Vaccum line routing

hi

heres a link to what I found

https://www.justanswer.com/gmc/5yd56-chevrolet-s10-blazer-4x4-vaccum-routing-transfer-case.html

Does a 2002 Dodge Ram 4x4 have a vacuum modulator ...

www.fixya.com/.../t25860408-2002_dodge_ram_4x4_vacuum_modulat...

14 mins ago - 1 Answer. Where do the vaccum lines go into the transfer case on a 2002 RAM 3500? I need a diagram of the vaccum lines into the transfer ...

Vacuum lines do not actually go into the transfer case, they go to the 4x4 actuator and there is a vent hose at the top...that is about it.

Hi, did you check the transfer case fluid level at all ??

Could also be your metal vaccum lines on the cross member and along the passenger side of the frame to the front axle assembly where they connect to the axle vaccum switch diaphragm. are rusty and leaking not engaging the 4 wheel drive all the way in gear.

If I read this correctly ( which I might not have, bit early for me ), the front drive shaft will engage ( from the transfer case ) but the front wheels are not engaged ?

If so, sounds like either the vacuum from the IWE ( Integrated Wheel End ) is not being released, or the IWEs have had an issue with part vacuum ( damage vacuum lines ) and the IWE gear is rounded off.

If you pull the vacuum lines at the IWEs ( there are 2 lines, 1 is the vacuum line, the other is the vent tube that routes up into the engine compartment and is not attached to anything ), the front wheel should engage ( might need a 5 * turn to mesh the gears ). With the vacuum lines off, jack up the front axle ( take precautions, chock the rear wheels, parking brake, jack stands, etc ) see if the front wheels are engaged ( turning one wheel should turn the other ). The option is to do this after the truck has sat over night, and the vacuum has been released out of the vacuum reservoir.

If the wheels turn correctly ( engaged ) I would think the contact plates in the transfer case are not making contact. Good starting point for this is the connector on the side of the transfer case, some times this gets gummed up, and the pins do not make good contact. The contact plates in the transfer case are used for a few things, one of them is to signal the IWE solenoids to release vacuum to the IWEs.

Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vacuum is removed the spring engages the IWE.

Here is a black diagram of the IWE vacuum system

Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vac is removed the spring engages the IWE.

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
If it turns it is a problem with the transfer case.
If it doesn't it is a front axle engagement problem.

- If the front drive shaft does not turn :
Shut of the truck ( still jacked up, and supported ) remove the vac lines from the IWE. The spring should push the gears in, without the vac line on.
Check the vent line ( tube that is routed into the engine compartment with nothing attached to it ), for blockages.
If the vent line is clear, and with the vac lines off the IWE should be engaged ( both front wheels locked ).
If they lock, the problem is with the IWE solenoid not shutting off vacuum to the IWEs. There is a TSB on the 2004-2006 IWE solenoids, a newer revision has been made, and used from 2007 and newer MYs.

Here is a block diagram of the IWE system


If the front drive shaft turns, it is either the connector to the transfer case or the transfer shift motor not functioning correctly.
Check the connector for corrosion on both the male and female pins.
Turn key to run ( do not start ) and have someone turn from 2WD to 4H and back again while hitting the transfer case with a dead blow hammer ( not a steel hammer ) to see if the shift motor is hanging up.

Not sure if selector does not engage 4x4 hi or 4x4 low means the lights on the mode selector switch do not change, or if the switch selects 4H, but the front wheels do not function, so hard to provide a true direction on where the problem could be.

Hi Buganbird22

I pretty much have the same problem. The odds are that it isnt the transfer case at all.

That model year has an electric over vacuum control switch on the transfer case and 2 electric over vacuum switches on the passenger side front fender well near the rear by the hood hinge, they are either green or blue and made of plastic, they both have vacuum lines and 2 wires connected to them.

From there the vacuum lines run down near the front differential where they connect to a slave cylinder. the vacuum routes one way, the slave plunger moves and the differential engages 4WD, the vacuum routes the other way, the slave plunger moves again and the differential disengages 2WD (similar to a 90's model dodge 4x4).

Run this easy test. Label the vacuum lines that come from the top of the vacuum switches on the fender well (front, rear) use masking tape.

Start your truck. (make sure one of those switches has vacuum, put your finger over the nipples where you unplugged the lines, if you feel suction, you got vacuum) trade the vacuum lines, front to rear and rear to front. shift into 4x4, you wont get a 4x4 light, but if you now have 4WD then the problem is in the circuit somewhere between those 2 switches and the master switch on the T-case.

I'll post more as I go. I've been switching mine that way for a week now, because i'm too lazy to fix it in 2 feet of snow.

if you crawl under the vehicle, trace vacuum lines to transfer case they terinate in a group of 3 (vent, vacuum from engine, line to actuator diaphram under battery) . Mark lines (bundle should have a pin to prevent bad replacement, but be safe) pop 3 hose unit , unscrew switch (count the turns to return it to same position). Transfer case side has a ball that should detent fairly easily. If stuck, work it loose or replace the switch. This manual detented switchsimply routes vacuum to diaphram which pulls cable to front axle, or vents it to atmosphere when in 2wd.

You should be able to feel if diaphram is pulling in when in 4wd and is relaxed when in 2wd mode to troubleshoot. Direct vaccum to diaphram line to test. I have used aquarium airline tubing and airstone manifold to provide quick fix when a garage and/or access to parts was not available. You want to be able to direct vent to diaphram for 2wd and engine vacuum to diaphram for 4wd.

youmight have the transfer case checked for faults

when the transfer case shifts into 4wd it activates a vaccum switch on the transfer case which sends vaccum to the accuator for the front axle. the accuator pulls a cable that locks in the axle. the switch on the transfer case is a well known problem. check for vaccum in and out of this switch in 4wd. if you have vaccum out then check the accuator under the battery. If the vaccum switch on the transfer case is bad you can find one at most parts store in the HELP section #49315. please rate if this helps