Gear ratio for ZF5

[stokers]

Looking for suggestions for gear ratio with a ZF5 trans and running on 33 inch tires. Currently have original 3.50 gears and its way too high to use the overdrive. I'm considering a 4.11 but maybe even lower. Please let me know what you think.
Thanks,
Bob

 

[Broncobowsher]

.78 OD if I recall correctly.
The 4.11s will cruise at an effective ratio of 3.20 Are you comfortable running at a slightly lower RPM then you cruise at in 4th now? (4th is 1:1 with current 3.50 gears)

The next two lower options are 4.30 which comes in a 3.35
and 4.56 gears which will equate to 3.55, which happens to be a touch lower then your current 3.50 in 4th gearing.

What does the motor feel like it wants to do? My feeling is the 4.30 ratio will make for the best gearing with that OD ratio. I ran a 3.42 effective ratio in OD and thought it was a bit low geared still, but that was also with a 351 engine.

Some people like to gear high. Something that takes a downshift for nearly every hill. I much prefer to be able to pull most hills and only have to downshift for just a couple of the bigger ones. I enjoy rowing gears, just not on each hill.

 

[Apogee]

.77 or .76:1 OD depending on whether it's a close ratio or wide ratio unit IIRC, but I agree with the above and would probably run 4.11 or 4.30 gears for hwy/street/mild off road use. Given the NP205 in your sig line, I'd probably go 4.56's if it's not a highway rig.

 

[sykanr0ng]

My choice would be at least 4.56 which has been noted as very close to the same final drive when in overdrive as the 3.50 gears used without overdrive.

If there is any chance of going to 35 inch tires then 4.88 gears would be better.

You should change the rear gears and test drive it (2wd only) before changing the front.
The Ford 9 inch is easy and inexpensive to change, the Dana 44 or Dana 30 are not.

 

[Galt72]

Myself, I can't stand the sound of my 5.0 long distance at that 2700 to 2800 rpm at 70 to 80 mph. Sounds like it's going to blow to me. I'm currently building 411 x 33" ZF and looking forward to a more relaxed engine.

 

[stokers]

This is just what I needed to hear. Thinking 4:30 gear is the way to go. Since it will mostly be driven on road I'll probably not go any lower gearing. Changing the rear gear first is a good idea just to be sure that it feels right. Thanks you all.

 

[bronconut73]

Let us know how it goes.

 

[needabronco]

4.88s and be done. You know you'll have 35s on day. Ive always said 'don't fear the gear'. Not going low enough gives you a gutless/useless overdrive and ZF's shift like your rowing a boat. If you don't like rowing, give it more gear. Broncos and 302's like around 2500 RPM's at 70 to buck the wind....

 

[sykanr0ng]

If you 'Fear the Gear' then you should swap in a 408 stroker, that way you will have enough power to move a heavy un-aerodynamic Bronco at low RPM.

 

[AZ69EB]

I have efi 302, ZF, 33" tires with 4.88 gears with Dana 20. Good all around Bronco. I can run down the highway at 75 mph with no problem and go slow through the rough stuff. 4.56 would be the minimum starting point I would suggest. If you play off road a lot go to 5.13's.

 

[Ranchtruck]

I was happy with 302, zf, 4.11's, and 32"s up a 5k altitude. Even happier with the 351w on the same combo. Which probably produces sea-level 302 power.

The not fearing the gear leads to annoyance on the other end. My mother has a subaru outback that they geared deep so people wouldn't complain it felt underpowered because they had to downshift on hills. 4.11's 0.87 overdrive and 27" tires. Things over 3k rpm all the time on the highway and I reach for the non-existant 6th gear every time I drive it. Screw that, I'd rather downshift when needed than listen to an engine howl for hours on end.

 

[BUCKWILD]

with a 205 I'd run 4:88's. if you dont have to run on the freeway a lot. but if you do the 4:56 is the better for that.