A Little Rear Caliper Disassembly Question (?)

[Peter Schulz]

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Gary/Folks:
(Bernie - please let me know if I missed something)
I got some hi-res pix of the caliper dis-assembly down to constituent parts...
I can email them directly, but make sure you have at least a cable modem

I'll try to reduce resolution for those with dial-ups...and forward to
Chris Miller and anyone else who wants to use them.

One big caveat here - If you do not feel comfortable working on your brake
system - then pay a professional
Mistakes on your part could lead to an accident - do to dissuade anyone, as
the brake mechanics are actually pretty simple.

It's important to do this in a clean environment and keep the parts clean
as you go - otherwise you will add contaminants to the caliper or worse -
add contaminants that score the caliper piston or cylinder.

The Bentley manual provides some guidance but does not detail the internals
of the caliper.

Ok - you have removed the piston.
There is a circlip at the bottom of the cylinder that retains a cage that
traps a spring and the threaded piston shaft.

Be careful in removing the cage as the spring has some string - definitely
wear some eye/face protection.

The end of the piston shaft contains a "peanut" or capsule which then fits
into a cutout in the emergency brake cam-
removed the threaded piston shaft and capsule and you will be able to
remove the ebrake/cam shaft - you may have to work it back and forth if it
is corroded to get it out of the caliper body.

clean the ebrake shaft cavity - polish the ebrake shaft to remove
corrosion, cover the shaft/fill the cavity with a high temp brake grease (
there is an oring on the threaded piston shaft that prevents contamination
of the brake fluid in the piston cylinder with the grease in the ebrake
shaft cavity.

You may have to replace the oring on the ebrake cam shaft before
re-installing it.

then clean and reinstall the capsule, thread piston rod, washers, spring,
and the cage,

Finally, re install the circlip - be sure that the cage "feet" fit into the
depression in the brake cylinder - other wise you will not be able to re
install the retaining circlip.

This next part tends to be the most difficult and dangerous - you need to
compress the cage over the spring while re-inserting and setting the circlip -
I ended up taking a few hours to figure out that I could use a "quickclamp"
bar clamp to compress the cage/spring while using a set of long needle nose
pliers to insert the circlip.  None of my circlip pliers would fit in the
narrow confines of the cylinder with the cage/spring/threaded rod in
place.  You may have to fiddle with the orientation of the cirlip relative
to the caliper body so that you have sufficient access with the long pliers.

BE CAREFUL - OTHERWISE YOU MAY END UP WITH A SPRING LAUNCHED INTO YOUR FACE!!

Once this step is done, clean the cylinder gasket and the cylinder bellows
gasket - install the cylinder gasket - put the bellows gasket over the rear
of the  caliper cylinder and reinstall.   I used brake fluid to pre lube
the caliper piston cylinder, piston, and the gaskets.  Be careful not to
tear them.

Apply pressure to the cylinder piston and slowly and carefully rotate the
piston clockwise while applying some downward pressure - again, be careful
with the gaskets - after I rotated the piston into the caliper body
completely, I partially rotated in back out to ensure that the bellows seal
had firmly reseated itself inside the caliper body.

After this rebuild, the emergency brake cam/shaft should easily rotate,
even without it's spring.

I would also take this opportunity ( prior to re-assembly) to remove the
brake bleeder completely (I had to use a 6 pt deep socket, because even
after soaking with Wuerth Rost Off, my flare nut (brake line) wrenches
started to slip!

Found out why - the thread cavity was full of rust - evidence that the
brakes had not been bled in years.  I cleaned the cavity with brake cleaner
spray, cleaned the threads on the bleeder screw, and used brake fluid as a
lubricant before reinstalling the bleeder.

Finally - Bentley recommends pre-filling the caliper with brake fluid
before reinstallation on the vehicle.



HTH
-Peter
Peter Schulz
1990 CQ
1991 200 20v TQW indigo mica
1991 200 20v TQW titanium grey
Chelmsford, MA USA
peschulz at cisco.com




At 09:01 PM 6/12/2002 -0700, you wrote:
>This is a multi-part message in MIME format.
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>Son is home from College, doing some maintenance with him (sound familiar?).
>
>Found rear caliper leaking (drips) from the emergency brake shaft.
>Have removed the piston with the infamous big allen wrench and am left
>with the threaded rod centered in the cylinder.
>Removed a circlip at the bottom of the cylinder....
>So the question is how to finish taking the thing apart?
>Everything moves, no binding, bad rust, etc. just leaking the e-brake shaft.
>
>Any suggestions off line will be appreciated.
>     BTW, this is a 1988 80q, looks very similar to other son's 4kq brakes.
>     (apologies for non 200 dialog here.)
>
>Is this generally a replace/rebuilt caliper situation?
>
>Thanks in advance,
>Gary Anderson in Sammamish WA.
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