4r70w/atlas help

[NM_outdoors]

Well, the bronco project is going to start getting some attention again now that the days are too short to scratch much off the honey-do list. I did the rolling chassis last winter/spring and am ready to bolt in the freshened up 351w and have sourced (almost?) all of the OBD I MAF Ford EFI parts. Just purchased my 4r70w Baumanator controller (thanks to the mass buy discount on this site) and have decided to retire the old T-shift D20 and go with an atlas 2 speed tc. I've done as much searching/reading as time will allow but have a couple of questions related to the overall drive train and speedo connection options.

Given the increased overall length of this setup and with a 3.5" suspension lift, I might be on the edge of being too steep on my rear driveshaft angle. My plan is to leave the rear spring perches "floating" until I get the final ride height established so I'll be able to rotate/aim the pinion and shorten the rear driveshaft as needed. Somewhere, I saw the option of two lengths on the atlas. One being with no speedo and one with. The option with a speedo will cause the OAL of this setup to be even longer so I'm wondering what others have done to avoid that. Can I go with an electronic speedo gauge (signal off the VSS or OSS?) to save some length on the atlas? My understanding is the Ford EFI setup interfaces with the transmission/controller but it seems like I'm overlooking something there.

Also looking for some suggestions on 3.8 or 4.3 Atlas ratio with that tranny. Leaning toward the 4.3 but I'm going 4.88 in the diffs and plan on being able to do some crawling but will be using mostly as a trail rig in NM, CO, AZ, UT.

Here's a couple of pics of the project so far.......

 

[Yeller]

my only input is do the 3.8 at most. You'll be happier in the long run. If it were mine I'd do a 3.0. IMO getting past 45:1 (and yes I do the stupid, retarded hard stuff) with an auto and your limiting performance, not enhancing it, and if the trail is easy/moderate, your always shifting the tcase, especially in the areas of the country where you will be wheeling. For referance your set up with a 3.0 is 41.6:1, just about perfect IMO. With a 3.8 it is 52.7 right at the point of diminishing returns for performance and 4.3 is 59.6 beyond useful. With the torque of a 351 you'll be happier with one of the 2 higher ratios.

 

[Broncobowsher]

I ran the 4R70W with a set of 3.15 Teralow gears. That was a real sweat combo. The absolute lowest I would recommend is the 3.8:1 if you did hard technical stuff, the 3.0 would be a good trail ratio. Going too low on the low range and you loose the normal low range. You have crawl and highway with no trail gearing. I have seen it several times when ego says to order super low gears. Crawls over the rocks great, goes down the highway great. Can't get up the sand was between the highway and the rocks with any dignity.

Now for the speedo. The OSS does have a usable signal that some aftermarket speedometers can take. It is roughly 3x faster then a typical speed sensor, but many speedometers can take that fast speed just fine, some cant. But the OSS won't read correctly in low range. It will read (what ever the low range ratio is) faster and the odometer will be fast as well. Really what you are after is a tone ring on the rear driveshaft.

There are also GPS signal generators that will feed a signal into a electronic speedometer as well.

 

[nvrstuk]

x3, go with the 3.0 or max 3.8 ratio in the Atlas...

You won't have any issues with driveline length. I have a the same setup but also have a KluneV stuffed btw the tranny and the Atlas.

You'll be fine with your suspension, lift, drivetrain...

 

[NM_outdoors]

Exactly the feedback I was looking for gents! I'll steer clear of the 4.3 and shoot for the 3.8. Even thinking a little about the 3.0 now but hate to drop that much coin and have regrets that I didn't go low enough. I've bounced my old bronco through the mountains for the last 30 years with the stock 3 speed, D20 and 4.1 axle gears and always managed. This new setup is really gonna be nice. Time to get in the shop and start working on this dude again. Really appreciate the help here guys.

 

[NM_outdoors]

Any thoughts on the need for the HD front output shaft upgrade? I'll be running 35" tires and don't see myself going much bigger.......ever. I also noticed JBG is running a 10% sale on (ALL?) items. Might be time to pull the trigger unless someone else knows of a better deal?

 

[Rox Crusher]

The Baumann controller has a speed monitor display coming from the 4r

 

[Apogee]

Any thoughts on the need for the HD front output shaft upgrade? I'll be running 35" tires and don't see myself going much bigger.......ever. I also noticed JBG is running a 10% sale on (ALL?) items. Might be time to pull the trigger unless someone else knows of a better deal?

No need on the HD front output for your application, however it does tend to be a desirable option for the buggy/comp guys. I picked up a used ATLAS w/3.8 with HD front and rear from a Jeep guy who was going 4-speed, but don't know that I would have paid extra for it since I'm only running a D44 front. If you see the possibility of swapping in a D60 (or something comparable in terms of strength) at any point in the future, then I would consider the front output upgrade mandatory...otherwise, it certainly can't hurt unless the money can be put to better use somewhere else.

 

[NM_outdoors]

Good point. Looks like the vendors are all pretty close in price on these units but aren't very specific about whether the output shaft upgrade is included..... I'll make some phone calls on Monday.

 

[Yeller]

The shaft upgrade is IMO a cheap enough option to never have to worry about. I'm a slow kid though that breaks D60 stuff with 37's....... Go 3.0 and you'll have no regrets I promise.

 

[Kyle.malone]

Agree with Yeller.. I am running a 3.8 case with the planetary gear to make mine a 4speed trasnfer case. I am also running 4R70W and have no probelms with the rear shaft being too short. When I ran stock my D44 and 9" , all I had to do is swap my front driveshaft to the rear and the rear to the front.

 

[NM_outdoors]

Thanks for all the input guys. Called around to some of the vendors today to get pricing and specifics and leaning toward the standard front output shaft and cable shifters.

Still thinking the t-case ratio over. With that 4r and 4.88 axles, from 1st to OD in high range I'll have 13.86, 7.56, 4.88, and 3.41:1

With a 3.8 in low I'll have 52.66, 28.74, 18.54, and 12.98:1

With a 3.0 in low I'll have 41.57, 22.69, 14.64, 10.25:1

I don't have much experience in this area to have a feel for what these crawl ratios will feel like except I see a bigger overlap between low/high range with the 3.0:1 option. Also, I'm reading/hearing that the 4r70 controller can be set up to start in 2nd gear which might help on the moderate trails in low range too? dunno......... I'm hearing (and understanding?) what is being said about the dangers of going to low and losing the mid-range but, between the auto and the torque of the 315w, I'm hoping for decent coverage. Shoot holes in this.......I'm all ears!

 

[Yeller]

Both my rock buggy and bronco are 41.7:1 in 1st gear, I usually settle the debate with all you gotta do is keep up. I feel its perfect. Unless your rig is going to weigh 6000 pounds, then he 3.8 will be better.

Don't laugh at the weight, most grossly under estimate weight. A built up rig weighs more than you think

 

[Broncobowsher]

the 3:1 should put you real close to 20MPH @ 2000 RPM in low range OD. This is a good pace for making it between tough spots and being able to just leave it in low range the whole time

 

[Yeller]

the 3:1 should put you real close to 20MPH @ 2000 RPM in low range OD. This is a good pace for making it between tough spots and being able to just leave it in low range the whole time

Exactly! or if your really whoopin it up 60 is 5900

Also the slightly higher ratio allows you to use a tiny bit of throttle to create a small bump to get up an obstical easy that your buddies with 5:1 are struggling with because they by the time their engines are winding up its too late and past where they need to be.

I'll give an example, I have built the #1 winning chassis in WeRock proffessional rock crawling series, its won the most number of races of any team. And its 43:1.

Gearing is like Ice Cream, too little and you're pissed, too much and your pissed, that happy medium is heaven.;D

 

[bax]

I like ice cream. "Said in my best Forrest voice to Lt. Dan."

 

[NM_outdoors]

Alright, sold. 3.0 it is!

 

[NM_outdoors]

Yeller, I owe you a trip to B.R. (31 flavors!).........

 

[Kyle.malone]

Yeller knows what he is talking about. He builds some sweet rigs!!

 

[bax]

Yeller knows what he is talking about. He builds some sweet rigs!!

Ford guy thru and thru.