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Does changing rear gears effect Front diff?

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Old May 29, 2020 | 11:20 AM
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Does changing rear gears effect Front diff?

What i'm asking is if i change my rear 3.55 gears to say something like 4.30's, and i engage 4wd, will it effect the driveline in a negative way? Because the front stay at 3.55.
 
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Old May 29, 2020 | 11:22 AM
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Yes, you need to change both.
 
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Old May 29, 2020 | 11:24 AM
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Disaster. Your front differential will be dragging the rear differential. Your antiskid will be continuously engaged and antilock will disengage when in 4WD. Everything from the transmission, transfer case, differentials and axles will be trashed.

 
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Old May 29, 2020 | 11:27 AM
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From: Chaz
Try it and let us know. Simple science experiment, try hitting 4Hi while on the freeway after you get the work done
 
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Old May 29, 2020 | 11:30 AM
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Originally Posted by Joe T
Try it and let us know. Simple science experiment, try hitting 4Hi while on the freeway after you get the work done

 
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Old May 29, 2020 | 11:31 AM
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Originally Posted by ForCal
Yes, you need to change both.
Originally Posted by C12H24
Disaster. Your front differential will be dragging the rear differential. Your antiskid will be continuously engaged and antilock will disengage when in 4WD. Everything from the transmission, transfer case, differentials and axles will be trashed.
Thank you!
 
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Old May 29, 2020 | 11:36 AM
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Back in the day it was pretty common to run a slightly faster gearing in the front diff but 3.55 to 4.30 is way too much and with all the electronic traction control systems I don't think that is done anymore.
 
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Old May 29, 2020 | 11:45 AM
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Originally Posted by Doc Rhen
Back in the day it was pretty common to run a slightly faster gearing in the front diff but 3.55 to 4.30 is way too much and with all the electronic traction control systems I don't think that is done anymore.
I was reading through some threads where people changed thier rear gears but never mentioned replacing them in the front.
 
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Old May 29, 2020 | 12:18 PM
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Years ago I ran one step taller (3.55/3.73) in the front for running mostly in the sand. It worked OK for snow and mud too, but not so much in the rain. Ended up twisting the rear driveshaft off off-roading. Not sure if it was the cause, but I wouldn’t do it again with all the electronics nowadays.
 
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Old May 29, 2020 | 12:37 PM
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Originally Posted by Spaceman_Spiff
What i'm asking is if i change my rear 3.55 gears to say something like 4.30's, and i engage 4wd, will it effect the driveline in a negative way? Because the front stay at 3.55.
If you never use four wheel drive you will be fine. From actual experience if you do engage four wheel drive you can expect the transfer case to explode.
 
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Old May 29, 2020 | 12:59 PM
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From: Chaz
I know you can do things interchangeable like 4.09/4.10/4.11 or 3.90/3.92.


But the OP should just try it out.
 
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Old May 29, 2020 | 01:33 PM
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My '64 came with 3.92 in the rear and 3.89 in the front. Pretty darn close. 3.55 and 3.73? Disaster. 3.55 and 4.30? Epic...
 
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Old May 29, 2020 | 02:13 PM
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Originally Posted by Joe T
I know you can do things interchangeable like 4.09/4.10/4.11 or 3.90/3.92.


But the OP should just try it out.
Originally Posted by stephen.osborne1
My '64 came with 3.92 in the rear and 3.89 in the front. Pretty darn close. 3.55 and 3.73? Disaster. 3.55 and 4.30? Epic...
I see where this is going.
 
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Old May 29, 2020 | 02:22 PM
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Originally Posted by Drothgeb
Ended up twisting the rear driveshaft off off-roading. Not sure if it was the cause, but I wouldn’t do it again with all the electronics nowadays.
Probably not the reason, as when you look at the parts involved, the rear drive shaft is much stouter than a lot of the front end parts. The weakest part will fail first, and my guess is the transfer case, or the front drive shaft.
 
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Old May 29, 2020 | 02:44 PM
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From: Chaz
Originally Posted by Spaceman_Spiff
I see where this is going.

You trying this concoction?
 
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