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Old 02-05-2018, 10:52 PM   #327 (permalink)
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Back to my Dana 20 and upgrades..

I've tracked down an NV4500 or two (~$1k each) but after talking to some other friends.. the NV4500/5.0 Atlas is losing ground to T19 &4spd Atlas.

The OD would make the 5.0 gears a decent performer (not much overlap between high and low range, but the OD would let me stretch that 5:1 'case into decent speeds), but a lot of gear whine running a 5:1 t'case in OD at 5000rpm..

If I stick with the T19 I save enough length to fit the 4spd Atlas.

I measured my rear 'shaft at 42" last night, with about a 13.5" drop at rest, with ~9" of shock shaft still hiding.

So droop would be a 22.5" drop.

Front is 24" long with a 6" drop at rest.

At 30deg of angle, you can get basically 1/2 of length as droop.

So my 42" shaft is good to 21" of droop (so hopefully I can squeeze a little more than 30deg - or the leaf springs will stop me before I bind the rear U-joints)

42" shaft at 15deg is 10.9" of droop. I'm actually around 19deg of angle at-rest right now.

Up front, with only 24", I'm looking at 12" of droop at 30-deg. That's about right for how I have things right now with the 10" short-body shocks.

Problem is a 4spd Atlas and the 23sp round adapter makes me ~34" rear and ~32" front.

The front is great!

But 34" to the rear, at 30-deg angle, is only 17" of droop. 3.5" beyond at-rest right now.

I need to measure - if I swing the pinion up I can make the angle less -but the driveshaft shorter.

Sort of rules out the long NV4500 with a long 4spd Atlas and a dinky 24" rear driveshaft. I would be beyond 30deg just at rest. (Nothing a pair of HP60s wouldn't fix.. )

I'm also thinking if I go this way, I might use a close ratio T19.

Right now I'm around 20:1 coming out of the 3.15 Dana 20 in low range (for 90:1 at the axles).

Wide box with a 10.34 is 65:1 at the rear output, or almost 300:1
Close ratio is 41.5:1 (more than double my current setup) and ~190:1 at the axle.

I'd get closer spaced gears, easier shifting (yes, for a T19).. and still be able to go half as fast as I can now.

In the meantime, I might add a spare rear output to my spares box.. :P

... so, looking up "how to break a Dana 20" and what do I stumble upon? A couple of old threads in here..
Transfercase Options for 36s

Funny how things have changed - and I find myself thinking a 4spd Atlas is a good buy now.

And I really think driveshaft length (and U-joint limits) are a deciding factor in all of this - same as when I was making plans for the racer. All the high-zoot stuff you want is limited by how much angle and how much length you have for a driveshaft... until I just mount a Tesla electric motor to the 14-bolt pinion housing..

I did find some other references to a Dana 20 girdle that bolts to the oil pan and the rear output housing and beefs things up. I haven't found one for sale yet.

I also found a deep billet aluminum oil pan (for a Dana 300, but I think it'd swap) that also may help a Dana 20 case stay together.

I have some aftermarket oil pan that's better than the stamped steel but short of that billet aluminum unit I found..

Edit - and one more GREAT thread from the BinderPlanet - makes it sound like I need to dig out one of my two 2wd T19s. One is an original wide-box, the other was converted to a close-ratio (someone else wanted to convert a 4x4 Scout II T19 from close to wide, and I thought having a close 2wd for the fullsize would be a good thing to have - until I got my T-35 instead and got to keep my granny gear AND the close ratio 4spd)

Last edited by tsm1mt; 02-06-2018 at 08:07 PM.
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