Actuator, Air Fan Clutch for M923a1

[nf6x]

AHA! Look what I found plumbed into the air intake! I need to trace the lines to figure out what they're for. They were well-hidden, and I didn't find them until I removed the filter, still heard the sound coming from both the intake mushroom and the filter housing, and then felt around behind the air intake pipe.

Loosening the left fuel tank lid (the one selected by the valve on the floor of the cab) didn't affect the air leak sound.

 

[Stonepicker1]

I would say your brake pedal is letting the air pass by the o-rings inside the brake pedal chamber and out the intake. You can take it out and clean the o-rings and that should fix your problem. Time to replace the check valves on the air tanks also.
I did this many times when we had these trucks in our motorpool.

 

[TiGWolf]

Just for fun, remove the air filter and leave the cover off to confirm it's from the intake. It it is truly coming from the intake, it should be much louder and the noise should move. I'm at a loss as well. Just be sure the area is really clean before you run the engine.. These things are huge vacuums.

 

[martinwcox]

Both my M923 and M936 make that noise at the air intake stack when I shutdown the truck. Figured it was normal (still do) and it's something venting out.

 

[nf6x]

The sound was still coming from the intake stack when I opened the filter housing, so it must be from one of those vent lines that I finally found plumbed into the stack, hidden behind the filter housing. A leaking brake treadle valve sounds like a likely culprit.

Back to the original topic, I drained a bucket of coolant out just before dark last night so I can remove the fan clutch actuator when I have a chance. I'll try to disassemble it to clean/replace the seals as some folks suggested may be possible, then give it a temperature test on the kitchen stove. If it doesn't seem repairable then I'll just order a new one. I'll keep y'all posted, and I'll post some pictures if I can get it apart. Mmmmm, pictures...

 

[halftrack]

http://www.steelsoldiers.com/5-ton-up/48709-m939a2-filter-numbers.html

I posted a lot of common parts and part numbers in the thread above. Title is mis-leading, it should be part numbers and not filiter numbers. Sorry. However, check here first and you might find what you are looking for.

 

[nf6x]

Thanks! I see the part number and supplier for the shutter stat in there. The one I just pulled out is rated at 190F while the one pictured is rated 180F, but I don't think that difference in fan turn-on temp should cause any harm.

I got my shutter stat out of the truck, and I'll try to take it apart to see if it's repairable sometime this week. I could see one of the O-rings through the output port when I removed it from the truck, and a couple quick raps of the aluminum head against the engine made the poppet slide a bit so the O-ring was no longer visible. So, it was clearly stuck in a position that was letting the supply air vent out the vent hole in the aluminum cap. The O-ring looked like a regular round O-ring rather than a specially shaped seal, so this thing might actually be repairable with off the shelf parts if the temperature sensing element is still good. I'll post pictures if I can get it apart.

 

[nf6x]

I think that I have fixed my shutter stat. I replaced three of the smaller o-rings for which I had the right sizes in my o-ring kit. I didn't have quite the right size for the larger o-ring, and I left the one under the crimped retainer alone. I cleaned out the valve and lubed the o-rings with silicone grease, and then bench-tested the valve with an air compressor and hot water from the kitchen stove. It appears to work properly without leaking, so I'll put it back in the truck. If it acts up again, I'll probably just replace it at that point.

 

[glj]

Me Too

AHA! Look what I found plumbed into the air intake! I need to trace the lines to figure out what they're for. They were well-hidden, and I didn't find them until I removed the filter, still heard the sound coming from both the intake mushroom and the filter housing, and then felt around behind the air intake pipe.Loosening the left fuel tank lid (the one selected by the valve on the floor of the cab) didn't affect the air leak sound.

I realize this is an old thread, but thought I'd try. I've had my 923 for about 900 miles now. Perfect machine at first. Whenever I'd shut it down there is a trumpet sound from the intake, and as I dismount I always say "Excuse me." I never thought much about it. But I just returned from a 300 mile trip and noticed engine temps very slightly higher (200), then noted the fan was not engaged. Outside air temps (10 degrees) and ram effect prevent presumably prevented significant overheating. Got home, parked it in the garage, and next am noted pool of what looked like clean motor oil just under filter cannister. Opened cannister and found oil had entered from the intake stack. That is when I explored and found the same 3 items of plumbing on the backside of the air intake before it opened into the cannister. So I conclude I must have a similar problem, but "where is the oil coming from?" Do you know yet what the above referenced plumbing goes to/comes from? Why oil? It was very clean oil; cleaner than what is on the crank case dipstick, so I checked the tranny. Noted that the military had way overfilled the tranny with EO/HDO. Does this make any sense to anyone? Does one of these tubes communicate with the transmission? I do suspect the "oh what a relief it is" sound, the failure of the fan clutch, and the drainage of oil (presumably tranny) into the air filter cannister are all related. Could this all have been caused by an overfull transmission? As an aside I was thinking about replacing the tranny motor oil with a NAPA hydraulic oil that is engineered for cat trannys, and Allison Powershift trannys requiring C3, C4 specification; 10 wt. See any problem with this? Many thanks.

 

[juanprado]

You are better off with dexron atf. Search the 5 ton forum as there are many threads on it.

Change all the pan and spin on filter while you area at it.

 

[Csm Davis]

Juan I am going to disagree with you and say stay with the 10wt these transmissions were built to run 10wt by Allison and I have talked about this with many transmission rebuilders and they said stay with the 10wt.

 

[nf6x]

I thought that they were built to run ATF, Allison recommends ATF, and the military used SAE10 motor oil just to simplify their logistics.

 

[Csm Davis]

As to the air sound on the intake the trumpet sound is normal when you set the park brake and release the foot petal, but a hissing out of the intake tube is not.

 

[glj]

I thought that they were built to run ATF, Allison recommends ATF, and the military used SAE10 motor oil just to simplify their logistics.

Hello, Mark. Born and raised in Corona. Left after grad from HS in 64; never come back except for reunions. Anyway, I wanted to draw attention to your "find" of the piping plumbed into the intake behind the filter canister. I suspect one of these is a transmission vent. As noted, after a recent trip I found motor oil in the filter canister, and next found that the tranny had been significantly overfilled. Do you think the overfill could be responsible for the oil in the filter canister? I suspect another tube is a TC vent, but I really don't know yet where any of these pipes go. Oil smells fine; not burned. Definitely not crank case oil (too clean). Do you know where the plumbing you found, which is the same that I am curious about, travels to? Regarding transmission fluid filters, someone told me that this Allison does not have an internal filter, in the pan. They said that the external screw on filter is the only one. He is not a Steel Soldier, though and is not familiar with these trucks. So, my next question is "If I change fluids is there another transmission filter in the transmission itself, like we see with cars?" I suspect there is, but am not certain. I have lots of HS friends that live in Riverside. Mostly VN buddies. A retired Riverside police officer, now quadriplegic, one of my best friends. Served his country honorably. Most of my VN buddies came back in bags, though; one, from Norco, with a posthumously awarded Medal of Honor. George Allen Ingalls. Sorry, getting off track. Just an old tired man reminiscing. Thanks for your help.

 

[glj]

As to the air sound on the intake the trumpet sound is normal when you set the park brake and release the foot petal, but a hissing out of the intake tube is not.

Thanks, Jeff. I will now stop saying "I'm sorry." I might still have to explain that "It's not me," though, for a few jokesters.

 

[glj]

You are better off with dexron atf. Search the 5 ton forum as there are many threads on it.

Change all the pan and spin on filter while you area at it.

Hello, Juan. Yes, I am aware that there are many dissenting opinions. I don't know enough to get involved in that matter. If I change fluids is there really an internal filter on this Allison, in addition to the external filter. I noted in another response that I was told that there is no internal filter here; just the external spin on. I doubt this info, however. Regarding Dexron, should I assume that the latest version of Dexron is the one to use, as I understand that higher numbers of Dexron supersede earlier Dexrons? Regarding the hydraulic 10 wt. fluids with C-3 and C-4 ratings that Allison specifies for their transmissions, these should not foam as motor oil does, but has the same high pressure and anticorrosion additives that Dexron does; or does it not? I have read where Allison recommends these fluids on their PowerShift transmissions but I don't know if the Allisons in the M939 series are "PowerShift" trannys. There is too much I don't know, and am on a learning curve. Thank you and best regards, Gary.

 

[juanprado]

There is definitely an internal filter. Napa 1892 or equivalent

http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=FIL1892_0287172672

You are correct that the latest dexron VI spec supersedes II & III

http://www.valvoline.com/products/c...sion-products/automatic-transmission-fluid/36

My recommendation to use dexron is based on my personal experience as my m923 came with it already and it shifts smoothly with no harsh shift points. Most here who have changed to it also report the same better results.

I am Leary of 10w oil as it has no additive package for tranny clutches, bands, internal parts etc. The 10w oil is basically the same viscosity as atf but motor oil has a completely different additive package for engine wear. Allison I believe specd 10w or dexron originally and now has their proprietary fluid.

In my parts selling days in another lifetime most commercial operators used dexron.

But in Jeff's defense and world of experience, I did see a post on here from a heavy duty mechanic that stated his company did use 10w because their trucks were always under a heavy load all the time and they got better service. Most of us will never carry the weight these trucks are designed for day in and day out 10 hours a day. Maybe the 10w holds up better to heat under extreme heavy load?

I did see tractor supply does carry the 10w oil in their stores.

Welcome and good luck with your new truck!

 

[Csm Davis]

Okay Juan the oil that we are talking about is not 10wt engine oil but 10wt hydraulic and transmission oil, different additives I would think, also atf has more friction and is thinner than 10wt correct?

 

[Csm Davis]

I thought that they were built to run ATF, Allison recommends ATF, and the military used SAE10 motor oil just to simplify their logistics.

Semi true the military does use 10wt to simplify logistics but the parts are bought to meet the military spec, and Allison would not have honored the warranty on 50000 transmissions if they didn't use a proper transmission fluid for that transmission. These trucks were not bought off a civilian lot and pressed in to service they were built to meet and or exceed mil-spec. Now I am not saying that Allison didn't look at what they were making and say this will work give it to them and not worry about warranty but I doubt it.

 

[glj]

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=MT1357EN.pdf

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1334EN.pdf

The above are the "Mechanic's Tips" for Allison transmissions, including the MT series. What is acceptable by Allison may be different depending on whether it is an MT, HT, or AT transmission, but by perusal of "both" publications you can see that for the MT series "on highway" trannys Alison would prefer you use their synthetic TES 295 for on highway use, or "TranSynd RD" for off highway use, but they also recognize Dexron (III at time of publication), C-4 hydraulic fluid, or even 0-20 wt motor oil (or at least they "recognize" it's use). C4 rated hydraulic fluid is acceptable for hard, off highway use. The manuals are pretty self explanatary, but I recognize they are "dated;" i.e., perhaps out of date. But their recommendations for our MT tranys were effective at their time of publication. You will have to carefully read both to get a clear perspective on their recommendations. There is minor lack of clarity in my mind, though, because when they talk about the MT 654 they specify the trans as MT 654CR? Is that our trans? Must be, because I cannot find any mechanical tips on an Allison MT654. No reference to such, that I can find, on their web site. But the general inferrence I take from this is that Dexron is fine for predominently on highway use, while 10 wt CR4 rated hyd fluid is for extreme off highway use.

Regards,

gary