Mismatched Front/Rear Axle Gears 4.56/3.73 - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 03-14-2007, 10:20 PM   #1 (permalink)
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Mismatched Front/Rear Axle Gears 4.56/3.73

I am just wondering exactly what happens when you use 4wd with mismatched front and rear axle gears? I know it isn't good and they will be fighting each other but I have never done it and was wondering if anyone has and what actually happens? I'm just curious because I am selling my 1996 Chevy Silverado which has 4.56's in the rear and I never got around to putting 4.56's in the front, so it's still stock 3.73 in the front, and I never use the 4x4 anyway....but I just want to tell the guy who is buying my truck exactly what will happen if he uses 4x4 without re-gearing the front. Thanks for the help
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Old 03-15-2007, 12:12 AM   #2 (permalink)
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Just bolt some 37s up in back and tell the buyer it's part sand rail!

No, seriously, nothing good can come from this assuming 4 identical tires. You should get the front gears put in, or at least tell him he's gonna have to before he uses the 4WD.
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Old 03-15-2007, 12:52 AM   #3 (permalink)
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if you do this your going to break something... ive been there... 3.55s up front and 4.88s in the rear. it will plow in the snow, gravel is OK, mud you couldnt tell, but dirt it will feel like the truck is bending in the center like a stick. your truck is goings to try to spin the front end almost a full turn compaired to the rear... id tell the guy to gear it or not use it. those front ends arent cheap-and neither is the transfercase...

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Old 03-15-2007, 10:50 AM   #4 (permalink)
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I had an old flatfender I changed the front axle in and didn't even think about the gears. 5.38 rear, 4.88 front put it in 4x4 at loon lake and ran the whole rubicon put 70 lbs. of air in the tires and chirped and hopped all the way. Never broke anything (real light with skinny tires and 4 banger) but I don't recommend it.
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Old 03-15-2007, 02:40 PM   #5 (permalink)
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Something is going to ******* break. That is about the dumbest & dumber!
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Old 03-15-2007, 02:43 PM   #6 (permalink)
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i replaced an np231 on a 2 door blazer that was broke in half because the guy didnt want to put new gears in the front
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Old 03-15-2007, 05:51 PM   #7 (permalink)
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I am just wondering exactly what happens when you use 4wd with mismatched front and rear axle gears? I know it isn't good and they will be fighting each other but I have never done it and was wondering if anyone has and what actually happens? I'm just curious because I am selling my 1996 Chevy Silverado which has 4.56's in the rear and I never got around to putting 4.56's in the front, so it's still stock 3.73 in the front, and I never use the 4x4 anyway....but I just want to tell the guy who is buying my truck exactly what will happen if he uses 4x4 without re-gearing the front. Thanks for the help
to specifically answer the question, the front tires will turn faster than the rear tires. on any high traction surface, it will bind and break something
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Old 03-15-2007, 06:18 PM   #8 (permalink)
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it would either pull apart or the axles would pull towards each other
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Old 10-23-2014, 01:37 PM   #9 (permalink)
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MisMatched Tire Sizes

on my z71 I had 31 streets when I bought it. I don't have enough clearance yet to put my new 35 toyo's on the front. I had 2 blowouts, and decided to put the 35's on the rear.

So now I have 31's in the front, and 35's in the back, and I'm scared to use 4x4. I did accidentally had 4wd engaged when I drove off once and left tire marks like a burnout.

I'm thinking about being stupid/smart and changing the rear axle ratio so my tires will match up

Do y'all think I can get the ratios close enough, or will the front and back always be slightly off until I install the lift kit and fronts
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Old 10-23-2014, 08:01 PM   #10 (permalink)
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Considering those are 17" wheels in the picture, your tires are not exactly 35's nor exactly 31's. I'm guessing 265/70R17's up front and 315/70R17's or similar in the rear? Maybe 305/70R17 rear?

Anyway, re-gear the rear axle so you get your power back. Leave it in 2HI until you can afford to lift the front to clear the same size as you have in the back, then re-gear the front...or SAS the front. With 35's and a 5.3L auto, I'd shoot for 4.10's for highway mileage, 4.56's for all around good power and 4.88's for offroad.
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Old 10-23-2014, 09:53 PM   #11 (permalink)
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Necro thread.......
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Old 10-24-2014, 12:11 PM   #12 (permalink)
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it will plow in the snow, gravel is OK, mud you couldnt tell, but dirt it will feel like the truck is bending in the center like a stick.

pretty much, ive actually done this with two trucks. my daily driver for a year had 3.08 in back and 373 in the front, if there was heavy snow on the ground i didnt notice at all. that truck never seen mud.

my k5 blazer i took offroad in the middle of the axle swap, 2.73 in the back and 3.73 up front. i just left it in 2wd til i got stuck in the mud, engaged and took it out soon as i got out of the mud but doing it on dry pavement wont work, it basically binds up and it feels like it slams on the brakes
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Old 10-26-2014, 07:56 PM   #13 (permalink)
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3.73 to 4.88 is a big difference.

I had a neighbor get a new front axle in his F250, shop forgot to check the ratio. it had 3.73's and his rear were 4.10's. he tried out the 4wd and screeched tires all the way down the street. I really want to see what 3.73 and 4.88 does...
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Old 10-29-2014, 12:52 AM   #14 (permalink)
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If you have the time and or money to change the rear ratio, why the hell wouldn't you put that towards the front lift instead and then just change the tires??????
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Old 11-03-2014, 09:25 AM   #15 (permalink)
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IFS in the front. I've already raised/stiffened them considerably. I already have a 3" body lift purchased, as well as the other 2 rims/tires mounted and balanced, but I have to put the body lift on before they will fit.

I will be wanting to change the gears anyway to regain my lost power.

In fact I already HAVE been mudding, and it acts just like abig84's k5. I only engage 4wd once I'm absolutely stuck, and disengage ASAP.
Perhaps that's why my rear diff pinion seal has developed a major leak.

*oops*

Oh well, i'm planing to rebuild the diffs anyways. perhaps w/ some manual lockers.
any price minded suggestions? I'm thinking air lockers.
also, do I really need 4.88 ratio?

this is becoming a primary mud truck.
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Old 11-03-2014, 06:03 PM   #16 (permalink)
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IFS + locker =

Actually, in my experience, IFS = eventually anyway, particularly if the torsion bars are cranked...


Suit yourself, but if it were me, I'd get four of the same size tires, cut the fenders to fit (you said mud truck), and save for an SAS and suspension lift to suit. Personally, I wouldn't spend the money lifting or regearing an IFS, and I'd avoid the body lift. It's probably not the end of the world on a mud truck, but they are real hard on cab mounts and the body in general if you do a lot of flexing.
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Old 11-14-2014, 03:12 PM   #17 (permalink)
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I always thought IFS gave better ground clearance over logs and mud, but everybody here seems to favor SAS. Why is that?

I am planing to cut the fenders, but the Windshield Fluid reservoir is just behind the bumper, and my wide tires will destroy it. do they make special reservoir that are smaller?

Even if I change over to SAS, I will still be changing out the Diff Gears for a more prefferable gear ratio. these 35's have taken away a lot of my power. Not to mention I have a 4.8L motor. What is the best gear ratios for my kind of wheeling, and where can I get them? I doubt Auto Zone carries aftermarket gears.
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Old 11-14-2014, 07:57 PM   #18 (permalink)
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True, IFS doesn't have a pumpkin hanging down, but that's pretty much its only advantage off road. It offers way less wheel travel and articulation, every part of it will wear out faster than an equivalent solid axle, the parts are expensive so it will cost more to maintain, and if you do much serious wheeling you will likely be breaking often, particularly with the 1/2-ton junk. Even if you upgrade to aftermarket halfshafts and run a quality lift ($$$), you still won't have much as the aluminum diff housings are known to explode. Putting a locker in one is a sure recipe for destruction if you plan on really wheeling it. If you are talking pure mud running with little power and little traction, it might live, but I still wouldn't sink money into it myself.

As to gears, you can get them all over (Randy's, Summit, Jegs, etc...), but since you are asking the question, I'm guessing you haven't had any experience with gear swaps. It's not as easy as simply bolting them in; they have to be properly set up. THIS should give you a pretty good idea of what is entailed. If you do decide to SAS it, the easiest solution would be to buy a matched set of axles if you could find them with the ratio you want. If you don't want to do the SAS, you might spend $1500 just getting the axles regeared (if you hire it done) plus whatever an IFS lift will cost you, and you'll still have a 1/2-ton rear and IFS.

Ultimately, you need to decide on budget, tire size, how hard you want to beat on this thing, and how much maintenance and breakage you are willing to live with.
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Old 11-14-2014, 08:18 PM   #19 (permalink)
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just shut up and run it. see what happens. please report back...
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Old 11-14-2014, 08:23 PM   #20 (permalink)
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For the OP...

Doing the math.....The following sizes would get you pretty close.
(one would need to make sure of the actual tire sizes as many tires are not true to the size on the sidewall)
F R
28 31
29 32
30 33
31 34
31.50 35
32 35.50
33 36.50
34 37
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