rear caliper 4000CS

Eric Henning spiders_2000 at
Mon Oct 17 09:53:43 EDT 2005

My son and I are working on his future 86 4000CS. 
Right rear disc was very rusty and appears not to be
acted on by the brakes.  Took the caliper apart
(removed piston only , not circlip).  I am not familar
with these types of calipers and see that there is the
piston, then the part that is threaded on the big rod.
 This part screws out to gain access to the circlip. 
Is the part that rides on this thread supposed to fit
inside the piston?  Cleaned everything and put in new
gaskets but cant seem to get the piston back in far
enough to fit the pads over the disc.  I've rebuilt
many calipers before but never saw this type.  What is
the purpose of this part that threads over the big
"bolt"?  The other three discs are nice and clean
indicating that the pads are working, but this right
rear was completely encrusted in rust telling me no
pressure was applied to the pads.  What causes this? 
and should that part that spins on the thread fit
inside the piston?


86 4000CS quattro 

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