M939 spare tire davit on M818

[MyothersanM1]

Fearing someday I may have to hoist one of these extremely heavy 11.00R20 tires back into it's carrier while on the road side, I decided an M939(A0) spare tire davit on my M818 would be fitting as standard equipment on my truck. I was able to find all the parts locally. I picked up the inner vertical rack, davit, boom extension and the eye-bolt trolley.


The M939(A0) inner portion of the spare tire rack is the exact same dimensions as the M818 except it adds the support pole for the davit welded to the back side. To do this mod this is the only part that needs to replaced. Everything just sits opposite on the M818 compared to the M939(A0) series trucks. The diagonal braces (2) and the stringer plate attached to the tool/utility box all stay in place. On the back side I added a diagonal brace requiring only one 3/8" hole drilled in the base frame. Just attach the diagonal brace to the vertical rack, mark the spot on the base frame and drill.


The davit then just slides over the top vertical rack pole and is steadied with a set screw. The end result without and with tire in place.

 

[MyothersanM1]

I also obtained the big "wing nut" that is part on the M939 outer vertical rack securing rod. I did a little fab work to make the rod and wing nut work. The shorter rod is the original and the longer is what I fabbed up. I did cut it down about another 4" when I finally got it all fitted up to the tire. I drilled an 1/8" hole through the end of the rod for a "diaper" pin. I added this just for safety sake in case the nut backs out. I added an "idiot strap" so I don't lose the pin when it is removed.


End notes:

• I replaced all the hardware with new Grade 5 hardware.
  
• I used my chain hoist to get the tire back up in the rack and it all worked well. However, I have ordered a smaller chain fall the should be a better fit.
  
• This mod only works for the spare tire rack designed for the 11.00R20 tires. The M939A1 and A2 super single set-up are of different construction and will not work with this modification.
  

 

[Ferroequinologist]

Very nice! I had a flat once and had to change the tire- getting it off the M818 wasn't a problem, but humping the flat up there took me many tries until finally someone stopped to help me get it up there.

 

[swbradley1]

Very nice! I had a flat once and had to change the tire- getting it off the M818 wasn't a problem, but humping the flat up there took me many tries until finally someone stopped to help me get it up there.

Helloooo!!! You've had more than one flat on The 818 of Death. I was there and it took a whole crew, new tires and a Bobcat to fix that one.


I do like the davit addition to the 818 though.

 

[MyothersanM1]

Very nice! I had a flat once and had to change the tire- getting it off the M818 wasn't a problem, but humping the flat up there took me many tries until finally someone stopped to help me get it up there.

Yeah, the clincher is getting the tire back up into the rack. I just rolled it off onto my grass to get it down.

Helloooo!!! You've had more than one flat on The 818 of Death. I was there and it took a whole crew, new tires and a Bobcat to fix that one.
When I did my torque rod project, I got real good at taking off and putting on tires.


I do like the davit addition to the 818 though.

I got real good at taking the tires off and putting them on when I did my torque rod project.

 

[ARYankee]

• This mod only works for the spare tire rack designed for the 11.00R20 tires. The M939A1 and A2 super single set-up are of different construction and will not work with this modification.
  

That is so true. I had to put the larger spare tire holder and davit on my M923A1 because the original set up was for the 1100s and the 1400 spare was mounted in the bed. I wasn't looking forward to changing a flat the way it was. It took some modifying to get it mounted but it works. It's just a really tight fit

BTW, nice setup!

 

[MWMULES]

"Great minds think alike" A little over a year ago I was by myself and got a flat in the 818 with the 5th wheel bed. No way in the world I could get the flat back on, so left it in the ditch. Came back the next day and luckily it was still there and got it. Within the week I made my first trip out to BFR in Salina and got a 923 davit and brackets from Glen, best up grade to that truck you can make besides seats and fifty little other things!

Doing a tire/wheel swap tractors, bob cats, skid loaders, backhoes or what ever else you can get to help even swbradley1 can be a help!

 

[MyothersanM1]

That is so true. I had to put the larger spare tire holder and davit on my M923A1 because the original set up was for the 1100s and the 1400 spare was mounted in the bed. I wasn't looking forward to changing a flat the way it was. It took some modifying to get it mounted but it works. It's just a really tight fit

BTW, nice setup!

Had to make sure I got that 11.00R20 ONLY disclaimer in there. I didn't want to be on the receiving end of a rant when that super single didn't fit

 

[emr]

LOL...I agree with the rant Great !! Idea and job for sure, and now since I want an 818 and I have to change my tire davit from the 1100 to the 1400 I am now going to keep my old one for the 818, looks cool too. I like things to stay mil , really think to much different stuff for me is sceevy, But that fits the bill nicely !!

 

[ARYankee]

Had to make sure I got that 11.00R20 ONLY disclaimer in there. I didn't want to be on the receiving end of a rant when that super single didn't fit

I understand that. I didn't realize how much work went into changing mine. I figured it would be an easy replacement. But you how those thoughts go. I should have known better but oh well it's done and works.

 

[Ford Mechanic]

Will any of those style spare tire holders fit a 395/85R20? And does the top part that has the pulley on it swivel by chance? I would like to put one in my M35 but need to mount it facing rearward instead of sideways.
Thanks

 

[ARYankee]

Will any of those style spare tire holders fit a 395/85R20? And does the top part that has the pulley on it swivel by chance? I would like to put one in my M35 but need to mount it facing rearward instead of sideways.
Thanks

The larger style for the 1400 super singles will. The davit with the trolley only slides out, it doesn't rotate. Well at least mine doesn't. Mine is flanged. Let me see if I can find some pictures of mine. Check out post #80 here: http://www.steelsoldiers.com/showthread.php?83549-What-have-you-done-to-your-5-ton-this-week/page2 Those are the best pictures that I can do for the moment. I actually thought about modding mine so that it would but decided against it. I'm sure that it can be and that possibly some one has.

 

[KsM715]

The style for the singles does not rotate. However I believe you could sleeve the inner bottom at the flange and slide the upper over it and make it rotate. Make sure to use a stout enough piece for it. I think Gimpy modded one to rotate that way. The davit off the trucks with 14.00 singles is built stronger than the one for the 11.00's.

 

[Ford Mechanic]

Thanks guys for the input, this defanetly is on my list. Just got to come up with enough $$$$ to get all the stuff on my list done!