Hi -

I am looking for some help on troubleshooting an issue with my 4x4. The truck is a 1997 f 150 with the shift on the floor (MSOF). When I shift into 4x4, the light in the dash does not illuminate and the truck doesn't go into 4 wheel either. I read through the old info and dug into this all day on Saturday and couldn't solve the problem. Any help would be appreciated as I am completely perplexed.

Here is the current status:

Transfer Case: Good shape, no issues. The front driveshaft spins when I shift into 4 wheel drive. The linkage is a bit rusted but moving freely.

Vacuum Solenoids on the Firewall: I thought this was the issue. One of the solenoids was cracked on the back when I inspected it and I replaced it. I figured the other way just a matter of time so I replaced it as well. This did not solve the issue.

Transmission Range Sensor: Appears to be in good shape, but I did not fully test functionality. I just removed it and made sure the ball in the sensor was moving back and forth. I also cleaned the electrical connections for good measure.

Vacuum diaphram on the front differential: moving back and forth freely. I found a definite issue here, but can't figure it out. When I shift from 2 wheel to 4 wheel, the actuator was not moving. I pulled the vacuum lines off and had my wife shift back and forth between 2 and 4 wheel. The line on which the vacuum was pulling DID NOT CHANGE. I am assuming this is not normal and wasn't sure what could be causing it.

Here is my current list of issues that I think it still could be:

1) Problem with a relay? Which relay grounds the solennoids and switches the one which should be pulling vacuum? I suppose it could also be the GEM, but I hope this is not the case.

2) Vacuum line leak somewhere? I checked everything and don't think this is the issue, but I could be wrong here?

3) Fork in the front differential broken/bent? When I took off the vacuum lines and moved the actuator back and forth, I still couldn't get the truck to shift into 4x4.

4) Issue with transmission range sensor?

 

I am thinking about pulling the GEM this weekend to test it and check for any water damage.

Any other thoughts. I've been researching this a bit more and wanted to know if the GEM directs a voltage signal through a relay or if it is a direct path to the solenoids on the firewall. If anyone has a wiring diagram, that would very helpful and greatly appreciated.

Any other thoughts? Any help or even simple ideas are appreciated as I may have missed something here.

Thanks,

Zack

 

GEM was shot, my windows and locks now work on the drivers side, but the 4x4 is still out of commision. My next item to pull and test is the transmission range sensor switch. Hopefully going to pull this weekend and see how things go....if anyone has any advice, I am still all ears.....getting a bit lonely here posting to myself.....

 

So how does the MSOF work now that you changed the GEM ?

Yea, a bad GEM can effect your solenoids. You have a 2wd and 4wd solenoid on the firewall.

That's all for now.

 

It ended up being the transmission range sensor switch that was the issue. There are a couple of other really good posts that pointed me in the right direction. If you type JackPiner or Revytrucks into google, you will probably get the right forum for troubleshooting the 4x4 for a MSOF. There are some nice pictures of the TRSS on this forum. It was on the front of the transfer case and the part number was 7E440 on the transmission case diagram. Hopefully going to try out the 4x4 this weekend if we get some snow in MN.