Auto 4x4 and Heater vacuum pump?????

[Kyle_1724]

OK I need help in understanding how the auto 4x4 works. Here is what happened. Heater controls where working fine but not the auto 4x4. Found one of my vac lines cracked. Ran all new lines from pump to both 4x4 hubs. Put in 4x4 and did not engage. Hooked up a vacuum gage and the pump is pulling 11" on the gage at both hubs. Hook the hubs back up and nothing happens. My question is how does this work? When I had the gage hooked up it would draw to 10" and then all of a sudden I would here a click and vacuum would go to 0, but the pump keeps running for a few seconds and then shuts off. Thought it was the vacuum solenoid switch so I replaced with a new on and it does the same thing. Pulls vacuum to the hubs and then all of a sudden "click" and no vacuum, but when I turn the 4x4 switch off the vacuum goes to about 3". It does this just for the auto 4x4. The whole time the heater controls work fine. I don't know if this is normal operation or what. Is this how it is supposed to work? Any suggestions will help. Thank you

Kyle

[Camoderek]

+1
I have been having a issue aswell to where heat controls working then when i was sitting in a dirt parking lot yesterday rear wheels started to spin i switch to 4wd and only rear spin, i switch to 4x4 low and still only rear spin. Does yours engage if ou manually lock the hubs?

[Kyle_1724]

Yes mine does lock with the man. hubs. Here is what I found out by a mechanic. Truck has to be moving for it to go into 4X4. Don't have to move much but it does have to a little. Here is what I found on my truck. So I found front bearing was bad and also the o-ring that seals the vacuum at the hub. Replaced the o-ring, bearing and seals. Now I had 10" of vacuum at both hubs. So To test i turned switch to 4x4. Vacuum pump came on and pulled 10" at hubs then solenoid clicked vacuum went away. turned switch 4x4 off and vacuum went to 3". This must be how it works because I pulled my truck out of my shop put it in 4x4 and everything worked. Still do not know how it exactly works but If you have vacuum at both hubs and truck is rolling then it should work. I would check the vacuum at you hubs. Sorry for the long reply. Hopefully this helps.

[tpar1220]

interesting.... i have an 03 f250, my heater only blows out defrost. figured it was vacuum related. i unplugged he vacuum supply to front hubs and plugged lines from pump and heater works perfectly, soon as i plug lines back in... heater flakes immediately.

figured i have a bad vacuum line to hubs somewhere, i had a look around but.... how do you unhook vacuum lines at hubs, i didn't wanna just start pullin on em.

how hard is it to replace those o rings?

any help is greatly appreciated as my feet are freezing in that thing..

[Kyle_1724]

Originally Posted by tpar1220

interesting.... i have an 03 f250, my heater only blows out defrost. figured it was vacuum related. i unplugged he vacuum supply to front hubs and plugged lines from pump and heater works perfectly, soon as i plug lines back in... heater flakes immediately.

figured i have a bad vacuum line to hubs somewhere, i had a look around but.... how do you unhook vacuum lines at hubs, i didn't wanna just start pullin on em.

how hard is it to replace those o rings?

any help is greatly appreciated as my feet are freezing in that thing..

Well to unhook the vacuum lines at the hubs I just pulled on them. I did break one and had to go to the auto parts store and get new lines. I just got a cheap vacuum gauge and t-ed into it hooked it up to the hub to get a reading. I blocked off the other hub and did them one by one to find wich one was bad. Passenger side was working but the driver side was not. To change the o-ring you have to pull the front bearing assembly out and there is a yellow o-ring on the bearing assembly. Can't miss it. Also there is an inner seal behind the bearing asembly that could be bad too. Mine was, so I replaced it. They are kinda hard to get out and put back. It is a wierd 2 piece looking seal. Getting the bearing assembly out and getting to the inner seal is not too bad. I changed a few bearings on my truck. I can have it all apart in less than a 1/2 hr. Did it in my garage. Hope this helps.

[tpar1220]

Originally Posted by Kyle_1724

Well to unhook the vacuum lines at the hubs I just pulled on them. I did break one and had to go to the auto parts store and get new lines. I just got a cheap vacuum gauge and t-ed into it hooked it up to the hub to get a reading. I blocked off the other hub and did them one by one to find wich one was bad. Passenger side was working but the driver side was not. To change the o-ring you have to pull the front bearing assembly out and there is a yellow o-ring on the bearing assembly. Can't miss it. Also there is an inner seal behind the bearing asembly that could be bad too. Mine was, so I replaced it. They are kinda hard to get out and put back. It is a wierd 2 piece looking seal. Getting the bearing assembly out and getting to the inner seal is not too bad. I changed a few bearings on my truck. I can have it all apart in less than a 1/2 hr. Did it in my garage. Hope this helps.

yes it does... thanks. so auto zone sells the entire plastic vacuum line/tube as one piece deal, pre bent oem fit? or you bought a roll and cut to length?

thanks again.

[Kyle_1724]

Originally Posted by tpar1220

yes it does... thanks. so auto zone sells the entire plastic vacuum line/tube as one piece deal, pre bent oem fit? or you bought a roll and cut to length?

thanks again.

I just bought it off the roll. Bring a piece of your old to match it up. I think its 1/8 " line. By some t's for testing

[tpar1220]

Originally Posted by Kyle_1724

I just bought it off the roll. Bring a piece of your old to match it up. I think its 1/8 " line. By some t's for testing

ok.. so today i removed the vacuum lines from hubs to top (it was all one piece), i then checked for leaks.... there were none, the lines are ok. i also checked hubs, also no leaks. then i checked lines from electric pump to pulse vacuum hub lock solenoid.... all are ok. put it all back together and still heat wont work right.

the only way i can get heater control to work is if i plug this off like so..



it works fine as long as this plug is blocked off..

any more ideas?

[Kyle_1724]

How did you check the hubs for no leaks? What I would do is hook up everything and then take off the vac lines at the hubs and block both of them. If that works then It sould be one of your hubs. If still doesn't work them I'm stumped as well. How did you check the puls solenoid? Did you try and block off the main lne gonig to the hubs before it t-s off to bloth hubs?

[tpar1220]

well, i removed the complete line as one piece... if i had known how easy it was to check i would not have removed it. but once removed i cappped off two of the ends and put the vacuum pump on 3rd end... it held vacuum, so line is ok.

i then put vacuum pump directly on hub itself, it took a lil longer to pull a vacuum, but once it did... it held, and did exactly same thing on other hub. so i assume they are ok.

i don't know how to check pulse solenoid, so maybe thats the problem... i dunno. but i removed lines and checked em for leaks, never found a bad line. the only way i can heat to work right is to block off that connector... just like it is in pic.

i am stumped too.