Wondering if these have the PVH system or are they constant engagement? Thanks for any input.

 

Not sure what you mean by that. This generation of F-150s has a part time 4x4 system. It puts power to the rear wheels unless you pull the handle to put it into 4x4. Use of 4x4 on dry pavement could damage your driveline, so it's for slippery conditions and off-road use only.

 

What exactly are you asking... PVH? I gather from the constant engagement you are referring to the front axle/hub set-up. So I'll guess you are referring to a positive vacuum system of some type.

The front diff uses a vacuum engaged ram to slide a fork assembly and engage the axle to the gear set. I'm unsure of the finer details. I do know there are no hub locks of any kind. The front end is all done by the vacuum solenoids found on the passenger side firewall. The axle shafts turn at any time the vehicle is moving, but the front drive shaft is not turning until the shifter or rotary switch is turned. The shifter also engages the solenoid and applies vacuum to shift the front diff into gear.

At least that's how I understand it.

-Kerry

 

I had a 1998 Ford Ranger with the PVH (Pulse Vacuum Hubs) 4x4 system which Ford no longer put in Rangers after 2000. Why, because this was a snip system which was prone to failure. The hubs would leak vacumm or not hld vacuum at all. The new Rangers have the front hubs locked in at all times...constant engagement front axle.

I was just wondering how the 4WD operates on a 99 Ford F150. When you shift electric transfer case into 4W HI, what happens??? Does it just switch the transfer case from 2WD to 4WD, or does it do that plus use a vacuum to "lock" the hubs in?

 

When you switch the transfer case to 4wd, several things happen. First, the lever activates an electromagnetic clutch that spins up the front driveshaft. Once that happens, vaccuum solenoids under the hood route vacuum pressure to motors on the front diff and in the t-case, and locks the driveshaft to the front diff and the t-case. Now, power goes to the front wheels.

I've heard it's a pretty reliable system, and I've never had any problems with mine. I have heard to keep the vacuum motors from sticking, use 4x4 on gravel or dirt once a month, and you should have no problems with it.

 

Does anyone have any schematics on how the 4WD system works? I have always been curious of it. The explanations in this post help a lot, but it would be neat to see it on paper.

 

Transfer Case —Electronic Shift on the Fly (ESOF) Operation

The electronic shift on the fly (ESOF) system is an electronic shift 4x4 system that allows the operator to choose between two different 4x4 modes as well as 2-wheel drive. The operator can switch between 2WD and 4H mode at speeds up to 88 km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 km/h (3 mph), the brake pedal depressed, and the transmission must be in NEUTRAL.

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to spin up the front driveline when shifting from 2WD to 4H mode at speed. When the control switch on the instrument panel is turned, the generic electronic module (GEM) recognizes that a shift has been requested and activates the electromagnetic clutch and the relays which power the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the GEM, power to the shift relays and motors will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle collar is engaged and the electromagnetic clutch is deactivated.

Shifts between 2WD and 4H can be made at any speed up to 88 km/h (55 mph). Listed below are the inputs and outputs needed by the GEM to execute a change between any of these modes.

Feature Inputs:

4WD mode switch (various resistances; go to Table 1).
Contact plate position inputs A, B, C, D (grounded when closed, open circuit when open; go to Table 4).
Feature Outputs:

4x4 shift motor relay outputs (go to Table 2).
Transfer case clutch relay (grounded when relay is activated, open circuit when relay is deactivated).
4x2/4x4 vacuum solenoid (grounded when activated, open circuit when deactivated).
Cluster indicators (ground when activated, open circuit when deactivated).
When shifting into or out of 4L, the GEM requires that the vehicle speed be less than 5 km/h (3 mph), the brake is applied, and the transmission is in NEUTRAL.

Feature Inputs:

4WD Mode Switch (various resistances; go to Table 1).
Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open; go to Table 4).
Output Speed Shaft (OSS) Sensor (Sinusoid Signal: 0.7V-20V, 2.2 Hz/mph).
Brake Input (battery voltage when brake is depressed, open circuit when not activated).
Transmission Range Sensor (grounded when transmission is in NEUTRAL, open circuit otherwise).
Start/Clutch Depressed Input (go to Table 3).
Feature Outputs:

4x4 Shift Motor Relay Outputs (go to Table 2).
4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).
Cluster Indicators (grounded when activated, open circuit when deactivated).

 

wow, nice reply!!!!

 

Dave... you're just showing off...

See... all we really need is an honest factory trained tech.

What applies when we use the manual shifted transfer case?

-Kerry

 

Is cutting and pasting cheating?

The mechanical shift on the fly (MSOF) system is a manual shift 4WD system that allows the operator to choose between two different 4x4 modes as well as 2-wheel drive. The operator can switch between 2WD and 4WD HIGH mode at speeds up to 88 km/h (55 mph). To engage or disengage 4WD LOW range, the vehicle speed must be less than 5 km/h (3 mph), the brake pedal depressed, and the transmission must be in NEUTRAL.

Shifts between 2WD HIGH and 4WD HIGH can be made at a stop or any forward speed up to 88 km/h (55 mph). At temperatures below 0°C (32°F) shifts should not be performed above 72 km/h (45 mph).

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to spin up the front driveline when shifting from 2WD to 4WD mode at speed. When the manual shift lever is moved this activates the 4WD indicator switch, 4WD electric clutch relay, and the electromagnetic clutch. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle collar is engaged and the electromagnetic clutch is deactivated.

 

Thanks, that clears it up. I'll just add this post to my list of favorites for future use.

The cutting and pasting is just fine, it gets rid of the third party editing problems.

-Kerry

 

Great site. I have kind of a twist on the above mentioned problem. Up to this point, both vaccuum solenoids on the front firewall have been replaced in an attempt to get the 4wd working. From what 2 people have said that looked at it, the transfer case is not my problem. The solenoid on the right, always has an audible click when the vaccuum lines are disconnected, either in 2wd or 4 hi. I've not had an indicator on the dashboard since I got the truck, and the 4wd has never worked either. The indicator does light during starting, so I know the bulb is good.

Like I said the solenoid furthest from the fender always has the audible click.

Had a buddy underneath the truck the other day and everything engaged when he swapped the vaccuum lines. However, I had 4wd, but no indicator on the dash.

I went back out this morning and tried the 4wd, (it's 24 degrees outside) and when I'm moving and attempt to engage the 4wd, I can hear a clicking that is faster, the faster the truck moves...... Hope some of this is the right information to get some troubleshooting help.

Thanks.

 

1997 Ford F150 with 133,000 miles on the above mentioned truck. With manual 4wd shift on the floor. Sorry about forgetting to post that info.

 

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