From: John De Armond
Subject: Re: Ford Cruise Control Recall Experience
Date: Tue, 18 Sep 2007 01:05:14 -0400
On Mon, 17 Sep 2007 20:25:46 -0700, "Kevin W. Miller" <i09172strudelyahoo.com> wrote:
>> Someone said a Hobbs pressure switch would be a real easy fix.
>> Do I just go to Napa and ask for a "Hobbs pressure switch" then take
>> it home and install it where that switch is now? Is the fix as
>> simple as that?
>> Will the wiring harness plug into the back of the "Hobbs pressure
>> switch"? Will the cruise control work the same way it does now?
No. Hobbs is a brand name. I see that they've been snarfed up by Honeywell.
Hobbs made its name in aviation. AFIK, they invented the small, sealed,
self-contained snap-action switch. Most aviation types use "Hobbs" as a generic term
for pressure switch. The photo on that page is the classic switch.
Hobbs also makes automotive switches. That cruise control switch may very well be a
Hobbs but it isn't the general purpose switch that your advisor was referring to.
Brake line switches are very specialized. First, they have to be compatible with
brake fluid. That rules out ordinary rubber parts. Second, it must operate with
very little fluid, lest it make the brake pedal soft or extend its travel. Third, it
must fail safe. If the diaphragm ruptures it must not leak brake fluid or else the
brakes could fail. Forth, the fluid fitting has to match the application. Cars
usually use an SAE spec straight thread fitting with a gasket and not NPT.
Hobbs switches are also very expensive. I bet that the one piece price of that
switch in the photograph is at least $30 and probably closer to $50.
The switch shown in Kevin's photo is a standard off the shelf automotive hydraulic
brake light switch. I'd be surprised if it cost more than $10 at the local auto
Buying a replacement part will almost surely fix the problem that is the subject of
the recall. The problem is most likely only with one or a few production lots. Maybe
they crimped the housing too tight and cracked the plastic or something like that.
Aftermarket parts seldom come from the same place as OEM parts so the replacement
will almost surely be a different brand. If the same brand then surely a different
Installing it involves nothing more than unscrewing the old one and screwing in the
new one. There'll be a little air in the switch body but a few pumps of the brake
pedal will work the air out and out the master cylinder vent.
>I've put a picture of mine here:
>Mine is still stock and I just received the recall notice yesterday. I'm not
>sure that changing the pressure switch is a great solution either. The
>pronlem is that, if it ever did leak, it still poses a fire risk as the wire
>is always hot and could be shorted by the fluid. I think the fuse idea is a
>good one but I wouldn't know what amperage of fuse to use. Maybe start with
>a 5 amp?
Brake fluid is non-conductive so it can't short out and start a fire. There are only
two risks that I can think of. One would be brake fluid squirting out of a defective
switch and hitting the exhaust manifold. The stuff DOES burn. Second, if the switch
disintegrated and the connector swung free it might hit something grounded and short
the wire to ground. The wire almost surely is fuse-protected in the fuse box.
I didn't pay attention to the recall details but almost surely, scenario number one
is the source of the alleged fire hazard. It's hard to imagine a short to ground
causing a fire before the fuse blows. If that switch only inputs a signal to the
cruise control (almost surely the case given the small wire size in your photo) then
the current flow will only be a few (hundred maybe) milliamps. Anything from a 1 amp
fuse on up would do.