Axle Gearing Recommendation

[okie4570]

We have been talking a lot of different setups here, started as non-overdrive and has progressed into an overdrive situation. So at this point, what is your exact same setup?

Stock 302, 33" tires, np435, 4.11. I guess I thought we were back to not gearing for the OD as of yet lol.

 

[sykanr0ng]

DaveLev,
How'd this thread get so morphed.?:? I thought maybe someone should bring it back in line.
You weren't asking about overdrive.%)
You were just asking for gear ratio recommendations for your 302/235 powertrain and 33" tires @ 65-70 MPH.
You're really asking a lot of even a good high revving 302 to maintain those speeds with 4.56 gears to do that kind of highway travel.

The thread went some of the way far afield when we discussed changing the transmission out for something more suitable for his intended use of his Bronco.
The OP was a part of this discussion, saying he had others interested in buying the rock crawler transmission he currently had in it.

Realistically, until he settles on which transmission he will end up using there isn't much point picking final drive gear ratios.

 

[muskrat]

I'm running something pretty close to you except for the engine with a few power upgrades (intake, cam, carb, exhaust).

The 3.50 gears are doing fine, but I do miss the torque I was getting with the 30" tires compared to the 33's.

When money allows, I'm going to 4.11.

I will say that the 3.50 gears on the highway is like having overdrive.

 

[DaveLev]

I drove it last night without overheating. So for the first time, I really enjoyed the vehicle on the highway. However, I need help calculating how fast I was going. My speedo is bad. I kind of liked the 3.50, but the rough ride made me think that I'd be okay leaving the gears this way for now until I decide on transmission. But I want a locker now, so I may go ahead and do 4.11:1 with locker just in rear end for now. Doesn't cost that much, and rear end doesn't appear to have been rebuilt ever. Rusty but not leaking.

I have 33" tires, the NP435 trans in 4th gear, the 3.50:1 still in it, and RPMs at 3,100. I think I was going dangerously fast - close to 90. That thing bounces all over the road. The speedo read 70. I was passing BMWs that looked like they were going 75 when I passed them.

 

[Broncobowsher]

Download a GPS app for a smart phone, borrow a phone or hand held GPS if you don't have a smart phone. Too much error with a tach and actual tire size to know what you were really doing.

 

[DirtDonk]

That. Or for a quickie, tag along beside someone you know with a known-good speedometer. Such as a family member running down the road in one of your more modern cars.
A quick phone conversation along the city streets, then another one at freeway speeds and you should be good.
For reference though, you should always get at least one reading at a known 60 mph from the other car, and an indicated 60 mph in your Bronco's speedo. If it can settle down long enough that is.

You were probably doing about 83-85 or so, if your tach is correct.
To be sure about things you should also measure the tire's loaded diameter. That's how it sits on the ground with the full weight of the truck on it.
Lots of "33's" on 15" wheels are only about 31.5 or so.

Paul

 

[DirtDonk]

The app mentioned would be handy to have in the future too. That way you won't have to ask someone to help out each time you mess around with things.

Oh, forgot to ask before. Why would you want a locker?
Planning much off-roading? Or aren't you going to be driving it almost exclusively on the street?

Paul

 

[DaveLev]

Street almost exclusively, but as we are doing gears, and it is a peg-leg now, and we have a lot of dirt driveways and parking lots in this area, would be nice to let my wife do doughnuts properly in the future. Not a need, more of a want, and would increase future resale value. Not air locker type, just clicky/ratchety type just in case.

 

[DaveLev]

Need to revive this old thread...with a stock gauge cluster, 33s, NP435 and 4.11 rear end, which speedometer gear should I put in the transfer case?

 

[bronconut73]

Street almost exclusively, but as we are doing gears, and it is a peg-leg now, and we have a lot of dirt driveways and parking lots in this area, would be nice to let my wife do doughnuts properly in the future. Not a need, more of a want, and would increase future resale value. Not air locker type, just clicky/ratchety type just in case.

What about a Detroit Tru-Trac,
Strong limited slip that operates very smoothly.

 

[DirtDonk]

Need to revive this old thread...with a stock gauge cluster, 33s, NP435 and 4.11 rear end, which speedometer gear should I put in the transfer case?

I'd normally default to the old, "drive it and measure the error so you can know how much correction you need" answer. But anymore there might be enough of us out here with your combo to know for sure.
But that "for sure" part still comes with a caveat. What drive gear inside the transfer case do you have?

Short of counting the spiral teeth inside the t-case, maybe Viper knows what gear should be in a particular case. There were two available from the factory, but I don't know which trucks got which gear and why. Maybe older rigs with 4.56 factory gears got one, or maybe later model J-shifts got a particular one instead? Don't know, but I'm sure someone does.

With my combo of 32" tires and 4.11 gears I seem to remember having to use the smallest driven gear available at 16 teeth. And that was to correct only a 5 or 6 mph error.
But I have no idea what drive gear is in my t-case. Never counted the teeth even when I had it apart. Since my speedo was spot on, it never occurred to me that it might be nice to know.

Good luck.

Paul

 

[DaveLev]

Thanks.
I did some research into my own rig, and according to Marti, it was ordered with the locker option on the 3.50:1 I have. So that saves me a little bit of money when I go to do the gears. Leaning towards AOD conversion. Not sure about Atlas II as well. Everything such a tight fit, and the engine will probably die soon anyway.

 

[DirtDonk]

You may already know this Dave, but just for clarity, or for others reading this down the road, the option was not a locker. It was a limited-slip which is a totally different animal.
The marketing guys for all the O.E.'s used to just love using the word "lock" or some variation thereof in their naming game.
But it's a clutch type limited slip differential nonetheless.

Which means, lucky you, that you should at least factor the cost of a rebuild with new clutches and any other wear items that might be inside that diff case.
Unless you know it's in great shape, it would be money well spent to do it at the same time obviously.
They wear out just from normal driving (going around corners) but could also have been rebuilt in it's previous life already.

Paul

 

[DaveLev]

Drat - did not know what they came with. Sad face. Will plan on rebuilding or replacing when I do gearing.

 

[DaveLev]

Will rebuild the limited slip when I do the swap.
Before I bite the bullet and do the 4:11 ring & pinion, will this also be a good choice (remember my 33 x 12.5 x 15 tires) when I switch from the NP435 manual to an AOD automatic? Thanks for reading!

 

[sykanr0ng]

Will rebuild the limited slip when I do the swap.
Before I bite the bullet and do the 4:11 ring & pinion, will this also be a good choice (remember my 33 x 12.5 x 15 tires) when I switch from the NP435 manual to an AOD automatic? Thanks for reading!

No.
You will find yourself wishing for 4.88 gears then.

 

[5001craig]

I'm pretty sure you are going to need a new differential case to go from 3.50 to 4.11.

Unless you get a set of 4.11 gears made (thicker I believe) for the 3.73 and below differential case.

 

[DaveLev]

Oh joy...you saying these early ford 9" are different sizes now, too? Geez...does the fun ever stop? I find it very hard to believe that at least 4.11 weren't available when the 3.5 option came from the factory.
how do I uncover which ford 9" I have?

 

[Broncobowsher]

The 9" uses the same differential case all the way from the 2.73 highway cruiser gear all the way dow to the 7.17 pinion only the size of your thumb gears.

It is the Dana axle that has different carriers depending on the ratio.

 

[DirtDonk]

And whenever gear ratio choices are confusing, just do the rear anyway. That way if you don't like it, you didn't just spend double to find that out.

It might not be as efficient in down-time to do one at a time, but this is a very critical moment balancing on top of that fence when deciding which way to go.
There are actually engine combinations that might like 4.11's with 33's and an overdrive, even in a Bronco. But most here are happier with 4.56's and 4.88's with that tire/transmission combo and their particular engines.
It's all about the powerband, final weight, actual tire size, how fast you drive (we know how you like to test, but how is this thing going to be driven?), what road conditions and all that, coupled with the aerodynamics (or lack thereof) of the EB.
Most of our engines won't pull well in overdrive at 2000 to 2200 rpm in a Bronco. They like 2500-2700 much better. But if your engine is a real stump-puller or just running sweet down low, you "might" be ok with 4.11. We just don't know out here other than to simply compare with what others have said. But like Broncos, every one of us is different too.

So just do the rear end first. Drive it and see how you like it and then decide what to do.
Just don't put it in 4wd until you get the front swapped over.

Paul