Front and Rear Differentials - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-03-2003, 12:10 AM
BroncoJoe
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Front and Rear Differentials

I am doing a change of gear ratio and have always been told that the front diff must match the rear diff. As I have been shopping I have found it hard to match. I have a standard setup for a 90 Bronco. TTb dana44 and Ford 8.8.
I want to run a 4.11 in the rear and can not find the same for the front. Maybe I am looking in the wrong place. Any help would be great. [img]images/graemlins/chair.gif[/img]
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post #2 of (permalink) Old 08-03-2003, 12:27 AM
Bluebeast
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Re: Front and Rear Differentials

you have stock 3.54 up front and 3.55 in the rear i think 4.11 and 4.10 would work but i would wait for the more technical gear heads to answer for a final decision. just my .02


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post #3 of (permalink) Old 08-03-2003, 12:24 PM
 
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Re: Front and Rear Differentials

Yes, the front/rears must match up to avoid binding in the driveline. Matching up though does not usually mean EXACTLY. 4.11 front, 4.10 just fine. Stock I think it's 3.54 front, 3.55 rear. That's no biggy and considered "matching ratios". 4.10 rear, 3.55 front won't work if you want to use 4WD.
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post #4 of (permalink) Old 08-03-2003, 01:03 PM
 
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Re: Front and Rear Differentials

what size tire are you planning on running i have the stock 3.50 in mine but want to run 35-36 with 37's in the future so i'm going with 4.56 as the gear ratio so it dont lag when and if i go with 37's just something to think about there are tables on the web that tell you what gear ratio is better for what tire size
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post #5 of (permalink) Old 08-04-2003, 09:58 AM
 
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Re: Front and Rear Differentials

Go with 4.56's if you have OD or you plan on going up to a 37" tire (Not advisable even though I'm considering it myself [img]images/graemlins/grin.gif[/img] .) Go with the 4.11s if Higway speed is important to you with 33 or 35" tires without OD.
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post #6 of (permalink) Old 08-04-2003, 07:55 PM
BroncoJoe
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Re: Front and Rear Differentials

I am running 33s with all intent on going to 35s. I found a 4.09 for the front and a 4.11 for the rear I do have e4od trans. This is my daily driver, I have about 30 min. drive to and from work. So I do want to keep the compramise of econo as well as power. I just want to know if 4.09 will work for the front with 4.11 in the rear. Could possibly have a good deal going on the 4.09 Thanks
post #7 of (permalink) Old 08-04-2003, 08:46 PM
 
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Re: Front and Rear Differentials

</font><blockquote><font class="small">In reply to:</font><hr />
So I do want to keep the compramise of econo as well as power.

[/ QUOTE ] [img]images/graemlins/chairfall.gif[/img] You do realize that you have purchased the aerodynamic equivelant of a brick don't you? Adding a lift will make it worse as your brick will now block more wind after the lift, ect. Enjoy it for what it is. In the best of circumstances MPG in our beasts equal about 12-14mpg and that's milking it for all it's worth. No I don't see those numbers and I doubt I ever will. There are some expert tuners here who try and nail it though.
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post #8 of (permalink) Old 08-04-2003, 09:52 PM
 
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Re: Front and Rear Differentials

4.09 to 4.11 sounds just right ...
*(with all the usual disclaimers)*

Any of ya'll with the ol' 9" rear &amp; TTB front might be able to confirm - I'll betcha the most common factory ratio with that axle combo was 3.50 rear &amp; 3.54 front ...

I think the theory is to set up a bit of a "pre-load?" by having the gears slightly different.
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post #9 of (permalink) Old 08-04-2003, 10:53 PM
 
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Re: Front and Rear Differentials

If the front axle has a numerically lower ratio, then the tires will turn faster. I always though this was done so that it would be easier for the front tires to turn if they were 'pulling' the truck, as opposed to being 'pushed' forward by the rear ones.
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post #10 of (permalink) Old 08-04-2003, 11:40 PM
 
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Re: Front and Rear Differentials

With 4.11s, 33s and the E4OD your gas mialge will be about 9 mpg, downhill, engine off, with a tailwind. 35's might make it 10-10.5 mpg.

I would save the money until I got the 35s.

Me personally, I would love a set of 3.73s but the diff between 3.55 and them with the cost factored in makes it silly.
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