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replacement of clutch slave cylinder on 016/20vt cars



following is the procedure for replacing the clutch slave cylinder on a
20vt/016 audi.  the procedure is the same with rhd or ldh vehicles, although
the rhd cars have separate fluid resevoir on the rhs firewall.

dave
'95 sr2
'90 ur-q

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part numbers:
the original slave cylinder for the 10v turbo cars w/016 gearbox is superceded
for the 20v (rr) cars to '893 721 261a'.  the new cylinder is located in the
bell housing by a single bolt, rather than by the peg and spring of the earlier
model.  this makes removal of the cylinder somewhat easier.  more recently the
slave cylinder has been superceded again to a new part number '4a0 721 261'. 
this looks the same as the old part, but is 2/3rds the price and contains a
synthetic (white) operating shaft, rather than the steel one of the older unit.
 removal of my old unit showed significant shaft corrosion which is probably
the reason for the change.

symptoms:
in my case the major symptom was the excessive use of clutch fluid.  as the
master cylinder is located in the pedal box on the inside of the bell-housing,
it is a easy matter to check where the fluid is leaking.  no obvious leaks
means that the slave cylinder (which would leak into the bell housing) is the
culprit.

tools:
required are 10, 11 and 12mm spanners and a 13mm socket with a long extension
and optional flexy joint.  also required are a long piece of plastic bleed
tube, dot 4 fluid and a cup/container.  you'll need a jack and a piece of wood,
triangular in shape, 2cm thick, of 6cm tapering to about 3cms.  i took a
triangular piece of wood and cut the narrow end until it was 3cms across.

time required: 
it took me 4.5 hours but, by following these instructions, 2 hours should be
more than enough.

access:
a real pita.  jack the car, put the front wheels on full right-hand lock,
remove the lf wheel and also the shroud around the driveshaft.  this gives you
the best access, as access from the top is hindered by the abs piping.

removal:
leave the old cylinder connected up and remove the 13mm bolt at the rear of the
cylinder.  the cylinder is actually located by a burr on the rear of the bolt
hole, so the cylinder won't move when the bolt is withdrawn.  ensure that the
gearbox is in 2nd or 4th gear, and remove the cylinder by moving it laterally
to clear the burr, and then rearwards until it is free from the bell housing. 
move the cylinder around to free it from the wiring going to the gearbox
sender, and withdraw the cylinder to below the driveshaft.  remove the clutch
pipe from the cylinder (12mm spanner) and let the fluid drain into the
container/cup.

replacement:
connect the new cylinder to the pipe making sure that the pipe "coil" is
located *above* the cylinder.  tighten the pipe enough to stop fluid leakage. 
with a helper, quickly bleed the cylinder into the container by moving the
operating shaft into the cylinder by hand (this gets rid of most of the air in
the new cylinder and simplifies the later bleeding procedure).  move the new
clyinder into location in the bell housing, and re-route the gearbox wiring as
before.

it is physically impossible to insert the new cylinder into the bell housing as
there is no way to exert enough pressure using your hands.  (as the slave
cylinder contains a strong return spring, this spring needs to be compressed
for the slave cylinder to be inserted into the housing.)  the only way i could
insert the new cylinder the 2cms or so into the housing was to use the gear
selector rods to force the cylinder forward.  in order to do this effectively,
the use of the wood block is vital.  insert the wood between the selector rod
and the cylinder and get a helper to force the gear stick forwards (ie into
4th).  once all the movement has been taken up (the slave cylinder should have
moved forwards about 1cm), get them to release the gear stick and increase the
purchase of the block between the rod and the cylinder (hence the requirement
for wood with a triangular shape).  repeat the procedure until the cylinder is
located longitudinally ahead of the burr (to the rear of the locating bolt
hole).  push the cylinder rearwards to locate with the burr, and get your
helper to release the pressure on the gear stick.

apply the 13mm bolt and tighten.  tighten the clutch pipe after ensuring that
the pipe coil is not touching the bell housing.  ensure that the ribber piping
prior to the coil is not twisted and if so, release the twist by turning the
rubber pipe against the metal pipe from the master cylinder at the point of
their join.  15mm and 12mm nuts.

bleed the clutch.  if the master cylinder has lost fluid, the angle of the
cylinder seems to mean that, in practice, it will bleed to the fluid resevoir
during inital pedal applications (after the resevoir has been filled).

top up the clutch resevoir (rhd) and road test.
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