Considering Manual to Auto Transmission Swap

[txtruk15]

I’m thinking about changing over to an automatic transmission on my 70 EB. The NP435 with granny gear drives loose and rough, is probably going to need a rebuild, and is not easy to drive for anyone but me in the family and was more of a setup for serious trail crawling by the PO. I’m going to use my EB for more street driving than trail crawling and just be ready for some mild to medium trail work in the future.

I’ve pretty much figured on the 4R70W and am thinking keep the d20 twin stick. I’ve done some reading on this and I think I’m more confused now about how much effort and cost it will take. I thought if I figured it out now I can decide to either save up and probably go for it early next year…I’m most likely not going to tackle this conversion myself but am willing to hunt for and collect all the parts necessary and maybe do some the less demanding parts.

Here’s my current setup:
1987 mustang 302 efi, JBA shorties
NP435, D20 twin stick
4.56 gears
Front: d44 w/e-locker, back: 9” w/ Detroit
37x12.50 BFGs on 17” wheels (more than I need I know but I do like the 37" tires)
Coilovers

Lots of questions – what are the major pieces to doing this?
Can I keep my flaming river tilt steering column and put the auto shift on the floor? Or do I have to change that out (It was a MAJOR pain in the a$$ to wire!)?
Is it best to keep the d20, give it some new parts, and just advance adaptor it to the 4r70W?
What gearing should I go to (4.88s, 5.13s?) to get acceptable good highway rpms without sacrificing street driving?
Do I need the computer programing from someone like Baumann EC?
Do I need to get a different cross member to get this all to fit?
Probably will need different drive shafts?

Thanks, appreciate any expertise on helping me to decide the future…

 

[sykanr0ng]

Just to throw another idea at you; why not an M5OD 5 speed manual from an F150 with a 4.2L V6?
Easier, more car-like shifting plus a low first gear and an overdrive fifth gear.

With the 37 inch tires I know I would want lower gears.

 

[txtruk15]

Just to throw another idea at you; why not an M5OD 5 speed manual from an F150 with a 4.2L V6?
Easier, more car-like shifting plus a low first gear and an overdrive fifth gear.

that sounds like it would easier - how hard to hook up to D20 and any special considerations to get it to fit? It sounds like it would be easier to drive too than the NP435...

 

[sykanr0ng]

that sounds like it would easier - how hard to hook up to D20 and any special considerations to get it to fit? It sounds like it would be easier to drive too than the NP435...

Uses the same adapter for the D20 as the ZF5, it is the same length as the ZF5 but slimmer so it does not need the body lift.
It does use the same hydraulic clutch as a ZF5 also.
The reason I suggest the ones from the F150 with a 4.2 is that the shifter tower is farther back from the dash on them.

 

[txtruk15]

Just to throw another idea at you; why not an M5OD 5 speed manual from an F150 with a 4.2L V6?
Easier, more car-like shifting plus a low first gear and an overdrive fifth gear.

With the 37 inch tires I know I would want lower gears.

would the M5R2 work? what year is best on the M5OD? what about the M5OD-R2 from the mazda truck or is that the same? thx....

 

[sykanr0ng]

would the M5R2 work? what year is best on the M5OD? what about the M5OD-R2 from the mazda truck or is that the same? thx....

Same thing, full name is the M5OD-R2
1997-2004, maybe 2004-2008
Only with the 4.2L V6

 

[Tiko433]

I started with a stock 3 speed ... tried out a C4 for about a year, I went to a AX15 and love it.

 

[txtruk15]

what are your guys' thoughts around the NV3550? Seems like a light, simple replacement for the EB and doesn't have the granny gear yet has the OD....?

 

[Broncobowsher]

NV3550 is out of production. No new ones. New parts for rebuilding are running out.
AX15 is comparable, Still making them and the parts for them.

Sounds like you are after some better highway driving. You already have the engine and the tires you plan on running. That should give you a pretty good idea how it will run. My ballpark gearing is 2000 RPM at 60 MPH. The mustang 5.0 is a pretty good engine and a lot of torque for a 302. But I am sure you realize that 37s have a lot of drag. And it takes some power to push all the rubber and wind at highway speeds.

The 60 at 2000 also stretches into 90 at 3000. For what you are going to be pushing down the highway, that is a lot of drag. I think you may want a bit more RPM to stay in the happy place for that drag. 2200 RPM at 60?

Once you figure where you want to cruise at, speed and RPM at that speed, work backwards through the gear ratio calculators. Divide out the overdrive ratio, that will be the gear ratio you will want with that new transmission. And the different transmissions will have different overdrive ratios. So you need to pick a transmission before figuring the ratio for it to match.

Don't fear the gear. One way to really hate your new transmission is to not run enough gear. Having to downshift for a hill every once in a while is fine. Having to downshift for every hill will suck huge. You will be lugging the engine in OD, and winding it out on the hills. That just wastes fuel. You need enough RPM to cruise with manifold vacuum to stay out of the power enrichment. The EFI is more willing to lug down then a carb, but only to a point. Run enough load and it will transfer over into open loop.

As for the 4R70W, great auto. The programming is pretty easy. It is designed for hobbists. It is the only auto I have ever been happy with coming from a long line of driving stick shifts. Program it to shift at the point you like as you would driving a stick. The lock up convertor makes it nearly as efficient as a stick. It does require a controller (there is a vacuum modulator conversion but you loose the benefits of being able to dial in the shifts). There will be crossmember and driveshaft modifications. The Dana 20 can be retained.

 

[txtruk15]

NV3550 is out of production. No new ones. New parts for rebuilding are running out.
AX15 is comparable, Still making them and the parts for them.

Sounds like you are after some better highway driving. You already have the engine and the tires you plan on running. That should give you a pretty good idea how it will run. My ballpark gearing is 2000 RPM at 60 MPH. The mustang 5.0 is a pretty good engine and a lot of torque for a 302. But I am sure you realize that 37s have a lot of drag. And it takes some power to push all the rubber and wind at highway speeds.

The 60 at 2000 also stretches into 90 at 3000. For what you are going to be pushing down the highway, that is a lot of drag. I think you may want a bit more RPM to stay in the happy place for that drag. 2200 RPM at 60?

Once you figure where you want to cruise at, speed and RPM at that speed, work backwards through the gear ratio calculators. Divide out the overdrive ratio, that will be the gear ratio you will want with that new transmission. And the different transmissions will have different overdrive ratios. So you need to pick a transmission before figuring the ratio for it to match.

Don't fear the gear. One way to really hate your new transmission is to not run enough gear. Having to downshift for a hill every once in a while is fine. Having to downshift for every hill will suck huge. You will be lugging the engine in OD, and winding it out on the hills. That just wastes fuel. You need enough RPM to cruise with manifold vacuum to stay out of the power enrichment. The EFI is more willing to lug down then a carb, but only to a point. Run enough load and it will transfer over into open loop.

As for the 4R70W, great auto. The programming is pretty easy. It is designed for hobbists. It is the only auto I have ever been happy with coming from a long line of driving stick shifts. Program it to shift at the point you like as you would driving a stick. The lock up convertor makes it nearly as efficient as a stick. It does require a controller (there is a vacuum modulator conversion but you loose the benefits of being able to dial in the shifts). There will be crossmember and driveshaft modifications. The Dana 20 can be retained.

awesome writeup and advice, - I appreciate it. I've heard some good things about the AX15, it seems like that would be easier and cheaper than going the 4R70W route. I'll go back and figure out gearing, that is a great point.

Bob

 

[Broncobowsher]

Really comes down to if you want an auto or a stick.

I am very much a stick shift person. But I wanted an auto for playing in the rocks. Of all the used cars I have bought, only one has ever been an auto. And I considered converting it to a stick.

 

[pcf_mark]

If you want stick you have the options above. If you want auto (isn't the topic considering manual to auto swap?) to me the only choice is 4R70W. Bullet proof, low first, OD, lock up converter. I had a 3 speed, C4 and now 4R70W and it is in my top 5 modifications.

I daily drive a manual but the Bronco is more fun as an auto because the 3 speed is such garbage. If you have 4 or 5 speed with decent gear spread it is probably a lot more fun.

 

[txtruk15]

....As for the 4R70W, great auto. The programming is pretty easy. It is designed for hobbyists. It is the only auto I have ever been happy with coming from a long line of driving stick shifts. Program it to shift at the point you like as you would driving a stick. The lock up convertor makes it nearly as efficient as a stick. It does require a controller (there is a vacuum modulator conversion but you loose the benefits of being able to dial in the shifts). There will be crossmember and driveshaft modifications. The Dana 20 can be retained.

just found your writeup on installing the 4R70W http://classicbroncos.com/4r70wtransmission.shtml - great writeup and required reading. Thanks for sharing your expertise

Bob

 

[73azbronco]

The Nv3550 is in about a billion jeeps so I don't see parts as an issue. Its a great tranny if you keep the HP/TQ below 400, otherwise the 4500 is th ticket.

For AT, if your going that way, look at newest to get bang for buck, I'd say 6r80.