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Mis-matched gears

centex77

Full Member
Joined
Oct 31, 2017
Messages
183
The previous owner of my truck said it had 4.10's in it. Doing the old fashioned driveshaft rotation count and I come up with 4.10's in the rear and 3.73'ish in the front. I've been told all of my life that you never mix gear ratios front to rear but I've seen cases of people doing it and people older and wiser than me with vehicles has said it's not a big deal. So before I go and drop the coin on new gears, what say ye? This thing will (sadly) be mainly road driven with maybe a little light trail work at the deer lease so 4wd use will be very rare.
 

broncodriver99

Bronco Guru
Joined
Jan 27, 2008
Messages
4,780
Loc.
Glen Allen, VA
They need to match. If you are a surface with slip it may not be that big of a deal but if have traction on all 4 wheels in 4wd it will bind up the drivetrain and could break something.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Get it as close as you can, but a 3.50 rear would use a 3.54 front, and a 4.11 rear would use a 4.09 front.
If I'm not mistaken, a 4.56, 4.88, and 5.13 front and rear are a match.
 

yakelys69

Sr. Member
Joined
Nov 20, 2006
Messages
732
It's not much work to pull the cover of the front dana 40 to verify the ratio. It's usually stamped on the ring gear.
 

Apogee

Contributor
Bronco Guru
Joined
Nov 26, 2005
Messages
6,033
You want them to be within a couple percent of one another...if they're not, and you run on any high traction surface, say goodbye to your transfer case and/or driveshafts.

My brother upgraded his Toyota and when with 5.29 gears front and rear, only to find out that the front's were mislabeled 4.88's...what a PITA. That thing couldn't get out of the driveway in 4WD without binding and scrubbing so hard, that the issue was obvious at once.

Other than competition mud racers who have in the past run numerically lower gears up front to increase tire speed, I've never seen or heard a good argument for staggered front/rear gear ratios.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
In 2WD, not a concern.

Before you drop any coin, drop the cover and read the engraving on the ring gear or count the teeth. 3.73 is not a common ratio in a Bronco. Someone would have to put that gear in. Never a factory option (in a Bronco). I'm betting the count the turns method is off. A little backlash being confused for rotation.
 

sanndmann3

Bronco Guru
Joined
Jun 13, 2007
Messages
1,774
I'm assuming the tires are all the same size... if thats the case, like others said, the 2 R&Ps need to match or be very close. I do recall seeing a truck in 4 Wheeler years ago that had much larger rear tires than front and his R&P were sized accordingly...
 
OP
OP
C

centex77

Full Member
Joined
Oct 31, 2017
Messages
183
I know someone has been in there as they installed lockers front and rear. Tires are all the same size.
 

Broncomt

Full Member
Joined
Oct 4, 2015
Messages
187
Back in the "old days the fronts were geared higher speed with the thinking that the front would tend to "pull" the vehicle opposed to being "pushed" which would tend to cause it to spin out.
 

garberz

Bronco Influencer
Joined
Jun 24, 2007
Messages
6,856
Loc.
Conejo Valley, Ca.
Back in the "old days the fronts were geared higher speed with the thinking that the front would tend to "pull" the vehicle opposed to being "pushed" which would tend to cause it to spin out.

I think that was what the marketing dept. came up with. With Ford making the rear, and Dana making the front, that's the reason they're slightly different. Mine's 4.56 up front, 4.57 out back.

Mark
 

Broncobowsher

Total hack
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Jun 4, 2002
Messages
34,834
3.54 front and 3.50 rear, so that would have been backwards of the front pulling theory.
 

Apogee

Contributor
Bronco Guru
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Nov 26, 2005
Messages
6,033
If you can't fix it, feature it, right? Different axle manufacturers (Dana front, Ford rear) and the limits of what can be made to fit with respect to ring/pinion tooth counts. Is some cases, like hand grenades and gears apparently, close does in fact count.
 

bmc69

Contributor
Bronco Guru
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Jun 11, 2004
Messages
11,852
3.54 front and 3.50 rear, so that would have been backwards of the front pulling theory.

Yep. As correctly noted already, Ford just got 'em as close as they could between the two different manufacturers.

It's only the extreme sand/mud drag guys that spin the front tires faster than the rear on purpose. ;)
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
You know how shifting out of from 4WD to 2WD the transfer case sometimes gets stuck and backing up helps?
That used to happen to me when I had 3.50 rears and 3.54 fronts. The rear was crowding the front.
Now I have 4.11 rears and 4.09 fronts. That sticky transfer case issue hasn't happened since the gear swap. I think it's because the front is turning faster than the rear.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
You know how shifting out of from 4WD to 2WD the transfer case sometimes gets stuck and backing up helps?
That used to happen to me when I had 3.50 rears and 3.54 fronts. The rear was crowding the front.
Now I have 4.11 rears and 4.09 fronts. That sticky transfer case issue hasn't happened since the gear swap. I think it's because the front is turning faster than the rear.

Mine was better with the same swap too.

I'd pull the cover on the front gear set and verify the gear count. I would expect if the gears were that far off you would have a hell of a time shifting it.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
Did he ever confirm that they really are 3.73? That just isn't a gear ratio that you normally find in a Bronco. Someone had to go out of there way to do it, if that is really what it is. I'm guessing that with backlash it just wasn't counted correctly.
 

sykanr0ng

Bronco Guru
Joined
Aug 11, 2014
Messages
5,363
I think that was what the marketing dept. came up with. With Ford making the rear, and Dana making the front, that's the reason they're slightly different. Mine's 4.56 up front, 4.57 out back.

Mark

There are actually 4.56 and 4.57 ratio ring and pinion gear sets made for the Ford 9 inch.

4.56 are 9 teeth on the pinion and 41 on the ring gear,

4.57 are 7 teeth on the pinion and 32 on the ring gear.
 

garberz

Bronco Influencer
Joined
Jun 24, 2007
Messages
6,856
Loc.
Conejo Valley, Ca.
There are actually 4.56 and 4.57 ratio ring and pinion gear sets made for the Ford 9 inch.

4.56 are 9 teeth on the pinion and 41 on the ring gear,

4.57 are 7 teeth on the pinion and 32 on the ring gear.

That’s interesting, I wonder what other ratio’s are matching between Ford and Dana?

Mark
 

Nothing Special

Sr. Member
Joined
Nov 25, 2016
Messages
804
For a week or two I had 33" tires on the back and 28" tires on the front of my F-150. That's about the equivalent of 4.10 gears in the front and 3.54 in the rear. During that time I got stuck on a muddy hill and needed to use 4WD. The truck was almost unsteerable. The different ratios meant that always both tires on one axle were sliding. Which axle was sliding would switch back and forth, and the net effect was that the truck pretty much went where it wanted regardless of where I pointed the tires. I was able to get up the hill and shift back into 2WD. But I proved, at least to myself, that mismatched ratios don't work on slippery surfaces either.


edit: The purpose of the mis-matched tires was to test how the truck would do with taller tires. I was going to lift it and put 33s on, but wanted to know if I needed to change the 3.54 gears. The 33s didn't fit on the front without a lift, but they did fit on the rear. So I changed the rear tires and drove it for a couple weeks, including a trip to tow a small farm tractor. I decided that the 3.54 gears were fine with the 33s and I didn't need to regear. So I put the 28s back on until I did lift it and could put 33s on both ends. I knew I couldn't use 4WD with the mis-matched sizes. But when I couldn't get up the hill, and knew that with it as slippery as it was it would never cause any bind problems I did it. It got me up the hill, didn't cause any problems (other than handling!) and gave me first-hand experience how bad that could be!
 
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