Which Transmission?

[notsoquick]

Ok, so I know that there have been posts in here before debating between the ZF and the NV3550. The ones I found were older and I wasn't able to read how they turned out. I've got a '69 with 411 gears and the three on the tree is netting me a whopping 9.5 mpg. I'm looking for a bit more but my concern is that if down the road I decide to beef up the engine, will the NV be able to handle it? I'm also looking at adding a 2.5" suspension lift and I have no issue with a small body lift. Which will be simpler and is easier on the wallet and install?

 

[slim811]

9.5 mpg! Wish I got that much.

 

[bronconut73]

IMHO. Based on the oem usage of these trannys.

The NV 4500 (5.6 ? to 1 Low gear) can handle big block torque at very high gvwr.
The NV 3550 (4.0 ? to 1 Low gear) is probably better suited to mild 351W builds.
The ZF has a similar low gear and can handle big block torque at very high gvwr.

 

[nvrstuk]

After you decide what torque rating you want, you'd better really figure out if you want a fun tranny to drive or a TRUCK transmission. I ran a ZF for over a dozen years and it worked great, BIG gear splits, not very quick shifts... 3550 is a great all around tranny, fun to drive, closer gear shifts.

Course you don't want to keep replacing a fun tranny that keeps blowning up huh?

 

[broncnaz]

What tire size do you run? The engine tune, build, and driving style effects mileage numbers as well. Just swapping in a OD tranny may not increase mileage any and can actually hurt it. although in most cases you will see a small gain. If your planning a lift and bigger tires a OD tranny probably wont gain you anything unless you swap in lower axle gearing as the bigger tires alone will give a OD effect on the current setup.

There are a lot of factors that affect gas mileage everything needs to be matched and running correctly to get the most out of your bronco. There is no one magic part that will make everything better.

 

[notsoquick]

Yeah, I'm doing what I can to make things a little more efficient. It currently has 32" tires on it and I'm only looking to go up to 33"s once I lift it. I really like the low end on the 4.11 but it hurts to see my buddy getting 14 mpg in his (on a recent road trip). He's running 3.50 with 35"s and a C4. I understand that one component doesn't gain mpg, but with a fresh engine, it seems like the logical next step.

 

[John Marinan]

Look into a new AX15. This is the unit that is still being made. It is better than a 3550, which was discontinued years ago, parts are still available for the AX15 which is still in production. Rockwell standard gear, Advance, as well as a couple of jeep conversion sites have them. This is the same unit offered in the Icon Bronco with the 400 HP engine.

 

[broncnaz]

Yeah, I'm doing what I can to make things a little more efficient. It currently has 32" tires on it and I'm only looking to go up to 33"s once I lift it. I really like the low end on the 4.11 but it hurts to see my buddy getting 14 mpg in his (on a recent road trip). He's running 3.50 with 35"s and a C4. I understand that one component doesn't gain mpg, but with a fresh engine, it seems like the logical next step.

Id step up to the 33's before doing the tranny swap. also you need to make sure your engine is properly tuned and the carb is jetted correctly.

Any mods in the engine ie cam, intake ect? A properly chosen cam will put the engines power band up where it needs to be with your current setup.