I have a couple of questions for the new generation truck experts out there
in list land. I'm hoping someone with M935 series experience, can possibly
give me some operator info.
I've been systematically going through the air brake system on a M936A2
wrecker that has been sitting for who knows how long. Every single air tank
check valve was corroded, two to the point that the spring was just bits.
The air drier valve was stuck, and wouldn't allow the system to build
pressure above 30PSI. The valve units above the axles were stuck, the
transfer case shift valves were sticky. Slow, tedious, and sometime calling
for contortionist positions of one's body. Some of the brake chamber
diaphragms were rotted.
I thought that I had covered all the bases, but if the air governor lock nut
is loose, and the screw isn't set right, it still won't build air! And it's
hidden under a nice little plastic cover on the end of the governor unit,
which was covered by a piece of that dissolving foam hood insulation that
had fallen down on the firewall. Anyway, it is now building the required
120 PSI of air to the brakes. Which leads to question one.
There is a black knob labeled 'spring brake override on the right side of
the center instrument cluster, above the front winch PTO controls. It has
'out for normal' across the bottom of it. With the air pressure built up,
and the spring brake override knob pushed 'in', a warning light illuminates
on the warning light cluster above the steering wheel. This is what is
confusing me. I'm thinking in terms of civilian trucks, and thinking that
the 'in' position would be for releasing the spring brakes and allowing the
truck to roll. But, why would that give a warning indicator light, and what
is the military idea of 'normal' position. Normal for parked, or normal for
released? Sitting on a slight incline, the truck will roll with the knob in
either position. Only the hand lever parking brake on the right side of the
drivers seat will stop it. (not using the foot pedal just now). I have
noticed that when I change the position of the hand lever, I hear an air
release. Is the truck's parking brakes being activated by the
solenoids/switches working off the hand lever? Is the dash valve for an
attached trailer? Could my brake linings be so bad as to not work with
spring brake pressure? While rolling, just the slightest tap on the foot
pedal stops the truck instantly. I'm getting paranoid. I know that the red
valve below the steering column is for emergency use to release spring brake
pressure. The valve on the dash is confusing me. (No, I haven't traced the
air lines from the valve to their destination yet.) It's been a long hot
day, and it got dark.
Question two. This wrecker has the 'small' 250 Cummins engine. It runs
like a dream. With the fan clutch engaged full time, (straight air
pressure bypassing the temp control unit) the engine temperature hits about
190-195 degrees after warm up, and holds it there. Is this the normal temp
range for this series engine? The truck hasn't seen the highway yet, due to
the brake question. So, I'm wondering about what the engine temp will do
under driving load.
I don't want to screw up anything in the driveline by trying to 'go' when it
is set to 'stop'. And I sure don't want to 'cook' an engine on my 'first
flight'.
Any good advice? Personal experiences? Words of wisdom from a current
operator?
As always, thanks in advance,
John Doherty
This archive was generated by hypermail 2b29 : Sat Sep 02 2000 - 09:32:26 PDT