The Stovebolt Site Forums The Shop Area Driveline Hydramatic Top Speed?

I own a 57 3100 with a hydramatic transmission. I took it out for a spin today im estimating it topped top out at 50-55 mph. With new 640 15 tires stock rear end. What is the top speed for these trucks with a 235/hydra? Bolt on rear end conversion? Thanks in advance.

What is the rear-end ratio? That will be the primary factor.

Do you have a rear-end conversion? Or, do you have the stock rear end (is that a 3.90)?

A 640 15 bias ply tire would have about a 27" diameter.

The H-M transmission high gear is 1:1. Same as a standard. The H-M also does not have the slippage of a modern automatic trans. Bottom line is that it will run the same speed as it would configured the same way but with a manual transmission.

Chevrolet 1957 Specifications-Truck
http://www.gmheritagecenter.com/doc...hevrolet-Trucks/1957-Chevrolet-Truck.pdf

Engine speed piston travel
PDF page 128 (bottom of page)
4 speed Hydra-Matic
Axle ratio, tire size, engine rpm @ 1 mph
rpm 1st,2nd,3rd,4th gear

feet per minute calculation on PDF page 129 (bottom of page)

Engine performance on PDF page 99

Hope this helps.

Let's pretend that you have 27" tires, and a standard 3.90 rear end, and a final transmission gear ratio of 1:1

At 55 MPH your engine RPM would be about 2700. A little high, but not really straining the engine.

The cheapest way to get lower RPMs and higher speeds might be to get larger diameter tires. 30-31" tires would get you 2500 RPM at 60 MPH.

Tim,
Nice Engine RPM cakeculator, I mean calculator.
I bookmarked that one!

I dont know the gear ratio. Im just trying to be able to drive the truck occasionally on the freeway and improve mileage if possible. Thanks

I know its stock 6 lug. Any suggestions on a donor rear end will bolt right in with the least modifications required?

Take a look at Patricks Antique Cars & Truck parts

When get to the page there is a separate side scroll bar,scroll down to page 13 about half way down, you will see a picture of a pickup with the word NOW in the picture.
High-Speed Rear Ends
'55-'62 pickup 1/2 ton 3.38:1 ratio
ring and pinion installation kit

You should be able to cruise at 65-70 mph with 3.38:1 ratio rear end. And get pretty good fuel economy.

After calling Patrick's.
Let me know what you find out.

Thanks,

Added more 3.38:1 ring and pinion installation kit links:
ringpinion.com
tomsdifferentials.com

the 3.38 is for the later open rear end assembly. The best you can get for up to 54 torque tube style is 3.55

The tires you're running are a bit undersize for your truck. The base size for the '55-'59 3100/3200 was 6.70-15. According to the specs I've looked up on the tire dimensions, the tires you have are about 1 1/4" smaller than the stock size, the 6.40-15s being approximatly 26.88" and the 6.70-15s being approximatly 28". Therw will be some varaince depending on manufacturer/tread design/inflation pressure. With the OE diameter tires and 3.9 rearend ratio, it looks like you would be turning a bit over 2600 @ 55 mph.

It's a 57 so it is an open driveline.