Plastigage - Hydraulic Problems

["Al Powell" <APOWELL@agcom.tamu.edu>]

I got a kick out of the recent Q & A on Plastigage - I first used it 
in a high school auto shop class in 1967.  Some tools NEVER go out of 
style - they simply do what they do VERY well.

Another topic - 

> cking@legend.txdirect.net (Chris King)  sent:
> 
> Lately I have noticed something very strange with my hydraulic system.  My
> "Brake" triangle light frequently comes on while driving, and I can feel
> the loss of pressure in the brake pedal.  It becomes very light, or
> sometimes even gets so hard that I lose power assist in the brakes.
> 
> Anyways, the other night I opened up the hood when the brake light came on
> to check the hyd. fluid level.  It was way up above "Max", as if the fluid
> was not going down in the system.  Well, I started thinking...(uhoh) Since
> the power steering and power brakes both run off the hydraulic system, they
> must affect each other.  So, with my foot on the brake, I turned the
> steering wheel all the way to the left, and then all the way to the right,
> then back to center.  Within 10-15 secs, the brake light goes off and the
> hyd. fluid level is down to "Min".
> 
> What gives here?  Could this be a faulty "bomb", or might it be a failing
> hyd. pump?  This fix I describe here works like a charm 100% of the time.
> Everytime I see the brake light, I just turn the wheel and off it goes.
> The dealer here in town had never heard of this, or so they say.
> 
> Well, any help would be appreciated.  Happy Holidays, everyone!
> 
Those on the list know I have been fighting hydraulic gremlins for 
some months...but this is a different one.  Chris, fo you have the 
Bentley manual for your car?  You might benefit by conducting 
hydraulic system tests as per the Bentley, as they can help direct 
you to the cause.

Thoughts:

It does not sound like the PA, aka Bomb, to me.  That generally 
manifests itself in reduced pressure assist and/or brake warning 
lights when you hit the brakes.

HEY!!!  Potentially bright idea just came to me!!  (This generally 
means I'm about to suggest or do something dangerous...)

The backing up of fluid makes me think you should look at the 
return line going from the bottom of your hydraulic canister down to 
the pressure acculumator/PA/Bomb.  IF it were collapsed or plugged, 
the fluid would back up or rise in the reservoir.  If it were not 
getting down to the bomb amd could therefore not circulate properly, 
maybe "bad things could happen, man..."

Sounds to me like you possibly have a restriction in the flow of 
fluid.  The LOWEST pressure point - therefore the easiest to restrict 
- would be in the screen in the bottom of the fluid reservoir- try 
pulling it and cleaning it - or the return line below it.  That line 
handles VERY little pressure - essentially just gravity feed - and 
could plug easily.  How the steering trick is bleeding the fluid 
through, I'm not sure - unless it just getsmore fluid moving.

You might also consider doing a total fluid drain to purge the system 
of any gunk or contamination.  I've occasionally experienced a brake 
warning light which goes OUT when I stab the brakes - making me think 
I have some debris floating around which might be hanging up in the 
check valve located in the bomb.

Good luck - if you flush the system and need Pentosin, fer crissake 
don't buy it from a dealer - holler at AudiOnly.  (Opinion, based 
upon $8 per liter...)

Good luck & Happy Holidaze!

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Al Powell                           Voice:  409/845-2807
Ag Communications                   Fax:    409/862-1202
107 Reed McDonald Bldg.             Email:  a-powell1@tamu.edu 
College Station, TX  77843-2112
W3 page - http://agcomwww.tamu.edu/agcom/rpe/alpage.htm

       "I'm for abolishing and doing away with redundancy."
           - J.C. McKay, Wisconsin St. Elections Board.
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