather/road tube and overheat. make sure you are doing this to an engine that can take it.

[AcampoDave]

If you change the gearing are you going to change your existing rear end gears or swap in a completely different differential? I went with the second option myself using a 5 lug half ton from the 70's. Have you determined what ratio you have presently? Joedoh is right about getting too much of a good thing. I had a 2.76 that I got for free, but eventually pulled it for a 3.07 because I wanted more throttle response from my 283.

[jbgroby]

I have a Dana 60 with factory 3.92. I switched to 3.23 from Precision Gears (I changed the ring, pinion and al the baring's out while I had it apart. $220.00

You can see the change out here

http://s1299.photobucket.com/user/jb...?sort=6&page=1

[scuderia]

doing the same thing with my '66 which has 4.11's stock. Going with 3.07's which require a new carrier as well. Used carrier and gears ran me $120. Just ordered a bearing/rebuild kit for $60.

[frankslagoon]

Originally Posted by Bass66C10

I have a 66 straight 6 250. As far as I know everything is original in it including the transmission. I was to keep everything original but I wAnt to know what would be best to get speed of 70/75mph on the interstate. I don't drive it on there much, but would like to know when I did I could keep up with traffic. I have no problems now with running 60mph, but the closer I get to 65mph it sounds like my truck is doing everything it before blowing up

Why don't you figure out the rear end gear ratio and we can go from there

[jayoldschool]

Run the tallest tires you can. 235 75 15s are cheap and readily available.

[BOE]

i am trying to follow you bass66c10 because i have the same question. the answers get farther and farther from simple. not everyone has a big shop and every tool. just want to know which? tranny or rear end or both. low budget

[AcampoDave]

Originally Posted by BOE

i am trying to follow you bass66c10 because i have the same question. the answers get farther and farther from simple. not everyone has a big shop and every tool. just want to know which? tranny or rear end or both. low budget

Low budget for me was determining what ratio I had (initially, a 3.73 or whatever) and deciding where I wanted to be (3.07), then I went to the junkyard and pulled one from a shortbed squarebody. I took a grinder and cleaned off the old squarebody mounts, then I put my truck on stands seated at the frame. At this point I checked my factory pinion angle with a cheap protractor gizmo and proceeded to yank my rear end and carefully cut my factory mounts off my stocker using a grinder and cuttoff wheel, a swazall, and a few well placed blows with a heavy hammer. Then I set the replacement rear end in the mounts while putting it on the truck, I then set the pinion angle back to stock and tacked the mounts to the tube. Then I pulled it out and arc welded it up.

[Captainfab]

Is your '66 a C10 or a C20?

Originally Posted by Bass66C10

I have a 66 straight 6 250. As far as I know everything is original in it including the transmission. I was to keep everything original but I wAnt to know what would be best to get speed of 70/75mph on the interstate. I don't drive it on there much, but would like to know when I did I could keep up with traffic. I have no problems now with running 60mph, but the closer I get to 65mph it sounds like my truck is doing everything it before blowing up

[frankslagoon]

X2 c10 or c20? pull the cover off the rear end and find the numbers on the ring gear and then we can give you the best options money wise. otherwise we just keep goin around in circles

[scuderia]

Originally Posted by scuderia

doing the same thing with my '66 which has 4.11's stock. Going with 3.07's which require a new carrier as well. Used carrier and gears ran me $120. Just ordered a bearing/rebuild kit for $60.

Just talked with local shop and $500 to swap out gears and carrier... so total will be about $680... FYI

[joedoh]

most shops wont swap gears without new bearings too. try the local hot rod shop though, I got $5-800 quotes and called the local shop who wanted $150. they required a master rebuild kit with new bearings and seals though, which was $100.

[scuderia]

Update:
Just got my truck back with new 3.07 gearing and couldn't be much happier.
Still take off in 2nd though 1st is now an option. 3rd is a lot more useable both around town and during freeway stop and go. And most importantly it's super pleasant at 55. Took it up to 65 and it's okay about the same as it was at 55 before meaning I can drive it there if I want without feeling it's going to blow up. Suspect I'll still spend most of the time at 55 on the freeway.
Glad I went with 3.07's and not 3.42's as even coming from the 4.11's it would not have been enough.

[zplightning]

Originally Posted by scuderia

Update:
Just got my truck back with new 3.07 gearing and couldn't be much happier.
Still take off in 2nd though 1st is now an option. 3rd is a lot more useable both around town and during freeway stop and go. And most importantly it's super pleasant at 55. Took it up to 65 and it's okay about the same as it was at 55 before meaning I can drive it there if I want without feeling it's going to blow up. Suspect I'll still spend most of the time at 55 on the freeway.
Glad I went with 3.07's and not 3.42's as even coming from the 4.11's it would not have been enough.

How much did you pay to get that done if you don't mind me asking?

[jayoldschool]

See post #15

[zplightning]

Originally Posted by jayoldschool

See post #15

hahahaha woops! Thank you!

[BOE]

@ scuderia. sounds like the solution i am looking for. did you have to alter anything? the yoke from driveshaft? i have 64 longbed with 292 but can't figure what tranny it has . 4 speed granny is all i know. it raps out at about 50 mph

[scuderia]

Originally Posted by BOE

@ scuderia. sounds like the solution i am looking for. did you have to alter anything? the yoke from driveshaft? i have 64 longbed with 292 but can't figure what tranny it has . 4 speed granny is all i know. it raps out at about 50 mph

what ever tranny you have will have a 1:1 final gear so the issue is with the rear end gears. if 4.11 like me it was happiest at 45 and would do 50/55without screaming.. too much. anyway, no other changes other than carrier, gears, bearings and seals. took the shop a day to turn it around. Hope that answers your questions.

[BOE]

thanks scuderia

[scuderia]

Little update..
Since swapping gears as I mentioned before, the truck seemed a lot happier at 55 but still didn't love 65.
I downloaded a speedometer app for my phone today to check actual speed and it turns out that 55 is now 65 with the new gears and 65 is just under 80 so all is good in the world. Got what I wanted.