Brownie Box

[connorm]

I am looking for anyone with experience with brownie boxes. What I am thinking about doing is putting one in my 1970 GMC C/2500. It is a 307, SM465, Dana 60 with 4:10's and 295/75R16. I am not looking to do this for gas mileage, I am looking for something that I can take the stress of high RPM off the engine. I am also wanting to keep the SM465, ruling out an NV4500, and am wanting to stay away from the Gear Vendors for multiple reasons. Cost, electric shift, and I would like to keep a manual shift for cool factor. I have also looked into Ranger Overdrives as this was my initial thought. With these not being made anymore finding them is hard, and I worry about finding parts 30-40 years from now.

I have been been primarily looking at the Spicer 5831C or 5831E. With the 5831E I would probably need to go to 4.56 gears with the higher 0.73:1 ratio compared to the lower 0.85:1 ratio. Overall, I think the closer ratio 5831C with 1.27:1, 1:1, and 0.85:1 ratio would work better for my purposes. I was mostly looking at the 5831 series, but a 6041 did pop up on eBay the other day. This was appealing as I have read that these had helical cut gears. These were also 4 speed units with gear ratios: 2.14:1, 1.24:1, 1:1, and 0.86:1 ratios.

Although I do worry about parasitic loss with this. I know I said that I wasn't doing this for efficiency, but it is still a concern. I guess my concern comes from looking at medium duty truck parts. The appeal to the 5831 series is that I do not believe that it is too big. From what I believe I have read is that the 5831 is not significantly larger than an SM465. If anybody has any experience with this I would like to hear it.

The other question that I have is about shifting. I would more than likely drive it 2nd Direct -> 3rd Direct -> 4th Direct -> 4th Overdrive 90% of the time. And I have read some on shifting patterns but I would like to know about the shifting itself. I do not believe the 5831 has synchros so does this mean I would float gears? Double clutch shift? Does it go 4th Direct, Neutral Direct, Neutral Overdrive, 4th Overdrive? None of this concerns me or will direct me away from doing this, just still gathering information.

Finding a brownie box has also been a challenge. I have only found one currently online for sale, a 6041 that is 27 hours away in Montana. I would like to try to find one more local. If anyone has any sources, either online or in the Southern Indiana area I am all ears.

I have attached links to the 6066gmcguy.com website that has charts with different gear ratios for Spicer brownie boxes, and for the 5831 series in general. I have also included a link to my build thread where I go into some more detail about driveline, plans/thoughts, and go into some cruising RPM's.

https://6066gmcguy.com/SM420.html
https://6066gmcguy.com/spicer-5831-b.html
https://67-72chevytrucks.com/vboard/...d.php?t=668003

I'm open to any and all discussion on this. I'm also open to other ideas. What I am really looking for is add an auxiliary transmission with overdrive, preferably stick shifted.