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  #16  
Old 02-03-2014, 06:04 PM
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chrlsful chrlsful is offline
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searchin out info

"My Bronco desperately needs lower t.case gears..."
Have U tried it to know (ie w/the NV)?

Have U tried the online calculators?
there's a bunch (some better than others). I would hafta use em due to my math. same w/the Taxes (I always owe them or they me, less I use my accountant).
kouwell! Bob the engineer! I shoulda known from the precision of those welds in yer pic!


"3.15 : 1 is a replacement crawler gear for the Dana 20"
is that the $800 I mentioned earlier "from the typical vendors"? I don't C it right now in JBG's, WH's, Tom's, or Duff's now... may B these catalogues are too new? As I recall it ended up more extreme (4:1). I think I'd rather a locker for that kinda money (if I had it!)...
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'70 LUEB 1/2 cab, '77 frame ie: D44, PS, trapezoidal BB 9"; w/411; "T" D20/PTO; 250cid mid-swap; 2"SL; 4 discs; 3.03/3 sp Hurst. Seeking: 240/300 1v low rise Carb. or Carter RBS, hydraulic Gear Motor for koenig &/or zf ptos, '2 wd' zf E-Brake, 3'X10" Auger.
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  #17  
Old 02-03-2014, 07:13 PM
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Quote:
Originally Posted by chrlsful View Post
"My Bronco desperately needs lower t.case gears..."
Have U tried it to know (ie w/the NV)?
I've only had one semi-serious off-road trip with the Bronco. With the stock trans and case it just doesn't go slow enough. I had to slip the clutch way too much to crawl over rocks, otherwise I was banging off them way too hard or stalling the engine way too often. The Jeep 258 was barely acceptable to me (I always wanted lower gears, but I could go where I wanted without slipping the clutch and without stalling the engine too much). The Bronco has the same crawl ratio my Jeep did, but the 302 just doesn't idle down and lug like the 258. I'm happy enough with the engine otherwise, but it needs lower gears than I have.

The NV3550 has a 4:1 1st gear compared to the 3.4:1 1st of the RAT 3-speed. That only drops my crawl ratio from 34.4:1 to 40:1. Looking at it another way, it drops my speed at 1000 rpm from 2.9 mph to 2.4 mph. That doesn't seem like enough of a difference, so I certainly don't want to bet the $459 cost of an NV3550-Dana 20 adapter that I'll be happy with it. I'd rather that $459 be the seed money toward an Atlas and just do it once. With the NV3550 and Atlas 4.3 at 1000 rpm I'll be going 1.4 mph.


Quote:
Originally Posted by chrlsful View Post
"Have U tried the online calculators?
there's a bunch (some better than others). I would hafta use em due to my math. same w/the Taxes (I always owe them or they me, less I use my accountant).
Haven't tried any so I can't speak to them.

Quote:
Originally Posted by chrlsful View Post
kouwell! Bob the engineer! I shoulda known from the precision of those welds in yer pic!
I'm an engineer, I'm certainly no welder! I can usually melt metal with a MIG well enough to keep it from falling apart. But I'm no artist.

Quote:
Originally Posted by chrlsful View Post
"3.15 : 1 is a replacement crawler gear for the Dana 20"
is that the $800 I mentioned earlier "from the typical vendors"? I don't C it right now in JBG's, WH's, Tom's, or Duff's now... may B these catalogues are too new? As I recall it ended up more extreme (4:1). I think I'd rather a locker for that kinda money (if I had it!)...
$800 for aftermarket crawler gears sounds about right, but I haven't looked that hard. I know there are 4:1 crawler gears for a lot of cases, but I'm pretty sure the crawler gears for a Dana 20 are 3.15. Add the $800 for the gears to the $460 to adapt the NV3550 to the Dana 20 and you're getting close enough to an Atlas that I decided not to settle for 3.15 gears.

Obviously with a project like this there are a thousand different possible combinations. I certainly didn't land on the cheapest, or the best. But I think I landed where I want to be. If someone else is making the decisions, paying the money and then living with the results they may well end up somewhere else. And that's fine.

Besides, I've already got a Detroit in the rear!
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'97 F-250HD Crew Cab, 460, E4OD
'71 Bronco, 302, NV3550 5 spd, Atlas 4.3:1, Detroit rear, 33" BFG AT http://www.ford-trucks.com/forums/12...ospective.html

My toys: http://www.ford-trucks.com/forums/12...-jeep-etc.html
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  #18  
Old 02-05-2014, 07:40 PM
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"thinkin out loud"

"...Looking at it another way, it drops my speed at 1000 rpm from 2.9 mph to 2.4 mph..."

OK! now that's more helpful to me than the "X:1 verses Y:1" I often see on these forums. It's alot more useable 4 me. How do you 'vert those ratios to mph, the way you've done? I could try that for more realistic personal info than I got now...

"... I landed where I want to be..."
AND -
that's a Great thing!
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'70 LUEB 1/2 cab, '77 frame ie: D44, PS, trapezoidal BB 9"; w/411; "T" D20/PTO; 250cid mid-swap; 2"SL; 4 discs; 3.03/3 sp Hurst. Seeking: 240/300 1v low rise Carb. or Carter RBS, hydraulic Gear Motor for koenig &/or zf ptos, '2 wd' zf E-Brake, 3'X10" Auger.
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  #19  
Old 02-05-2014, 07:57 PM
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Quote:
Originally Posted by chrlsful View Post
How do you 'vert those ratios to mph, the way you've done? I could try that for more realistic personal info than I got now...
The "simple" answer is engine speed (rpm) x tire diameter (inches) / overall gear ratio / 336 = vehicle speed (mph)

Overall gear ratio is all of your gears multiplied by each other. So if I'm interested in how fast I'm going in 1st gear, low range, my overall gear ratio is 3.41 (1st gear ratio) x 2.46 (transfer case low range) x 4.1 (axle ratio) = 34.4.


(Edit: Ran out of time last night, adding more content)

So at 1000 rpm in 1st gear low range I'm going: 1000 rpm x 33 inches / 34.4 / 336 = 2.9 mph

Once the NV2550/Atlas is in my overall gear ratio in low-low will be 4.01 x 4.3 x 4.1 = 70.7.
So at 1000 rpm in low-low I'll be going 1000 x 33 / 70.7 / 336 = 1.4 mph

Or in 5th gear, low range my overall gear ratio will be 0.78 x 4.3 x 4.1 = 13.8 and at 2500 rpm I'll be going 17.8 mph. So 1.4 to 18 mph will be my useable speed range in low range.

It's also helpful to be able to figure out what your engine speed is at any given vehicle speed in any particular gear. A little algebra rearranges the equation to be:
vehicle speed (mph) x overall gear ratio x 336 / tire diameter (inches) = engine speed (rpm)

So as an example, with my current setup my overall gear ratio in high gear, high range is:
1 (3rd gear ratio) x 1 (transfer case high range) x 4.1 (axles) = 4.1

So 70 mph in high gear is: 70 (mph) x 4.1 x 336 / 33 = 2922 rpm

After the NV3550/Atlas my overall gear ratio in 5th/high will be 0.78 x 1 x 4.1 = 3.20
And my engine speed at 70 mph will be: 70 x 3.20 x 336 / 33 = 2281 rpm
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'97 F-250HD Crew Cab, 460, E4OD
'71 Bronco, 302, NV3550 5 spd, Atlas 4.3:1, Detroit rear, 33" BFG AT http://www.ford-trucks.com/forums/12...ospective.html

My toys: http://www.ford-trucks.com/forums/12...-jeep-etc.html
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  #20  
Old 02-13-2014, 08:53 PM
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For me, a systems analyst (human systems and buildings; 2 very different systems) - the formulas always look just as they should. I.e. U read them and they say what is intended/give the answer sought.

But heck, I could never figure them out/design them myself. I need metrics to analyst building performance, use the blower door and advise contractors on new construction, retrofits, and energy efficient or renewable energy design. On the other hand, human systems (families, schools, ship's crew out at sea, municipalities, businesses, etc, etc) go by a whole nother format ('self organizing')...

So I will thank you for these 2 useful ones and pocket them w/the hundreds of others.

VEHICLE SPEED (MPH)=(RPM) X TIRE DIAMETER (INCHES) / OVERALL GEAR RATIO / 336

ENGINE SPEED (RPM)=(MPH) X OVERALL GEAR RATIO X 336 / TIRE DIAMETER (INCHES)

Hummm, hope I never have an unknown in the right half of the equation. Get a lill tricky for this pea brain. Also I see the magic divisor, 336... may B the Golden Mean for the auto...


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Chad
'70 LUEB 1/2 cab, '77 frame ie: D44, PS, trapezoidal BB 9"; w/411; "T" D20/PTO; 250cid mid-swap; 2"SL; 4 discs; 3.03/3 sp Hurst. Seeking: 240/300 1v low rise Carb. or Carter RBS, hydraulic Gear Motor for koenig &/or zf ptos, '2 wd' zf E-Brake, 3'X10" Auger.
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  #21  
Old 07-22-2014, 12:19 PM
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Update. I ended up going with an NV3550 5 speed and an Atlas 2 with 4.3:1 low range (4,10:1 axles and 33" tires behind a 302 in a '71 Bronco). Finally got to try it off road and I love it! 5th gear low range is high enough for almost all trail riding, so there's not too much hunting between low and high range, that was my biggest concern. And 1st gear low range makes the rocks a lot easier! I used to have to run the engine at least at 1200 rpm to keep it from stalling too much. That was 3.4 mph in low-low. Now it will idle at 800 rpm, giving me only 1.1 mph with the new gears. That means I'm hitting the rocks with about 1/10th the energy I used to. Very noticeable!
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'97 F-250HD Crew Cab, 460, E4OD
'71 Bronco, 302, NV3550 5 spd, Atlas 4.3:1, Detroit rear, 33" BFG AT http://www.ford-trucks.com/forums/12...ospective.html

My toys: http://www.ford-trucks.com/forums/12...-jeep-etc.html
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  #22  
Old 08-01-2014, 10:31 AM
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Obviously not what you're looking for, but this would be stupid low.
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Old 08-01-2014, 10:31 AM
 
 
 
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