M939 Modifications/Upgrades

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BrushMaster Builder

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Killeen, Texas
Two things that always drove me crazy about the M939 Series vehicles was the terrible cab heater systems and the mechanical throttle accelerator foot feed. The heater wouldn't hardly warm the cab period and the old pedal causes response issues and is very sloppy.
That being said, I decided to convert the heater system and fuel pedal to something a little better with off the shelf parts for the brush trucks we build.
For the heater, I'm now installing two Arctic Fox 17,500 BTU (a piece) 24vdc (or 12vdc if we're converting) heaters under the dash in the A2 models. The old system gets completely removed and thrown in the scrap pile. Gives you a lot more room in the engine compartment and the heaters work like a champ...
For the foot pedal, I'm converting all our trucks now to an air throttle system using Williams Controls.
Pics are attached. SAM_1902.jpgSAM_1901.jpgSAM_1903.jpgSAM_1898.jpgSAM_1900.jpgSAM_1899.jpg
 

BrushMaster Builder

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Killeen, Texas
30 degrees last night here in Central Texas with frost this morning. Usually does not get too bad here but my customers in North Texas and the Panhandle get the same weather that Nebraska and Kansas gets......25 MPH winds at 20-30 degrees equals a 15 degree windchill most of the winter for the folks around Pampa, Borger, Amarillo and Childress.
As a matter of fact, thats what caused me to change the heaters. Was driving one of demo M939 fire trucks to Dalhart Texas and Guymon, Oklahoma a few years back for a Fire Chief meeting and froze my butt off....it was 9 degrees those two days.....
 

BrushMaster Builder

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Killeen, Texas
For our brush trucks we do lose the throttle cable as we have no requirement for high idle operations unless we have a winch application remaining on the truck in which we case we add a pneumatic air lever operated switch for the high idle which is set at one speed and cannot be manually manipulated without linkage adjustment.
 
461
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18
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Sandyston, NJ
Posting up part numbers for both conversions would be great. Does the throttle pedal make a huge difference? Mine is out of my M923 right now and I may go the air route if it is worth it and noticable.
 

emr

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In Northern NJ the heater works just fine for me ,Even my girl thinks it is good enough :) But really I never felt a deuce needed one , and I mean at zero the cab has enough engine heat for driving, but that's me...
 

74M35A2

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Livonia, MI
Costs? Can hurt a little more when individuals vs a company is buying.

I've kept my throttle linkage well lubed and changed the return spring config, it works perfectly, and love the poor mans cruise control as well.

Heater performance can be a drag. It is a combo of a cab that seals like a screen door in a submarine, as well as the diesel engine heat rejection rate, which is near zero when not under load.
 

dougnash

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Long Island NY
I've kept my throttle linkage well lubed and changed the return spring config, it works perfectly, and love the poor mans cruise control as well.
Would you be able to explain and maybe post a pic or two of your reconfigured return spring ?

Mine is very stiff and after 30 minutes of driving, my knee starts complaining

Thanks so much
 

Jbulach

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Sunman Indiana
Would you be able to explain and maybe post a pic or two of your reconfigured return spring ?

Mine is very stiff and after 30 minutes of driving, my knee starts complaining

Thanks so much

If you have an a2 that hasn’t had the accelerator linkage MWO, and you can find the kit it’s well worth a few $ to ease that gnarly stiff pedal.
 
Last edited:

tim410

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Maryland
Costs? Can hurt a little more when individuals vs a company is buying.

I've kept my throttle linkage well lubed and changed the return spring config, it works perfectly, and love the poor mans cruise control as well.

Heater performance can be a drag. It is a combo of a cab that seals like a screen door in a submarine, as well as the diesel engine heat rejection rate, which is near zero when not under load.
any pics of return spring config you did?
 
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