Stuck Fan Clutch

osteo16

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So got the 1988 M998 fired up last month. Run it in 10-15 minute intervals to keep battery's topped and get to temp. Noticed my fan is engaged and wont disengage when I unplug my Caddy Valve..I can see its working because hoses flex under pressure. Any good fixes for stuck fan clutch??? Can I get good access from driver side splash guard if removed to fix clutch?? Or I'm i gonna have to remove stack for optimal accessibility??? I'm handy in tight quarters so knuckle busting doesn't bother me... Any info would be appreciated..

Ocho Out
 

Coug

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So got the 1988 M998 fired up last month. Run it in 10-15 minute intervals to keep battery's topped and get to temp. Noticed my fan is engaged and wont disengage when I unplug my Caddy Valve..I can see its working because hoses flex under pressure. Any good fixes for stuck fan clutch??? Can I get good access from driver side splash guard if removed to fix clutch?? Or I'm i gonna have to remove stack for optimal accessibility??? I'm handy in tight quarters so knuckle busting doesn't bother me... Any info would be appreciated..

Ocho Out
the system fails to engaged.
If you unplug the cadillac valve then it will lock the clutch in the engaged position.
 

papakb

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The HMMWV fan works backwards from what you'd expect. The Cadillac valve holds it disengaged most of the time. Disconnecting the valve connectors causes the fan to engage. This is a fail safe mode so if anything dies the fan stays engaged all the time.

Disconnect the line from the Cadillac valve to the fan shroud feedthru and blow 90 psi air into it. You should see the clutch move forward and backward about 1/4". If it does that then the fan clutch is working. The stuff that typically dies is the temp sensor on the water crossover manifold, the time delay module, and the Cadillac valve.

There's no easy way to change out the clutch. Wear gloves and have band aids handy.
 

Milcommoguy

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We just went over this and related fan / overheating issue here for the last month. Check overheating and fan threads.

Couple up some fittings to your clutch line so that you can apply 90 +/- PSI air to clutch (no leaking). when applied lightly tap all around metal hub ring, just behind fan. There's not much there. Rotate fan and do it again and again. Tap... maybe little wack, rotate and tap-wack some more. Nice to have a trigger valve to give it a a few air blasting shots to wake it up. Maybe full of sand and crap too. So put the nozzle back on hose and give the hub ring area a blow out or two.

Hammer time...Aim at the hub ring with a 1x1 or whats handy piece of wood. Tap-Wack only the metal hub ring Not the plastic fan. If lucky might free up. Engine OFF of course.

Air applied to a working clutch should move forwards about 3/16 inch. Gummed up, rusted, broken clutch lining, you could be in for a treat.

Take it from there. It's your call... and didn't we just discuses this direct messaging?

I GOT TO SAY THIS... IT's IN THE TM's ! THERE I said it, CAMO the old grouch.

Going to sit in the corner for a time out.
 
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osteo16

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yes yes yes... you guys jump all over crap.. Im not having an issue troubleshooting fan clutch or overheating or anything else. Ive memorized all the 2800 pages of TMs.. And I dont think whacking the metal clutch to un-stick it is in there (Camo :ROFLMAO:) Maybe you have access to the redneck guide to fixing HMMWV supplement.. Can i get a copy from you? I simply asked if anyone has attempted access to fan clutch (which i know is clearly stuck (not moving in and out when i engage/dissengage caddy valve) from the driver side splash gaurd removed, or if stack needs to come out.. Guess ill try to whack it from the top first with something i can reach down with.. Thanks for the input though.. ;)

Love Ocho

Guess I could have put "SIEZED" fan clutch in the description.. That would be my bad
 

TOBASH

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A stuck fan clutch that is not leaking fluid is preferable to one that does not activate or one that leaks.

For the time being, I would leave it alone.

Like I just posted elsewhere, I will follow another old post here in this forum and swap in a mechanical GM clutch just like is on all my other vehicles. I don't ford water and I don't need the damned thing to turn on and off.
 

86humv

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yes yes yes... you guys jump all over crap.. Im not having an issue troubleshooting fan clutch or overheating or anything else. Ive memorized all the 2800 pages of TMs.. And I dont think whacking the metal clutch to un-stick it is in there (Camo :ROFLMAO:) Maybe you have access to the redneck guide to fixing HMMWV supplement.. Can i get a copy from you? I simply asked if anyone has attempted access to fan clutch (which i know is clearly stuck (not moving in and out when i engage/dissengage caddy valve) from the driver side splash gaurd removed, or if stack needs to come out.. Guess ill try to whack it from the top first with something i can reach down with.. Thanks for the input though.. ;)

Love Ocho

Guess I could have put "SIEZED" fan clutch in the description.. That would be my bad
Don't whack the nose cone...it will break.....Add 90 psi air to the hose going to clutch....and whack body only.
 

Milcommoguy

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Been off line, out of town.

Mr. 86Humv is Right. I figured the guys wouldn't be able to get at the nose piece with the fan / shroud in the way. Too much work.🛠 Should have stated it better for the clever ones.

I was clear as where to tap. The tap and wack is a controlled wack. More on the side of tap, but didn't want to sound lady boy for the rednecks or offend the BLM gang looking to tear stuff up. Big Lazy Mechanics.

And as stated over and over and over... there are NO dumb questions (OK sometimes) BUT to filter the dumb ones out, get the picture book "TM" study the exploded views...before you explode the parts you'er working on or trying to explain. You can read the TM's cover to cover, But I would say you need to talk to a doctor about that constipation and just get back to wrenching.

Back to the ongoing fan tricks. With 90 PSI +/- to the clutch and fan is still locked-up ( hasn't or isn't blowing ATF and air out) see you can work it free by rotating it a little clockwise - then a little counter-clock wize (easy big boy's) don't WANT to snap any old brittle blades off.

I too had a hate relation with this cooling system. (got a big one for the smart box) After getting a feel for the goings on, IMO it's no better or worst than any other, unless you have gear driven one. Thought about flex fan, electrics, viscous fluid and circled right back to factory. Biggest issue a little brain work and understanding. Add in a dirty OLD neglected coolant system that could be throwing off the logic to keep it factory.

Now if the hood's in the corner and one is hot to tear into the cooling stack IMO no need to stop there. This exposes a lot to check and piece of mind parts ie: hoses, pumps, idlers, coolers, radiator and the crutch to work on easy...er. Good time to check out the dif and brakes too. Dig a little deeper IP timing parts.

Going for new never ends, CAMO

If these types of problems are showing up look back at any of the threads showing cooling, running hot, temp gauge, fan, overheating, etc.
 
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osteo16

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This is what a forum should be like 👍🏼👊🏼

Since I’m working my way around the HMMWV, cooling system purge and clean are close on the agenda.. I’ll probably pull stack so I can thoroughly rinse out the radiator. Also need to do some brake work up front anyway with some odds and ends.. This will force me to wait to road ride it till it’s road worthy I guess.. Better safe than sorry.. Will continue on my arduous quest to bring her back to glory.. Hell, not like I don’t have another few months to burn 🙏🏼

Post Adjourned

Ocho
 
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