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why different gearing front to back

culp

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Mar 21, 2008
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6
why is dana 44 front 3.54 geared and 9" rear 3.50 geared. am i going to break something or am i just not educated here? any knowledge appreciated.
 

Tito

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Dont sweat it, just the way it is because of how the axles are built. They are different sizes (carriers) so tough to get the exact ratio but they are close enough.
 

thegreatjustino

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x2 a very common discrepancy. Front Dana gears are 4.10, rears are 4.11 from what I understand. I have always been told that as long as they are within .05 of each other, they are fine.
 

Apogee

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I've always been told that anything within 2% front to back should be fine. There are usually several mathematical combinations to get close to a certain gear ratio, but not exact within the mechanical limitations of the diff design. A Ford 9" use a 10 tooth pinion and 35 tooth ring gear to get a 3.50 ratio. The Ford 9" diffs are limited to running a 6 to 15 tooth pinion gear and 31 to 45 tooth ring gear. Below is a list of the gear ratios and how they're achieved for the different applications based on some notes I had...I'm sure a Google search would turn up the same info:

Ford 9:
Ratio - ring/pinion
2.80 - 42/15
2.86 - 40/14
2.91 - 32/11
2.94 - 47/16
3.00 - 39/13
3.07 - 43/14
3.25 - 39/12
3.33 - 40/12
3.40 - 34/10
3.45 - 38/11
3.50 - 35/10
3.55 - 39/11
3.60 - 36/10
3.70 - 37/10
3.75 - 45/12
3.82 - 42/11
3.89 - 35/9
4.00 - 36/9
4.11 - 37/9
4.22 - 38/9
4.33 - 39/9
4.44 - 40/9
4.50 - 36/8
4.56 - 41/9
4.63 - 37/8
4.71 - 33/7
4.86 - 34/7
5.00 - 35/7
5.14 - 36/7
5.29 - 37/7
5.43 - 38/7
5.50 - 33/6
5.67 - 34/6
5.83 - 35/6
6.00 - 36/6
6.20 - 31/5
6.33 - 38/6
6.50 - 39-6

Dana 44:
Ratio - ring/pinion
2.87 - 43/15
3.00 - 45/15
3.07 - 43/14
3.23 - 42/13
3.31 - 43/13
3.50 - 42/12
3.54 - 46/13
3.73 - 41/11
3.92 - 47/12
4.09 - 45/11
4.27 - 47/11
4.56 - 39/8
4.78 - 43/9
4.89 - 44/9
5.13 - 41/8
5.38 - 43/8
5.89 - 53/9

Keep in mind that just because something is mathematically possible doesn't mean that the gears are readily available. There are several preferred gear ratios for front to rear matching as well as optimizing gear strength. The larger the pinion, the stronger the gear...hence the 4.56 Ford 9" ratio being the obvious choice over a 4.50 or 4.63. HTH.
 

DirtDonk

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What they all said culp.
Another thing along this subject line though, is why it's not generally recommended to run in 4wd with hubs locked on hard/dry pavement. At least in older four-wheel drive vehicles with part-time 4wd.
You've probably heard or read this at some point, but it's basically because of those odd gear ratios coupled with the rigid connection between the front and rear systems. Nothing to worry about under conditions where the tires can slip, such as dirt, sand, snow or wet slippery pavement, thereby releasing any built up tension.
Those same odd ratios are enough to cause some binding in the transfer case if the tires can't slip. Such as on dry pavement.
Even slight differences in tire size due to wear or air pressure can be culprits too. Add uneven tire wear to a couple of different ratis and you increase the chance that internal binding is going to make it very hard to shift back out of 4wd without first releasing the tension.
In some extreme cases, potential damage to components is possible.

Though I've never experienced any damage of my own, or even known anyone who's had problems, I still don't run it in 4wd (with locked hubs) on the pavement unless there's a real good reason. Like pulling a stump out or testing your system, where you're only going a few feet. Stuff like that.

Sorry if I'm just re-hashing things you already knew, but figured this was a good place as any to bring the subject back up for those that never had the opportunity to read an owners manual. Or wouldn't have even if they'd had the chance!

Paul
 

chrlsful

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Oct 21, 2009
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1,344
clup,
I heard they hadta B different so they wouldn't mesh. Ie if same exact gears frnt/rear and tires rotated just right, a tooth in the front could match a tooth in the back and they'd have a fight that could chip 1 off (or may B both).
 

markperry

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clup,
I heard they hadta B different so they wouldn't mesh. Ie if same exact gears frnt/rear and tires rotated just right, a tooth in the front could match a tooth in the back and they'd have a fight that could chip 1 off (or may B both).

X2 on that! Plus you would periodically your your truck in 4wd on pavement to keep the gears lubricated?
 

chrlsful

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Messages
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<periodically your your truck in 4wd on pavement to keep the gears lubricated?>
Yes, I would agree, 1X a mo. into 4w for a little bit, but no, I wouldn't do it on pavement, as suggested above. The ol horse would prob appreciate even a 500 ft. jaunt that 1X p/mo.
 

Broncobowsher

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clup,
I heard they hadta B different so they wouldn't mesh. Ie if same exact gears frnt/rear and tires rotated just right, a tooth in the front could match a tooth in the back and they'd have a fight that could chip 1 off (or may B both).

I know of many 4WD vehicles that do have matching gears. So matching that the same ring and pinion fit front and rear. That don't fly.

As for being all paranoid about different ratios, have you ever looked at the paths traveled when the vehicle makes a turn? The front axle travels a much greater distance then the rear. That is why we have part time 4WD and not full time 4WD. Full time those different paths would require some sort of equalization. NP203 did it with a center differential. Newer stuff does it with eletronics and a clutch pack in the transfer case. But the simple part time 4WD you only use when traction is very low. At that point you just slip a tire. Since you have 4WD there are 3 other tires still moving you. Slip a tire in 2WD, not you are looking at getting stuck.
 

22213evl

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Rio Rancho N.M.
clup,
I heard they hadta B different so they wouldn't mesh. Ie if same exact gears frnt/rear and tires rotated just right, a tooth in the front could match a tooth in the back and they'd have a fight that could chip 1 off (or may B both).

not exactly true,
dana dosen,t have a 4.10 ratio for the 44 so it's 4.09
ford 9" ratio to match is 4.11

markperry
X2 on that! Plus you would periodically your your truck in 4wd on pavement to keep the gears lubricated?

not true.
the oil in the tc splashes in two wheel drive the same as 4.
 

blubuckaroo

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Ridgefield WA
Ford even claimed the slight mismatch was for traction.%) The truth is that Spicer and Ford ratios just don't match up. Purely economics (cheaper).
When I had 3.54 front and 3.50 rear the gear bind was pretty bad if you got on pavement. Probably since the rear was driving faster than the front and crowding the gears. Now that I've changed to 4.09 front and 4.11 rear the gear bind hardly happens at all since the front is now pulling the rear and also the mismatch is less.
 

DirtDonk

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And when someone says to "run it in four wheel drive" or "lock the hubs" occasionally to keep things lubed, they're not telling you to fully lock it in. Or, if they are, they probably specify doing it in a loose traction situation or, if on the pavement, just don't do it for long.
You EITHER put it in 4wd and leave the hubs unlocked, OR lock the hubs and leave it in 2wd. That way you're turning all that stuff but not locking things together and causing a binding issue.
Same thing happens either way. Almost. Either way, you're turning some of the axle gears to spin up some lube in the diff and you're spinning the front driveshaft to keep things all nice and loosey goosey.

In adverse conditions many people just leave their hubs locked all season, or while they're in said conditions, and simply put it in and out of 4 wheel drive when needed. Saves you from having to get out to lock the hubs in the snow or driving sleet!

I do both occasionally (but at separate times of course) just for fun and to see if the hubs have gummed up or if the transfer case has somehow magically become hard to shift like so many others are.

If you needed to put it in 4wd to lube the transfer case though, we'd all have toasted cases because the rear main output bearing and shaft, which require a fair amount of lube to keep happy, would only get it in 4 wheel drive. And that wouldn't be very often for most of us.
By the same token, the front output and gears are almost always in a constant bath of lube, so they're not in any distress no matter what you do.
The intermediate gear and associated parts might benefit occasionally, perhaps, but it's probably getting a decent quantity of that stuff that's lubing the output shaft and draining back down as you drive.

Anybody with one of TOFIC's cleargearz covers verify this? Be interesting to watch video of a Dana 20's internals while driving!

Paul
 
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DirtDonk

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Ford even claimed the slight mismatch was for traction.%)

I remember that too. Can't remember if it was in a magazine or one of Ford's pamphlets, but they said that the front tires would turn faster so as to "pull" the truck forward when in 4wd and keep things more straight when climbing.
Made sense to me at the time, but there are certainly going to be times when that's not quite so desirable.
But then again, like everyone is saying, the difference is so minimal that you'd have a hard time testing the theory.

Putting a front 3.73 in with a rear 3.50 or .4.11 however, now THAT would be a problem.

Paul
 

DirtDonk

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clup,
I heard they hadta B different so they wouldn't mesh. Ie if same exact gears frnt/rear and tires rotated just right, a tooth in the front could match a tooth in the back and they'd have a fight that could chip 1 off (or may B both).

Like the others said, it doesn't happen that way. There is no "matching of teeth" going on since the teeth are all the same. Sure, the gears are round and just keep going in circles, so could at some point match up to a zero point, but only if there was one, which there isn't.
There is no difference between one tooth and another. In other words, there is no such thing as tooth #1 or #2 or #3 and so on, so the front can't ever rotate just right to be on the same tooth as the rear. They're all the same already.
And in some vehicles, like my '79 F350, with Dana 60's at both ends, the gear ratios are exactly the same right from the factory. In my case, 4.10's (as opposed to the Dana 44's 4.09) at each end.

Someone may have mixed up a couple of different scenarios when they told you that chrlsful. There are certain ratios that the manufacturers (especially GM) learned to avoid because at some point the number of teeth on the pinion gear, rotating against a specific number of teeth on the ring gear, created a harmonic vibration that caused a very annoying hum/rumble through the body. Might be fine for a mud-bogger, but not grandma in the station wagon.
The other scenario might be the larger differences we were talking about before. If you get a big enough difference, you can build up enough tension in the system (if it's not capable of releasing it) to break a gear.

Might have just got the two mixed together somehow?

Paul
 

Apogee

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...Someone may have mixed up a couple of different scenarios when they told you that chrlsful. There are certain ratios that the manufacturers (especially GM) learned to avoid because at some point the number of teeth on the pinion gear, rotating against a specific number of teeth on the ring gear, created a harmonic vibration that caused a very annoying hum/rumble through the body. Might be fine for a mud-bogger, but not grandma in the station wagon...

Paul actually brought up an interesting point with respect to hunting versus non-hunting gear ratios, if that is indeed what he was referring to. When you have gears that are both evenly divisible by the pinion tooth count (for example 9/36=4.00 ratio), you have what is considered a non-hunting gear set, meaning that the same pinion gear tooth contacts the same ring gear teeth every time during operation. This can lead to funky wear patterns, harmonics, etc over time. I've read that the non-hunting gear sets should be timed per the timing marks on the gears from when they were lapped together during manufacture, but I've never seen the marks myself.

Generally, hunting gear ratios are considered more optimal for even, consistent wear throughout the life of the gear set.

Tobin
 
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Broncobowsher

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There are also semi hunting gear ratios. 3.50 is an example. A single tooth of a ring gear will contact only 2 different teeth on the pinion. Full hunting will contact all of them and non-hunting will only contact 1.

The harmonics thing generally is only a factor of the number of teeth on the pinion regardless of the number of teeth on the ring gear. Engines usually produce 2,3 or 4 pulses per revolution. You generally don't find pinion gears with the number of teeth divisable by the number of power pulses from the engine to avoid harmonics. It can be done, usually it won't be an issue. But good engineering pratices generally avoids it if possible.
 

Steve83

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...the front tires would turn faster so as to "pull" the truck forward when in 4wd and keep things more straight...
It's about steering - not going straight. With the higher (numerically lower) front ratio, the front end will pull itself around curves better than if the rear is able to keep up (same ratio).

Obviously, any ratio that can be made for one axle brand/model/size can be made for any other. So considering the number of axles Ford ordered (orderS) from Dana/Spicer, if they had wanted matching ratios F&R, they'd have gotten matching ratios. And for many axles, you can now find aftermarket gearsets in ratios that were never offered by the factory. So it was never an issue of "that ratio isn't available for this axle" - Ford got exactly what Ford wanted: mismatched ratios, and always 0.01 higher in the front.

I've done a VERY little off-roading (in a gravel parking lot) with 3.07F & 3.55R; talk about turn-on-a-dime! ;) I could almost spin in place. :D
 

DirtDonk

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While I can't actually dispute that (besides, it's logical enough), GM and Chrysler engineers didn't see it that way and Ford wasn't the only Dana customer. And even if so, then Ford must have changed their minds later, because the Ford Sterling and 8.8 axles match the Dana gears down to the last digit.
And the Dana/Spicer axles were REAR drive axles first anyway (except for the high-pinion versions of course), if I'm not mistaken (which I could be). Before they were front axles for four wheel drive trucks, a Dana 44 and 60 at least, were rears. So the gear ratios already existed before they were put in the front of anything.
Do we know when the Ford 9" was first introduced? Maybe they were designing the gear ratios for the 9" to be that shorter ratio that we're discussing, but since I think it first showed up in passenger cars, I'm not sure how that all would tie together either.
At least that's where I remember seeing these different axles first.

As usual, more stuff to muddy up the clear waters with.

Paul
 

sprdv1

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Dont sweat it, just the way it is because of how the axles are built. They are different sizes (carriers) so tough to get the exact ratio but they are close enough.

DITTO...!!! :)
 

Steve83

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Maybe it's just too early in the morning for me, but I don't follow what you're trying to say. ?:? But I can absolutely agree that you're right about one thing: GM & Mopar don't build things the way Ford does! ;D
And the Dana/Spicer axles were REAR drive axles first anyway... So the gear ratios already existed before they were put in the front of anything.
Yeah, but the gears are different for front axles because they're (usually) reverse-cut, so they'd still have to decide what ratios to offer for the new front versions of the old rear axles.
 
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