• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

How To: Troubleshoot/Fix your PVH hubs


Active Member
TRS Banner 2012-2015
Aug 23, 2007
Reaction score
Homer, Ak/ Anchorage, AK/Fairbanks, AK
Vehicle Year
1984, 1999
Make / Model
Engine Size
2.8L, 3.0L
Original Poster: Original_Ranger84

Difficulty: 3 out of 10

Time to install: 30min - 1 hour

Disclaimer: The Ranger Station.com, The Ranger Station.com Staff, nor the original poster are responsible for you doing this modification to your vehicle. By doing this modification and following this how-to you, the installer, take full responsibility if anything is damaged or messed up. If you have questions, feel free to PM the original poster or ask in the appropriate section of The Ranger Station.com forums.

After having people ask on here, and reading most of the answers to my PVH problem to be "replace them with AVM's" or "do the manual hub mod" I got tired of those and wanted to just fix my hubs (because they worked from the factory). So here is 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!

What makes up the 4x4 hub system?

Well... there is the 4x4 switch in your truck which sends signals to the 4x4computer box located in the passenger kick panel. This controls everything about your 4x4 system, 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 is a vacuum line that runs from the engine to the relay that is constantly pulling vacuum. The relay will direct this vacuum where it needs to go (i.e. the hubs) when it is told to. Lastly, the vacuum lines from the relay run to a 3-way connector and then to the hubs (1 on each side).

How do the hubs work?

Well, PVH stands for Pulse Vacuum Hub. The hub works on a pulse of vacuum to engage and disengage it. When changing to 4x4, vacuum is sent to the hub to pull the hub all the way in and then the vacuum is released, unlocking the hub. This pushes a splined collar out, connecting the CV shaft and hub assembly. When changing back to 2wd, a reduced amount of vacuum is applied to lock the hub back in allowing the splined collar to come back out.

The 3 main pieces:

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)

Now, I'm going to go over how to trouble shoot your system of these parts.

Tools you will need:

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

Checking the vacuum solenoid relay.

The first thing you need to do is open the hood and remove the air cleaner assembly (the whole thing not just the top) to gain easy access to the 3 way vacuum port. Once you get the cleaner assembly off and locate the 3 way port, you will need to identify the tubes. One tube should go up into the fender to the solenoid and the other two should go to the hubs. Unplug the tube running to the solenoid from the port 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, start it up, and engage 4x4 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 approximately 20mmHg after about 30-45 seconds, then the relay will click, and the gauge will read 0mmHg (this is the pulse part of the system).

Did it work?

If yes, then have your assistant turn the truck off, and the gauge should read about 6 - 7 mmHG for approximately 20 seconds to disengage the hubs. If it works both times then this is not your problem. If the relay 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 it is actually pulling vacuum. The relay also sends vacuum to your HVAC unit, so if your heater is stuck on one setting this could 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 Stealership and get one. At this point you should continue to check the system regardless if the relay was your problem or not, because other things may have gone bad as well.

Next is the relatively easy test: vacuum lines and seals. Is your vacuum pump hooked up to the inlet hose barb where the solenoid connects? (That sentence needs more described; it is not fully clear what goes where) 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 may not get any reading because your problem lies somewhere in the lines or hubs. Ha-ha, all that pumping for nothing! Wrong. It told you that something is leaking. 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 20-22mmHg and see if it holds vacuum. Also, spin the tire, and if the hub is working properly you should hear a click and the axle shaft will start spinning. If it does not click, then more than likely your hub is locked up or sticky from some sort of gunk. Alternatively, if it does not 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 it is cheap insurance so they do not crack soon. It’s approximately 3 - 5 bucks for 6ft of new vacuum line at your local parts store, so grab some and replace both sides with 3 feet of line (don't worry most of it is hard line running to the other side, except the last few feet) being sure to clean up the barbs the hoses attach to ensure the best possible seal. Test them again (20-22mmHg 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, but it doesn't matter if not. Now get the garbage bag and rubber bands and spread the garbage bag fairly tightly over half of the hub (leaving the edge closest to the knuckle, i.e. the locking tabs edge, exposed) 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 sealing the hub to the knuckle is still good. If it didn't, you’re looking at a new O-ring for that side.

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 you are not getting vacuum and both the lines (which should be new now) and o-rings (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 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 have the cover off it is really simple. The rubber disc is the first thing under the cap (this is the vacuum seal) along with a white plastic hub part behind the seal.

Now I am really not sure what can be done besides to try and clean up the lip of the rubber disc, as well as the little groove inside of the hub, that seal sits in, as well as the cap. Clean those all off really well with a rag or something just do not get stuff in the hubs. Put it back together and test for vacuum. If it worked that’s great; 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 does not work then either the seal is just not working right or it is the whole hub. In which case, I recommend the manual conversion. It is really simple as you already got the cap off. Remove the screen on the cap, clip off the pinwheel inside, and smooth the edges to your liking so you have a nice hole in the center of your cap. Put the cap back on and just insert your finger to lock and unlock the hub. Push all the way down to lock them in and about half way in to unlock the hubs (until it clicks).

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 become more dependable!

Start off by removing the caps of the hubs like before. Remove the rubber disc and the white plastic hub part. Take the white plastic hub thing and completely compress it and release so it pops apart (Caution! The pieces will not be held together at this point and you could shoot yourself or your buddy with the pieces!).

First notice the metal clip? The tongs are 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 well 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 it is working properly and moving easily. Lastly, clean up the mounting area for the rubber seal and the disc really well and reassemble. Now go turn on the 4x4 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 whether or not the advice will work for all. It worked just fine for me and I hope you as well. Neither I nor TRS are 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)

A special thanks to Tim (triumphrider-1) for editing it so that it now resembles a proper write up and the vacuum diagram.

Rock Auto 5% Discount Code: 7FA902352B4C01: April 5th, 2021


New Member
Jul 5, 2013
Reaction score
Vehicle Year
Make / Model
99 Ranger 4x4 vacuum hub lines


I really appreciate your post. I couldn't find hardly anything on this except R/R or modify hubs. I don't want to do that unless absolutely necessary. Do you happen to know what size vacuum line (hose) I need? I just did a brake job and upper control arm and lower ball joints and I noticed they were cracked and deteriorating. I haven't even tried the 4WD for some time and am afraid it'll get stuck. The rubber lines look terrible. So I want to start with just trying to replace the lines in prep for winter. Please advise. thanks!