4r70 question

[SteveL]

If doing a 4r70 swap what's the difference between a 2wd tranny or 4x4 model?not sure whether using the dana 20 or going atlas. Looking at options.

 

[stretch]

Nothing more than the obvious. If you are planning on running an atlas, the 4x4 tranny will bolt right up. The 205 is a good place holder in lieu of the atlas if you need to save dollars. I would look for a 98+ 4x4 tranny, I believe they are a slightly upgrade from the 96-7 4r.

 

[SteveL]

What's up with the 2wd ones? Do you have to spend extra on an output kit? Was also wondering if you can order an atlas for either. If you go 205 do you have to notch the frame?

 

[Broncobowsher]

The 2WD needs an adaptor. You will be spending money to modify the transmission to accept a transfer case. No transfer case can be installed unless you add the 4WD parts. I know that is at least tail housing and pretty sure the output shaft as well. And the output shaft, that takes a full rebuild to change. It is literally the first part installed in the bare transmission case.

The 4WD has the adaptor for a full size transfer case already on it. You don't have to change it. An Atlas properly optioned will bolt straight to a 4WD 4R70W.

 

[SteveL]

Good to know. About to have my 72 back to dd status but dont think my back is gonna handle the clutch. I have a complete c-4 set up I can put in but I'm also piecing together a efi 351 and looking at putting the 4r70 behind it. Slowly buying parts as I see deals.

 

[Broncobowsher]

The 4R70W needs a lot of gear to be effective and happy. What size tires and what gears are you planning on running?

 

[SteveL]

35s and 4:56. About to swap arbs in.

 

[SteveL]

I'm not worried about mileage and it won't be a dd for work or anything. Is it better to stay with a well built c-4?

 

[904Bronco]

35s and 4:56. About to swap arbs in.

I ran 4:56's and 31's and you started to get the rpm's up at around 70mph in OD. Not that any of the components complained... Gas mileage concerns, well its a Bronco right.

I think with the 35's and the 4R70W you will be fine with those gears. Dirtdonk has this rig now, you can always ask his opinion... It was a 2wd tranny too.

Doug

 

[Fitz24]

Skip the 2wd version and go for a 98 to 2001 4x4. If you decide to go Atlas, bolt it up. If you decide to get an adapter to keep the D20, you just need to cut about an inch off the output shaft. Either way you have to rework driveshafts due to changes in lengths. I used 4x4 version and adapter for D20. Overall length was 3 1/2" longer than the C4 but the longer front DS helped angle a lot and shorter rear still works good and not too steep.

 

[jmhend]

Steve, I currently have a c4, dana 20 with 4.56 gears and 37” tires. I drive it about 1.5 hours (a few times a year to wheel) on the interstate. Generally 70-75 mph. Yes it is turning some rpms but it works.

Now a few thoughts / opinions and questions.

1- another option is to look for a 90’s AOD (no computer needed) and use the 4R70W gear set.

If I ever go to an automatic OD. that is the direction I am going.

 

[Viperwolf1]

Another option is 4r70w with manual valve body.

Difference between 2wd and 4wd 4r70w is not really relevant if a D20 is going behind it. You need an adapter either way and you probably should open the trans up no matter what, unless you have personal knowledge of its condition. I personally wouldn't go to the trouble of installing a transmission without rebuilding it first.

 

[EricLar80]

I would go 4.88 if I were you.

 

[SteveL]

Another option is 4r70w with manual valve body.

Difference between 2wd and 4wd 4r70w is not really relevant if a D20 is going behind it. You need an adapter either way and you probably should open the trans up no matter what, unless you have personal knowledge of its condition. I personally wouldn't go to the trouble of installing a transmission without rebuilding it first.

With my back I'm relying on friends for the install so whatever I go with is getting checked out first before installing.

 

[SteveL]

I would go 4.88 if I were you.

I thought about this if I go with an od tranny but I already have all the gears and lockers on the shelf.

 

[Broncobowsher]

I was going to suggest 4.88s, but it sounded like you already have the 4.56s. Close enough.

 

[SteveL]

Already have the gears and lockers. They're going in as soon as I figure out why my brakes aren't right. I plan to drive it a bit with the 4spd but if it's too much for my back(pretty sure its gonna be) then it's getting an automatic. I do like that idea of an aod with the 4r70 gears and have less electronics to fail. That would go well if I stay with the q-jet.