Axle Gearing Recommendation

I have a stock engine, NP235 (?) 4 speed transmission, Dana 20 transfer case, and 33 x 12.5 x 15 wheels. Currently it has the 3.50 gears with factory (rebuilt) Dana 30 It will be used for street driving only, no rock crawling.

I know by research that many of you are still running 3.50 with similar wheels & transmissions, and have no overheating or overrevving on the highway or underpower on the street.

We hope to go up to 85 MPH max, and most driving will be 65 -70 MPH range.

What gearing do you suggest? Several have mentioned 4.11, others 4.56.

What do you think?

I have the same setup as you, running the 4.11s. 15 miles into town, running down the highway at 65, I don't want 4.56.

It also does fine in the rocks with 4.11.

What okie said.... Ran the same set up with stock gears ..... On the highway it was just right.... 4.11 at the most with that combo

Thanks gang - if you haven't already, please use the polling feature if you can so graphically we can see what the consensus is. I really wish I did 4.11 when rebuilding my dana 30. My 3.50 was worn out, and cost 300 or so to replace the 3.50 stock ring and pinion. Will probably have to pay $1000 to replace front and rear I'm guessing :-(

I voted 4.11 too, but what about the future (to avoid doing it a third time!) with the transmission?
Your NP435 has the granny low that you don't need for a street rig and it's a clunkier shifting tranny than some other more modern ones.
That first/low gear has probably saved you a time or two with the current 3.50 setup I would think, but if you ever decide to go with something different, with perhaps an overdrive, then the 4.56 will come in very handy with your stock motor.

If you had EFI I'd say you could get away with taller gearing, but with a stock setup in a Bronco, you would not even be able to fully utilize 4.11's with an overdrive trans.

Just thinking ahead here. For the time being, with your current setup, I'm still firmly in the 4.11 camp.

paul

Why do you have a rock crawler transmission in it if you are never going rock crawling?

For a purely street/road Bronco the NV3550 makes more sense.

sykanr0ng said:

Why do you have a rock crawler transmission in it if you are never going rock crawling?

For a purely street/road Bronco the NV3550 makes more sense.

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Or an AX-15

I vote for the 3:50's Mine is about like yours. But My motor is the cummins diesel. I too have the NP435 & DANA20 WITH 285/75'S R16.
If I had 4;11's I don't think I'd every get into town. I can only run about 55mph.
But luckily for me I use mine on the farm so I'm even in low range about 50% of my time.
With my 3:50's I like low range & 2nd & 6rd gear to cruise the pastures checking my cows.
... I keep thinking I'd like to have 4:11's until I head into town.

The NV3550 or AX-15 paired with some 4.56 gears would be great IMO, but pretty spendy at th end of the day. I might just throw a RAT/RAN 3-speed (can be found for free all day long) back into it with a floor shifter and call it a day with the 3.50's. It may not be ideal, but it'll work just fine for what you're asking it to do. I've run mine with 33's, 3.50's and the manual 3-speed for a while, but I have a torquey 351W motivating it down the road...it does quite well and hangs with traffic at 75 MPH on the interstate and still can outpace most Civic's off the lights if I want it to.

Apogee said:

The NV3550 or AX-15 paired with some 4.56 gears would be great IMO, but pretty spendy at th end of the day. I might just throw a RAT/RAN 3-speed (can be found for free all day long) back into it with a floor shifter and call it a day with the 3.50's. It may not be ideal, but it'll work just fine for what you're asking it to do. I've run mine with 33's, 3.50's and the manual 3-speed for a while, but I have a torquey 351W motivating it down the road...it does quite well and hangs with traffic at 75 MPH on the interstate and still can outpace most Civic's off the lights if I want it to.

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That too makes more sense than an NP435 that the granny low never gets used.

DaveLev...

With your tranny, tires, and planned use, I can't vote for any of your options, so I selected "other".

The 3.50s are too high, and 4.11s are too low. I know there are those telling you "don't fear the gear", but here's the world according to Blu...

Your 235 is basically a three speed with a granny low. The second gear (starting gear) is a good deal lower than the first gear of a stock three speed. But with 33" tires, you'll still need lower gears than those 3.50s, or your clutch is really going to suffer.

4.11s? At the highway speed you're wanting, it's going to drive you crazy.

I did a test, the other day after reading more from the "don't fear the gear" guys.
I have 4.11s, 32" tires, and a NV3550.
While driving along at 65 mph at 2200 RPM in 5th gear, I shifted down to 4th which is a 1 to 1 ratio, just like the high gear of your 235. The engine now has to run at something just over 3000 RPM.

The test results? Sure the engine may have been happy, but I wasn't. The engine actually sounded happier in 5th if you ask me. And 65 MPH on the interstate is going to get you run over here.

With your lower second gear, and highway usage, I think you'd be happier with 3.73-3.90 gears.

You were asking about gearing weren't you??:?

Great, fun replies everyone. I have had this rig for 6 months, first Bronco, and having a rough experience with it so far. I did not do the swap to the NP235, it was in there already. I've never taken it offroad yet - haven't tested the trans case or manual warn locking hubs yet - and the granny low is great for idling up a steep driveway sans throttle - just crawls right up, no gas needed. Otherwise, yes, I start in 2nd all the time, and get it into third, but I think I can do about 55(?) in 3rd gear and the 4th just drops the RPMs down to the 2,000 range at 65 MPH or so. That part I guess tells me I have an okay setup.

If the concern with this trans and stock engine and 33x12.5x15" tires is that the 3.50:1 gears will burn out clutch/transmission problems, then I could see the argument for 4.11:1 However, it sounds like based on some posts that the RPMs for 70 MPH would be too high. I confess the engine is loud at 3,000+ RPM, IMHO.

Honestly the plan is to go with an automatic at some point without heavy modifications, so probably the C4. Until I can afford this swap, I might as well consider changing the axle gears.

I should note I already have 2 interested buyers for my NP435. It is a solid truck-like transmission. Like driving a 5 ton military vehicle. The throw on the shift lever is huge - like 18" between 2nd and 3rd. May be closer to 22". Full upper body workout. Not very streetable transmission.

If your engine pulls strong enough at 2000 rpm to pull you along at 65 and you're happy with it, don't have to downshift every time you hit an incline or have a slight headwind, then you should be fine.
However, I don't know of any year stock Early Bronco V8 engine that was happy doing that. I know mine would not have. With that much wind resistance I would think it'd take at least one downshift just to be able to accelerate.

So either your engine is not stock, your tachometer is giving you the wrong info, your speedo is giving you the wrong info, or you just happen to have a very strong engine in the lower rpm range.
I know I'm talking in absolutes again, like I know every Bronco ever built and all circumstances, but 33's and 3.50's all happily strumming along at 2000 rpm at 65 mph just doesn't sound normal to me.
In fact, it doesn't sound correct either. Shouldn't it be closer to about 2300 rpm? If so, that would be a good range for a decent running engine as long as the hills weren't too steep. Still too low for my engine, but maybe mine was a bit tired.
Is this a "33" tire, or a metric like a 265x75? Just curious, as maybe your tire diameter is different from my experiences being metric instead of a flotation size.

Were you asking about the gear change because you'd read it would be a good idea? Or were you thinking yourself that the truck was pretty sluggish as it sits now?

DaveLev said:

I know by research that many of you are still running 3.50 with similar wheels & transmissions, and have no overheating or overrevving on the highway or underpower on the street.

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Well, I agree with the no overheating or overrevving conclusions, but not underpowered? Most of the threads on the subject of gearing were brought up precisely for that reason. Lack of power and accelerationability.

DaveLev said:

We hope to go up to 85 MPH max, and most driving will be 65 -70 MPH range

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Define max. Do you want to go 85 at the redline, or just be able to pull it if needed? I'm guessing that the cruising rpm is more important, since that's where you'd spend more quality time. And just let the max speed fall where it may. Right now, you should be somewhere just north of 3000 rpm at 85 I would think. Maybe as much as 3200? But that's no big deal for the engine.

I could go 85 in mine with 32's and 4.11's with no problem. Sure, it was revving at probably 3750 or more rpm, but that's no danger to the engine. They start to kind of run out of breath at about 4500 rpm anyway in stock form.

So anyway, just curious how yours is feeling right now with the tall gears and tall tires. The trans change is not a bad idea. Especially if you have a ready buyer for the old one.
Remember too though, that a typical C4 is going to raise your cruising rpm approximately 200 rpm or so at freeway speeds. So if you're using a calculator, add 200 rpm to your final answers.

Have fun!

Paul

Oh, and if in all this you don't have an actual tachometer, you can't go by engine sound alone. Just the slight variations in exhaust type/style can make a HUGE difference in your perceived engine speed.
I thought I was revving mine to the moon when I first bought it. Changed the exhaust to a completely different setup (mufflers vs glass-packs) and thought I'd changed the gearing instead!

Definitely good to have accurate and repeatable info. Many a speedometer is not calibrated for 33's, so if you have a GPS unit it's good to compare numbers. If yours is off, there are different driven gears available for the speedo cable that might work.

Paul

I went 4.11's with my 32's and after doing so I like it SO much I kind of wish I had gone 4.30's I made the classic mistake of "Fearing the Gear"

Tim

If you plan to switch trannies to a C4, then don't do anything now.

Your Transmission choice will most likely change. Which will then cause you to rethink your gearing choice.

My little 170 needs at least 4.11's to start on a hill at a traffic light.

I couldn't imagine having 3.50's, you would be replacing clutches more often.

I remember my first Bronco having 3.50 gears and 31s. Second had 4.11s and 33s. Drove both everywhere, in town, on the highway, etc. Both had manual transmissions.

The 4.11s with 33s drove so much better than the 3.50 with only 31s. I really wanted larger tires than 31s, but I could barely live with the gearing and could not accept the added loss of going to 33s. And this is from a person who likes to lug an engine down low.

Anyone who claims that there 3.50 gears and taller tires "drives just fine" has not experienced the added joy and comfort of properly geared axles.

Broncobowsher said:

I remember my first Bronco having 3.50 gears and 31s. Second had 4.11s and 33s. Drove both everywhere, in town, on the highway, etc. Both had manual transmissions.

The 4.11s with 33s drove so much better than the 3.50 with only 31s. I really wanted larger tires than 31s, but I could barely live with the gearing and could not accept the added loss of going to 33s. And this is from a person who likes to lug an engine down low.

Anyone who claims that there 3.50 gears and taller tires "drives just fine" has not experienced the added joy and comfort of properly geared axles.

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Going to 4.11's was like a 50 hp jump in performance.

Thanks for replying everyone. I see 28 responses in the poll, too. If you haven't voted yet, please do so!

I do not know the actual speed I'm going. The tach and all gauges are new, and the tires are true 33 x 12.5 x 15 on 10" wide rims BFGs mud terrain that are tall and fat. The speedo is also new - all gauges autometer - but the gear into the transfer case has not been changed since I went to 33s.

As far as sluggish and power goes, on a long grade uphill even only at about 5% grade it does want me to push further down on the gas, and I have had to downshift for sure. On level ground, I usually go the speed of traffic which is 65-70 MPH 90% of my driving. I don't believe the rigs next to me are going slower than the speed limit - where I live people either go the speed limit or 2-5 MPH over max. 15 minutes away from my small town the interstate turns into 80 MPH, but most go 82 MPH. I like to go the speed limit, not speed over it, and I can't imagine needing to downshift to 3rd at 80 MPH - not sure if possible. I don't like to revv the engine, and frankly don't recall on the freeway exceeding 3,000 RPM ever. The tires are tall, the gears are 3.50:1, and the tach is accurate. My recollection of the RPMs at various speeds - 65 MPH, 80 MPH - may be inaccurate, but I have illustrated the speeds I typically drive and want to continue to drive it. Don't care about MPG or fuel cost - I care about the engine surviving and me not burning out the engine or trans.

As far as the 3.50:1 with 33" tires and the 4 speed NP435 trans I have being the right transmission, as mentioned I bought it this way and hope to convert to auto someday, but not in the budget this year whatsoever. I can afford gearing soon, though.

I don't know that I'm burning out any clutch with this setup, and not sure why people think I will. Is it because the weight/brick-like nature of a lifted bronco and rolling resistance of the tires and high gearing that would put too much load on the clutch plate and flywheel? Is it because I start in 2nd gear instead of the rock crawling 1st? I don't feather the clutch at lights and seldom use it for downshifting. The manual 4 drum brakes work pretty darn good surprisingly in this rig. Is the concern that the motor is so powerful and torquey (made up that word) and the engine/tires/gears will resist the powerful bone stock 289/302 I have in this 1968 and cause the clutch to slip?

Seeking to understand.