The Stovebolt Site Forums The Shop Area Engine Shop 3 speed brownie box, Useful? Value?

I have a chance to buy a three speed brownie box, 20% underdrive, 1:1, and 20% overdrive.

I really do not need the underdrive, but it seems like a decent solution to the very low gears in my '57 3600 for longer trips with the overdrive.

Are these decent set ups?
Fair price to pay?
Availability of the shift mechanism?

It seems I would have to mount it about where the original drive shaft center support is, then modify my drive lines.

I think a shifter should not be too hard to make, particularly if I do not have to use the underdrive.

What is the down side to these?
Weight, noise, weak?

Lot of trouble for a 20% decrease in engine speed.

On a 3/4-ton truck I think you have better options. On a 4000 series or bigger truck I think they make a lot of sense.

You'll need to mount it, modify the driveshaft and create a shifter, but none of those are a big deal, right? The only ones I've seen available seemed too expensive to me, but I've sure considered that option.

Find out what model it is, if it was designed for a smaller truck it might work for you. If its one of the really heavy models you may add more weight by time its mounted than the reduction in engine speed can justify.

I have one in my 69 C50 and it works rwal good in the mountains and hiways, but in your case you may be better off playing with tire sizes and rear end gearing, because of the mechanical effeiciency of the unit, the fuel used driving the extra transmission you will most likely get the same fuel mileage.

I am in the process of putting an overdrive in one of my 3/4 ton pickups. It is a chevy front box with a Warner .70 overdrive. It is the same overdrive that Ford used in their T86 which was offered with about 300 cu in engine. That's a whole lot easier to do and .70 OD with 4.56 rear is better than .80. I had a Brownie in an old truck tractor and was going to put it in my 57 GMC wrecker, but it fell victim to moonlight auto parts. They left the shifter which resembles the stick on a SM 420. Usually they were mounted between the driver and the door. As OldSub said,its a lot of trouble for 20% reduction in rpm. Of course I guess you could lock it into OD and not worry about shift linkage. I think the smallest one I have seen is about 400lbs.

I already have the largest tires I can run with the flat bed.
Gears are about 5:38, thread I have read here indicate that changing them is difficult and expensive.

A Gear Vendors unit would be nice, but VERY expensive.

A 4.56 was standard for a 3/4 ton. The 5.14 was an option for 7.50 tires. If you find a 3/4 ton with a 4.56 rear that will be a noticeable difference and it is a simple bolt on. There were also a few years 3/ton in the late 60's used a 3.90.

Ken, I've heard that rumor many times before about the 3.90 gears for the Eaton HO52 housing, if you find any documentation to back that up I would sure like to add it to my reference file. I've been unable to find anything that refers to that in any of the parts books. The 4.10 seems to the the lowest gear that was made for that Eaton rear axle.
Denny Graham
Sandwich, IL

All I find in my Hollander is 4.11 for 67-72 automatic with coil spring suspension. I may have been thinking of the 3.90 for 4.11 swap for 1/2 tons. Something interesting I learned a few months ago when I traded my 06 pickup on an 09 is that since 07 a 3.73 ratio is offered. I traded for one and the 3.73 really makes a difference over the 4.10 that was in 3/4 tons for years. It has the 6L with the 6 speed auto. It gets as good a fuel mileage as a half ton on the highway and pulls a trailer like a Diesel. I spoke with one of my cousins old parts men. He owns a Chev dealership and a GMC dealership. He will look through some old books when he has time.

Toward the end of the Eaton's run Dana axles were installed under some of the trucks. My bet is people are looking at a Dana when they see 3.90 gears under an early 70's 3/4- or 1-ton.

I've heard the story for years that they are out there, but no one has ever claimed to have one or even know someone who does.

A couple of years ago I considered buying a '72 C20 with a 402/TH400 and a Dana rear. I don't remember what Dana and don't recall what gears it had, but that truck opened my eyes a bit.

Most likely was a Dana 70 with leaf springs and the Camper Special package. My Grandpa had a '69 that was setup that way. I beleive those ran 4.10 gears. BTW, they truck is still in the family, my Uncle Louis has it.

My cousin's old parts man just called me back. He couldn't find a 3.90 in a 3/4 ton but the did discover that a 3.54 was offered behind a 396 in the 70's. They are probably hard to find and the people who have them probably don't know what they have. If I could find one of them, I would forget about an OD and just keep the old SM420.

The '72 C20 I've been using as an IFS donor probably had one of those, it was a big block truck. Unfortunately the rear was gone when I got the truck, and today only the back 2/3rds of the frame remain.

I agree 3.54 would be great gears in a truck with a six as long as you didn't need it to haul a capacity load. I've actaully got 3.42 gears under the 1-ton I'm building but I'm not muzzling the power by staying with an original motor.