4x4 Problems?
Fleet Mechanic
Joined: Feb 2005
Posts: 1,797
Likes: 1
From: Northern Colorado
You need to start with a decent vacuum guage. Test the vacuum at the pump to make sure that it is working properly then begin to work out from there. There is a vacuum canister, PVH solnoid (Pulse Vacuum Hublock) next to the vacuum pump and then the actual lines going to each hub assembly. If all those check out OK, then pull the autolock hubs and check/clean the o-rings on them. The last thing to check would be to pull the wheel hubs but if you do that, have a couple of new yellow o-rings on hand first as they need to be replaced anytime you pull the wheel hubs (yellow o-rings are a Ford item).
I have not had to buy new vacuum lines but I understand that the cost is not too bad at the dealership.
I have not had to buy new vacuum lines but I understand that the cost is not too bad at the dealership.
Lead Driver
Joined: Oct 2004
Posts: 7,413
Likes: 1
From: Columbia, MO
Originally Posted by guzzle92
You need to start with a decent vacuum guage. Test the vacuum at the pump to make sure that it is working properly then begin to work out from there. There is a vacuum canister, PVH solnoid (Pulse Vacuum Hublock) next to the vacuum pump and then the actual lines going to each hub assembly. If all those check out OK, then pull the autolock hubs and check/clean the o-rings on them. The last thing to check would be to pull the wheel hubs but if you do that, have a couple of new yellow o-rings on hand first as they need to be replaced anytime you pull the wheel hubs (yellow o-rings are a Ford item).
I have not had to buy new vacuum lines but I understand that the cost is not too bad at the dealership.
I have not had to buy new vacuum lines but I understand that the cost is not too bad at the dealership.
Senior User
Joined: Jan 2005
Posts: 124
Likes: 0
Somebody correct me if I'm wrong but doesnt the vacuum to the hubs also operate the heater controls and doesnt the heater controls default to the defrost mode if a vacuum leak occurs. So if its a vacuum problem your heater should only have the defrost working Just a thought
Lead Driver
Joined: Oct 2004
Posts: 7,413
Likes: 1
From: Columbia, MO
You're correct about that. Most of the time, my climate control works just fine. But, every once in a while, especially when it's cold out, I do only have defrost. That's part of the reason I was wondering what vacuum the pump should be making. I hope that the pump is fine, and I just need to track down the vacuum leaks.
New User
Joined: May 2004
Posts: 4
Likes: 0
From: Fremont,Ca.
4x4 woes
This happen to me acouple wks ago,I try to excerise the 4x4 system once every month-dirt roads to lubicate the system.I have a 2002 cc w/sotf system . I fliped the switch to 4-hi and nothing, no clunck,no sound puzzled i flipped it to 4-lo still nothing.I shut the engine off and restart the motor, as it fired off my 4x4 lites on the instum. panel came on and went off like it should. So I tried it again and flipped to 4-hi nothing,so I check the fuses and they where ok.I even tried to manualy lock in the hubs and they couldn't be turned.so since the truck is still under warranty I took it to the ford stealership, and what them found was the wireharness and 2-relays were green with cororrtion and burnt.Everything but the relays and r/r the wireharness was warrantied. I hoped that helped you JRCIII56 good luck.
Thread Starter
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Elder User
Joined: Mar 2006
Posts: 751
Likes: 0
From: Greeneville,TN
Thanks for the help! I have not had a chance to track the vacuum leak down yet. I am in the middle of teaching and coaching baseball right now. About the only day off I have is Sunday.
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Fleet Mechanic
Joined: Feb 2005
Posts: 1,797
Likes: 1
From: Northern Colorado
Originally Posted by jtharvey
Do you know how much vacuum the pump should be making? And, any idea how much vacuum the hubs should be holding to make them lock?
When doing my needle bearing lube, I pumped the hubs up to 7 in.Hg to test for leakage at the hubs and they would lock at that vacuum. I did not check for a minimum vacuum needed to lock.
Last edited by guzzle92; Apr 7, 2006 at 09:38 AM.
Lead Driver
Joined: Oct 2004
Posts: 7,413
Likes: 1
From: Columbia, MO
Thanks guzzle. 
That at least gives me a place to start and some reference numbers. I'm thinking, (just a thought - no tests yet) that I'll need a new pump and new o-rings on the hubs. And, while I'm in there, I can lube the auto-locker hubs folllowing your excellent instructions. 
That at least gives me a place to start and some reference numbers. I'm thinking, (just a thought - no tests yet) that I'll need a new pump and new o-rings on the hubs. And, while I'm in there, I can lube the auto-locker hubs folllowing your excellent instructions.
Senior User
Joined: Sep 2006
Posts: 484
Likes: 0
From: CT
i know my 4x4 works, i havent tried the auto yet, i lock my hubs when iv been in 4wd.
iv only had the truck a few weeks now. but anyways, when i go to start the truck, the 4x4low light comes on and all the other lights on the dash like normal, then it goes out when started. but when i switch the 4x4 hi the 4x4 light comes on on the dash, but when i switch to 4x4low, the 4x4low light dosent come on. im not sure if im really in low or not, how can u tell if its in low? dose the truck just really crawl and stays in first gear? but im going to try and listen under the truck this weekend while some one switches the switch to hear if the motor in the transfer case is working.
iv only had the truck a few weeks now. but anyways, when i go to start the truck, the 4x4low light comes on and all the other lights on the dash like normal, then it goes out when started. but when i switch the 4x4 hi the 4x4 light comes on on the dash, but when i switch to 4x4low, the 4x4low light dosent come on. im not sure if im really in low or not, how can u tell if its in low? dose the truck just really crawl and stays in first gear? but im going to try and listen under the truck this weekend while some one switches the switch to hear if the motor in the transfer case is working.
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Elder User
Joined: Mar 2006
Posts: 751
Likes: 0
From: Greeneville,TN
2002, First on all you dont have to crawl under the truck to hear the transfer case. Just turn the switch on and turn the **** to 4x4 or 4x4 low. You will hear if the transfer case is working properly. You will definatily be able to tell if the truck is in 4x4 low. The truck will just crawl around and you wont be able to drive it at normal speeds. Hope this helps.
Elder User
Joined: Sep 2004
Posts: 851
Likes: 0
From: N. Georgia
Originally Posted by 2002f2507.3LPS
i know my 4x4 works, i havent tried the auto yet, i lock my hubs when iv been in 4wd.
iv only had the truck a few weeks now. but anyways, when i go to start the truck, the 4x4low light comes on and all the other lights on the dash like normal, then it goes out when started. but when i switch the 4x4 hi the 4x4 light comes on on the dash, but when i switch to 4x4low, the 4x4low light dosent come on. im not sure if im really in low or not, how can u tell if its in low? dose the truck just really crawl and stays in first gear? but im going to try and listen under the truck this weekend while some one switches the switch to hear if the motor in the transfer case is working.
iv only had the truck a few weeks now. but anyways, when i go to start the truck, the 4x4low light comes on and all the other lights on the dash like normal, then it goes out when started. but when i switch the 4x4 hi the 4x4 light comes on on the dash, but when i switch to 4x4low, the 4x4low light dosent come on. im not sure if im really in low or not, how can u tell if its in low? dose the truck just really crawl and stays in first gear? but im going to try and listen under the truck this weekend while some one switches the switch to hear if the motor in the transfer case is working.
New User
Joined: Dec 2009
Posts: 3
Likes: 0
If I may jump in, I'm having the same problem with my 98, I've replaced the selanoid and the motor, but I still have no 4x4, the light for 4H comes on in the dash, but it does not engage and the light for 4L won't even come on. I'm at a loss.
Laughing Gas
Joined: Jan 2006
Posts: 1,045
Likes: 5
From: Gig Em, Tx
First off if it doesn't go into 4 hi I don't think it will go into 4 lo. Is yours a manual shift to 4x4 or esof? World of difference, but don't know if 98s were made with esof or not.