FMTV Fan Clutch Repair

Ever since I got my LMTV, the fan has been running full time. Makes a huge amount of noise, it is unmistakable. Well after troubleshooting the electrical and solenoid end of the system, I came to the conclusion the clutch was stuck in the on position, and I needed to R&R it. To get to it, you have to remove the upper fan shroud. To do this, the charge air cooler lines have to come off. Next the fan comes off with 6 allen head screws. Next, the manual says to "apply air pressure so you can rotate the clutch to get access to the screws that hold it to the harmonic balancer". Well of course the holes were not lined up and what was I to do? Cut it off with a torch? I decided to try to get the clutch free. I turned up the air on my compressor to 180 psi and rigged up a line. After applying pressure, I hit the clutch as shown with a hammer. Well guess what, it popped loose and now is operating just fine. Maybe if this happens to anyone else, you can try to hit the clutch with a long bar and a hammer on the end of it, and save the disassembly.

Got to love a BFH for assembely disassembely,and light maintance of all lifes little problems.

I had the same problem. Used a large piece of rebar and tapped with 4 pound hammer and it worked to knock clutch free, thanks for the suggestion!

took 2 mins

HHHMM.... Just roaded my LMTV home about 275 miles yesterday. It tried to overheat when I climbed long hills or when I consistently held the speed above 56 MPH. Had to slow down to 50 to keep the temp under control. I never did hear any distinctive fan noise so my fan clutch may be stuck off. Thanks for the info.

Remember, air pressure off, fan engaged, air pressure on, disengaged. The clutch's resting position is engaged. So in your case, air pressure is being supplied continuously and preventing the clutch from driving the fan. Follow the TM's diagnostic process, it is very helpful. The air pressure solenoid is under the PDP next to the turn signal flasher.

Ok, checked fan operation out today. Looks to be operating as specified as far as the clutch itself. Engages and disengages as it should when I remove air and reconnect.

Must have another issue so I will have to investigate further. Got sidetracked today troubleshooting the cab lift/hydraulic panel.

http://www.steelsoldiers.com/showthread.php?145266-Checking-the-FMTV-fan-system

wyocommo,
There is a detailed thread floating around that talks about troubleshooting the valve/solenoid behind the kick panel that activates the fan clutch. On my LMTV when it gets over 200 degrees, between 205 and 210 I think, you can hear the solenoid release/click under the power panel and the clutch engages with the fan roaring like a freight train in your backyard. Temps immediately drop below 200 (less than a minute or so). I bought a replacement solenoid just as a backup in case mine fails.

OD

That fan clutch works on the same principle as a HMMWV, what happens to them is the 3 internal clutch pads kind of fuse themselves to the housing...before I install even NOS ones into a truck,I air them up and beat on the back side with a dead blow hammer till you see the unit separate, it only moves less then an 1/8in to the disengage position...and as we know, when no pressure, settles into the engaged position.

Thanks! Mine is stuck engaged, so I'll be trying this out soon.

When you truck reaches 200 degrees you should hear a release from your compressor and the fan will kick on to engage the fan. Take the air supply line on the front of the slip clutch, after removing fan blades, and rig up 90 psi to the opening where your supply line was. It should activate the clutch. If not look into supply line issues or slip clutch replacement.

Does anyone know if a solenoid for an HMMWV will work in an FMTV/LMTV? I know there'll be some wiring and air line plumbing issues but I'm wondering if it can work.

walshjuice said:

Does anyone know if a solenoid for an HMMWV will work in an FMTV/LMTV? I know there'll be some wiring and air line plumbing issues but I'm wondering if it can work.

Click to expand...

Same answer as the other post-no. Air - vs - hydraulic