The Stovebolt Site Forums The Shop Area Engine Shop 3/4 tran and rear option

Have broused through the many different forums on making the larger 3/4 and 1 ton AD trucks better equiped for faster travel. The rear end swap to a 68-72 4:11 ratio or the upgrade to a T-5 or NV4500 transmission. To keep the work to one or the other, which is the best for these bigger truck. Also has anyone discussed how the transmission upgrade would perform if the original 4:57 rear end remains on the truck?
What are your thoughts?

If you can find the 4.11 gears that will help the Eaton axle go faster. Some people are still searching them though not alot available. You could put a 14 bolt or Dana 60 or 70 under them and get a much lower ratio gear set and still keep the 3/4 and 1 ton capacity. 14 bolts can sometimes be found cheaper than a Dana, but the new gear set won't be cheap for either.

I'm keeping the SM420 in mine, but gears is gears. If your gonna change the engine to a bent 8, then why not change the tranny as well (assuming it will all fit nicely). A 0.8 (or abouts) overdrive with a 3.38 gear set and some 285/70R/19.5 tires will give you a nice slow engine at 70 mph (1800 rpm). With this setup the question is do you have enough gear left in it to pull out stumps!

Using an NV4500 with a .73 overdrive ratio and 30 inch tires, your engine would be spinning 2615.5 rpm at 70 mph with 4.57 gears. The overdrive gives you an effective ratio of 3.34. On paper it seems to work pretty good to me.

John

P.S. I just put a NV4500 in my 59 1/2 ton with 3.90 gears. I still have the low end grunt with the 5.61:1 first gear, and dropped cruising rpms down to 2480 at 70 mph. I have 27 inch tires. Taller tires would drop the rpm even further.

I have just put my 1951 1 Ton on the road and it has a 1971 4:10 ratio gearset in the rearend. With the stock 216, it cruises along at 50 mph although hills can be a challenge. It will max out at about 60 on the flats. What this means to me is a ratio any higher than the 4:10 would probably not help because it just wouldn't have the power to push the truck any faster.

I have a 4.10 rear with a T5 in my 3/4 ton. I'd love to tell you my RPM's at each speed but I don't have a tach. Also my speed is not hooked up. I'm guessing I'm at 2,300 r's at 70 mph. I have a chevy 235 and the power is fine.

If you're going highway speeds, just make sure you can slow down and stop.

I have a 1-ton frame with a 14-bolt and 3.70 gears I got from a guy who used the cab on a hot rod he'd built.

He said the 216 with an SM420 just didn't have enough beans once he installed the 3.70 gears.

Yo Fred, do you have your 1971 C-20 carrier code numbers written down somewhere? Looks like there were a half dozen that year with a 4.10 and I was wondering which of them were Eatons.
I would have to agree with ya about over gearing the 216 in my 3604 with the SM420. This was one of my concerns, even though I'm not gonna be doing any hauling, I'll bet she would really be a dog with anything much higher than a 4.10, even without a load.
Man I've been looking all this year for something with a 4.10 and just taint having any luck.
Denny Graham
Sandwich, IL
Denny Graham

Denny,
I have been looking to find the Email where the part number/ID was written down and I haven't found it. If I do, I will definitely forward it to you.

Fred

Thanks Fred, I would appreciate it, I want to add it to my referance file.
Denny Graham
Sandwich, IL

Some good ideals here. Sounds like the rear end swap is the easiest but limits speed increase to around 60mph, but on the possitive side will maintain the 3/4 ton power. It's off to find a 68-72 4:10 rear...thanks
The combined T5 tranny and 4:10 rear swap done by Tlorber above sounds good. Tlorber, did you keep all your E-brake set up original with that swap? This 3/4 ton has the E-brake on the floor. And what vehicle did you get the T5 out of to bolt to the engine. There is a 1955 261 six in my truck that I am going to keep.So I am not sold on the trans swap yet, so if anymore 3/4 or 1 tons out there have any input on tranny swaps for the bigger trucks?

Thanks,

Eric Crow
Phoenix, AZ.

Your 261 has a lot more power than a 216 so higher gearing would be a pretty decent option. There is an outfit that makes new T5 tranny kits and they are pricey. However, you get the choice of shifter position and also the correct clutch. If I remember correctly it also uses a spacer to put the transmission a little further back. I may have the article on this. I will go and look for it.