I've got a 99' f-150 4wd with the vacuum operated hubs at the diff. vacuum pod is mounted on a bracket that allows it to pull on an arm to engage or disengage the front axle. I got under the truck and had my wife operate the switch and it's trying to engage it but no go, any help with this out there?

 

Hi and welcome to the forum

If you help move the lever will it engage?
If not then you might have low vacuum getting to it possibly due to a cracked vacuum line etc.
If the lever moves but it still doesn't engage then you may have a shift fork problem in the diff. I've replaced quite a few of them.
If you do a search in here you should find quite a bit of info in the problem.

 

Hi Blue oval, Here is a link to a simple problem I had. It shows the inside of the axle at the point of the vacuum switch. The front axles need to be turning to fully engage the front end as the gear inside the vacuum switch must slide ever to engage the differential and the passenger side axle.<a href="https://www.ford-trucks.com/forums/archive/index.php/t-379249-Help%21%2097%27%20front%20axle%20problem.">Help! 97' front axle problem.</a> This should link for you, but if not just cut and paste. let me know if you can get to it or not and I will copy the pic and send it to you.

 

it won't go moving or not, i think it's the fork or the coupler itself is damaged, thank's for the info.

 

These front ends come out very easy also. Just unbolt the cv shafts and there are three other bolts and the drive shaft and the center section comes out very easy. Take the front diff. cover off and the axle is held in with a c clip. Slide the axle out and then you have access to the vacuum switch. I put the gear in backwards when putting in new gears and had to pull the front end back out to flip the gear in the vacuum switch and it only took about a hour to an hour and a half and was back on the road. Good Luck!

 

how often should you have to replace the gears or how often do they go out. or does it depend on how often you use the 4X4 and how much abuse you give them off road?

Lance

 

I have not blown a gear yet. I have blown up a CV though(Mud Bog). Nice thing about these front ends, they are easy to work on. Not the stongest, but easy to work on. I am running 4.56 gears in mine and no troubles so far. 140,000 miles.