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No 4x4 - front diff shift fork?

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Old Dec 9, 2020 | 06:37 PM
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No 4x4 - front diff shift fork?

'03 F150 4x4, manual t-case... no 4wd

Checked everything and everything external works as it should. T-case is engaging, all vacuum is good, actuator moves arm at front diff, but nothing.

Finally removed vacuum actuator and found that arm (finger indicates) can move fore/aft maybe 1/8". By messing with it I can get it to engage, but it'll eventually stop working again, even if I don't shove it fore/aft again.

When it stops working, it still swings, it just doesn't cause anything to happen. IOW the arm (again, finger indicates) ALWAYS moves and doesn't lock up or get stuck - it's just that sometimes that movement engages the axleshaft and other times it doesn't.

I'm afraid I'll have to crack open the axle tube here and see what's going on. Are there shift fork PADS that wear here?

I'm open to all experiences with this issue. edit: I did not see this covered in the Sticky at the top of this forum

Arm will always swing left/right but won't always engage or disengage RH axle
 
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Old Dec 9, 2020 | 10:46 PM
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Internally, the fork slides a splined collar to link the two CV shafts together on the passenger side.
You have to take it apart to find out what's going on if you sure the shaft/arm is not slipping on the outside.
Good luck.
 
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Old Dec 10, 2020 | 12:49 AM
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Ok, found a great thread. Even before having taken it apart I was wondering if I could somehow repair the shift fork, then I see that user Boozer89 did it back in '10. I may have to try this tomorrow!

I don't know that I have any brass or bronze lying around but I might even try aluminum. Solid tech here:
https://www.fordf150.net/forums/view...9efd58533b0eab

This problem seems rampant in the '03 MY; was something specific to '03 for this fork setup?
 
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Old Dec 10, 2020 | 01:14 PM
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The Carnage



Just for reference/searchability later: use a 5/32" roll pin punch. If ya wanna get fancy use 4mm
 
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Old Dec 10, 2020 | 01:44 PM
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Another little tech tidbit: if you pull the FRONT bolt for the diff, loosen the rear one and remove the d/s you can tip the whole pumpkin down for less interference w the RH CV flange (RH shaft can stay in place). All that i learned from a brief YT video.

But what I found was that it's still a battle with the axle flange. The pumpkin will only swing down so much before the diff cover augers into one of the mounting tab ears. I shortened that ear with a cutting disc and now the diff will drop until the LH shaft rests on the A-arm. Should make reassembly much easier.


Ear hits diff cover and prevents further down travel
 
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Old Dec 10, 2020 | 01:47 PM
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Shortened tab and resulting down travel of pumpkin:



The cut ain't pretty but it'll never be seen. Tricky to get any rotary cutting tool in here or i would have finished it mo betta.
 
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Old Dec 10, 2020 | 06:05 PM
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I decided on a slightly different approach than the thread I linked above. I may or may not regret it.

I tapped the fork 8-32. If the bushings want to try to spin in use this might cause one of them to back out, but I did assemble with COPIOUS red threadlock 'cause I really don't want it moving

Then I found a little drop of what I ASSume was oil impregnated bronze 'cause it noticeably leached oil while turning. I opted to make my bushings .200" thick with a .520" OD. I thru-drilled .171" and counterbored for an 8-32 SHCS .170" deep



 
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Old Dec 10, 2020 | 06:08 PM
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Installed
Installed here, it moves wonderfully by hand, so next test is if vacuum moves it just as well.
 
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Old Dec 10, 2020 | 09:06 PM
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Confirmed, getting the front diff to swing down as low as possible is well worth it.

Otherwise, put it back together 100% and the shift fork appears to operate perfectly when I apply vacuum to the actuator in either direction. I topped off front gear oil after it was buttoned up because I feel even a thin film of lubrication on that fork and collar will help with longevity.

Front pumpkin dropped as low as it will go after cutting mounting ear and CV axle held against frame w bungee cord makes for easy installation
 
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