4x4 Issues Need Explanation - Ford Powerstroke Diesel Forum
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post #1 of 2 Old 01-01-2014, 01:25 AM Thread Starter
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4x4 Issues Need Explanation

My last Ex I bought the 4x4 didn't work so they replaced the front hubs, U joint, actuator and repaired the vacuum line. That 4x4 worked well until I sold it. When I bought this truck one of the hubs was slightly hanging out so I knew I would need hubs and the shop that did my engine work replaced both hubs and repaired the vacuum line and said 4x4 worked. I picked up in the fall and didn't get a chance to test it but recently when I tried the HVAC went from vent to defroster and I didn't notice any changes in the steering effort so I knew it wasn't working. The shop told me to just put the auto hubs in manual and I did that and found out that I still had to put the dash switch on 4x4 to engage. I tried it in a snow filled lot and could tell the difference.
What does the dash switch do?
What happens in the hubs to engage 4x4?
What else is engaged/turning in the front driveline when in 4wd compared to 2wd?
Is I harmful to drive with the hubs locked and the dash switch on 2wd?
What wears or what damage happens if it is driven in 4x4 on dry surfaces? Does driveline binding only occur in sharp turns?

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post #2 of 2 Old 01-01-2014, 10:18 AM
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Some of your questions are answered in the 4x4 supplement.

Sometimes you have to stop and roll back and forth for it to engage. Sometimes the hubs will not engage automatically even if nothing is broken. This happens frequently in extreme cold, but can happen in warm weather as well, usually when you want it to work now! Manually locking the hubs will fix this issue and most air related problems. With the hubs locked manually, the front drive-train will turn mostly just causing lower MPGs. Binding can occur anytime the 4x4 is engaged, but most systems are not differential locked, so it typically isn't an issue except when turning or when tire size or wear creates a problem.

The dash switch engages the T/C shift motor that enables the T/C synchronizer, that in turn engages the front drive system and turns on the dash light. It also opens the vacuum switch to lock the front hubs that will engage once the wheels and axles are spinning at the same speed. If the motor can not engage the 4x4 system after 20 seconds (?) it de-energizes and must be reset if you want it to try again.

In the hubs the locking gears are pulled in place via vacuum force or manually via a spring when you turn the selector. If for some reason it does not line up or slightly binds, it will not engage properly.

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