My truck has a 3.55 in the rear and 3.54 in the front. I know that they are suppose to be within 1% of each other. They are stock gears so i would assume that is the way it is suppose to be. Why do they do that, is it to help with binding when in 4x4?


Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster American Thunder Exhaust, Sunroof, CD player with 2 10" subs and some 32" BFG Muds .

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Then theres:
99' Mustang GT 4.6L
88' F-250 Superduty 4x4 351/c6
95' Mercury Cougar 4.6L V-8
80' E-350 300/6 with a
3 spd column shifter. Top speed is 65mph, Go Baby Go!

 

[updated:LAST EDITED ON 24-Jul-02 AT 10:22 PM (EST)]I don't know why they are different other than maybe because of different manufacturers between the two axles.I can say that with the front axle pulling a little faster your truck will want to track straight in slippery conditions.For example,nailing the throttle in snow and steering at the same time your truck will remain relatively straight.That is if you don't turn the wheel all the way or close to it.

 

That's just the differnce in the axles as to what gears are available, just like in my dad's old 77 F-250 it had 4.09 front and 4.11 rear, I think it is the same way in the 91 F-250.


Brian

 

That's why the 'cases are part timers. A true full time case would have to allow for the slipping needed to drive on hard packed surfaces similar to limited slip rears. Even if the ratios were matched, without a way to cause the binding to go away (i.e. clutch pack slippage) you'll have a very expensive repair bill and a lot of down time.

-Kerry

 

Yeah that happens because the tires arn't exactly the same size and don't spin at the same speed. But does having 3.55 rear and 3.54 front help to keep the binding to a minimum, vs both having 3.55s?


Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster American Thunder Exhaust, Sunroof, CD player with 2 10" subs and some 32" BFG Muds .

Check out my Gallery for a look-see.


Then theres:
99' Mustang GT 4.6L
88' F-250 Superduty 4x4 351/c6
95' Mercury Cougar 4.6L V-8
80' E-350 300/6 with a
3 spd column shifter. Top speed is 65mph, Go Baby Go!

 

One thing to think about the ratios being different is are they really different?

When you consider the radius of the front tire is usually smaller than the rear, due to it being compressed with the greater weight of the engine, is there really a difference in an unloaded truck?

 

It doesn't do a thing as far as getting rid of binding. That is accomplished through the use of 4wd on a slick surface. I have a 3.54 front and 3.50 rear, stock. It doesn't matter whether the lower ratio is in the front or the rear, or even if they are matched. As long as the 1% or less is met and you use it as directed, binding shouldn't be a problem and can't be relieved by the ratio difference. You are talking about a tiny difference in the overall numbers. Don't get me wrong the closer the numbers the better, but like I said we aren't talking about true full time cases.

For your next homework assignment: calculate how much force is being applied by the engine and surface on which the vehicle is traveling on every component in the drivetrain. Assume ideal conditions.

-Kerry

 

there is really no difference between 3.55 and 3.54 gears these are calculated ratios they are really the same gear like 4.11 and 4.10

 

If you have a pinion with 11 teeth and a ring gear with 39 teeth your gear ratio is 3.5454 your gear ratio diff. I believe is a rounding change and not a true gear change
Bryan

 

Your front is a Dana 44 and the rear is a Ford 8.8. One mfg rounds the number up and the other down. It is really the same.

Jim

 

Hi all,

Very interesting thread. I can't remember where I heard it but I read/heard that the difference in ratios was intentional to maintain a small amount of tension on the drive line. This was to prevent gear "slapping" or "banging" when coming on and off the throttle. In other words the drive line is in constant tension without slack and the gears have no room to bang. Anyway, that's my story and I'm sticking to it!

Lee