Upgrading from a C4

[Johnnyb]

I'll be upgrading a friend's Bronco from a C4 transmission to something else. This is a stock Bronco which would be used for light Wheeling at most. Not lifted and no large tires.
If I went with an aod are there crossmember and or drive shaft modifications required?

THX,
JB

 

[Broncobowsher]

Yes. Any transmission upgrade will require crossmember and driveshaft changes.
Skip the AOD. 6R80 is where it is at today. 4R70W is good, way better than an AOD. But the 6R80 is better. I would do the 4R70W if I was doing an Explorer driveline swap. But just a transmission swap, 6R80.

Now with that said, what are the axle gears (there were multiple different ratios available in "stock") and what size tires (not large doesn't mean small either).
There is a valid reason for these questions. If the gearing/tire size is wrong upgraded transmissions won't actually be an upgrade. There is a good chance that the best option is to actually keep the C4.

 

[Johnnyb]

6R80 behind a 1975 302?

 

[Broncobowsher]

6R80 behind a 1975 302?

Yes, it can be done. Adapters to exist.
member here nvrstuk probably knows the most about them.

 

[Master Chief]

Here’s his article…

https://classicbroncos.com/forums/a...-trans-into-a-bronco-behind-any-sbf-engine.2/

 

[Johnnyb]

That's a great write up on the 6r80! I think it's way too much for my friends Bronco if she wants to maintain near stock appearance and functionality. That means keeping the column shift.
If I were ever tempted by an automatic, this would be it!

 

[Broncobowsher]

I think you can still do the 6R80 with column shift.
If not the 4R70W can be done with column and is still a way better transmission than the AOD it is based off of. You still need the right axle ratio to use the overdrive.