School Me on RAD Front Axle Disco

[OldButStillJeeping]

For you more knowledgeable folks...
I'm trying to wrap my mind around the 'Shift into 4H on the fly" capability vs the front axle disconnect (FAD).
So, while in 2H driving forward, the front left axle shaft is turning forward, and the front right outer 1/2 axle also is turning forward. But the inner right 1/2 shaft is turning the opposite direction thru the diff spider gears. In theory, the front driveshaft is more or less stationary in 2wd.
But these trucks allow shift on the fly.
As you shift on the fly (while moving) the rear driveshaft is spinning and the front driveshaft is relatively stationary.
So, my question is:
Where is the clutch that enables shift on the fly?

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[Renegade]

It’s my understanding that there is a synchronizer on the front output of the t-case. The FAD engages after the front driveshaft matches the rear, and the intermediate shaft matches the outer.

 

[OldButStillJeeping]

It’s my understanding that there is a synchronizer on the front output of the t-case. The FAD engages after the front driveshaft matches the rear, and the intermediate shaft matches the outer.

What, exactly, is a synchronizer?

 

[Hootbro]

This is the best explanation I have seen.

https://project-jl.com/index.php/20...y-a-transfer-case-modification-may-be-needed/

 

[ShadowsPapa]

It’s my understanding that there is a synchronizer on the front output of the t-case. The FAD engages after the front driveshaft matches the rear, and the intermediate shaft matches the outer.

In earlier FAD systems, the FAD engaged FIRST, then the transfer case engaged. And when going out, the transfer case disengaged first then once that happened, the FAD disconnected.
Modern FAD has a synchronizer on the axle shaft to get things spinning the same speed - the first ones did not and you had to stop the vehicle, flip the switch or pull the lever, THEN engage or you'd grind parts in the FAD.
They also had a sort of interlock - if the FAD didn't engage, the transfer case didn't either.
Once that FAD is engaged, the front driveshaft is turning at close to the same speed as the rear.

You should see the early diagrams for these systems!

 

[OldButStillJeeping]

This is the best explanation I have seen.

https://project-jl.com/index.php/20...y-a-transfer-case-modification-may-be-needed/

Thank you Hoot! Great info there.

 

[Blade1668]

Hootbro great link.

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