The Stovebolt Site Forums The Shop Area Engine Shop 3/4 ton truck with 235 motor, will it go higer than 65 speed with 4.10 rear

Hi all,

I have 1952 3/4 ton truck, recently I changed the motor to 235 from 58 Apache, it is going only at 55 miles and my rear end is like 4.56 something like that, here in the salvage yard they have pumpking with 4.10 gear ration for $375,

1. Is it worth the money for that?
2. Will the truck go at 65 to 75 miles speed

Can someone throw some light please

Ganesh

I would put that money towards an overdrive. Does it have stock brakes, tires, and steering? If so, are you sure you want to drive it at those speeds?
Fred

Yes it will.

I had a 235 in my '52 GMC with a 4.56 rear end, and I managed an absolute top speed of 72 mph. However, I always cruised it at 65 mph which translated to about 3200 rpm, if I remember right. A 4.10 gear should add at least 5 mph to that.

It's hard to say if it's worth it. You should see if you can get a guarantee that if it's bad, you can get a full refund. Then pay a shop to check the gears out for you and change the ancient oil.

HotRodDad,

So 235 motor with 4.56 rear end you made it 72mph, what changes did you make to the engine because mine with great difficulty it touches only 55 miles nothing more than that. From what you said if I can go 72mph with all what I have I would not need to change anything for 5 more miles speed.

Yes I have everything stock

I will look forward to see what changes you made

Ganesh

Look here, near the bottom of the page, http://www.onlineconversion.com/bigger_tires.htm

The short answer is no, not for long.
To go 65 regurlary you need even faster gears than 4.10, with only 4.10 and 28" tires you have to turn 3200 rpm, and that's more than a 235 wants to run for a long time.

Grigg

Thanks Grigg, that answers my question

Ganesh

I was about to say my 250/3 speed and 4.10 rear end doesn't like much more than 60-65 max...I'll be looking for a overdrive to make this more highway friendly

Grigg I hate to disagree with you, but you're wrong.

I drove 12 round trips from Santa Fe to Denver last year in my truck, and that was 800 miles a round trip. Every single one of those trips averaged between 65 and 70 mph.

So I think the 235 is a LOT more durable than you give it credit for. Either that or else your 235 is not very well built.

I just finished installing 4:11s in my 53 flatbed. And though I haven't attempted any new land speed records as yet, it really accelerates noticably better than with the old 4:56s. My next move I believe will be for taller tires in back.

I think this should put me at just about the limits of my bravery with the old flatbed, bias tires and a front end that needs rebuilding.

BTW, I'm running a '54 235, toilet bowl carb, dual exhaust with orginal 4 speed.

I am sorry to say I don't have any personal advice so take this comment with a grain of salt.


I'm doing my rebuild and also concerned about drive train and modern speeds. The truck had '56 235, 4 speed w/ granny, 4:56 rear end. My dad last drove this truck regularly. He said he has achieved 80 mph multiple times and believes the truck will perform fine at 65mph

Either he is wrong or the truck could achieve that max speed.

Yes, it is more durable than I give it credit for, and as such I expect it to last a long time with proper treatment.

My experience comes from driving my 52 3800 with a 55 235 that I rebuilt, Dana axle with 4.56 gears, and about 33" tires.
I drove this truck 8,000 miles in less than a month, from VA to CA to WA to NY to VA.
I also had a digital tachometer on the dash, but no working speedometer, speeds were figured by dividing the number of miles driven on the highway by the time, usually about 20 or 30 miles in a calculation.

I drove west at about 2400 rpm, and the engine was happy, and fuel consumption was not bad, speeds were about 50-55.

Driving east I was running out of time, and pushed it faster, about 26-2700, and the engine still did fine, but burned noticeably more fuel.

At one point in Canada driving from Windsor to Niagara falls on the highway I was in the right lane and being passed as if I were in reverse, so for a few hours we drove at about 3,000, still no problems.

Just for fun a few times I did have the truck over 70.

I am not saying that a 235 can't be driven fast or at reasonably high RPM, just that above 2500 rpm or so there is no point, as fuel consumption increases and engine life is shortened.
For me, if I had the choice of gear ratios, I would gear for about 2500 rpm or just faster, at highway speed, as I feel a 235 is happy at this speed.

Grigg

Using one of the calculators at Grigg's link (above) here are some calculations regarding rear-end-ratio, tire diameter (loaded), MPH, and resultant RPM:

4.56 rear end; 1:1 top gear ratio; 65 MPH; 30" tires: 3,300 RPM
4.56 rear end; 1:1 top gear ratio; 70 MPH; 30" tires: 3,575 RPM

4.56 rear end; 1:1 top gear ratio; 65 MPH; 28" tires: 3,557 RPM
4.56 rear end; 1:1 top gear ratio; 70 MPH; 28" tires: 3,830 RPM

Just for the heck of it, let's assume you have a larger diameter tire and ran at 80MPH:
4.56 rear end; 1:1 top gear ratio; 80 MPH; 32" tires: 3,830 RPM

Sure, a 235/261 could run at 3,800 rpm, but, for how long? Maybe someone has/had a speedometer that needed calibration, or very wide diameter tires? I think a high-pressure 235/261 would be hard-pressed to run all day at much over 3,200 RPM.

Around 2,800 RPMs is what I got at 65 mph in a 1/2 ton 54 Suburban with stock 3.90 rear-end and about 31" radial truck tires. I got 18 mpg on 350 mile trips at 60-65 mph. A switch to 3.55 rear gears brings it down to 2,500 RPM.

Tim

I'm a new guy to this forum and this is first attempt at jumping in on a conversation, so have patience. I have a '54 3/4 ton with the stock 235 and I am geting 18 to 20 mpg regularly. I changed out the 4:57 rear end by bolting in a dana 60 with 3:54 dropping the ratio a whole point. Adding taller wheels and tires, changing the Carb to a Carter and rejetting and using the appropriate metering rod. I use my truck for my daily driver, so I have added power steering and pay attention to my brakes. It was a pretty cheap fix and am amazed with the durability of the truck.

B_H54,
That's a great example of proper gearing for the vehicle, engine, and intended use.

lots of people don't realize how important gear ratios are, you are obviously not one of them..

Grigg

Welcome B_H54 and thanks for joining in. A lot of folks will want to know about your power sterring as that is a FAQ.

Thanks again and we hope to see lots of you.

I think Shellogy's dad had a inacurate speedometer. The point I made before, do you really want to compete with the Honda crazies at 65-80 MPH in one of these trucks. I have a 350 in my 56 with PS, disc brakes, 3:90 rear end, and an OD. It will cruise nicely at 65 but I don't feel comfortable at higher speeds. Forget about stopping at 70 with stock brakes if somebody does something stupid in front of you.
Fred

Sounds like the laws of physics dictates that 70 to 80 mph is possible. Especially going down a long hill in neutral. On the other hand, running these tough engines at 65, although not desired, sounds do-able. I'm hoping atleast 60 mph will not be to much regular burden. Think I could live with that for casual driving. I use my Honda Accord to run expressway everyday in Atlanta where you'll need to go 90 mph and then sit in traffic rest of trip.

Lots of good advise guys, I think lower rear end gears are really needed and I cant see how to make 80 with the stock.

Thanks for taking time to answer my questions.

Ganesh

My '55 1st GMC Suburban will easily run 65 and 70 and faster. I'm running 3.08 gears and a GMC 270 and would not expect it to carry a real heavy load, but its comfortable on our local highways.

My 57/235/4.10 half tonner would do 65, even 70, but it was really pushing it to do it. 60 was much more comfortable. That was with 235/75/15 tires, about 28" tall.

My current 55.2 has a 235 with 3.54 gears and is much happier cruising 65. With the granny 1st, it still has all the gear I can use. Haven't checked mileage due to irregular use, but I'm guessing it's somewhere around 10-12.

Devin

My 3200 runs very nicely at 60-70, even at 80+. 235, overdrive trans, 3.90 gears and 30" tires.

Bill

What kind of gas mileage you are getting?
What kind of overdrive trans you have?
What rearend did you slap it in?

These are in list of things to do!!

Appreciated much

Ganesh

I agree that the lower highway speeds are more comfortable. Even though I could go 70+, the engine ran awfully hard to do it, but it held up. I usually cruised at 65, and although I got passed a lot, it did teach me the rare virtue of patience.

I've gotta tell you though, there were two modifications which helped me obtain that last 500 rpm, as well as enough torque and power to exceed 65 mph at will. That was a 2 barrel Holley/Webber carb from Langdons, and a Pertronix electronic ignition conversion from Summit. Before that, any mild grade uphill and exceeding 60 was a challenge.

If you think about it, the Blue Flame 235 in the Corvette made its peak horsepower at 4200 rpm. I know it had its own cam and some mods, but the thing to observe was that the rotating assembly was tough enough to take those kinds of rpms. I think the bread and butter 235 feels like it's running so hard at 3500+ rpm mainly because of the extremely mild cam, the choking 1 barrel carb, and possibly the points. Naturally, a set of split exhaust headers would improve things a lot too, but it appears Fenton for some reason decided not to make those anymore.

However, I've seen tubular split exhaust 235 headers at Speedway Motors.

Gas mileage? What gas mileage?!!! I get around 14-16, if I keep the ol' size 14 out of it. I am running dual Holleys on an Offy intake, it does run a bit on the rich side, plus we have E-10 here. The trans is an SM318/Borg Warner, original type option for that year truck. The diff is also the original. About the only real change from stock is the tires, a 30x9.50x15 Michelin radial LTX MS. I can run around 70 at 2100 rpm with that combo.
I should mention, mine is a 1/2 ton, not a 3/4.

Bill/HotRodDad,

Thanks for all the info, it is helpful. Today when I was driving I ran out of gas and my friend came for rescue. My fuel guage doesnot work and I really donno which mpg is my truck giving. I need to do lot more work get my truck to be reliable for me.

Ganesh

With a 235 I would go with 3.73 or 3.54/3.55. They still pull well without taxing your engine. Your rpms should be about 2400-2600. A lot more comfortable for your engine. Dana 60 had 3.54 or 3.73 in their 3/4 and 1 ton axles. Unless you are towing something extremely heavy those gears would work much better. I have had both. My truck came with 3.73 but has OD. Just a nickels worth.

Don't pick a gear ratio without considering tire size, a few inches in diameter makes a big difference on overall gear ratio.

Henry G's example above, while it is good advice if you have the same tire size he has, it could be wrong if you don't.

An example, at 60 MPH, same transmission, same gear ratio of 3.54.
One with 28" tires (like a 3/4 ton) will turn 2,549 rpm.
One with 38" tires (like a 2 ton) will turn 1,878 rpm.
Quite a difference, and with a 235 and 38" tires 3.54 gears would be a really bad choice. Then the chosen engine makes a difference, in my case 3.54 is just right with my diesel and 38" tires.

To decide gear ratio you first need to know several things:

RPM you want your engine to run, usually figured at cruising speed on the highway.
Transmission high gear ratio, for direct drive it is 1:1, overdrive, depending on transmission, can be between about 0.60 and 0.84:1.
The rear tires actual outside diameter.

Then with a gear calculator like on this page near the end http://www.onlineconversion.com/bigger_tires.htm you can choose what rear axle ratio may be best for you. Or if you already have one, and want to pick a transmission, or tires, the same stuff applies.

Grigg

Thanks Grigg. That's really informative.

I have a Dana 60 I want to put in for the posi, the tougher gears, the bigger brakes, and the taller ratio. It is an 8-lug and looks like it'll match my wheels, spacers notwithstanding.

I calculated with my tires (275/65R16 if I remember right...I'll have to go look again), 3.54 would give me a 75 mph cruise at around 2900 rpm. 3.73 would be around 3000 to 3100 rpm, so the 3.54's would be a more relaxed cruise.