Hey guys, this is my first post. I'm working on my dad's 99 f150, and it doesn't have 4x4. Both 4hi and 4low lights come on in the dash and the front driveshaft doesn't spin when engaged. Where my question is, is that the actuator on the front axle isn't holding vacuum, would it be safe to say that a new actuator would cure the problem? We're just not wanting to spend money where it's not needed right off. Thanks a lot.

 

i assume since the 4 x 4 lights come on, that you have the electric motor on the transfer case working. it would appear the front axle engagement is the problem. i would start truck , leave in park and move the 4 x 4 **** while somebody looks at the vacuum cylinder on the front axle. see if it moves. pull both vacuum lines off and see that you have vacuum on one in 2 x 4 and vacuum on the other in 4 x4 . If not, follow the hoses up to the connection on the right fender well below the battery area adn see that it is connected. follow up to the solenoids on the firewall and see if you got vacuum into and out of the solenoids..... if you have vacuum and will not switch, spray the vacuum cylinder and stroke by hand , then retry.

 

did you put a vaccum pump on it and it won't hold vaccum? if so then i would say that yeah your actuator is bad odds are the diaphram in it is out. i had to change mine it was all coroded and rotted out other thing it could be is that on the firewall by the battery there are 2 solonoids one or both could be bad. hope this helps a little

 

I've already gone through all the vacuum lines, starting up by the solenoids, every connection on both lines to the actuator. The diaphragm in the actuator is leaking, I believe. I'm not sure, and the guys at the local Ford dealerships won't tell me anything on how to check the actuator. In 4x4, the pink line holds vacuum. 4x2, the blue holds. And neither hold at the actuator in 4x4 or 4x2, it's just frustrating.

 

yep i would say the actuator is shot, i bet if you pulled it off it would rattle like there is crap in it. i bought mine off ebay for a fraction of what the dealer wants

 

If the front driveshaft isn't turning then your problem isn't the actuator.
It's probably the motor on the transfer case. Even if the actuators aren't
working the front driveshaft will turn. If the front driveshaft is turning then
you can try to work the actuator by hand while someone turns the switch.
Of course you should put the truck on 4 jackstands to be safe.
I did this on my 99 4x4 and it was only stuck do to lack of use by
previous owner.

 

Sounds like your transfer case is fine if I took your post correctly. When in 4X4 and driving forward, the front drive shaft should turn. Everyone has a different way to test this -- easiest way is to get someone to drive the truck forward a little while you peek under from the side.

Transfer case check

You said you checked the solenoids and vacuum hoses -- easiest way to check all of this is to pull the two hoses off the actuator on the axle. Put your finger over each while someone shifts the truck to 2 and 4. If they alternate and both feel the same (not very strong pull is fine - they don't pull much).

Solenoids and hoses check

To check your front differential still engages, shift it in by hand while someone shifts the truck to 4X. To do this, remove the cover over the actuator so you can get your hand in there and push the shaft in towards the actuator to engage. It should move relatively smoothly and you should also be able to pull it back out when the truck is shifted to 2wheel easily.

If this is good, I would say it is a tear in the vacuum diaphragm and it would be quite safe to replace the actuator. In my case, I engaged the shaft by hand and couldn't disengage it. If this happens, a bit of lube in there and shifting back and forth by hand and with the truck and my 4X4 worked again! Hopefully this is your problem too and it will save you some cash -- if not, ebay is the way to go for the actuator. Ford was going to charge me $460 and they are $100 on ebay! worth the wait

 

Steeven is on the right track. Your prob isn't on the front axle, its transfer case related. If the front driveshaft going to the front axle isn't spinning while in 4x4, then your problem is "behind" the front driveshaft. It almost sounds like a broken planetary chain inside the transfer case, which usually doesn't happen unless it see's a lot of abuse.

 

Waiting for another post to help as well, but just read your thread. I wished I had read it before I put a new transfer case motor on and a new actuator. I think both of them were okay (although the truck has 210,000 and may need them eventually) I did this entirely backwards.

1. My light was on with no engagement
2. When I turned my switch, I could hear clicking at the transfer case so I
I have to figure it wasnt the motor which I replaced anyway
3. Had the wife hit the switch while I watched the actuator move the fork
arm but figured not enough movement so bought another actuator which
moves it the same
Still no engagement

This leaves me to thinking it is inside the differential and I have no desire to tackle this.

I am checking vacuum at solenoids after I figure out how to get the hoses off without pulling the brackett from the dash. Oh year, it would have been nice if I saw the retaining ring no the actuator before I took my chiesel to the brass. Once I saw the retaining ring and pulled out, the brass insert came out.

So, still no 4wd and wife wondering why I dont get a new truck

If I get another truck, no more electronic vacuum BS. on the floor shifter and stop to engage.

 

There is a company that makes a retro-fit kit that gets rid of the vacumn solenoid system. It is a cable that comes up into the cab that positively slides the actuator on the front diffferential. I beleieve it was somewhere in the area of $180...
Rich

 

I have a 98 Expedition 5.4 EB with what I believe is an acuator issue. I have lights, a new t/c motor, can hear the clunk in 4 lo but no engagement. I live in Michigan and only use my 4x4 in the winter. It worked last season, but this year, nothing. I will go through the diagnostics you clearly outlined. I have a question: When you say "spray the vacuum cylinder" and manually work it, what should I spray it with and where should I spray it? Also, how do I manually work it? Is there a visable post I will know to grab? Thanks in advance for the help.

 

I have a 98 Expedition 5.4 EB with what I believe is an acuator issue. I have lights, a new t/c motor, can hear the clunk in 4 lo but no engagement. I live in Michigan and only use my 4x4 in the winter. It worked last season, but this year, nothing. I will go through the diagnostics you clearly outlined. I have a question: When you say "spray the vacuum cylinder" and manually work it, what should I spray it with and where should I spray it? Also, how do I manually work it? Is there a visable post I will know to grab? Thanks in advance for the help.

 

...Do you mean 4LO or 4 HI? for 4LO to engage, you have to have your foot on the brake and be in neutral, and I believe you can only go up to 25mph or so in 4LO....
Rich

 

normally the spray is used on the engagement cylinder on the front axle. that just just on- off, as the piston goes in and out. you can look at the side of the pmpkin, take the small sheetmeatal cover off, and see the vacuum piston with two hoses. if the piston is stuck or rust, that could do it.. take the hoses off and work the lever from 2 to 4 wheel drive and see if you get vacuum at one hose or the other. If you have vacuum, and piston dont move--- then spray and work it in and out.

 

What kind of spray would you use? WD-40? Or something else. Also, the vacuum piston is visable with the cover off, it that right? And if it's visible, I should be able to work it or move it? Thanks, your input is awesome.