75 Bronco converting to 4R70W Auto transmission

[tlyoung003]

I purchased a 75 Bronco that the PO installed an NV4500 transmission with an adapter for the Dana 20 transfer case. For my use, I will be converting to a 4R70W transmission. The Bronco is non running today but has a rebuilt 89 5.0 HO engine running about 400HP. Is has a new painless wiring harness. It also has the RJM EFI engine harness for classic fords.

1. What make, model and year 4x4 4R70W should I be looking for a rebuildable tranny from?
2. The PO had routed but not terminated the wiring. He seperated body fuse box in the glove box and engine fuse box on the passenger fender. The CPU I have for the motor is EEC-IV SFI-MA12A01B14 A3M1. What do I need to do to have them communicate with each other?
3. Also, if I want to cruise on the highway at about 70-75 MPH at low RPM's, what gearing should I have in the front and rear differentials?

Thank you

 

[904Bronco]

The later 4R70W trans have the better upgrades internally, so 98 and up.

A3M1 ECU will not communicate with the 4R70W. You need a stand alone controller for the Trans. Kind of like apples and oranges, OBDI technology trying to talk to OBDII.

You did not mention what size tire you will be running? 4:11's mininumum for say a 31" tire. 4:56 > 4:88 for larger tire sizes

 

[tlyoung003]

904Bronco, thank you for the response. The 75 Bronco currently has 35" tires on it. I will either run these or more likely go to a 32" tire.

Regarding the stand alone trans controller, do you have a source for buying one?

Thank you

 

[hyghlndr]

US Shift, they know Broncos and support the bigger events. They also have very good customer service. Either quick shift 2 or 4 model.

Wish you were closer, would love the nv4500 setup.

 

[Broncobowsher]

You need a 4R70W from a pushrod 5.0 (96-01 V8 Explorers are generally the go to source). Another option is the 4.2 V6 from an F150, '97 to somewhere around '03?

What you do NOT want is a 4R70w from a modular engine. 4.6 or 5.4 are a bad choice.

Sometimes you may see them refered to as a 2-bolt or a 3-bolt starter. You want the 2-bolt starter. the 3-bolt starter is for the modular engines.

'98 and up is generally regarded as having the best box of parts to start with.

 

[tlyoung003]

Thank you all for the replies. I'm still trying to understand the gear ratio's. Again, this is totally out of my level of understanding today. But I'm learning. If I am running 32" tires with the 4R70W overdrive transmission, what gear ratio is best? What I have today are 3.50 front and rear. If I stayed with what I have, will I be ok? The use will be City driving 90% of the time, highway driving 10%. I won't be rock crawling. I may go on a few snow runs. Thank you, Tim

 

[clintOK]

http://www.grimmjeeper.com/gears.html

This should help

 

[Broncobowsher]

Good rule of thumb is gear for 2000 rpm at 60 mph with a 4r70w.

 

[tlyoung003]

Thank you both. There are a couple questions asked that I don't know how to answer. 1. Manual or Auto with lockup torque converter? or 2) Auto w/o lockup torque converter? Also, I currently have a Dana 20 transfer case and will need an adapter. But I read on the forum that an Atlas transfer case will bolt right up to the 4R70W. There are several choices when it comes to Atlas. You have 2.0, 3.0, 3.8, 4.3, 5.0 and 6.0. For my application, is the Atlaas a better choice or the Dana 20 with an adapter and if so, which one? Thank you

 

[Broncobowsher]

Question about the 4R70W? Is it a 4WD/AWD version? If it had a transfer case it would be easy to option up an Atlas and be done. But if starting with a 2WD transmission you will need adaptors (and a rebuild to install them).

As for what ratio, it would depend on what you are planning on using the Bronco for after you are done. The 2.0 is a poor choice, 3.0 will be a fairly normal low range and a pretty good choice. 3.8 will be on the lower stuff, if you want more slow technical and less speed it could be an option. 4.3 is as low as I would go, that is for slow crawling, you loose your normal low range and just have super crawl and fast with nothing between.

For calculating gears, use the manual/lockup convertor.

 

[tlyoung003]

I plan to find a 4R70W 4wd tranny. And I plan to have it rebuilt. On the Atlas, since 90% of my driving will be in town and 10% highway. Almost zero 4 wheeling. It sounds like the Atlas 3.0 would be a good choice. Thank you