Military Vehicles, March 1997,: Re: M-37 Advice

Re: M-37 Advice

Jim Rice (jimrice@iamerica.net)
Thu, 06 Mar 1997 21:20:41 -0600

To all list members,

To all others, this is a long posting. If your not interested in M-37 or some general
maintenance practices, you might want to delete now. I intentionally posted this to the
list instead of just to Russel so that everyone interested could see some of my personal
methods. I would encourage others to still let us in on how you do things.

JR

_____

Russell,

If the brake pedal moves from full extension to the floor, it means the master cylinder
is likely still free which is a good sign. Even if it were stuck though, it can likely
be restored. Both my M38A1 and GPW had the master cylinder rusted stuck. I thought I
would break the housing on the GPW master getting it apart. But once apart, it honed
and cleaned up well and worked fine with a new kit installed. The best thing about an
M-37 is that parts are plentiful and many parts can be found at your local autoparts
store, NAPA is especially good because if you can give them the size, they will match it
in brakes. Most of my group has yet to order any brake parts from anyone but a local
autoparts store (Car Quest, NAPA and one independant specifically).

As for the oils and lubricants, about any modern oil you use would be an improvement
over what was available 40-50 years ago when the M-37 was designed and fielded. I
personally use Penzoil in my vehicles. The jeeps call for 30W oil. You would likely
want to use a 40W in the M-37. As for the tranny and xfer, you would use any gear oil.
I buy mine in five gallon buckets at Sam's Wholesale Club.

Bleeding the brakes is a two man job. I need to do it on a friend's M-37 I work
on/maintain for him. You fill the master cylinder and one guy slowly pumps the brakes
while the other opens the bleeder screw on the backside of the wheel cylinder and lets
the air escape. The easiest way to ensure you no longer have air coming out of the
bleeder is to slip a length of hose (I prefer clear so I can see bubbles as they travel
through) over the end of the bleeder screw with the other end submerged in a small
container of CLEAN brake fluid. The bleeder screw looks much like a grease zerk
(fitting), but smaller. Once the majority of the air is out, have the first guy hold
hold steady pressure on the brake pedal while number two just cracks the bleeder screw.
With the free end submerged in the container of brake fluid, you will be able to see
bubbles so long as any air is coming out. Once there are no bubbles, you move on to the
next wheel cylinder. Once all four are bled, you should be in business. Be sure you
keep an eye on the level of fluid in the master cylinder during this process. You will
have to add more fluid several times during the bleeding process, especially on the
first couple of cylinders. Don't let the master cylinder run out. If you do, you will
end up pumping air into the lines you've just bled! It really isn't difficult procedure,
but one guy just can't do it alone. It is also much easier if you take the wheels off
too.

As for the type of brake fluid, well that depends. The military used Silicone fluid.
It is great because it repels water (non-hydroscopic). Regular DOT 2 or 3 brake fluid is
alcohol based and will readily absorb water.

What are the trade-offs? Silicone is about $7.00 per pint, but you can sometimes find
it for $40 per gallon from some Mil-Veh dealers. If you are planning on spending alot of
time in really wet and nasty conditions, I would recommend it. Also, if you live in a
high humidity region, you might also consider it. The advantage of regular "car" brake
fluid is the cost. It doesn't do nearly as good of job of preserving the brake system
though. A big issue is what is currently in use? The two types are not compatible and
you must completely flush/clean the system when switching from one type to another.

When I mentioned the water in the tranny and xfer, it can cause two problems. One is
excessive rust and gunk in the cases. But more importantly is the possiblity of the
cracked cases. I've seen trannys cracked very badly from water freezing in them. This
will hopefully not be too much of a problem with the M-37 since the shifter is somewhat
protected, even without a top on the vehicle, due to it location under the dash. Unless
the vehicle is in an area of very heavy rainfall, it should be okay. You definitey want
to drain both and replinish with fresh fluid before you make any attempt to drive.
Unless the gears are rusted solid, you can drain and refill and drive several miles and
then repeat. This will break loose most of the rust and gunk so it will be carried out
when you change it the second time. Of course, the best thing to do if it has a bunch
of gunk and rust is to disassemble, clean and reassemble.

Good Luck,

Jim