4wd Hub Switch question

[okaussie]

I don't know if this question has been asked.

I would like to know if the front axle switch on the right hub could give you a false engagement of the axle other than the switch itself being bad, ie, the contacts in the switch are touching all the time.

When you switch from 2Hi into any 4wd position the light flashes then goes solid.

I was wondering if something other than switch failure could give you a false positive on that system...

Just a question enquiring minds just have to know...

Bill

[okaussie]

Update:



We are suppose to have a cold rain with the possibility of ice and snow on Saturday.

I work 16 hour shifts over the weekend so I can't call in due to bad weather.

Went out this morning and put concrete blocks in the back and went to check the front axle for 4WD. Guess what, I have none...

The dash flashed when I put it in 4hi then went solid, as it should, put it in 4lo and it flashed like it should. Went out with the park brake on and jacked up both front wheels.

Turned the front driveshaft in park, no go, like it should. Put it in neutral, and it turned like it should.

The front wheels are another story, they free wheeled in any transfer case position. Did not turn with the front driveshaft when I manually turned it. Went to each front wheel and turned it. The driveshaft did not turn at all and both wheels had no resistence like it was connected to the driveshaft.

So, I disconnected the battery and shorted the + and - cables together and will let it set for a while.

Don't know what else to do at this point.

All indications inside the cab is that the front wheel are locked in. However, checking it by the above methods, they are not...

Thinking maybe a shorted front axle switch on the right front wheel, as well as something from the transfer case to that wheel, like the actuator, actuator cable, etc.

Any other thoughts???


TIA

Bill

[HenryJ]

Ok, If I read this correctly you have the light on as it should and the front axle is still not engaged. The transfercase is.
That would point to a shift fork or collar problem.
Keep in mind that the front axle is an open carrier. In order to check to see if it is properly engaged only one front tire can be off the ground. With the transfer case engaged and one tire on the ground try to turn the lifted wheel. It should be the one that has the power, therefore locked. If it does not turn, things are working as they should. If it is still free the shift collar has not engaged the passenger side axle. The light being solid says the actuator has pulled the cable and the shift fork has activated the switch. You could have a bad shift fork or collar.

[okaussie]

That was what I was thinking. I first lifted just the right wheel and checked it. It was still free wheeling . I could turn the front driveshaft in 4wd in neutral and have no movement in the right front wheel. I could turn the wheel and have no movement in the driveshaft. However in all tests that I performed, the indicator on the dash showed that the hubs were engaged.

Looks like I have quite a bit of work ahead to fix this...

Thanks Henry,,,

[HenryJ]

Try one more time and with the front driveshaft locked (engaged) Lift the right front wheel and see if it is locking.. Keep in mind that the wheel must turn for the collar to engage and the light stay lit. If it does not, you are going to need to pull the front axle apart to fix the problem.

I did have this very thing happen on a fleet rig. The mechanic on the other end pulled things apart to replace a seal and did not get the shift fork on the shift collar properly. It said it engaged when the fork moved, but the shift collar was not on the shift fork. Easy fix.

[roadrunner]

Been reading through this thread and gotta ask. Was the truck running while you were checking for engagement of the front wheels? Not being sarcastic. Just couldn't tell from the posts. If not it has to be for the vacuum to engage the actuator and subsequently the cable and shift collar.
If it was running then you may have a vacuum loss, hose off, bad t-case vacuum switch, or a damaged or loose actuator pod under the battery tray. If in doubt run a vacuum line directly from an engine vacuum source to the shift actuator and with the engine running and the shift indicator in either 4wd position then check to see if the wheels lock in. If not then either the actuator, cable, or front shift fork or internal front end gears are broken or damaged.
As for the light blinking it is normal for them to flash briefly while the shift is occurring then go solid after completion.

[okaussie]

Yes the engine was running. I know I have a vacuum leak from the "T" fitting under the hood to the vacuum transfer case switch. It is causing my actuators on the HVAC system to work only when there is no acceleration on the engine. I verified that by removing the vacuum line to the transfer case switch at the "T" fitting and capping off the fitting. My HVAC problem went away.

I know I need to replace the line from the "T" fitting to the transfer case switch.

My original post posed the question of a "false positive" on the dash lights. This seems to be the case. You can have the lights work appropriately signifying full engagement of the axle, however it is not. It only looks at the shift of fork for engagement and not the full actual engagement of the axle and the axle is connected and turning with the driveshaft.

So, Roadrunner, are you saying that the dash lights can work appropriately and have a bad actuator pod as well as the shift fork or collar issue???

Another false positive on the dash lights???

Bill

[HenryJ]

Another possibility is the actuator is not working and the switch is stuck. Unplug the switch and check it. See if it is open when disengaged and closed when engaged.

[okaussie]

I manually moved the 4wd actuator and I could hear the front axle click then click again when I released the actuator. I then hooked up a hose from the actuator to the "T" fitting and unhooked the line going to the transfer case switch, thus forcing the front axle to engage when the engine creates enough vacuum. Started the engine and put the switch in the dash from 2hi to 4hi. Test drove it. Definitely in 4hi. Everything works like this. Mine is a 2002 and can't find the transfer case switch. I have felt the transfer case and can't find it. I got a new switch and new line to replace everything from the "T" fitting to the 4wd actuator, if I could only see the switch.

Does anyone have a pic of where it is located???

TIA,,,

Bill

[HenryJ]

Revised transfercase switch

I was able to reach over the left side of the transfercase , Just above the ID tag. follow the triple vacuum hoses to the switch.





Most of this is done by feel, since it is very hard to see up there. Pay attention to where the pin is on the switch. You will have to feel for it's position and reattach the hose connector correctly.

[okaussie]

Thanks,,

I will see if I can find it. BTW, does anyone have a pinout for that connector? I am going to replace all the hoses and reroute the vent so it is all by itself, thereby eliminating the transmission fluid into the vacuum line problem.

I am also going to take it to a place where I can rent a stall by the hour and put it on a lift to get a better view and angle of the switch.

Right now, I can use 4WD by just hooking the 4wd actuator hose to vacuum then pushing the 4wd switch in the cab. This will get me by until next week when I have time off to work on it..

Thanks Henry

Bill

[roadrunner]

When the shift fork moves (by way of the vacuum actuator) in the front axle it triggers the switch located there on the front axle which is supposed to indicate to the shift buttons (blinking lights) that the shift has been completed. If the lights are working properly on the indicators the only way I can envision a "false positive" would be if the front fork shift switch is shorted or stuck in the engaged position or is only moving far enough to trip the switch and not far enough to fully engage the front axle. Unlikely but not impossible. I have personally had an over-sensitive switch on the front axle cause intermittent odd problems with the indicators on the dash.
Your adding a vacuum hose direct to the actuator proves there is sufficient vacuum loss that the actuator is unable to engage when connected to the oem lines and routing.
Re-routing the vacuum lines as you indicate in your previous post will prevent fluid from being able to enter your hvac and other systems but be aware the switch on the t-case if still leaking will simply be able to leak directly through your new lines to it's new vacuum source.

[okaussie]

RoadRunner,

I found a place that will rent me a stall with lifts, tools, etc for $15/hour. I intend to replace the switch next week when I am off. I am also going to vent the switch separately from the original vent so the tranny fluid issue never arises again. I am also going to run new hoses all the way around.

I do agree with you that the 4wd actuator is getting insufficient vacuum to full engage the front axle. The switch thinks it is engaged but is only partially engaged due to the vacuum problem. It also causes the HVAC problem as well.

Replacing the switch and hoses and rerouting the vent hose, I should think will fix all of the above.

Let you all know next week..

TIA,,

Bill

[HenryJ]

I am sure you probably know that it is not the vent for the transfercase switch that is the issue. It is the fluid entering the vacuum system from the switch. I see little choice in selecting a better source. Selecting another vacuum source may not be a fantastic ideas as you need to still be sure it is one connected to the reservoir as to avoid any drops during acceleration. This would cause erratic front axle engagement.
I would replace bad lines , but not alter the source location. In my mind there is not a better choice right now. I can not say I know of an approved method to create an isolator or separator either. Use a good switch and fix the lines would be my direction.

[okaussie]

I planned on running a vent line from the switch to under the hood instead of using the factory that is "T"ed into the transfer case and tranny.

I thought that was the problem not the switch sucking it in from the ball.

In that case I will just replace the transfer case switch and the hoses from it to the 4wd actuator and to the "T" fitting where the vacuum is.

I did not plan on getting vacuum from another source. I still planned on getting it where it has always come from, which is the "T" fitting next to the reservoir.

It is starting to rain here now and won't get to it til next week.

Looking forward to using the rental place with all the good tools.

Only so much you can do with what I have..

Thanks guys,

Til next week...

Bill

[HenryJ]

I am not quite sure who is confused. Right now it is me for sure. I just need to make sure we all understand this correctly.

The seals in the switch fail. That is where fluid is sucked into the vacuum system and tends to accumulate in the vacuum reservoir.

The switch has three lines. the switch has one closed port and two that are connected together. When depressed the combination shifts.

A supply line from the vacuum system. That line does tie into the vacuum reservoir as do lines from the HVAC controls.
The next line on that switch goes to the front axle actuator.
The last is a vent. It does end up by the trans dipstick.

How does it work?
Disengaged: When it is in the closed position the vacuum supply line is plugged or closed. The front axle actuator line and the vent line are active. Those two are linked. This is how the spring over comes the vacuum and disengages the front axle. The front axle actuator is vented.

Engaged: The switch is depressed and the closed position is now the vent line. The vacuum supply line and the front axle actuator line are now linked. This over comes the spring pressure and pulls the shift fork to engage the front axle.

This is my understanding of how the switch works.

Where does the fluid come from? It does not come from the transfercase vent. In the disengaged position it is tied to the front axle actuator. Fluid in that line has not been an issue to my knowledge.
The fluid is sucked in from failed seals in the switch. Instead of being closed to the vacuum supply fluid leaks by into the supply line. From there it tends to accumulate in the reservoir and eventually into the rest of the system. The HVAC system is the biggest consumer and the first casualty.

I planned on running a vent line from the switch to under the hood instead of using the factory that is "T"ed into the transfer case and tranny.

I thought that was the problem not the switch sucking it in from the ball.

The "ball" / reservoir, sucks it in from the switch.
Sounds like you have the right idea. Let us know how it all works out.

[roadrunner]

Excellent explanation HJ! Nothing for me to add at this point.

[okaussie]

Just like a single pole double throw switch.

The actuator line is either connected to the vent or vacuum depending on which position the switch is in, which is dictated by the transfer case.

The fluid problem came into play when the seal on the ball leaks and puts fluid into the switch.

All makes sense...

Bill

[roadrunner]

Bingo! You got er Bill.

[okaussie]

With a background in electronics and computers, I look at everything like that.

Converting it to electrical it totally makes sense to me...

Should of thought of it sooner..

Bill