4x4 wheel spin
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7th Gear
Joined: Jun 2006
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4x4 wheel spin
I have a 2002 F350 7.3l and having challenges with the 4x4 system and it made me wonder how does it work.
In 4x4 high i have one rear wheel spinning and 1 front wheel spinning
In 4x4 low it seems that only one rear wheel is spinning. I think this because it will spin much easier than it does in 4x4 high. Something wrong here. I do hear a loud click when switching from 4x4 high to low.
In 4x4 high, i know the "auto" hubs work off of vacuum, is vacuum still required in 4x4 low?
the system will build on vaccum but it does leak down, Small vacuum lines seem to hold a vacuum the larger vacuum line, the final 1.5 feet to each hub seem a little too large and I think leak.
Question: Should I expect all 4 wheels to spin in 4x4 low?
In 4x4 high i have one rear wheel spinning and 1 front wheel spinning
In 4x4 low it seems that only one rear wheel is spinning. I think this because it will spin much easier than it does in 4x4 high. Something wrong here. I do hear a loud click when switching from 4x4 high to low.
In 4x4 high, i know the "auto" hubs work off of vacuum, is vacuum still required in 4x4 low?
the system will build on vaccum but it does leak down, Small vacuum lines seem to hold a vacuum the larger vacuum line, the final 1.5 feet to each hub seem a little too large and I think leak.
Question: Should I expect all 4 wheels to spin in 4x4 low?
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7th Gear
Joined: Jun 2006
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I always thought the difference between 4h and 4L was that all 4 wheels would spin, like a straight axel. I guess 4L just changes the gearing, thus more torque.
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Joined: Apr 2004
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With open differentials if traction is limited, it is possible that one front and one rear will spin.
If your truck had a limited slip differential, it may be worn to the point where it is no longer effective, rendering it basically an open differential.
All other things being equal, it should be easier to spin the tires in 4x4 low, as you have more reduction and torque multiplication in the drive train.
Again, in really poor traction conditions, 4x4 high will spin and spin a lot faster since it is higher gear with more wheel speed at any given rpm than low range.
If your hubs are vacuum, you need vacuum at all times, high or low.
You should correct the vacuum leaks as soon as possible.
As for all 4 spinning in 4x4 low, no, not always.
If your truck had a limited slip differential, it may be worn to the point where it is no longer effective, rendering it basically an open differential.
All other things being equal, it should be easier to spin the tires in 4x4 low, as you have more reduction and torque multiplication in the drive train.
Again, in really poor traction conditions, 4x4 high will spin and spin a lot faster since it is higher gear with more wheel speed at any given rpm than low range.
If your hubs are vacuum, you need vacuum at all times, high or low.
You should correct the vacuum leaks as soon as possible.
As for all 4 spinning in 4x4 low, no, not always.
Super Moderator
Joined: Apr 2004
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You got it while I was typing the other response. 4x4 systems like this lock the front and rear together, but do not change your axle differential action.
Lead Driver
Joined: Nov 2008
Posts: 8,449
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From: South Jersey
Are you sure the tcase motor is engaging 4low? They click u hear oa the motor moving the tcase lever BUT if it was never used or rusty the motor tries to engage 4low but cant. So its stuck between 4high and 4low...you'll still have the rest tires mo ing but will loose the engagement on the front axle. Also the 7.3 when in 4low YOU WILL KNOW! The motor whines and it just CRAWLS with an absurd amount of torque, no missing that
Logistics Pro
Joined: May 2017
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From: Southern OH
If you lock the hubs manually they are supposed to work without vaccum. 4x4 low is a 2.72 reduction gear for increased torque multiplication at lower speeds. The only way you can have all 4 tires spin in 4x4 is if you had lockers or working limited slip differentials in the front and rear axles. The factory configuration is an open front differential, and the rear can be either an open diff or a limited slip that isn't that effective when new and it wears out over time and becomes an open differential.
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