questions about rear end gearing

[busjockey]

I am going to restore a 1947 3/4 ton chevy with 4.57 rear end. Am considering changing to 3.98 rear with original transmission for added speed on highway. If I make this change will the truck still be able to pull a large boat or trailer? Do not need to pull over 55 mph but still would like to have some usability. Any advise.

[mr48chev]

I don't think you would have any problem with it. You could probably get away with 3.73's ok unless either is really heavy. The biggest issue is probably pulling the boat up a steep ramp out of the water but with the granny four speed that shouldn't be a real issue. The main thing is to have the engine running at a speed it is comfortable with when you are driving at the speed you want to drive at.

[busjockey]

I would like to be able to drive around 60 to 65 in the truck most of the time and still get decent fuel mileage. I will not pull things with it much but would like to be able to when needed. This truck is going to be my daily driver.

[tmoble]

>>> I would like to be able to drive around 60 to 65 in the truck most of the time and still get decent fuel mileage.

you need an OD tranny.

What engine do you have? with a 3.98 and taller truck type tires you'll be running it over 3000 at 60. The stock engine won't make it past the first trip.

Want performance and mileage? you need an OD tranny. you can set it up to loaf down the freeway at 1800 RPM at 70. With a 3.42 or rear gear and the low first gear of the OD trannys you won't have any trouble at all pulling a boat up the ramp. If you hit some hills drop it out of OD and the 3.42 gear will give you power to pull.

think 200-R4 or 700-R4, 3.31 to 3.73 rear gears. 3.42 is nice.

with the stock engine and 3.98 you're going nowhere fast.

[busjockey]

I plan on running a stock 216 engine and keeping the truck fairly original. I have thought about an s-10 transmission, but the stock one is in good shape and was trying to decide which way to go, or what gears would give me the best solution to the problem. With fuel at $4.00 per gallon I want to get more than 10 mpg. Thats what I got in a 48 chevy 1/2 ton 20 yrs ago with 4.11 rear end. I am in the research stage right now and am interested in all opinions. Thanks

[DetroitDan]

20 years ago the gas available was a lot better. All our gas mileage has suffered with the corn subsidy gas. So that giant farms owned by NYC based corporations can enjoy even more government million dollar handouts.
Sorry for the rant.
I too vote for an OD trans. I hate the th400 in my 82, but there's no inexpensive swap options that would stand up. A stock 700 won't take it, and I can't afford a built one. And if I could afford one, I'd probably buy a Gear Vendors OD. Have you thought about one of those? Might be just what you need, but they are pricy.

[busjockey]

Have not looked into aftermarket od transmissions. Would like standard tranny, and just trying to get any and all advice on this matter I can get.

[tmoble]

those auto ODs aren't going to work with your 216. Keeping that severely limits your choices.

there's a 80s - 90s 4 spd manual that has OD high gear, I believe is standard Chevy manual tranny mounting dimensions. I don't recall what it's called or what it came in.

[busjockey]

I have a neighbor who has the s-10 standard tranny in his 47 half ton and he seems to like it. I have not been in the truck yet to see how it works but would like to soon. I keep leaning toward that solution.

[tttuba]

I too have been contemplating an s10 trans and new rear end. If you find anything out would you let me know please?

[northerngmc]

You will get some extra speed on the highway but not a lot.

Using an engine RPM calculator, with 29" diameter tires.....

4.57 55 mph 2912 rpm
3.92 55 mph 2536 rpm

Still screaming down most highways.

Going to an overdrive transmission with a 216 and try to pull is much weight is probably going to be under powered at highway speeds.

Sounds like you might be looking at the impossible.

I am considering changing my 59 rear gear from 3.90 to 3.38 for highway driving and have talked with a couple of guys who did this. Great on the highway but loss of low end grunt. Which for my pavement cruiser will work just find.

[busjockey]

Just wondering if the overdrive with the 3.42 would give me the highway speed when driving but would be able to pull say 50 to 55 mph when the boat or trailer is behind the truck in a lower gear? Could change the 216 to a 235, but from looking at the hp numbers it does not seem like it is worth it.

[busjockey]

I am wondering how you calculate the rpms at 55 mph with the different size gears in the rear? Would like to know.

[jfnar]

http://www.csgnetwork.com/multirpmcalc.html
This is the easy way to calculate engine speed. I don't think your 216 has the ponies to pull anything at highway speed. You might want to consider a 292 swap if it'll fit.

[tmoble]

what he said. recall the time and intended usage of the 216. it was made to be used in farm trucks that never saw the far side of 40MPH. It was never meant to be hitting a freeway. There weren't freeways then. Think along lines of hauling hay around to different parts of a farm. This is not related to hitting the interstate with a trailer.

I think you need to fall back and re-group, define your goals and requirements carefully.

[Russell Ashley]

Here's another good site for calculating engine speed and other things.

It's Randy's Ring and Pinion at http://www.ringpinion.com/

Just click on the "calculators" tab.

[busjockey]

I guess I need to give up on pulling much and just try to get around 60 mph out of it with out tearing the motor up. Never intended to drive it much over 60 any way with stock brakes and such.

[tmoble]

measure the diameter of your current tires, then use the calculators to figure out what gear ratio gives 60MPH at the safe RPM for a 216.

keep in mind that cruising for an hour at 2500 is not similar to hitting 2500 between shifts on a farm road.

I'd guess you'd want to keep it to about 1800 - 2000RPM.

Is the 216 an oil pressure engine or does it have the splash trays in the pan with the dippers on the rod caps?

[busjockey]

216 is an oil dipper. I do have the option of going with a 235 which is a presured oil system I am just not sure what I want to do yet. I am in the research stage and asking a lot of questions. If any one has any suggestions on the engines 216 or 235 which one would be the best in a daily driver give me some feed back.

[jfnar]

IMHO, the 235 is a significant improvement over the 216 and an easy swap but you still won't have enough power for pulling a trailer on a highway. A 261 would be even better if you can find one.

[busjockey]

I think i will go with the 235, and as far as pulling I doubt I will ever pull much more than a small boat or u-hall with it and if it only goes 50 while pulling that I will be ok with that. Thanks for the info.