M923A2 Fan Clutch Repair - Any Clutch Gurus Out There?

[brasco]

The fan on my M923A2 was running all the time and I thought it was a bad shutter stat. I put in a new shutter stat and that was not the problem. (Yes, I know I should have tested it first) I then removed the fan clutch and took it apart yesterday. I found that the thrust cap inside the clutch was only being held in place by one of 8 bolts and it was nearly ready to let go itself. One loose bolt was bouncing around the inside as well as the remaining 6 screw heads that were broken off See pictures! I used vice grips to remove the broken off bolts. In the right hand picture, the threads in the 6 o'clock and 9 o'clock positions are damaged.




Has this happened to anyone else? At first, I thought my entire fan clutch was toast but after cleaning and inspecting, all the bearing seem to be OK. The thrust cap has deep grooves worn into it but it appears that I could actually bolt it back together and it would work with no issues - maybe it would be a little out of balance when the fan runs? I'm also going to price a new one tomorrow. My biggest concern is that 2 out of the 8 threads in the outer house are damaged. I'm thinking about putting helicoil inserts in these two threads and putting it back together. Has anyone done this with these clutches? I'm just looking for past experiences with successes and failures.

Don

 

[Swamp Donkey]

I just rebuilt mine a couple of weeks ago and while I'm not a guru, I did learn a lot and can share some information.

That is an Evans FC367E, correct?

Comfort Air has all the parts you need to rebuild it. That's the one in Grand Rapids...www.comfortairgr.com. The man that answers knows his stuff and is very helpful. They also have a rebuild manual on PDF on the site that has all the parts listed if you haven't seen it yet.

New clutches are expensive, especially when they were made to be completely serviceable and parts are available. Are you SURE the shutterstat is working correctly? Does the fan come on as soon as pressure is built or just when it reaches activation temperature? It sounds like the piston is getting hung and the spring can't push it back in, or air pressure is keeping it engaged due to an internal leak.

Have you tried chasing the threads in the damaged holes? If that doesn't work you could always retap to the next larger size and get new screws. Have you removed the piston yet to check the 2 large O-ring seals? Once my fan came on, it stayed on until the engine was shut down and the air pressure released. It leaked from the back side but only when the fan was activated. The 2 internal seals for the nose cap were worn out on mine. I replaced the cap and the 2 large seals on the piston. I thoroughly cleaned everything and greased everything real good. Do not allow grease to get into the area with the clutch material or anywhere around it. Now everything works perfectly.

 

[Coffey1]

I know this much they are expensive.

 

[brasco]

Swamp Donkey... thanks for the input. Yes, the clutch was pretty much the problem. The spring was pushing the "thrust cap" up against the main pully sub assembly and locking everything together. there was still enough relative motion to wear a big groove in the thrust cap.

My clutch appears to be a FC200158. I am familiar with comfortair in Grand Rapids... that's where I bought the shutter stat. I plan on giving them a call and see how much new parts will cost. I think I'm going to buy a new thrust cap, part number FC030061 if it is not too expensive - I found it in both the TM and the Evans catalog.

I can get screws into the 2 damaged holes; they are just really loose. On the worst hole, I can push the bolt almost all the way in before it will engage the remaining threads. I'm thinking adding the helicoil insert will be the route I take because the repaired thread should be better than the original - it will be stainless steel instead of aluminum. I used helicoils almost 30 years ago when I repaired chain saws and threads would get stripped in the soft aluminum and magnesium parts. They should work in this application too I just don't know if anyone else has tried this.

I haven't tried to dig into anything else like the piston o-rings. I'm still working on the most damaged parts.

 

[Swamp Donkey]

The part number you listed looks like their current or updated part number format. Appears to be about the same as the older ones. Mine is an '84 923A0. The nose piece ran around $80-$85 and the big O-rings were around $15 for the both of them. He had all of those in stock.

FWIW, the shutter stats are rebuildable most of the time too. There are a few O-rings in them that can be replaced. Add a little lube in them and most work good as new. So don't throw the old one out. There are at least two different styles though. The older style has a brass needle with an O-ring and the newer style has a plastic needle. If the plastic needle get messed up I'm not sure there is anything that can be done.

The clutch I rebuilt on my truck had a rebuild tag on it with fresh clutch material and new piston seals from the military. They used a lot of grease behind the piston and for good reason. Water can accumulate there and cause rust. The spare I have was neglected and the piston was frozen and seals cracked. The only lube anywhere was in the bearing chamber. Everything else was dry and rusty. On reassembly coat everything with grease (except for the clutch surface) and use a descent amount behind the piston. It helps keep everything moving and stops corrosion from the moisture that can accumulate in there.

When you get the new nose piece look at the 2 inner seals. The new seals should be pointed and the old seals are probably worn flat. Important: Apply grease between the 2 inner seals. It will stay there and help to keep the wear down. The end of the shaft that goes in the nose piece should be chromed and smooth. It can be cleaned up if need be but needs to be smooth. The spare I have had missing chrome and had started to corrode. I was able to bring it back smooth with emery cloth to form a good seal. A little dab of grease on the end of that shaft will also help with moisture. I used marine bearing grease for its moisture resistance.

The torque values for the bearing nut, thrust plate screws and cap are in the instructions. After assembly it can be bench tested @ 90psi with air pressure to engage the clutch.

 

[brasco]

So.... I have decided not to repair this broken fan clutch now and obtain a good used fan clutch. I have found a couple of options. One is a Evans unit like one I have but the other unit is made by Horton which also appears to have been a supplier for these parts.

Does anyone have any information on which brand is better of have any history behind the two options.

Thanks,

Don

 

[rosco]

If you get a used one, regardless of what the sales pitch is, i'd rebuild it. Sometimes they can go into a free-wheeling mode too. Observe on the front of it, there should be a couple of holes that you can insert a couple of cap screws into, and lock it into fixed rotation/drives all the time mode (keep these in your tool box). That will get you in. Also, its best to put an air shutoff valve on those little air lines, so if/when you have problems, you can control air loss. Seasoned drivers keep a hand full of brake shoe rivets in the tool box too. You can disconnect an air line, drop in the rivet, re-do the line, and that will stop the air leak!

 

[acme66]

I hate to revive but do you remember the noise it was making or more importantly did the hub rock back and forth. I know I have a bad shutter stat and the fan is locking up BUT when locked up I can still move the fan back and forth a bit on the clutch, not in or out or any wobble just back and forth. That seems odd to me. Can you remember at all?

Ken

 

[brasco]

I hate to revive but do you remember the noise it was making or more importantly did the hub rock back and forth. I know I have a bad shutter stat and the fan is locking up BUT when locked up I can still move the fan back and forth a bit on the clutch, not in or out or any wobble just back and forth. That seems odd to me. Can you remember at all?

Ken

Ken,

Hmm, I think it did rock back and forth a bit (rotation-wise), and I recall that it seamed to be be sticking out a bit as if it was engaged even with no air on it. (Obviously checking with the truck off! ) I later found out this was because the spring was pushing it out. You can see in picture on my first post how the metal wore down from the spring pressure. Not shown is the opposing casting which was worn down the the bearing.

It really didn't sound bad at all. It would sometimes make a rattling sound that would go away after a few seconds.

I don't think it should be locking up when cold and no air built up, even with a bad shutter stat.

 

[Swamp Donkey]

I hate to revive but do you remember the noise it was making or more importantly did the hub rock back and forth. I know I have a bad shutter stat and the fan is locking up BUT when locked up I can still move the fan back and forth a bit on the clutch, not in or out or any wobble just back and forth. That seems odd to me. Can you remember at all?

Ken

In Brasco's second picture, the ring around the hub with the bearing is actually the piston that engages the clutch material. Air comes in behind the piston and pushes it out to engage the clutch.



In this picture you can see the piston removed, along with the pins it slides in and out on. These pins are what keeps the front half from turning when the piston engages the clutch material. Since these are slide pins, there will be a slight open tolerance to prevent binding. The rotational movement will be very small if measured at the clutch but can be anywhere from 1/16"-1/2" if measured at the tips of the blades. The length of the blades multiplies this movement. The movement from this area wouldn't have any resistance when turned back and forth. If your clutch looks like this on the inside it needs some attention.



In this picture you can see the return spring for the piston and the clutch material recessed around the screws that keep it from rotating. The clutch material can move slightly since it's not clamped down by the screws. This movement would have a decent amount of resistance to it, but can be felt.

All of this movement when the clutch is locked is normal. I've rebuilt 7 of them, all with various issues, and all of them had some amount of movement due to slide pin tolerances. FWIW, the ones that look the best on the outside usually look the worst on the inside from my experience.



This is a picture of the rear thrust plate with the screws removed. The thrust plate and screws in the back keep the return spring compressed and keep the two halves together. If the screws were to loosen or break, the back half would move towards the engine while the front half stayed in place. These screws can be felt from the back without removing anything although the clutch will have to be rotated to check them all. I can't say for certain if there is enough room to tighten them without removal but you should be able to at least feel them. They are small and fragile, given their torque spec, and shouldn't be tightened excessively or they will break.

Most of the problems caused by the clutches themselves deal with air leaks. Most problems with clutches engaging and disengaging are from the shutterstat. There are exceptions but in my experience, having done multiple rebuilds of both, the above holds true. Brasco's case would be one of those exceptions. If the clutch is found to be the problem when tested with shop air, I'd suggest taking it apart. It's probably going to be dry and rusty like the one in the pictures above.

 

[jarhead1086]

The only marking on my clutch is on the cast arm "FR5790". Different than the other pictures I see. My truck is an '86 923A0. I took it apart per TM 9-2320-272-24-3 section 4-61. The spacer (8 on page 4-356) was stuck and rusty. Seal plug (1) had a little grease but everything else was dry. I removed the screws ( 12 on page 4-357) and the spring was unable to push things apart so I tapped it while containing it with my arbor press. I see now what Swamp Donkey was talking about on the O-rings. They are plastic not rubber and they were worn flat. They are contained in a pressed in cup which I will have to use a bearing puller or something on? The cap was ridiculous expensive so I hope I can replace the O-rings ( plastic ones and the rubber ones )and reuse. My fan was stuck on, now that its getting colder I'd like to have it work like it should.

 

[timntrucks]

im going to be working on my clutch fan on a 89 925a2 next couple weeks. ill be contacting you guys if i need any help thanks for the usefull info so far. my truck makes a rattling noise . i was told it was fan clutch

 

[Swamp Donkey]

im going to be working on my clutch fan on a 89 925a2 next couple weeks. ill be contacting you guys if i need any help thanks for the usefull info so far. my truck makes a rattling noise . i was told it was fan clutch

We'll be here. Make sure to take pictures though.

 

[74M35A2]

Mine is a Horton, and generally well behaved. I have noticed that recently, on a cold start, meaning less than 40F outside, it will be engaged and spinning the fan on initial start up, with zero truck air pressure. I know that is how todays big rigs are as a fail safe, but for ours, the opposite is the case, requires air to engage. I have not had one of these apart yet to study the mechanisms. Anybody have any input on what could cause cold engagement with no air pressure? Once it has ran for a while, it is fine. Almost like it is icing up, but I don't believe so. I have not looked into it yet, not even opened the hood yet, but I have heard it sucking air twice now on cold starts when I hop out of the cab and walk past it as it is idling on warm up, and just thought "Oh, that's strange, I don't think it is supposed to be doing that.".

 

[Rmtaunton]

I am pretty sure swampdonkey knows them well when mine had a problem he offered to rebuild it

 

[Swamp Donkey]

Mine is a Horton, and generally well behaved. I have noticed that recently, on a cold start, meaning less than 40F outside, it will be engaged and spinning the fan on initial start up, with zero truck air pressure. I know that is how todays big rigs are as a fail safe, but for ours, the opposite is the case, requires air to engage. I have not had one of these apart yet to study the mechanisms. Anybody have any input on what could cause cold engagement with no air pressure? Once it has ran for a while, it is fine. Almost like it is icing up, but I don't believe so. I have not looked into it yet, not even opened the hood yet, but I have heard it sucking air twice now on cold starts when I hop out of the cab and walk past it as it is idling on warm up, and just thought "Oh, that's strange, I don't think it is supposed to be doing that.".

I haven't been into a Horton before. If the shutterstat is NC on your truck I can't imagine the inner workings can be much different than an Evans. They'll probably look different, but operate the same.

You need to verify if it's locking up or if it's just bearing drag. I usually roll up a magazine (use one you don't like) and with the fan going, let it drag across the blades. If the fan is locked you won't be able to even slow it down. If it slows down or stops then it's bearing drag, where either the grease is drying out or there is a bearing problem.

If you want to test locking and unlocking, unscrew the outlet line on the shutterstat and supply shop air to the clutch. The fitting that screws into the shutterstat should be 1/8" NPT. Unscrew the line from the fitting, remove the fitting then screw the fitting back into the line. This will give you some more common threads to work with.

Before starting the truck, can you turn the fan with your hand? If it is truly locked, you won't be able to turn it. FWIW, my fan always turns but it's because of bearing drag. I can easily stop it with a magazine if it's not locked.

I'd be interested in the model number of your clutch if you don't mind.

Also, Acme66 has a YouTube video where he shows how to relube sealed bearings using a vaccum table. It's pretty slick (pun intended) and I plan to try it if I need to go into my clutch again.

 

[PapaPumpSD]

im going to be working on my clutch fan on a 89 925a2 next couple weeks. ill be contacting you guys if i need any help thanks for the usefull info so far. my truck makes a rattling noise . i was told it was fan clutch

Hey timntrucks, my 1990 M925A2 is also experiencing rattling/jingling from what appears to be the fan clutch. Have you resolved your issue? If yes would you mind sharing any troubleshooting tips and how you resolved it. It would be greatly appreciated.

Thanks to all of those sharing their tips and offering help.

PPSD

 

[gottaluvit]

Hey timntrucks, my 1990 M925A2 is also experiencing rattling/jingling from what appears to be the fan clutch. Have you resolved your issue? If yes would you mind sharing any troubleshooting tips and how you resolved it. It would be greatly appreciated.

Thanks to all of those sharing their tips and offering help.

PPSD

I second that! Mine makes the rattle sound at idle, but if I give it a tad of throttle it goes silent (other than the fan blasting air). Not like it overheats when it rattles, as it still cools, but it seems not quite right.

 

[Boi]

Hey timntrucks, my 1990 M925A2 is also experiencing rattling/jingling from what appears to be the fan clutch. Have you resolved your issue? If yes would you mind sharing any troubleshooting tips and how you resolved it. It would be greatly appreciated.

Thanks to all of those sharing their tips and offering help.

PPSD

I second that! Mine makes the rattle sound at idle, but if I give it a tad of throttle it goes silent (other than the fan blasting air). Not like it overheats when it rattles, as it still cools, but it seems not quite right.

I also experience this rattle when the fan kicks on. It is quiet when at idle in neutral, but when the vehicle is at a stop, the brakes applied, and the vehicle in 1st gear, the rattle becomes loud. I haven't noticed any issues with the fan turning on/off, or any problems while spinning, just the awful rattle. If it isn't too much work, I might take it apart in the coming weeks and have a look inside.

 

[74M35A2]

Blade attachment bolts are loose. Reach in front and you can feel the washers will be loose, indicating the bolts loosened up. Common on these. Done mine twice so far, will add Loc-Tite next time, but I think it may be caused by the multi-layer composition of the fan blade hub actually.