Actuator, Air Fan Clutch for M923a1

[nf6x]

My previous shutter stat repair worked for a while, but after using the wrecker yesterday, the shutter stat valve started venting air out the small hole in the end again. I guess I'm going to need to order a new one after all.

 

[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 The manuals are pretty self explanatary, but I recognize they are "dated;" i.e., perhaps out of date.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

I read a very recent (past few months old) report that Allison no longer acknowledges C-4 as an acceptable fluid for their MT 654CR. This report was from Allison. I have it bookmarked on my laptop, and can't give you the citation right now. But let's just say that C-4 was good enough by them for this tranny awhile back. What's changed? Marketing? Me thinks we be too compulsive sometimes.

 

[Carlo]

Here are pics of it.

It does look pretty similar to the TNJ Murray Item.

My mechanic tells me that this is an "Air to engage" for the fan. The problem with ours, is that it is continuously letting air through.

Mine on my 923A2 stopped working but now I see how it works thanks to your photo I will remove it and see if its stuck before I buy a new one.

 

[kdaniels]

Just my .02 on the Wd40 on these orings...that product will work for a while but will cause your Orings to break down over time. A good air grease like Dow 33 or Dow 55 would last MUCH longer and not dry out your orings. A tube of Dow 33 can be had for $9 -15 retail depending on source and would be enough to last you for several years and would reduce the chance of future failures greatly.


SEMPERFI !!



keith

 

[djhenley]

what was the part # ........... thanks

 

[max1008]

I am trying to rebuild one of these actuators. I cant see to get the piston? (part with the o-rings) out of the brass fitting. nf6x- how did you get that apart?

 

[Floridianson]

I am trying to rebuild one of these actuators. I cant see to get the piston? (part with the o-rings) out of the brass fitting. nf6x- how did you get that apart?

I think someone said they just used a little air pressure. pop it out

 

[djhenley]

Go to the site fanclutch.com, they made me one. Just give them the thread size and temp stamped on unit, for around 90$
It was really close fit in length, when you screw it in almost hit the back side of the radiator pipe

 

[nf6x]

I am trying to rebuild one of these actuators. I cant see to get the piston? (part with the o-rings) out of the brass fitting. nf6x- how did you get that apart?

I don't remember. It was too long ago. I still haven't gotten around to putting in my replacement actuator, because I've been fixating on other hobbies and ignoring my green trucks. I'll become re-obsessed with the trucks again eventually.

 

[TexAndy]

Question: Is there a good reason not to just install the override bolts and replace the actuator valve with a straight through fitting?

I think the fan clutch actuator valve on my 923A0 is bad. Fan runs all the time, but the override bolts are not installed on the clutch.

The operator's TM says only to use the override bolts in emergency operation, but it doesn't say why. What are the potential downsides to direct driving the fan with the override bolts? Will it wear out the clutch or the fan faster? Not too worried about the engine running too cool in south Texas...

 

[machinist75]

I am trying to rebuild one of these actuators. I cant see to get the piston? (part with the o-rings) out of the brass fitting. nf6x- how did you get that apart?

If you go to napa or wherever to get your o-rings, please get a part # for me for the large o-ring. Found the two small ones no problem but the big one is eluding me.

 

[jwesley74]

Has anyone done an actuator bypass using an air toggle switch or electric solenoid air switch to turn the fan on manually? I've entertained the idea because I've been in sloppy mud up to the bottom of the fan. If the fan kicks on it sprays mud everywhere and coats engine in the mud. Clearly I wouldn't run excessively without turning switch on to cool the radiator. The other issue is if the fan is on and in sloppy mud it pulls it thru the radiator thereby creating another issue of clogging/filming up the front of the radiator. Had that happen to us too. Had to spray out with pressure washer. Semi's have a fan over ride switch to turn on. Same concept but eliminating the actuator all together is the goal. I bought an air toggle switch that I could run DOT line into dash and back to fan clutch.

FYI, I have bought 7 M939 series trucks and only 3 of them the actuator worked correctly. Took apart and cleaned it most of the time. Bypassed 1 of them all together, got tired of truck getting hot. But I just learned from this forum there's override bolts we could've used. Huh, wished I woulda known that before getting all kinds of fittings to bypass it. LOL

 

[jwesley74]

Stupid question, but are the fan override bolts provided screwed into fan clutch somewhere or do I need to carry bolts with me that fit in the event I need them?

 

[TexAndy]

Stupid question, but are the fan override bolts provided screwed into fan clutch somewhere or do I need to carry bolts with me that fit in the event I need them?

They're in a bracket right there at the clutch. Installed in threaded holes. Talks about installing them in the Operator's TM (not in the maintenance TM)

 

[jwesley74]

Yep, sorry for the question. Found it in Operators Manual Emergency Service Override. Awesome to know.

 

[TexAndy]

Has anyone done an actuator bypass using an air toggle switch or electric solenoid air switch to turn the fan on manually? I've entertained the idea because I've been in sloppy mud up to the bottom of the fan. If the fan kicks on it sprays mud everywhere and coats engine in the mud. Clearly I wouldn't run excessively without turning switch on to cool the radiator. The other issue is if the fan is on and in sloppy mud it pulls it thru the radiator thereby creating another issue of clogging/filming up the front of the radiator. Had that happen to us too. Had to spray out with pressure washer. Semi's have a fan over ride switch to turn on. Same concept but eliminating the actuator all together is the goal. I bought an air toggle switch that I could run DOT line into dash and back to fan clutch.

FYI, I have bought 7 M939 series trucks and only 3 of them the actuator worked correctly. Took apart and cleaned it most of the time. Bypassed 1 of them all together, got tired of truck getting hot. But I just learned from this forum there's override bolts we could've used. Huh, wished I woulda known that before getting all kinds of fittings to bypass it. LOL

A solenoid operated air valve? Yeah, I guess that would be the easiest way to go about it.

If you wanted it to be automatic, you could install a thermostat to output open/close signals to the coil on the solenoid, too.

I'm not sure where you'd install it without drilling new holes, tho. Maybe take the stock input radiator hoses out, and put two shorter hoses in it's place with a metal coupling. Then you can drill/tap a hole in the metal coupling for a thermostat probe. Something like that? I'm loth to do permanent modifications to my trucks, just in case a collector expresses interest with money in hand.

 

[max1008]

My buddy got the thing apart. A nice wrap against a work bench and it popped right out!

 

[nf6x]

My buddy got the thing apart. A nice wrap against a work bench and it popped right out!

That jogged my memory. I think that's how I did it, too.

 

[70deuce]

Removed, disassembled cleaned and lubed my shutter stat. Fan still not locking up on my 936A2. On nf6x's post #50 you can see on the coolant contact end (thermal bulb end) it has a locknut on the shaft holding the thermal bulb. Has anyone tried adjusting that shaft in or out to try to change the temp the fan clutch locks up? My shutter stat has 200 stamped on it. Using a handheld laser temperature sensing unit here are the temps I found at various locations on the block and radiator cross tube where the shutter stat is mounted. I'm thinking its not getting hot enough at the shutter stat to activate the fan clutch which I put air to via external compressor and it locks right up. At the temperature sending unit for the cab temp gauge - 220 degrees. At the top of the radiator where the cross tube is mounted - 195 degrees. At the base of the shutter stat where it mounts to the cross tube - 180 degrees!! So it appears to me the shutter stat sensor is not reaching 200 degrees and actuating the fan clutch. I also notice the 90 degree fitting on the pressure side of the shutter stat seems to have shiny brass steel wool looking material in it for its full length. Is that used to slow the pressure application down so when the valve opens it won't immediately get the 120 PSI from the trucks air supply? Air does flow through this fitting at a very slow rate when tested separately. May be this fitting is restricted to much?? For piece of mind installing a cab mounted switch controlling an solenoid activated air valve would the way to go.

 

[Floridianson]

I don't know if I would do it myself but yea just a air switch like one that is on the Deuce to engage the transfer case would be the simple way just to turning on and off the air to the fan.