[200q20v] Re: [200q20v]PS Rack R&R
b.m.benz at prodigy.net
Tue Dec 12 02:38:37 EST 2000
> From: C1J1Miller at aol.com
> Date: Mon, 11 Dec 2000 14:54:32 EST
> To: <b.m.benz at prodigy.net>
> Cc: <200q20v at audifans.com>
> Subject: Re: [200q20v] Re: [200q20v]PS Rack R&R(was Clutch Pedal)
> In a message dated Mon, 11 Dec 2000 2:44:00 PM Eastern Standard Time, Bernie
> Benz <b.m.benz at prodigy.net> writes:
> FYI, I have replaced and overhauled the rack on a 5KTQ. The R&R is the
> worst part of the job. About a day to remove, and 1/2 day to replace.
> Cleaning and replacing the high pressure seal in the rack was the easy
> part of the job.
> Per the proc's on my site, one person estimated 4-5 hours, another a
> Apparently Jorgen adds a stainless steel sleeve; I've heard that failure is
> due to wear, and not just a blown seal (actually, the seal blows due to
> wear)... But, no BTDT info.
> Bernie: did you do the work pretty much per these:
I did the PS rack overhaul about 1.5 or 2 years ago, so I don't remember if
I utilized those really good R&R write ups from your web page or, if I just
muddled through. (They do bring back memories of all the foul language and
defaming of the Audi gods that is required for an effective R&R job!) I
can't add anything meaningful to these R&R instructions, but will give you
my thoughts and experience on rack overhaul for your site, if you should
wish to include it.
The 44 chassis PS differs from the 89 chassis PS system in that the 44
operates at a higher pressure, derived from a piston pump, as opposed to the
89's lower pressure, vane type pump. Accordingly, the 44 rack cylinder can
be, and is of smaller diameter than that of the 89. Further, I expect that
the 44 system's higher average pressure most probably is the primary cause
of the apparent higher failure rates for the 44's rack and hoses relative
that of the 89s.
I have only "overhauled" one Audi rack, but all ZF racks are of the same
basic design, and I've done many when I was into the late '70s and early
'80s Lancias. IMO, the major, if not the only failure mode is the failure
of the only external high pressure dynamic seal in these racks, the piston
rod seal. Further, I have never seen a wear scratch or any other type flaw
in the fine chrome plated piston rod surface that could be considered the
cause of this seal failure. The long term sealing of high pressure linear
motion hydraulics is just technically very difficult, and seals fail. So
for long rack, hose and pump life, keep the peak system pressure down, i.e.
don't turn and hold the steering wheel against the limit stops. Back off a
IMO, Jorden's SS sleeve is a sales gimmik to dupe those unfamilar with this
rack design. What would they sleeve and why? The cylinder sees no metallic
contact with the the piston, only a plastic piston ring (or was it an
O-ring?) contacts the cylinder walls. The cylinder is just not subject to
wear, even in the presence of foreign particles, which are pushed outside of
the active area. If you must buy a rebuilt rack, demand a ZF rebuild. ZF
has a rebuild plant in the US, and has a good warranty, without sleeves.
Rebuilding the rack:
Bentley has a detailed R&R section on the rack. The rebuild kit (about $30
from TPC, as I remember) contains the critical piston rod seal as well as
assorted O-rings, the latter, most of which are not needed. Do not bother
to disassemble the valve body from the end housing, as the shaft seals
therein see only reservior pressure and will not be leakers. In the absence
of the special tool to reassemble the piston rod into the new seal, I
slightly rounded and polished the sharp corner on the piston rod such that
it could be forced through the new seal without damaging it. Take care, this
step is critical to a sucessful rebuild. Bentley also mentions that the
steering gear can be repaired by installing "a remanufactured short rack
assembly". Apparently, this is the cylinder end of the rack, minus the
valve body end (which as I said above, does not need to be touched). I've
not tried to find one.
Oh, what fun!
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