Re: [MV] HMMWV questions

From: Mark J. Blair (
Date: Tue Feb 11 2003 - 17:33:17 PST

Tony Castagno wrote:

> I recently had my fan clutch replaced... and I'm not sure it its working
> correctly... I'm getting strange feedback in the brake like a slight
> modulation... and it makes kind of a whirring noise when turning the
> wheel and accelerating which I assume is tied to the power steering
> pump.

A whirring noise might indicate that there's a leak somewhere, allowing air
into the steering fluid, or that the steering fluid level is low. I'd check
the following things first:

1) Check the fluid level. I found that I had to fill mine a little bit higher
than the dipstick indicated in order to stop occasional aeration of the fluid
when turning. Maybe I was doing something wrong; your mileage may vary.

2) Check for aeration of the fluid by shining a light into the reservior and
looking at the fluid while the engine is running. It should be a nice, healthy
red color. If it's milky, pinkish, foamy, or there are any bubbles, then air
is getting in somewhere.

3) Check all of the hoses and fittings in the hydraulic system for leakage.
Make sure those hose clamps on the low-pressure return lines are TIGHT. If
necessary, the return lines can be replaced with fuel line of the appropriate
sizes from the local auto parts store. If you need to take off any of the
high-pressure hoses, replace the O-rings.

4) Bleed the hydraulic system. It's easy: Start the engine, turn the wheel all
the way laft and hold it there for several seconds, turn it all the way right
and hold it for a few seconds, repeat. If the fluid is already aerated, after
fixing any leaks and correcting the fluid level, let the vehicle sit for a
while with the engine off so the foam can dissipate and bleed it again.

I had to replace the seals in my power steering pump (a $17 kit, as I recall),
replace some damaged return lines, and since I needed to change belts anyway,
I splurged and bought the parts to convert to the newer configuration in which
there's a quick-disconnect fitting at the fan clutch to make future belt
changes easier (I wouldn't bother doing that unti, you have to remove the fan
clutch line anyway, to replace the fan clutch again or to change belts). It
took me a while to get rid of the last leaks, and I got pretty good at pulling
over, finding a leak, fixing it, and bleeding the system on the side of the
road when I heard that whine return.

You can force the fan on by unplugging the two-pin connector on the solenoid
valve next to the washer fluid reservoir. You'll probably need to rev up the
engine to hear the fan roar unless you have good ears and know what it sounds

Remember that "unplug the fan solenoid" trick, in case you ever start
overheating and need to force the fan on to limp home.

> Additionally I don't hear that roar I've heard others describe
> when the clutch kicks in... actually the fan is always turning even when
> cold... is this normal? Thanks in advance for any advice.

It'll always turn due to friction in the clutch assembly, but when it kicks
in, the roar is pretty noticable at mid to high RPMs.

Although I've had a lot of problems with my HMMWV as I worked out the bugs
that crept in during its hard life and extended down-time before I bought it,
I'm happy to say that it's running very well now, and it really comes in handy
when I need to move the occasional ton of crap around. Now that I've worked
out the kinks, it's not only a cool collector truck, but also a strong working
truck. I went for a "motor pool ready" restoration; I fixed any functional
problems I could found, but didn't bother with purely cosmetic stuff like
repainting it. Some would call that surplus brush guard cosmetic, but it
serves a function on my truck: I use it as a mounting point for the wreath and
  blinky lights around Christmas time. :-)

Good luck!

Mark J. Blair, KE6MYK <>
PGP 2.6.2 public key available from
Web page:

This archive was generated by hypermail 2.1.4 : Wed Apr 23 2003 - 13:25:28 PDT