Troubleshoot / Fix Your PVH Hubs


Ok well after asking people here and mostly reading the answers to my PVH problem to be “replace them with AVM’s” or “Manual Hub mod” I got tired and wanted to just fix my hubs (because obviously they worked from factory). So heres a write up on how I fixed my PVH hubs which I am proud to say in over a month have had a 100% success rate of engaging!

First off what makes up the 4×4 hub system?

Well… there’s the 4×4 switch in your truck which goes to a computer box in the passenger kick panel. This is your 4×4 computer (retarded right, yeah). This will control everything about your 4×4 system, it goes to the Transfer Case electric motor located on the Transfer Case, and what I am going to call the vacuum solenoid relay located under the air cleaner box under the hood. There’s a vacuum line from the engine to the relay that is constantly pulling vacuum. The relay will direct the vacuum where it needs to go (IE the hubs) when its told to. Then you got the vacuum lines from this box to a 3-way connector and then to the hubs (1 on each side).

How the hubs work… Well PVH stands for Pulse Vacuum Hub. The hub works on a Pulse of vacuum to engage and disengage it. When in 4×4 vacuum is sent to the hub to pull the hub all the way in and then release unlocking the hub. Then a reduced amount of vacuum for a time to lock the hub back in for 2wd.

The (3) main things that I am aware of are:

  • 1. The Vacuum solenoid relay (rarely goes out i assume)
  • 2. Vacuum lines to the hubs (over time can crack)
  • 3. The Hubs (nightmare waiting to happen)

I’m going to go over how to trouble shoot your system of these parts.

The Tools you will need:

  • A vacuum gauge
  • Vacuum pump with gauge
  • 2 or 3 average sized flat head screwdrivers
  • Blocks for the wheels
  • Jack and jack stands
  • Clean rags
  • Garbage bag
  • Rubber bands
  • A buddy (highly preferred)

First I will start with the Vacuum Solenoid Relay. The first thing you need to do is pop your hood and remove the air cleaner assembly (the whole thing not just the top) to gain easy access to the 3 way vacuum port. I will note you can also just go through the passenger fender area but you gotta feel around for the tube and pull on it (not recommended). Once you get the cleaner off and locate the 3 way tube, identify the tubes 1 should go up into the fender to the Solenoid and the other 2 should go to either hub. Unplug the one to the solenoid from the others and hook your vacuum gauge up to it making sure to have a good seal. Now it helps to have an assistant here, have your buddy jump into the truck and start it up and engage 4×4 high (block the rear wheels to be safe) the solenoid should click on and start directing the vacuum into the tube with the gauge attached. The gauge should read about 20 mmHG (or whatever the vacuum gauge measures by) after about 30 – 45 seconds it should click and read 0 again (this is the pulse part of the system). Did it work? If yes then have your assistant turn it back off, and the gauge should read about 6 – 7 mmHG for some amount of time, 20 seconds I believe, to disengage the hubs. If it works both times then this is not your problem. If it doesn’t work then I would suggest checking your fuses and connections, also follow the vacuum to the engine and hook the gauge up to that line to check if its actually getting vacuum. Also I believe this relay also sends vacuum to your HVAC unit, so if your heater is stuck on one setting this could also be the culprit. I have no clue where to get these units as I have looked for them everywhere, you may have to go to the dealership and get one. Now you should continue to check the system regardless if this was your problem or not because other things may have gone bad as well.

Next is the relatively easy to test vacuum lines and seals. You have your vacuum pump hooked up to the section where the Solenoid connects? Do that and start pumping away! This may take some time… as you have to pump out all the air in the lines and hubs to achieve vacuum. After a few minutes of pumping you probably won’t get any reading because your problem lies somewhere in the lines or hubs, Haha all that pumping for nothing! Wrong it told you that something is wrong here with seals. If you did get a reading well your seals are good… for now. Jack the front tires up and put the stands under them, (still got the blocks in the back? good). Now separate the lines from each other so you can test each side individually, and as stated test each line by pumping them up with the vacuum pump. If one side starts showing vacuum pump it up to about 20 -22 mmHG and see if it holds vacuum. Also spin the tire and if its working properly you should hear a click and the axle shaft should start spinning. If it doesn’t click then more than likely your hub is locked up or sticky from some sort of gunk. Or if it doesn’t hold vacuum remove the line and plug the other end WELL and pump it up. did it hold vacuum? It did? Replace it! I figure cheap insurance so they don’t crack soon. Its like 3 – 5 bucks for about 6ft of new vacuum line at your local parts store, so grab some and replace both sides with 3 feet of line each (don’t worry most of its hard line to the other side except the last few feet) being sure to clean up the parts the hose attach to for the best possible seal. Test them again (20mmHG and spinning the tires). Did they both work this time? if so awesome! keep reading though! If not well its time to keep going. One side may be working by now (or hopefully one side) doesn’t matter if not. Now get the garbage bag and rubber bands and spread the garbage bag fairly tightly over the hub and seal it with a rubber band or two, start pumping away at the line again, is the bag getting sucked in? yes? that’s really good news! it means your O-ring inside the hub is still good. If it didn’t, your looking at a new o-ring for that side. I don’t know how to do the o-rings so you’ll have to ask someone else. Well if your bag got sucked in that means it time to move onto the hub.

The hub is the last part to check before you just go berserk and think about shooting a rocket at your local Ford dealer Haha. If your not getting vacuum and both your line (which should be new now) and o-ring (garbage bag test) are fine then it has to be the seal in the hub. There is a big rubber disc that is pinched against part of the wall of the hub that is the last part of the vacuum. First things first, you have to take apart the hub. This isn’t as hard as one would think. Take the 2 or 3 screwdrivers and put one in the slots of the hub and one 180 degrees off or just opposite it. Hold them firm and try to turn the center counterclockwise (if this is difficult, I found a third driver between both of the other ones and turned give good leverage) Once you got the cover off its really simple. The rubber disc is the first thing under it (this is the vacuum seal) along with the white plastic hub part. Now I am really not sure what can be done besides try cleaning up the lip of the rubber disc as well as the little groove inside the hub that seals the deal and the cap. Clean them all off really good with a rag or something just don’t get stuff in the hubs. Put it back together and test the vacuum. If it worked that’s great and if not all i can say is either the discs are bad and you need to get new ones or you can try putting a thin layer of RTV gasket maker around the rubber disc edges. If that still didn’t work then either the seal is is just not working right or its the whole hub that’s screwed… IN which case I recommend the Manual conversion. Its really simple as you already got the cap off, just clip off the pin wheel inside the thing and punch out the screen, and smooth the edges to your liking so you have a nice hole in the center of your cap. Put it back on and just insert your finger push all the way down to lock them in and about half way in to unlock the hubs.

Well that’s all you need to know about troubleshooting and fixing the hubs to my knowledge. Now on to making them work better and be more reliable and dependable!

Ok well. Basically you start off by removing the caps of the hubs like before. Remove the rubber disc and the plastic hub thingy… Take the plastic hub thing and completely compress it and release so it pops apart. First notice the metal clip? they’re probably getting bent a bit so I just bent them back until they were straight and lined up with each other (you can put it back together and look at the clips and adjust them accordingly as well so that they clip and unclip every time you compress them.). Next clean up the plastic things really good so they are white again and put an ever so slight layer of lithium grease all around the outside of the one that is smaller and slides on the inside (I stress very thin layer as I don’t know what could happen if you put too much and some of it mixes with the axle grease). Once you put the plastic thing back together click it in and out a few times to make sure its working properly and moving easily. then clean up the mounting area for the rubber disc as well as the disc really well and reassemble. Now go turn on the 4×4 and spin the wheels. They should lock in every time (or as was my experience).

I cannot say how all of these tests will work for the individual or weather or not the advice will work for all. It worked just fine for me and I hope you as well. I nor TRS is responsible for possible damages to your truck as this is at your own risk, take all safety precautions and if something doesn’t work you can refer to the 4wd section in the forums for advice.

Good Luck

Written by Nick Beeker (Original_Ranger84)

Note: To see the original submission, click HERE.

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