Atlas TC vs Dana 20 with HD shaft

[rcmbronc]

Trying to decide if what TC to run. Got a good Dana 20 in the truck now. 4R70W, 5.13 gears and 35" tires. Not heavy crawling but decent trail running. Trying to decide to go with an Atlas or modify the D20 with HD output. Truck is pre runner style build with a healthy 427 probably 550-600 hp. Like the compactness of the D20 but dont want to spend good money on it for nothing. Also dont want to break it. Whats everyones opinion? I think most say Atlas but looking for opinions.

 

[markw]

My 408 with 500 ft/lbs didn't break the TC with HD output in 1000 miles of the NORRA Mexican 1000. 4:56, 35". Just for comparison. Your extra power might be the tipping point but I doubt you'll beat on it any harder.

 

[rcmbronc]

Thats good to know. I am sure you were pushing it maybe harder than I will. Wonder if there is any more power loss through an Atlas or less?

 

[sanndmann3]

I broke 3 '20s before going NP205. I spend alot of time in low range at high revs (dune running). The Dana 20s low range gears aren't very strong... I'd go Atlas.

by the way, never broke a stock rear output. probably due to sand...

 

[Apogee]

What ratio ATLAS would you run if you were to go ATLAS? 2.0:1? 3.0:1? 3.8:1? 4.3:1? Would it be safe to assume that you'd be looking at a PRO series box? Nothing is unbreakable, but the ATLAS is definitely stronger than the D20 in most ways, plus gives you some options with respect to ratios, so I guess I would lean that way if money isn't part of the equation. The higher ratio ATLAS boxes are weaker than the lower ratio units, hence the prevalence of 2.0:1 boxes on Ultra4 type applications.

Just a thought, but if you just want beef and don't mine losing some gear, an NP205 is about as bomb-proof as you can get with minimal investment. Given your power levels and low axles gears with only 35" tires, the ~15% hit on low range may not matter much from a driveability perspective.

I would guess that the efficiencies for D20, NP205 and ATLAS (D300) are all somewhat comparable given that they're all gear driven cases with similar designs.

 

[rcmbronc]

I was probably going 3.0 or maybe 3.8

 

[Digger556]

I went Atlas for peace of mind. The gears are huge and it has the added bonus of being shift on the fly for both High and Low range.

I like to rub my Toyota friends a little by coming off the trail and not stopping to shift into High as I hit the highway, leaving them behind. ;D


Torque and shock loads are the killer for drivetrain parts.

 

[Local Boy]

Went through a few D20's with the previous motor...I just could not put it behind this one... Atlas was the call for me...

Aloha

 

[markw]

Forgot to mention my D20 is filled with O'Brien gears. I think they're pretty strong relative to stock gears. If I break it I'll go to Atlas rather than 205.

 

[BanditBronco]

RCM do you have a 1 or 2 inch body lift? We have very similar setups, I just stuck a 3.0 atlas in mine because I could bolt it right up to the 4R, if you have a 1" body lift you will either have to mod the tunnel as the T case will set to far back under the flat part of the body and not inside the tunnel as designed. Or you push the drivetrain forward 1/4-3/8" to get it up in there. Mine fit rather well after I pushed it forward a bit. With the parts you are throwing at your build I think it atlas is your only option.

 

[rcmbronc]

1" body lift. Mod the tunnel probably not a big deal. How much longer is an Atlas? I was planning on not using the extension spacer and cutting the output on the tranny and also probably a short output to keep my rear driveshaft as long as possible.

 

[garberz]

1" body lift. Mod the tunnel probably not a big deal. How much longer is an Atlas? I was planning on not using the extension spacer and cutting the output on the tranny and also probably a short output to keep my rear driveshaft as long as possible.

The AtlasII will be 1 1/2” longer than the D20, settlng it up like that.

Mark

 

[BanditBronco]

I wouldn't worry about length, I am actually an inch or so longer than a few buddies that runs a ZF and 2 speed atlas, and a NV3500 and 4 speed. My rear driveshaft was 29.25" I also have a speedo housing so it is slightly longer than the shorter housing. I trimmed the output shaft on the trans also. I pushed the rear axle 1" with spring perches. You might have binding issues though depending on how much droop you have with your rear set up. Might have to strap it right before the driveshaft binds.

 

[Yeller]

I'd do a 3.0 with your set up, you have more gear and power than I do and I rock crawl very heavily with a 3.0.

Ultra 4 the 2.0 is very common, many of those run low range at some very high speeds (personally been 110 in low range)

 

[sprdv1]

I was probably going 3.0 or maybe 3.8

yeah for sure...

 

[okorangebrnco]

I have the 5.0 Atlas and feel it is way to low for my world of wheeling, now. However, the peace of mind once the Atlas went in has been great. Yeller can attest to seeing and being under a few too many Broncos with broken outputs even on some very conservative builds.

 

[stout22]

Okorangebrnco, what's the specifics of your Bronco setup?

 

[landshark99]

I also have the Dana20 with atlas output housing/shaft, its behind a C4 and thats behind a 408 stroker with 500+ ft lbs torque. no issues.

Also have a Dana20 with just the hardened output shaft behind a ZF-5 and a very well built Ford 400 in my other bronco which primarily sees rocks - no issues there either. But I would not consider myself an extreme wheeler.

That being said - I would like to swap the rock crawler to an atlas for the gearing and on the fly shifting at some point.

 

[nvrstuk]

D20's don't last long when you are in low range...torque multiplication is a D20 eater.

Go with the Atlas if you need the lower gears otherwise to 205-which are almost bombproof and thousands of dollars less expensive.

I grenaded D20's like there was no tomorrow. I NEVER bounce or hop when wheeling, they just grenaded due to torque when climbing due to extreme traction and tire size.

The output shaft is extremely weak. The low range gear teeth are less than HALF the width of a NP205 gear teeth-I've got pics and the difference is impressive.

The cases are weak. IF you put a lot of stress on the case they will crack. I'm not talking dropping onto a rock and cracking it, I"m talking crawling up a waterfall and "CRACK"...it just let's go.

Go 205 or Atlas. I removed my Atlas and run a 205 behind my Klune 2.7:1 doubler now.

I use the throttle a lot on sand and snow but there's absolutely no comparison between torque load on sand compared to Moab slickrock.

Also, I ran a 21.5" long rear DS behind my ZF/203/D20 for 12 years with a full 14' vertical suspension travel and had 31deg on my CV...no issues. Run a GOOD antiwrap bar or 4 link it.

Good luck

 

[garberz]

I’ve seen and read about the short comings of the Bronco Dana 20. That’s why I never went down that road of pouring money into it. I’ve had a couple friends lose their Terra-Low gear set out on the Fordyce trail. Like I’ve heard from nvrstuk many times, the gearsets are just too narrow. The D20 holds up much better in hi range, but it’s still a weak link with low axel gearing and large deflated tires. I bought a twin stick for mine early on, then sold it when I bought my AtlasII. I gave away my D20. Just glad I never started spending money on it to try to make it something it’s just not capable of being. It’s not that much more money to buy an Atlas. How much would a ruined trip to Moab cost? Or any other big destination trip!

Mark