[200q20v] Re: [audi20v] Re: PS Advice

Bernie Benz b.m.benz at prodigy.net
Tue Apr 3 11:19:54 EDT 2001

99.5% of all rack failures, Audi and otherwise, are high pressure rod seal
failures.  In today's rack designs all other high pressure dynamic seals are
designed to leak into the return fluid volume within the rack, and therefore
cause no problem and are never obvious external leaks.  A high pressure,
linear motion dynamic rod seal is just one tough design problem under
automotive cost constraints.

Type 44 rack failures are more prevelent than are type 89 failures because
the 44 operates at a higher average pressure (smaller piston area), the
reason for requiring a piston type pump rather than the vane type of the 89.
All racks have relatively large "dead" volumes at either end of the piston
stroke that serve as debris deposit areas.  Such deposits cause no harm and
can not be removed by flushing, only by disassembly.  The rod seal is above
and out of this debris deposit area, thus uneffected by it.

The best way to prolong the life of your rack's high pressure rod seal, is
to limit the peak pressure to which it is subjected.  NEVER hold the
steering wheel against the end stops in parking, back off just an 1/8th


> From: Chris Woodward <chris.woodward at wcom.com>
> Reply-To: chris.woodward at wcom.com
> Date: Tue, 03 Apr 2001 11:39:23 -0400
> To: "'Bernie Benz'" <b.m.benz at prodigy.net>, "'Audi 20V'"
> <audi20v at rennlist.org>
> Subject: RE: [audi20v] Re: PS Advice
> So to what do you attribute the common type 44 rack failure?  Does not fine
> grit accelerate
> wear?
> Chris
>> -----Original Message-----
>> From: Bernie Benz [mailto:b.m.benz at prodigy.net]
>> Sent: Tuesday, April 03, 2001 12:55 PM
>> To: Audi 20V
>> Subject: [audi20v] Re: PS Advice
>> Chris,
>> I've R&R'ed and overhauled the rack in a 5KTQ, a larger rack
>> but probably
>> just as tight, removal being the biggest PITA.  IMO, too many
>> beers, if you
>> held that dirty, dripping rack over your head!
>> I disagree with your subjective logic that somehow "changing
>> Pentosin is
>> cheap insurance".  My belief is that all it really buys is
>> "that warm, fuzzy
>> feeling of a thinner wallet".  Just topping up to replace
>> normal hose and
>> pump leakage is change enough.  Any dirt or crud entrained in
>> the fluid that
>> will pass through the reservoir screen, will also pass right
>> thru the rack
>> without harm thereto, the pump being the more contamination critical
>> component.  But few pumps fail because of internal failure,
>> usually just
>> external leakage.
>> Another contrarian opinion worth >.02
>> Bernie

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