Tranny and rear end combo question

[bpl0807]

Hey guys, first post here. I have a 1966 Chevy C10 pickup, and in it is a 250 straight 6 paired to a column shifted muncie 318. I absolutely love this truck and wouldn't consider trading or selling it. The truck drives wonderfully for the entire drivetrain being all original, however, this truck is terrible on the highway due to it's gearing. It currently has what I believe to be a 4.11 rear end in it, and at about 62mph im pushing 3k rpm. Recently I have been researching swapping either the muncie 318 for a 319 o/d or the 4.11 rear end for a 3.08. My question being, what do you guys think about either of these swaps, and would the 3.08 gears be ok with the muncie 318 and the 250 straight 6? Thanks, any help is greatly appreciated.

[Captainfab]

The size of your rear tires play a part in this also. If you are running say a 235/75R15 then I wouldn't go any higher than a 3.42 gear with an OD trans. You do not want the lowest rpm's possible. Instead you want the engine to operate in it's peak efficiency rpm range.

[bpl0807]

My rear tires are 225-75/15, I think that's like a 28" diameter. But I think 3.42 gears with an o/d would definitely be enough, however I was considering swapping the rear end to 3.08 gears or swapping the transmission for the o/d tranny, not both.

[geezer#99]

To decide if your truck will be happy with a 3.08 gear or o/d just drive at 45 to 50 mph on the highway and see how it accelerates from that speed.
If it just sorta bogs down and refuses to go faster then you'll know a swap is a waste of time.

[curvedglass]

I have a 63 with the same combo. The PO added 3.08's. what a dog. the truck runs out of steam going up hills. Rowing the boat the whole way. 2nd/3rd over again.

I was told by Langdons to just put the 3.73's back in and go to a 30% over drive. Adding power on helps on the top end. Got to love that shop. Actually giving good advice and not trying to sell you something first.

On the plus side I am getting 18.4 mpg.

[LVPhotos]

The HP for a 283 is listed as 184hp. So the 250 would be less. So you have to stay in your power band. Here is a Gearing chart. I run a 28" tire with 3.73 gear and a .67 OD gear or 33%. Around 2000rpm@75mph

[ELDiablo]

Greetings from Oakland CA. I've got a '63 with a 3 sp (no OD) and a 411 dual posi on the rear. Tires: 275/60R15. You know the problem, I'm hittin high revs at 60mp and the gas just disappears. I'm trying to fiqure out via this forum of smart wrenchs, how to re-gear my ride for higher top-end and mpgs. Do I need to change the tranny and obviously regear the rear too? I'm a bit lost on this. Your thoughts and knowledge of the subject would be helpful- thanks mtg!

[hotrod66]

my old truck wasn't the fastest off the line with the 3:08 and the 250 but it still would pull a load. it also really loved the highway and where i live thats all there is. it did good as far as mpg at 70 was running @2000 rpm

[Captainfab]

Welcome to the forum

You didn't say what engine your truck has, which does play a part in the recommendation. Just guessing I would say you would need to change the differential gears to either 3.42 or 3.73's and also go with an OD trans, either manual or auto. You could alternately keep the 4:10's and go with an OD trans and a taller rear tire.

Originally Posted by ELDiablo

Greetings from Oakland CA. I've got a '63 with a 3 sp (no OD) and a 411 dual posi on the rear. Tires: 275/60R15. You know the problem, I'm hittin high revs at 60mp and the gas just disappears. I'm trying to fiqure out via this forum of smart wrenchs, how to re-gear my ride for higher top-end and mpgs. Do I need to change the tranny and obviously regear the rear too? I'm a bit lost on this. Your thoughts and knowledge of the subject would be helpful- thanks mtg!

[ELDiablo]

Thanks Captainfab.
Sorry, the engine is a 351 so it's got plenty of get-up. Appreciate your thoughts. If you have any add. suggestions plz send along. I'm just trying to sort this out so all info is helpful. I stumbled on the forum and it's very helpful and plenty of great trucks.

[Captainfab]

OK, so I assume that your '63 is a GMC with the 351 V6? If so the your engine has enough low end torque to pull a taller gear. The problem with changing the gears to anything higher than 3.73's is that you will have to also change the carrier. Which means you will loose your posi unless you buy a 3 series posi unit. That adds about $400 to the cost. The next issue is that with the GMC V6 you are limited as to which OD trans you can use. You will not be able to use the NV3500 or NV4500 trans. You will have to go with either a T5 or the MY6/NP440 trans.

I would say you first need to set a budget and see which changes you can get done within your budget.

[AcampoDave]

342 was common in the 5 lug squarebody wasn't it? Should be a cheap n' easy one to score. You could roll it without o.d. see how it goes and still go with Captain's idea of adding an overdrive later if you want. Plus then you can go with 5 lug disc up front later too and the rear would be matched.

[AcampoDave]

My longbed has a 308 rear with a stock 283. It still has a column shift and it drives great on 225/75-15 tires. But any less motor and it might need numerically higher gears. Especially if I wanted to pull a boat or something. I believe I would struggle a bit to pull anything larger that a personal watercraft and camping gear as I am, but have never tried it.