I'm about to pull the trigger on a 4 speed Atlas. Something I've wanted of for a while. I'm pushing the Bronco budget to the max, but I want to get my ZF installed, and ditch my 435. I also know that my D20 has never been serviced, except for adding oil, at least, since I've owned the truck (1996). Its probably the last original big part on my truck.

I can order the t-case with the shorter tailshaft (about 2" shorter) but it has no provision for a speedo. I can run the speedo I have to install in my truck from a GPS module (about $170). But this configuration would not offer anyway to add a VSS to my EFI. I'm not running one now, and don't seem to need it. This would give me a little longer rear driveshaft, & probably a little better driveline angles. The ZF/4 speed Atlas, is obviously long, so it seems saving 2" in length is probably valuable real estate. Since I want to be able to drive on the highway, this seems like the best route. Others seem ok on the highway with the longer t-case.

Since my truck runs good without a VSS I don't really think I need it. The longer tailshaft design would allow me to run a VSS that would run my speedo & double as a VSS for my EFI

I'll probably order the t-case tomorrow, just need to decide how to outfit it.

I vote shorter tail housing and no vss. Your going to redo your dash anyway and could go with a GPS speedo. Or use your phone.

I never installed my vss for the efi/computer either and haven't had any issues

The gauges I have for my dash has a GPS module option instead of a VSS.

I'm leaning that way too. I haven't had a problems because of no VSS.

X2, GPS & short tail shaft.

I usually recommend people keep the VSS, some that don't suffer from stalling on decell.

However, given your specific scenario I think I'd go with the shorter housing. You aren't having any problems without the VSS now so I doubt it will give you problems later. The extra money for the GPS unit probably wouldn't be much more than the special cable and VSS, stuff that you'd need to buy anyway. I used my phone in my beater when the cable broke for a couple of weeks, seemed to work just fine.

Thanks for the info.

I have stalled out a few times on decelleration in the 2+ years I've run the EFI, but it doesn't seem to be persistant.

Hmmmm.

Forgive my ignorance, what all is the VSS supposed to do ?

Its a Vehicle Speed Sensor. It senses vehicle speed.

I'm not running one, some do. Are you?

I really don't know what it does, and am hoping getting a fully functional ECU or changing motors won't make me need one.

I'm planning on never buying another t-case. Ever.

I have a VSS but it isn't connected.

I don't have any idle / stalling issues at all.

I was wondering if it would have any other functional capability in relation to my 4R70W. In terms of determining shift points for various engine RPM and speed conditions.

There are functions inside the PCM that depend on the VSS signal, how critical they are is the bigger argument.

On the A9P decel fuel shutoff (DFSO) is speed dependent along with closed loop rpm control. I can't see either one being that big of an issue because they are minimum speed cutoffs. Both are set to 5 mph from the factory. If the speed is always showing 0 then closed loop rpm control is always working, and DFSO never cuts the fuel at all.

On the A9L lack of VSS can be an issue for sure. In addition to DFSO the A9L has a function called dashpot (just like on a carb) that controls how fast the idle speed is allowed to drop on decel, this is to prevent stalling on decel. This function is always active above 7mph. If you are going slower than 7mph the idle speed will drop faster because dashpot won't be active.

When tuning, if I force the PCM in to a neutral state then dashpot becomes active at all speeds without a VSS. So, in theory grounding pin 30 may help with the stalling if it's an issue. Just be sure that pin 30 isn't also connected to the start signal.

I haven't looked in to the newer Baumann units. But, the old Baumann TCS is supposed to be wired to the VSS. The newer units may only require the use of the OSS (Output Speed Sensor). I disable the VSS in the Explorers and make them run off the OSS instead.

Chad I think the shorter case will be valuable. Since I am cheap, I took apart my cv driveshaft and ground down around the center ball to get better angles instead of buying a high angle driveline. It's worked so far. I run the stock speedo with the appropriate gear.

And I would be willing to bet for a couple hundred bucks you can swap tail housings later if you want to go VSS.

I do recommend the clock-flat version if you feel ok with modifying drivers side frame. I think I've also mentioned in the past you will likely have to run a 3/4" spacer to mount it to the zf5.

Thanks,

I agree. I expect to clock the Atlas flat someday, but not yet. I expect a body lift to be in my future. I want to step up from 33's to 37's when these tires are worn out (1 or 2 years- probably).

I think you are right about replacing the tailhousing if VSS is needed.

I've measured my output shaft on my ZF and will be ordering the spacer, you are right.

Thanks for the advice guys.

There is no turning back now. I melted down the Visa card & placed the order I've been putting off for a couple years now. 4 speed, 11.7:1 low ratio, short tailshaft, no speedo.

Plans are to install the ZF & Atlas, but I'll be waiting on axle gear changes for a while. I'll be driving the ZF as a 4 speed till then. I'm tentatively planning a jump to 37" tires on 17" rims in a year or two, depending on how my tires hold up. By then, hopefully, I will have built a new set of 8 lug axles. I've started accumulating the parts for a Jana 654 (HP D44 axle housing, D50 gears, & D60 axles, brakes & hubs). RJLougee has helped me source the parts & learn what it will take to do the axle build. I'll probably end up with a GM 14 bolt (maybe shaved) in the back. But till then I'll just have to put up with my 3.50 gears.

ZFxAtlasx3.50 gears = 54.45:1, 86:1, 234:1 crawl ratios. I think it will be ok.

4-6 weeks for the t-case.

I'm not sure about the swap. September? There is a lot of stuff I want to do at the same time or before, and I'd like to do some runs this summer/early fall. So probably after the summer stuff is done, but before hunting/snowboarding/garage gets too damn cold.

Awesome! I guess I better enjoy the "CCB's lowest crawl ratio" while I can. Mine is 10:1, so we'll be even until you swap axle gears. So If I stick with 35's, I still may be slower, but I also want 37's on 17's

This will be one helluva upgrade !

Sounds like a fun project.

4-6 weeks=9 days?

P1020222.JPG

Well so much for trying to get a few "smaller" projects done first.

Thinking about pulling the Bronco into the garage, and tearing it apart to do it all at once. It might be a few weeks before I can start, there are a few remodel & F250 projects on the top of the "to do" list.

Pretty!

Yep, too bad it has to be tucked away under the truck.

I'll give it a warm home and purpose until you're ready.

Woot!!!
I'm trying to remember where mine leaked from. I think it was a loose tail housing. So tighten it all up while it's on "the bench".

And remember that it'll be super stiff at first. In other words, don't take it out of gear unless you are on a hill and can roll at least one direction. After you get it in, take your bronco for a nice hr long ride to warm it up and that helped mine a ton!! Still it doesn't like to shift when in a bind. Do you have a rear locker?

Zach, thanks for the offer. I think I'll find the motivation with it sitting on the floor of the garage.

JD, I have a Lock-Rite in the back. I've been reading the booklet that came with it, it kinda said the same thing. I'll follow your advice on the brake in. Sounds like they are tough to shift when they are new.

The instructions have conflicting info. One part says to use "Castrol Syntec or Mobile 1 synthetic motor oil for the first 500 miles, then switch to the supplied Amsoil gear oil". The other instructions said to fill it with the supplied Amsoil gear oil. I think I'll send AA an email to be sure.

I don't recall what I did for break-in oil, but I know I did it. Castrol rings a bell, but I can't be certain. It can't hurt to run a break-in oil, so if you don't get a straight answer, I'd do it that way.

So with a locker, when the case is new, you'll want to be going in a straight line with the ability to roll either way before you try to shift into other gears. Open diffs don't put much bind on a t-case, but a locker can and you might find yourself sideways on a side street, stuck on level ground, as I did! LOL!

Jealously is a bad trait I hear, I'm trying my best...

Joe - I considered that. Believe me! We're so close to finishing my atlas install to discover the shaft bottoms out. The reason I didn't is breaking that shaft on the trail somewhere. Having to shave an inch off before the install would just complicate the process. On the other hand, how likely is that shaft to break? Probably not too much!

Those '77 Lincoln Mark V rear calipers on mine - Are they efficient for an e-brake? I'd really like to be running one.