[s-cars] Upper strut mount R&R time?

[Charlie Smith]

Earlier, Joseph Pizzimenti wrote:
>
> Okay, guys, I need you on this one as I'm stumped and
> about to bash my head into a wall.
>
> Steering:
> No Servo relay
> New rack
> New bomb
> New pump
> New J hose
> New control arms
> One new tie rod, other one has fresh ends
> H&R/Bilstein Sports
> ASW Camber plates
> Cleaned out filter in reservoir
> Flushed and replaced w/new Pentosin
> ATE Superblue in brake reservoir
> Big Reds w/Pagid Orange pads up front
> Both levels fine, but superblue is a little high
>
> Symptom:
> When turning the wheel, intermittently there is what
> feels like a hydraulic hiccup, i.e., steering will
> turn normally, but I will suddenly lose assistance for
> a brief sec and hear a mooing come from the system.
> Mooing also happened when I was cleaning off the
> rotors the other night (accelerate to 100 or so at 3AM
> on straight road and warm up pads, gets rid of noise
> somewhat from Orange Pads) and as I was coming under
> 50mph, I heard the mooing again.  Did not sound good.
> I also get it when the car is starting off and feel it
> through the steering wheel, as I do when the "hiccup"
> happens.  Please help, I don't want to break anything
> else.  Upper strut mounts, perhaps?  I'm at a loss
> here.
>
> Thanks,
> Joe
>

Let's consider the situation for a moment.

Since he is losing power assistance to the steering when this happens,
I think the problem is related to temporary loss of hydraulic pressure.

The bomb stores pressure to preserve the power brakes when the engine
powered hydraulic pump loses pressure (like when the engine quits),
it does not provide a backup pressure source for the steering. [* see note]

This means that even a momentary loss of pressure from the pump will be
something you will feel in the steering.  Like you said - suddenly lose
assistance for a brief sec.

I don't know about the "mooing" sound, what's the list think - if the pump
briefly sucked air instead of pentosin would it make a noise?  What could
be blocking fluid pickup on an intermittent basis?

If it's something like this going on, I'd think the worst that could happen
would be if the pressure loss were prolonged then he might lose power
assistance for the steering for the duration.

Joe - one way to bleed all of the air out of the pentosin hydraulic system
is to cycle the steering wheel lock to lock several times.  If your repairs
that included replacing the pump and rack are very recent, maybe there's
still some residual air in the system.

What do other folks think?

    - Charlie





[* note]
The bomb does not store very much fluid under high pressure.  The brake
assist unit uses very little hydraulic fluid for a single application,
thus the bomb can provide high pressure fluid for a number of brake
applications.  On the other hand, the steering rack uses quite a bit
of fluid volume when you turn the steering wheel; this is way more than
can be stored in the bomb.

It would be interesting to see the operating pressures of the brake assist
and the steering rack.  I'll bet the rack operates at a lot lower pressure
than the brake assist.  Has anyone taken a pump apart to see if it's really
set up with a high pressure output (for the brakes) and a lower pressure
output for the steering?