The Stovebolt Site Forums The Parking Lot Big Bolts Speed -up?

I have a 56 chevy 2-ton. I am able to get 50 mph out of it. I know it is geared low. I have two options to get more speed. I can get a 2-speed rear-end out of 65 chevy C-60, or a 5-speed transmission out of a 61 Chevy 2-ton. I would like to obtain around 65 mph out of it. May need to use both? Any suggestions?
Ed

I would like to hear this as well. I need to be able to get mine to cruise at around 60 without massive fuel consumption.

This tech tip will be helpful:
http://www.stovebolt.com/techtips/calculate_rpm_tire_axle.htm

I like the first link for the gear calculator http://www.onlineconversion.com/bigger_tires.htm

On the last one, lets assume the following, until you correct the figures you know are wrong.
65 mph
Tires are 8.25X20, so about 38" OD
5.14 rear ratio (what is it really?)
The above figures give you 2,900 rpm at 65 mph is that suitable for your engine?
Or if you had say a 0.80 OD ratio, you then get 2,363 rpm, that would be OK, perhaps a little slow.

This 5 speed from a 61 Chevy you mention, what model is it, is it overdrive?? If it is not OD, then it won't help you go any faster than the 4 speed you already have.

Grigg

Ed,

I'm not sure about the interchange, but it's all about the ratio of the final rear end gear, whether you have a 2-Speed or not. A 2-Speed's purpose is to have a Low Range for "Split Shifting" to give you more gears pulling heavy loads. Going to a 5-Speed trans won't make a difference unless you have an Overdrive. They were no 4-Speed or 5-Speed Overdrive transmissions available in the old days that I have ever heard of (info revised on Pg #2). Not sure if there are any newer 5 or 6 Speed OD's that would interchange. I believe there were OD Aux. Trans that would work (you would then have 2 sticks) and there are a few on here that have some good experience with them who I'm sure will be jumping in soon, but I would say that it is not a very easy installation. The most sensible fix would be to find a rear with a higher gear and depending how you use the truck, a 2-Speed rear may be necessary.

Bill

We need more info from you to be able to make informed suggestions.
What engine?
What transmission?
Rear axle gears?
Tire size?
Weight of truck empty?

What transmission and or rear axle gears do you have available to swap, if any?

Grigg

Aux. transmissions were mainly used in tandem axle trucks and they did provide an OD. But they are difficult to shift (not synchronized), are also large and would take considerable effort to mount into the frame rails. An old brownie 2 spd may work if you can find one. I agree with Bill that a replacement rear with a higher gear would be the cheapest and easiest way to go.

JAMES

Thanks Guys,
The truck will be used to haul a car, around 3500lbs. The ttruck weighs 6300lbs. empty. The motor is a 235 in-line 6 cylinder that is a sweet running engine. The tires are 8.25 X 20 inch. The 5 speed transmission is overdrive according the guy who is selling it? The truck may have to get on the interstate for a few miles sometimes, thus the need for a higher speed. Are there casting numbers and there locations that I might look far to help determine gear ratios?
Ed

There should be a fair amount of numbers on the trans. I would take them all down and post them on here. We can try to determine what it is.

Bill

You won't have any extra power to go 65 mph with a load.. 55 loaded at 2,800 rpm will probably be about all you want to do, or all the engine can do. Then in OD and empty you could go faster, 65 may be OK, preferably at about 2,500 for a little better fuel mileage.

Run the ratios and speeds in the calculator, see what you find?

Grigg

The more I read the more I am aiming towards a Tandem setup with a pusher front (dummy axle).

I am thinking a GM 14-bolt since I already have a 454 and a TH400 that i will be wedging into the frame.

My main thing is that I want to keep the factory wheels and go all wheel discs. Granted a air brake system for the rear axles isn't out of the question either.

Any recommendations of opinions?

Hello Bill,

The guy that has the transmission for sale called me back with the numbers. On the top case C9723, on the sides NP(D)/ C91171/ 72123263. Out of a 61 chevy 2-ton. The top of the case is alum.
Ed

Well, I don't recognize anything there, except the "NP" could very well stand for New Process. I tried to identify a date code but the 2 set of numbers that start with C has one too many numbers on it. Maybe some one with some more knowledge than I have will jump in and help.

By the way, looks like I'm wrong on any possible older 5-Speed Overdrives.

I found this list over at Jolly's site:

http://www.6066gmcguy.org/SM420.htm

Scroll down to the listing of 5-Speed Transmissions and there is at least 4 that were available.

Bill

Adding a pusher to these old trucks is not for the inexperienced. It would require a drop center axle for openers and having a both a hydraulic and an " air brake system for the rear axle" is not only totally impractical but would be dangerous to boot.

Don't try to re-invent this truck. If it's the old cab look your after then put the cab on a late model chassis with the things you want (disc brakes, etc.) and call it a day. You'll be way ahead of the game and have a drivable and safe vehicle. Don't mean to rain on your parade but your statement makes me very suspicious of where you seem to be headed.

Hello Bill,
NP

Top plate #97293 Corrected Number

NP
Right Side #72123263
#11-21-60
#C-91171

Front #C-94G02-H New Number

Ed

np is new process

np is new process and they were 5 speeds no overdrive and you can achieve 60mph unloaded cruising or faster as i have a64 with a 292 5speed new process and 2 speed rear end dont know gear ratio though

Ed,

The only other thing I have found out is that the NP date code uses no letter prefix. So it looks like we can safely say that the #11-21-60 numbers that you have listed is Nov 21, 1960 which would be correct for a '61 model truck. The other number(s) could very well be casting numbers and my 2-Ton Chevrolet Parts Book or any other book I have does not list them. We need someone to drop by that has Transmission knowledge or Transmission books to help.

Bill

That is what i was planning to do but if there is a more direct option I like to explore it. Not to mention modifying the axles to fit the truck will be a necessity either way.

Just exploring options.

If the wheel makes one revolution and the drive-shaft makes 6 reveloutions, the rear-end ratio is?

Bigwheel,

My guess would be 6.0:1.

Stuart

One wheel, or both wheels at the very same time, make one revolution?

If you turned both wheels once at the same time, and you got 6 driveshaft turns then your rear axle ratio is 6:1, probably 6.17:1 in reality, that's believable.

If you left one rear wheel on the ground, and turned the other one turn, got 6 driveshaft turns, then your rear axle ratio is 3:1, which is unlikely for that size truck.

A more accurate method is to turn the driveshaft 20 turns, let only one wheel turn(open differential/no locker), then 20/2=10 to account for the differential action of only one wheel turning.. Now 10 divided by number of wheel turns is your ratio.

It's confusing, If I didn't get my head wrapped around it right, please correct me.

Grigg

One wheel on the ground, drive-shaft 3 revolutions to one for the jacked up wheel. Was it right to double the revolutions of the drive-shaft? So the ratio should be 6:17 you think?

Bigwheel,

6.16:1 is a pretty common ratio for 1 1/2 ton rigs. However you did your calculations, you know 3.0:1 isn't feasible for a large rig, so yes...you did it right!

Stuart

Thanks for everyones help. I have a 65 chevy 2-ton with a 2-speed rear-end. Truck not running at this time. The high low gear is operated by vacum? I can jack it up the same way and try to determine ratio, but not sure about the high low range? I want to put this rear-end into the 56 with the 235 engine.
Ed

Then 6.17 sonds right,

Give the driveshaft more turns to reduce the % error in your calculations, see if you get closer to the likely 6.17?

(Driveshaft turns/2)
-------------------------- = ratio
single wheel turns

On your two speed just check it in whatever gear it is in now, same as before, then look at the likely choices in the service manual.
You'll spot the ratio you calculated, and the corresponding higher or lower ratio. A truck that age won't have many axle gear choices, should be easy to single out the one you have.

The 65 has a 10 hole wheel patern on the rear and a 6 hole patern on the front. Did it come that way from the factory?
Ed

Not likely

Sounds like a front axle/hub swap.

It could have been the rear. Look on your glove box door and see if the sticker is still there. Try to see if it says 5-10 wheels anywhere. 5-10 means 5 lugs on the front and 10 on the rear. I really like 10-10's but that's how they designed it and I'm sure it is plenty strong enough. The reason of the 5-10's is so you can use the same wheels on the front as you can on the back.

Bill

A little tip for the 5 spd transmissions if 5th gear goes forward its an overdrive, if it goes toward the seat it is not. Yes there were 5 speeds in the early trucks we had a 47 with a 270 5th gear and a 3 spd brownie all factory. And I beleive there were the odd lug nut combos in the mid 70's yet

My personal opinion is that regardless of what size tire, transmission and rear gear ratio you use in that 1 1/2 ton or larger truck, youll have to be going down hill, unloaded with a tail wind if you expect to see 60mph with a 235.

Even if you stepped down to a 1 ton truck, with a gear ratio in the 4.somethings, you would probably still be to darn low to tow anything very fast for very long.

Jeff

I have been following the posts on speeding up and I am convinced I will be happier just going slow down the back roads. If I wanted more speed it would make me alter my truck too much. Besides, it gives people more time to admire your truck. : )

The issue is can you speed up a old truck, sure you can with enough time and money. The reality of the fact is that its not practical nor is it safe to expect a piece of machinery that was designed to operate in the 45-50 mph range to compete with the speeds that we have on the roads today. I operate a trucking company and we have Sterling trucks and these trucks are properly equipped and will go 65-70 mph on the freeways but still can be a handful at times with a truck maxed out at 33,000. As been said above, examine what you really want to do and then figure out a safe way to accomplish it.

Good Luck
Don

Guys,
Got the 65 C-60 with the 2-speed running. Had some brake issues, drove it up to around 40 mph. In low range. Jacked one side up and had 1 turn of the wheel for 6 turns of driveshaft. 6:17 ratio. With vacum leaks to the rearend, shifted it by hand into high range and got one wheel turn to 9 revs of the driveshaft?
Ed