so i was looking at devins' 6.9 build thread ..

and that got me to searching for more info on the brownie box ..

and that lead to looking up alternative overdrives ..

and just what kind of stuff people have put in there to add range to their gears ..

a few ideas .. some more promising then others .. reversed transfer cases and such ..

and then i came across this one .. it really looks promising ..

this fella here ..

https://www.ford-trucks.com/forums/5...ed-w-3-od.html

he mounted a NP 435 backwards and got his regular gearing .. plus 3 syncro'd overdrives .. in a lightweight .. compact package ..

there seem to be few transmissions or transfer cases that are up to the challenge of running in reverse as an overdrive ..

but it would seem this one works ..

he claims here to have put 20k on his so far with no problems ..

the unknown factor is if such a combination could handle the torque from the diesel motor ..

and i don't know what motor he had this setup running with ..

but these transmissions are very common .. used on fords from the 60's-90's ..

**
" New Process NP435

Donor Vehicles: Ford trucks from '66-'92 and Dodge trucks from '64-'93

Identify: It is 107/8 inches long with a cast-iron case and an aluminum top cover. There are three different First gear ratios available: 6.68, 4.90, and 4.56:1. Spin the input in low to count output revolutions.

Gears: 6.68, 3.34, 1.74, 1.00 (First through Fourth); 8.26:1 Reverse

Pros: Similar weight and length as the SM420, but much more readily available in junkyards, and it is 60lbs lighter than the SM465."
**

so i might have to collect some parts .. i'm not yet committed to the concept .. but a triple OD would be awesome .. no doubt drop those rpms right on down for some cheap cruising highway miles ..

and it is nice to have a working demonstration .. as proof of concept

i would build it with a crossmember and with double u-joints .. one coming one from the output of the transfer case .. and another to the output (now input) of the NP 435 ..

and have a shorter shaft cut if a swb shaft from another truck were unable to make the distance ..

i would also delete the stick shifter and build an air shifting device

just food for thought ..

post up your crazy ideas ..

 

sounds like it can handle alot of horsepower and torque

 

they can handle the torque and HP in regular design use. but things get muddy when power is reversed.

 

Glad I provided some motivation. But isn't it more like 12 gears, with some possible duplication in final drive ratio. Because I you have your first 4 gears X 3 gears. Also the ratios seemed pretty tall, the brownies ratios are like .87 1:1 1.27. But you have me thinking. Subscribed.

Devin

 

https://www.ford-trucks.com/user_gal...133769&width=0

link to gallery ..

i this overdrive setup would have received the attention it deserved had it been in the idi forum ..

looks overlooked in the antiques F- series forum ..

but with close ups of the setup it looks pretty simple and easy to do ..

i really think i might try this .. the u-joint fits in there nice .. maybe build a 'tiny' driveshaft with the slider portion to make u-joint servicing easier and reduce the driveline vibrations ..

put rubber pads between mounting points on the tranny and the frame rail crossmembers ..

take the angle down a bit to reduce shaft binding ..

build an electronic solonoid shifter or air shifter ..

and size the remaining rear shaft to length of a front shaft ..

 

yep .. usually the thrust bearing are pushed opposite the normal direction ..

and that causes problems .. but if it's overbuilt by 300 hp .. maybe not a problem

i don't know .. someone talking about moding a transfer case removed the stock thrust bearings and had stronger ones machined ..

but that was a torquer 4x4 with a race motor ..

maybe this case could handle the power ?? maybe ??? hmm

 

yep .. there are alot more gears multiplied .. but one is 1:1 and one would be too tall to use .. so looks like 2 overdrives and 1 to pull just straight through ..

yea .. just throwing out ideas .. and thanks for the inspiration ..

i'm really glad to have found diesel_johns thread .. i can't take any credit .. not my idea .. he done the work but just shining light on what looks like a possible OD build resurrected from the land of lost threads ..

i think if it works and could be improved upon .. this could be a way to add gear on a budget

 

As much as I am in favor of overdrive gearing behind an IDI, I see a couple major problems with this.

First is the spacing between gears. If you look at a regular transmission, the steps become smaller as the gears go up. If you have a reversed transmission behind a regular one, your overdrive ratios will be too far apart for practical shifting. You would have to rev it through the roof and still probably lug once you went into your overdrive gear.

The other issue is the usefulness of the ratios themselves. With stock tires the IDI really likes +/- 2.50:1 final drive ratio at freeway speeds. Get much higher than that and you loose more than you gain. I talked to Justin about this since he has a ZF-5 and DNE-2 overdrive in his truck. Since he runs 35" tires, that gearing (in double overdrive) is equivalent to 2.13:1 on stock tires. He said in double OD that even the slightest incline or headwind would bog the truck down. EGT's would climb, and his MPG's were even a little less than without the second overdrive (i.e., straight 5th gear 4.10's and 35" tires). On stock tires, Macrobb has good results with 4.10's, ZF-5 and a GearVendor overdrive (0.78 OD gear). This results in a 2.46 final drive ratio, and is what I will also be running in my truck. Another good combination is 3.55 gears and a ZF-5. The final ratio is 2.73, and produces very good mpg at highway speeds. So 3.55 with overdrive transmission, or 4.10 with double overdrive both get you in a pretty good sweet spot.



I suspect the results of a reversed transmission would be disappointing. Your first overdrive step would be 3rd gear on the NP, correct? 1.74 reversed becomes a ratio of 0.57, so if you have 4.10 axle gears your final drive would be 2.34:1... This is pushing that point of diminishing returns and is a whopper of a shift from 4.10 to 2.34 kind of like skipping a gear in your shift pattern. If you have 3.55's or bigger than stock tires I think even the first overdrive ratio would be too much. The 2nd or 1st gears on the NP would not work. The ratios would be crazy high.

 

I think the point here and I have yet to do this myself, but is to make one of those ratio charts with different scenarios. I've seen it on the forum somewhere. Honestly my biggest concern is just that, doing all the work and finding out it didn't actually work how I imagined.

Devin

 

i have to agree with this also. for reduction gearing for offroad use, i can see doing it with great results. but not in reverse for overdrives.

 

I have posted up several charts like that for different gearing scenarios. I know there are excellent easy to use ratio calculators out there, but I do all my own calculations in spreadsheets. I trust my math, and I understand it better that way.

 

The only thing I will add to this is that at first, I wanted to get a big higher final gear in my ZF5+GVOD+4:10+stock tires setup. However, after installing a turbo and an injection pump that doesn't have a problem with revs over 1800, I've realized that the final drive I have is perfect. It might even be a little high as it is; 1600 at 60MPH is good for economy, but my turbo doesn't even kick in until above that, so I really don't have much acceleration in top gear.
Of course, going 75 MPH on faster highways... it's perfect. In the 2K RPM range, gives me good turbo boost power, and isn't too loud or clattery.

And having the extra gearing available(vs, say, a 5 speed + 3.55s) is good for heavy trailer towing(7K+). I've had to go 1st, 2nd, 2nd over, 3rd, 3rd over, 4th, 5th when accelerating up a hill some times.

 

well i'm not into affirmation based on nothing ..

and i do like critical thinking ..

but it would seem like no way possible not to have useful gear out of this setup ..

of course not in all the gear combinations ..

but then again .. i have no real interest in working 2 transmissions at all the gear ranges ..

this is probably the shift sequence that i would envision working effectivly while not wearing overly much on the 2nd through torque multiplication ..

{1(1-4)} * {2(2-4)} * {3(3-4)} * {4(3-3)} * {5(4-3)} * {6(4-2)}

my setup is T19 X 3.55 X 35 tires

it seems there are 4 very different gear ratio box setups ..

if someone with better math figuring skills than myself

would like to .. can someone figure up a chart like the above one ..

for what rpm's my setup would turn with each of these E A D L transmissions ..

with each of the above listed shifting combinations ..

perty perty please ..

i think one of these tranny's must give good double overdrive range ..

and i'd like to know which one to look for when i start hunting ..

also i don't have any turbo .. so no need to keep rpms up too high for boost ..

i usually keep it between 1,200 and 2,200 .. for economy .. though in some gears higher as required ..

and would be okay lugging 1,400 -1,500 rpms down the highway

 

ohh here's the ratio list

 

I will run the numbers on my spreadsheet. Which NP were you wanting to use? And you have the diesel ratio T19 I presume...