www.ColoradoClassicBroncos.com

I am seriously looking at getting an Atlas T-case and never realized how many options there are. For some reason I just thought it was 2 spd vs 4 spd, now I have realized there are at least 3 options for the 2 spd. I am looking for any input on what the best options are, I know I have seen the 3.8 and 5.0 2 spds in Broncos.

I have the 4spd with the low-low at 10:1. I LOVE it! if you intend on doing some serious wheeling, go with the deep gears. What is your setup? Auto or manual? What are your ultimate goals for your drivetrain?

I don't know what the current offerings are and while my crawl ratio is outrageously low - I have used it many times! Plus having the 4spd allows me three different low-ranges to suit the conditions.

Most of the options I saw where for the 2 speed. My current set up is pretty much irrelevant at this point, I am in the process of an axle swap and decided to start looking to do the trans and t-case immediately after. I have full widths with 4.88's that will be going under it and a 302/C4/D20. I am planning to swap to a ZF-5 and Atlas, the 302 will stay until I find a 351W. I am hoping to have everything done within the next 6 months so I am not as worried about the 302, the only thing holding me back on the 351W is looking for the motor itself.

I wont talk you out of a 4speed because they are awesome, but I love my 2 speed 6:1 with a ZF5. Crazy slow with the low 1st plus 6:1.

I have to imagine the 5:1 is pretty awesome as well.

As mine sits now, front and rear driveshafts are the same length, so that is a bonus when it comes to carrying spares.

I'll admit that the 4spd can create an issue with the rear driveshaft. You really need a high-angle driveline and push the rear axle back as far as you can. Is your new rear a 9"? With a 4spd behind the ZF you need to run a 3/4" spacer, so that pushes things back even further. Perhaps you need an excuse to get a HP 9"?

Note my signature. I'm running what you are planning to do. It's done me well and while I still want to push the rear axle back a few inches, I wouldn't change a thing in regards to gearing. I'm even at 4.10's in the axles.

If you choose a 2spd get the lowest you can and then just use the 5spds in the ZF to get the gearing you need. In the rocks, I think it's all about finesse and you need control to do that. It's just a big jump down to 6:1 from 1:1, where in 5th gear in the ZF @ 6:1 will go only slightly faster than 1st gear @ 1:1. I use my range box or the planetary box when I am snow bashing, or perhaps mudding where you need some wheel spin. You may encounter a situation where you need something in between.

I believe that you can't go wrong getting lower gears in your t-case. It just makes the most sense as you are not sacrificing on-road performance, but gaining so much off-road.

Thanks for the advice. Rear end is a 9" but I'm not ready to push the rear end back so I think the 4 speed is out. I was already leaning toward the 2 speed but just not really sure if going all the way to the 5:1 would work out. I want to be able to get on the highway yet still be able to crawl.

Digger wrote:I wont talk you out of a 4speed because they are awesome, but I love my 2 speed 6:1 with a ZF5. Crazy slow with the low 1st plus 6:1.

I have to imagine the 5:1 is pretty awesome as well.

As mine sits now, front and rear driveshafts are the same length, so that is a bonus when it comes to carrying spares.

Trying to read through three different threads at the moment and was wondering did you need to notch the frame for the 2 speed?

Jesus_man wrote: It's just a big jump down to 6:1 from 1:1, where in 5th gear in the ZF @ 6:1 will go only slightly faster than 1st gear @ 1:1. I use my range box or the planetary box when I am snow bashing, or perhaps mudding where you need some wheel spin. You may encounter a situation where you need something in between

That is why I ultimately went with the 4 speed. With a 5:1 box, you either have normal 4 high (1:1) or 5:1. I wanted to be able to keep up with non-Atlas rigs on no-so-tough trails, without running in 4 high. With a 5:1 case, you will be going about 1/2 the speed you can with the stock D20 in 4 low. JD has his installed without pushing the axle back much. I went a little further, and it cause a TON of work. I haven't driven mine yet, and that's why I dont have a lot of input for you.

You can clock the Atlas when you install it. So you have some choice where it sits. You don't have to notch the frame, but your expensive t-case will be hanging pretty low, if you don't. And we didnt buy Atlas t-cases to crawl over the parking blocks at Costco. I feel its worth the extra work to tuck it up into the truck. But if you don't have a body lift, you'll probably want to keep it lower than I did.

Yeah, my axle is back the 1". I want to go another 2-3", but as Gunni says, that gets into a ton of body work. The 1" is easy and that is where I am at and it works. So don't discount the 4spd if you really want it. I also didn't help myself clocking my atlas flat so it is completely above the frame. My setup is about the worst case scenario.

I think you can get your Atlas pretty flat before you have to notch the frame, but it will still be exposed below the frame. Chad may have better numbers on there and how it compares to the stock orientation of the D20.

I am still considering the 4 speed, at this point I am really just trying to gauge the amount of work. The 1" does seem pretty easy and I could probably get that accomplished when I swap axles. Did you do any body mods with the 1" move? Definitely going to check out all your guys threads better when I have some free time.

No body mods required and actually this 1" puts the axle back near the stock location. A lift generally pushes the axle forward.

Jesus_man wrote:No body mods required and actually this 1" puts the axle back near the stock location. A lift generally pushes the axle forward.

True, I wasn't even thinking about the lift. Thanks for the info, I am still new to all this so I am trying to do as much research as possible first.

That's what we are all here for! Someone has likely done what you are contemplating and we are all too happy to share experiences.

One more question before I head out for the day. I currently have a 2" body lift, is that enough?

Yep. That's what I have. Unless you clock it flat, you should not have to modify the body.

Regarding clocking options. It will depend on which spacer you choose to use. You should be able to use either a 1/2" spacer, or 3/4" spacer between the Atlas & ZF. They install slightly differently, so they each will give you a different set of clocking options.

JD used the 3/4" spacer and it allows for a flat clock. I used the 1/2" spacer, and it does not allow for a flat clock, I believe. Mine is set like this right now:



Advance Adapter's literature & instructions suck, but their customer service has been very helpful. I'd call them and ask for the clocking options with a 1/2" spacer vs the 3/4" spacer. I'm sure they can explain the options. I wasn't going to clock mine as flat as I did, but when it was hanging clear of the frame, it looked really vulnerable to getting caught on obstacles. So I went the extra mile to notch the frame and clock it up. I think with the 1/2" spacer, and a 2" bodylift, you could clock the Atlas like mine, without getting into the tub floor.

I have a 3/4" spacer kit, that I didn't use. They wanted a restocking fee, a discount because it was 'scratched' from test fitting, plus freight back to them. So I didn't return it. I'll make you a nice deal on mine, if you end up going with the 3/4" spacer. I think you'll need a spacer with the 2 speed or the 4 speed.

1" back is easy. You can just redrill the spring plates for the centering pins. More than that is a bigger deal. I extended the wheel wells for a longer stretch. It was easy, but my 23 gallon fuel tank is now a limiting factor.

Justin wrote: It was easy, but my 23 gallon fuel tank is now a limiting factor.

Justin, I'd love to know how far you went back and then get a ground-up vertical picture of your axle/tank clearance. The co. that Gunni ordered his tank from is open to customizing their tanks, so I was thinking of taking a radius out of the center of the tank to clear the pumpkin. When I get that far. But having your picture and measurements would allow me to modify their design appropriately!