School me on T-cases

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    School me on T-cases

    Im very knowledgeable on chain cases, but have some questions on gear cases.

    First, I know that a 205 and a Atlas are "all gear". I was under the impression that a Atlas was simply a "repackaged" 205. Meaning that it had 205 gears in a custom aluminum housing to save weight. Is this right or is it all differnt?

    Second, I've heard on here (or P) that you can shift a 205/Atlas into front wheel drive only for "front digs". This is one option you don't have on the chain case. I assumed that the simple, all gear design was the reason. It seems like I've seen a diagram of a 205 where the internals were the same front and rear, so that would make sense. Is there any reason not to drive in front wheel drive for long distance?

    I realize your front diff might not be as strong as your rear. (In some rear steer they are both the same) Also, driving in front wheel drive might cause some handling issues at speed, but my question is T-case specific. Will it hurt the T-case?

    The reason I ask is I've often thought of building a rear engine 4wheel drive truck. I thought the way guys did that was simply spin the drive line around and flip the axles. But that would mean you have front wheel drive or 4 wheel drive. On a chain case, even if you unlock the front wheels, you would be driving on the chain all the time. (Doesn't sound like a good idea) So I thought everybody that builds a rear engined buggy must have a 205/Atlas so they can drive the rear tires only. (Which would actually be front wheel drive only on the case) Have I got this wrong? Does everybody with rear engined buggies drive in 4 wheel drive all the time?

    Check out my project
    https://irate4x4.com/general-4x4/2779-amphibious-hemtt

    #2
    Atlas 2 and NP205 are "similar" in design but afaik they do not use the same gearsets. Do to the design of the gears and how they are shifted there is a shift rail/fork for each output, this is what allows you to shift only the front output into high or low and leave the rear output in Neutral. On a NP205 you have to grind/replace the rails to allow you to shift them independently. The danger there is if done wrong you can shift the outputs into high and low at the same time and blow it up. Np205 uses an "oil bath" for lubrication so other then putting all the torque through the front output, lubrication should be fine.
    Last edited by Toreadorranger; 05-29-2020, 11:28 AM.
    88 Ford F-turd50 IDI Crawler

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      #3
      Atlas and hero are more of a blend of d300 and 205 than any one specificaly. And any parst derived for any existing case are coincidence than intent. Pretty much all gears cases can be modified to shift into front drive only

      Id tell you the 2 big issues drinving a steer axle as a rear would be gear cut pressure/pinion bearing load and stub shaft spindle bearing lubrication. Both issues can be resolved by chosing the proper axle pinion location and outer design. Id tell you to use a fixed stub unit bearing like a dodge outer that doent unlock and no spindle the stub runs through. Fords would also work but not as ideal in my opinion. The biggest thing when building an axle like this is pinion presure and gear face. Rears are low pinion because it pushes the gear and the pinion pushes on the larger inner pinion brg. Same applies for a hi pinion in the front. While the over whelming majority of front are lowpinion they are typicaly locking hub or cad axles. It also makes more clearance around drivetrain.

      Now all that being said. Rear engine throws another loop in the rope. You want the pinion pushing the ring not pulling. But you need to flip the axle to reverse the physical rotation change. A flipped hipion axle would be your ideal rear and flipped lp for the front. Oiling can be an issue but not a big one as per the pinion will be in the bath and have a slinger. The one issue you will find is youll need to use a stock style housing opposed to a rock jock style as you dont want the diff cover facing the ground.

      The other big thing is that..... no one realy puts thousands of miles a year on a rear engine rear steering rig. Theyre trailer rigs. But picking the right axles can resolve that.

      You didnt say how big you were building but axles like axletech and rockwels wont give a shit and pretty much negate everything i just said as far as axle design.
      Last edited by total newb; 05-29-2020, 02:19 PM.
      :ogre:

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        #4
        Originally posted by Toreadorranger View Post
        Atlas 2 and NP205 are "similar" in design but afaik they do not use the same gearsets. Do to the design of the gears and how they are shifted there is a shift rail/fork for each output, this is what allows you to shift only the front output into high or low and leave the rear output in Neutral. On a NP205 you have to grind/replace the rails to allow you to shift them independently. The danger there is if done wrong you can shift the outputs into high and low at the same time and blow it up. Np205 uses an "oil bath" for lubrication so other then putting all the torque through the front output, lubrication should be fine.
        Thankyou for the info. I was looking at the Atlas site and they said that front wheel drive high range is not offered. (Front low range is) What is the reason for this?

        As far far as differnt gearsets in the Atlas, it's hard to believe they can use custom gears at the price point they are at. I use to be involved with a small manufacturer using custom gears and they cost us nearly what an Atlas costs. Maybe they are useing gears from another "stock" application.

        Ps, Total newb, good info, but I was mainly interested in the T-case end of it. I was aware of most of the diff issues. This project is way down the road. (I have to finish my current project first. Lol.
        Check out my project
        https://irate4x4.com/general-4x4/2779-amphibious-hemtt

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          #5
          I have a Atlas II. It allows rear 2wd H, 2wd L, 4wd H and L, and front wheel drive only in low. The manual cautions using front only for any length of time because it can damage the axle, not the case. I think its AA's way of keeping people from driving down the highway in front wheel drive only, then complaining when they lose control or break.

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            #6
            Originally posted by WaterH View Post

            Thankyou for the info. I was looking at the Atlas site and they said that front wheel drive high range is not offered. (Front low range is) What is the reason for this?

            As far far as differnt gearsets in the Atlas, it's hard to believe they can use custom gears at the price point they are at. I use to be involved with a small manufacturer using custom gears and they cost us nearly what an Atlas costs. Maybe they are useing gears from another "stock" application.
            They have been making cases a long time, I'm sure their designs are long paid for, and they probably buy in a decent quantity since I believe its essentially the exact same case for every application (minus the race specific ones) and they only have a few available ratios.
            88 Ford F-turd50 IDI Crawler

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              #7
              I believe if you called AA and specially ordered for a rear engine, they could swap the detents or whatever and you could still have rear high, out of the normal front output. And you would not have front high, out of the normal rear output.

              I don’t know because I never tried and I don’t care because I am not building a rear engine rig, but I saw it on the internet once.

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                #8
                Buy one. Take it apart. Figure out the detents and solve the problem. A hero case 3spd of stack my be a diffent issue because they have more gears stacked internaly where a atlas/205 only has hi/low and uses an external panetary to make 3-4 spd.

                I can tell you the tj atlas shifter is a packaging issue where the shifters are inline to eachother rather than side x side and cant cross eachother to select front hi/rear n.
                :ogre:

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                  #9
                  Originally posted by BDK View Post
                  I have a Atlas II. It allows rear 2wd H, 2wd L, 4wd H and L, and front wheel drive only in low. The manual cautions using front only for any length of time because it can damage the axle, not the case. I think its AA's way of keeping people from driving down the highway in front wheel drive only, then complaining when they lose control or break.
                  I don't know why the front diff would break. I've driven down the highway in front only for 400 miles once with no issues. (The rear driveshaft was broke) The steering was a little squarely because of the locker, but not really a big deal. If you had two D60's (rear steer), there really wouldn't be any strength differnce. It would seem to me that driving in snow, it might be advantageous to drive in front wheel drive. (On road)
                  Check out my project
                  https://irate4x4.com/general-4x4/2779-amphibious-hemtt

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                    #10
                    Originally posted by Toreadorranger View Post

                    They have been making cases a long time, I'm sure their designs are long paid for, and they probably buy in a decent quantity since I believe its essentially the exact same case for every application (minus the race specific ones) and they only have a few available ratios.
                    The cases are aluminum and could be made easily by any number of outfits. (They might even make it them selves) Gears are a bit more tricky. Especially, high quality gears hardened and ground to exact standards.

                    Unrelated question, can we not quote more than one person here?
                    Check out my project
                    https://irate4x4.com/general-4x4/2779-amphibious-hemtt

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                      #11
                      Originally posted by WaterH View Post

                      The cases are aluminum and could be made easily by any number of outfits. (They might even make it them selves) Gears are a bit more tricky. Especially, high quality gears hardened and ground to exact standards.

                      Unrelated question, can we not quote more than one person here?
                      I meant cases as in complete transfer cases. not the case specifically. as far as I know the atlas 2 has been out for about 20 years, per the history portion of the website the initial prototypes used gears from another case and they kept braking so they had to redesign them larger, so at this point and costs associated with that design are long paid for, and it sounds like they own the tooling for them.
                      88 Ford F-turd50 IDI Crawler

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                        #12
                        I have a rear engine front steer only buggy. NP205 t case and flipped 9" axles. I operate in every combination of high,low,fwd,rwd and 4wd. The NP205 couldn't care less. fwd/hi does get quirky steering. Rwd hi just hauls ass.

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                          #13
                          When I toured AA years ago, they had the cases forged by a domestic forging house and then machined in house. They hobbed gears in house. That was 10+ years ago, things could have changed. I bet if you call them they'd answer your questions.

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                            #14
                            Originally posted by RustyC View Post
                            I have a rear engine front steer only buggy. NP205 t case and flipped 9" axles. I operate in every combination of high,low,fwd,rwd and 4wd. The NP205 couldn't care less. fwd/hi does get quirky steering. Rwd hi just hauls ass.
                            Thankyou, I was hoping that was the case.
                            Check out my project
                            https://irate4x4.com/general-4x4/2779-amphibious-hemtt

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