Axle Gearing Recommendation

[DirtDonk]

I find it very hard to believe that at least 4.11 weren't available when the 3.5 option came from the factory.

I think you were missing the point of the carrier change. In fact 4.11's and even 4.56's (some years and engines) were available from the factory during that period.
Just that if your front end has the 3.50-ish combination, your front "3-series" carrier (3.54 actual ratio I think?) needs to be changed to the "4-series" (3.73 and down, vs 3.92 and up split for a Dana 44) to accommodate the 4.11-ish (4.11 rear, 4.09 front) gears.

OR, you just need to buy the thick gear set mentioned, to use your existing carrier. Not a big deal and, as far as I remember, virtually the same price for a thick gear vs the standard gear.
So if you're changing gear ratios anyway, or adding some different type of differential, then it's not really a stumbling block either way.
Money-wise, or time-wise.

how do I uncover which ford 9" I have?

Might be a tag still under one of the bolts. If not, and you can't tell from decoding your VIN (someone here might be able to do that for you) then there are easy tests to do this too.
Or you can change the oil in the front by pulling the cover, and count all the teeth at the same time. Ring gear divided by pinion gear equals gear ratio.

... Geez...does the fun ever stop?

No.

Paul
(edited above to reflect info for a 44 and not the 30 that I forgot was still present)

 

[DaveLev]

Thanks Paul. Marti report shows 3.50 for my diff, and it is a rebuilt Dana 30 front end, and I heard something about a carrier being wrong somewhere else.

My engine is stock, and does terrible in 4th with the NP435 right now when going 50 or so. It does better 70 MPH plus - not sure of RPMs, though - tach is out right now while I replaced the dash.

Because we are going to AOD, perhaps the 4.56 or 4.88 is best.

I'm guessing the recommendation will be with my stock engine and AOD to go to 4.88, but if more high performance engine, the 4.56. Am I correct?

 

[NYLES]

ID go 4.88, them 35s aint too far in your future!

So says my magic ball!

 

[DirtDonk]

Pretty much, yes. However, if you even think that larger tires could be in your future, you might go big with the gears now. Instead of doing it again after the larger tires are installed.
Check out some of the gearing with overdrive threads and you'll see a distinct trend.
A very few are happy with their 4.11's, some love their 4.56's and still others are digging their 4.88's. It's all about where the engine is happy and if you drive it in that range.
Or, for those that do intend to go off-roading in their rigs still, they are typically the ones that err to the low side (high numerically) and will often opt for the next step up just because of the better off-road experience that lower gears afford.

Paul

 

[DaveLev]

Fair enough. But with zero off road driving to date, and this is a street rig for my wife who already has trouble getting in and out in heals driving it with zero body lift and 3" suspension and 33x12.5x15 setup..and a stick shift..I don't forsee 35s on this rig in the future. If you do AOD conversion you don't need a body lift I hope. I will be looking for an auto trans soon - over winter - and be only looking at options that are support zero body lift.

If however a body lift is required, then bigger tires, a side step, and 4:88 gears may be in our future.

It may be that misery loves company, though - perhaps those with 4.88:1 really wish they had done 4.56 or 4.11. Buyers remorse. Remember this is a street rig for the wifey...her daily driver.

 

[DirtDonk]

Well that's the deal. No off-roading and only street driving would generally go with the taller of two gear choices. But there can still be a sweet spot for the engine just for acceleration purposes. You might not need to crawl over rocks, but you'll still need the engine to pull strong for best driving experience.
And sometimes even better fuel economy (Yeah, when the planets align!) for keeping the engine in it's torque band.
Which is why you might still find a 4.56 is better than a 4.11 in your case.

Good luck. Definitely check some of those other discussions. Lots of good input if you read between the lines regarding what the person commenting actually likes to do with their rig, and if perhaps their preference is hauling the family to a campsite, rolling down to town for some ice-cream, or jumping sand dunes.

Paul

 

[NYLES]

Id pick the tranny then the gears, I have 5.13 and wish they were 5.38s. Ive done 3,50s with 33s, 430s with 35s behind a C4, 5.13s are behind a ZF 5 speed.

You really need to know which tranny BEFORE you pick your gears. It makes life easier and price bout the same, and time is on your side.

 

[5001craig]

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.

Thanks for the correction. My apologies.

 

[sykanr0ng]

Thick gears for the Dana 30 are made for high pinion J**p diffs, you will need another carrier.

The Dana 30 break is 3.54/3.73

http://www.crawlpedia.com/thick_gears.htm

 

[DirtDonk]

Thanks. Forgot we were talking about a 30 even though he mentioned it after.
I added that bit for clarification in one of my posts.

Paul

 

[Mtgrizzlymn]

I want a nv3550 for my mild 302. It's on bfg35x12.50x15 inch tires. Right now according to tach I'm around 2900 at 63 mph gps 60 on gauge. Not sure what gears but power and driving is good all around now just want lower rpm on highway so I can go a lil faster. Any ideas on my gear ratio and if I'll be happy with this conversion. I'm a highway daily driver guy


Sent from my iPad using Tapatalk

 

[DirtDonk]

How much faster are you wanting to go, and for how long?
That current gearing should be good for 70 or so all day long, without stressing anything but you.;D
These things will spin at 3500 rpm all day long and not complain. It may not sound great depending on your exhaust and fan setup, but the engine is working fine.

But it sounds to me like you're geared pretty low already. If your tach is correct, and your tire diameter is more in the 34" range, then you're already running 4.56's. If so, an overdrive is just what you need and your engine might just be happy to pull your Bronco through the air at speed with that setup.
Using the same theoretical specs, you should be humming along at 75 mph at about 2600-2700 rpm.

No need for changing then, until after you've done your trans swap and see how you like the rpm at that point (in overdrive). If it's perfect for your driving style, bingo! If not, it should be pretty close to what most want, but maybe one size lower would put you in the sweet spot.

For accuracy, measure the rolling diameter of the tires to make sure. That's from the top to the ground with the full weight of the truck on them. Then we can get some accurate "assumptions" going.

Paul

 

[sykanr0ng]

The overdrive ratio of an NV3550 is 0.78 so multiply the RPM that you are at now by that 0.78 and the result will be where you will be running with an NV3550 in fifth.

Unless your oiling system is hosed you can't run a 302 or 5.0L fast enough to hurt it.
It may bother you, but it won't bother the engine.