V8 rear caliper repair question #2

[Kneale Brownson]

The following assumes the V8 rear caliper is like the 200q20vt rear caliper 
which is the same basic design as the rear calipers on 5ktq's.  I've 
stripped out both a 5ktq and a 200q20vt caliper.

You're trying to get the center post out, right?  That's machined out of a 
piece of material that extends down into the bottom of the cylinder maybe 
3/4 inch below what you can see when you look into the cylinder.  It's a 
close fit, and it's been in place quite a while, so it requires a bunch of 
persuading to remove.  What finally worked for me was to pry with two long, 
heavy screwdrivers, one on each side, applying upward force against the 
threads on the post while using the cylinder edge as a fulcrum.  I couldn't 
find anything else to latch onto the post with.  Anyway, by applying steady 
pressure and then varying the amount slightly to sort of rock the thing 
side to side (nondiscernible rocking initially),  it eventually worked 
loose.  Beneath the stem, at the bottom of the pit it slides into, you'll 
find a little rod with rounded ends, kind of like a stretched football (I 
described it as a long peanut).  That's just in there loose.  Remove it and 
you can work the parking brake arm assembly free if you've removed its 
retainer bolt and washer from the outside.

The calipers I took apart both had corrosion on the cylinder and piston 
that I think wouldn't have been there if the brake fluid had been changed 
annually.  I think that's the source of the pads not retracting properly, 
causing undue rotor wear and even wheel overheating.

The parking brake arms on both the calipers I disassembled were the 
same.  The 5k's caliper (it's an '86) was frozen solid.   I had to drive it 
back and forth with a hammer and punch to free it. The PO or maybe the PO 
before him had had the parking brake cables cut.   The 200's caliper 
parking brake arm moved easily but the brake pads still didn't release from 
the rotors reliably.

The parking brake arm goes into a chamber that's at the bottom of the pit 
into which the center post fits.  The peanut goes into a depression 
machined into the side of the inner end of the rod to which the parking 
brake lever arm is welded.  When the parking brake arm is pulled up, the 
rod turns and the peanut pushes out against the bottom of the center post, 
pushing the piston against the brake pad, thereby applying the brake.

On my 200, the special brake paste that looks like really heavy vaseline 
was clean and lubricating.  As I noted, the parking brake arm moved 
easily.  Again, I think corrosion in the cylinder and on the piston caused 
the brakes to not release.

On the 5k, that chamber with the peanut was full of rust.  There was no 
lubricant left, just rusty powder.  It doesn't look like it from the 
outside, but there's a rubber seal around the rod the parking brake arm is 
welded to.  I think you want to make sure that's intact and all the 
surfaces on that rod and in the parking brake assembly chamber are clean of 
all corrosion and fully packed with the brake paste.   Someone (maybe 
Bernie) posted that the rubber seal is included in the caliper resealing 
kit, which also provides the rubber boot on the piston.


At 04:25 PM 08/27/2001 -0700, Tony Lum wrote:

>Hi gang,
>
>I'm in need of further help on a V8 rear caliper rebuild.  I managed to 
>pull the snap ring that locks the spring loaded collar surrounding the 
>helical threaded center post, but now I'm stuck again.  There looks to be 
>another plate with 3 holes and a alignment notch that sits below the snap 
>ring.  Does this unscrew or need to be removed?  I feel like I'm 
>dismantling a bomb fuse.  I hope I don't need to make another special tool 
>to take this thing apart!  I might mention that the parking brake cable 
>arm is almost frozen.  It will move, but only under very high pressure.
>
>TIA,
>
>- Tony
>lots of I-5 Audis
>
>
>