939 series 14.00 x 20 air pressure

[Csm Davis]

Okay this got brought up in a different thread and because it is a safety issue I thought it deserves it's own thread.
The -10 says the wreckers should have 90 psi on highway, but the wheels are marked 85 psi maximum. I have looked at many different wheels and have not found any marked higher than 85 psi. I personally have run some higher than that and found that I popped the o-ring on some and feel lucky not to have blown a wheel apart as I just noticed the stamp about a month ago. Here's a couple of pictures.

 

[Ford Mechanic]

Yeah I noticed it some time back and had mentioned it in another thread also.

 

[Csm Davis]

I am going to get in touch with the maintenance shop at Camp Shelby and see what is correct I think it is odd that this has gone for 25 years uncorrected.

 

[Csm Davis]

Got in touch with CSMS and they don't know and said after Christmas we can send it to TACOM.

 

[infidel got me]

If your already aired up to 90 psi. cold, by the time you factor in heat transfer from the road you are way over 85 psi.

I never caught the rim stamping either.

Thanks for the post, you may have saved us a lot of grief, and maybe a few lives as well

 

[hklvette]

The 90psi is probably a hold-over from the 11.00-20 tires, which would need that much. What does the M936-correct CTIS unit fill them to?

 

[Csm Davis]

The TM, the stencils on the wreckers, the valves for the wreckers CTIS, everything I can find says 90 psi but the actual stamp on the wheels.

 

[goldneagle]

The question is: Do we inflate to the maximum 85 PSI or go maybe 80 PSI? What about the lighter trucks in that series like the M923?

 

[hklvette]

The question is: Do we inflate to the maximum 85 PSI or go maybe 80 PSI? What about the lighter trucks in that series like the M923?

The 923 uses 70 psi if memory serves. My 931A2 inflates to about 80.

 

[Csm Davis]

The question is: Do we inflate to the maximum 85 PSI or go maybe 80 PSI? What about the lighter trucks in that series like the M923?

I will keep mine at 80 until I get to the bottom of this.

The 923 uses 70 psi if memory serves. My 931A2 inflates to about 80.

This primarily is for 936A1 and A2 wreckers, all other 939A1 and A2s are to run 70 psi for highway use but can be adjusted for load.

 

[jonesal]

**Edited fro accuracy based on Post 13** (I put my glasses on)

With the exception of the M936, the current -10 TM (dated 31 July 2012) shows 11.00x20 (A0) 90 psi front and 70 rear for highway and 14.00x20 (A1/A2) 70 psi front and 70 psi rear for highway. It shows the M936 as 90 psi both front and rear for A0/A1/A2. See pages 0002-18 to 0002-20.

Al Jones
'84 M923

 

[tbar123]

I also found the same stamp on 2 different type of wheels ,That I installed the 14's on. I almost didn't see it either until I took a smoke brake after flipping one and started to air it up. The paint was just enough to cover it from plain sight.So I keep mine at 70psi.

 

[Csm Davis]

The current -10 TM (dated 31 July 2012) shows all 11.00x20 (A0) 90 psi front and 70 rear for highway and all 14.00x20 (A1/A2) 70 psi front and 70 psi rear for highway. See pages 0002-18 to 0002-20. Are you using an old TM?

Al Jones
'84 M923

Look all the way to the right under 936 A2

 

[chadande]

here are the CTIS pressures.

 

[Csm Davis]

Look at table 1-10 page 1-25

 

[MuleMac01]

Can you change the CTIS tire PSI if it's set to high? just wondering because I might want to lower mine.

 

[MtnSnow]

Depending on what version of programming your CTIS unit has it will be 60 or 70 psi for the hwy setting for the Non wrecker trucks...
70 psi is the current programming version

 

[Andrmorr]

Got in touch with CSMS and they don't know and said after Christmas we can send it to TACOM.

Just curious if you were able to track down a definitive answer on this...