96 Ranger. 4.0. 4wd. Getting occasional whine/ clunk from left front side when on highway. Pretty sure it is 4wd sometimes trying to engage even when dash switch is in off position. Does not do all the time. Ideas? Does my truck have a 4wd actuator pneumatic / vacumn system for each front wheel that maybe is leaking and causing?

 

Welcome to the forum

No, PVH(pulse vacuum Hubs) were only used from 1998 to 2000.

Your 1996 will have "Auto Hubs" they were activated by the front axle spinning.

Usually you will get a "clicking" noise if auto hub is trying to engage or disengage when it shouldn't.

Auto hubs need to be clean and LIGHTLY OILED, to work well.
People often pack them with grease which causes problems.

How to here: Automatic To Manual Hub Conversion

This is for swapping to manual hubs, but shows the disassembly and parts inside.
It isn't to complicated to take these apart and repack the wheel bearings then clean and lightly oil the auto hub parts.

Wheel bearings could be making the noise as well.

Auto Hubs are pretty simple, when transfer case is in 2WD the front drive shaft is not engaged so it doesn't turn and neither will either front axle.
When you select 4WD the drive shaft and axles will start to turn when you move, the Auto hub will then slide into place locking front wheel to axle.
When you go back to 2WD the Auto hubs "should" slide back out as soon as wheel turns but axle doesn't, if it doesn't then you need to backup 30-50ft to unlock them

 

Thanks RonD. Really appreciate it and very informative and helpful! Will let you know how it turns out.

 

Final report. Took the front hub and bearing assemblies off and apart. Hubs WERE really dirty and full of heavy grease. Wheel bearings were a bit worn out as well. Cleaned everything up and replaced bearings. All is good now. No clunks or whine. Thanks for the help!

 

Good work

Thanks for the update and fix