To start Im new here and hope to learn alot from the site as I already have. So here is my problem. I have 98 F-250 light duty and I plow with it. Yes comercially. It has worked great Up until the other morning. I was half way done plowing an account and I heard a nice Big thud from the front axle. All the sudden I had lost 4wd. I know that it is not the vaccum Becuase I had read in another thread on here if the vaccum system fails while the truck is in 4wd then the truck will stay in 4wd to prevent the truck from getting stuck. That being said heres what i know. Nothing is visibly broken. The front drive shaft is turning its not the transfercase. I am positive I snapped something in the front axle or the front diff. Correct me if I am wrong Any insight on this is greatly appreciated as this problem is annoying the crap out of me and I lost alot of money having a truck down. I need to have this fixed before the next snow fall Or I am back out shoveling driveways and telling my boss that I can no longer sub for him. Please Thank you -Robert

 

bump I need help

 

jack the truck up off all four tires, put it in fourwheel drive and see if the front wheels turn.

 

Did that already front wheels never moved played with everything I could with out taking the truck apart, nothing worked

 

Well do you see cracked vacuum lines. Did you try searching? Are the cv shaft turning?

 

If the truck is in 4wd and the vaccum fails the truck will stay in 4wd supposedly anyway. but the vaccum is working i watched it work to make sure. cv shafts both turning. driveshafts both turning.

 

Need new cvs at the wheel end?

 

wheels turn the cvs.... is it possible that the fork in the front diff broke??

 

bump......... anybody got any idea what happened??

 

OK, first off there is no default 4x4 when you loose vacuum. That only applies to the new style 2004 F-150 and newer trucks.

Raise and support the front of the truck with the wheels off the ground. Truck in Park engine running T-case in 4Hi try turning the front drive shaft. It should not turn. If you want to test 4Lo shift to 4Lo. The front driveshaft should not turn. Shift back into 2Hi and the front drive shaft should turn.

Post results.

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Thank you I did not know that. I got the 4wd to work my manually engaging the front axle. I disconected the vaccum and flipped that lever or what ever you want to call it over and now it has 4wd. My buddy told me that it is a fork that broke in the front diff. But what do we know were only 18 lol. Transfercase is ay ok though if thats what you were thinking the problem was. I thought the same thing at first.

Edit: nevermind it popped again and it no longer works.....

 

Flipping the lever just allows it to sit there. When it is engaged by the vacuum motor a constant pressure is applied so it stays in place. I would imagine that the constant vibration from plowing allowed it to eventually vibrate loose. I have made temporary repairs by either using chicken wire or zip ties to hold it in place.

Regards

Jean Marc Chartier

 

I did use a zip tie to hold it in place. I think what was left of the mechanizm inside the differential is complete trash now. Thanks for the help

 

I might be asking alot infact i know I am but does anyone have a part number for said fork in the front diff? Or a "politicaly correct" part name?

 

Here is the kit that I purchased for mine.
Revised fork kit - #F75Z-3N139-KT FORK
Before you purchase the kit, did the zip tie break allowing the axle to disengage? Or was the lever still zip tied in place?

Regards

Jean Marc Chartier