In the center of (and attached to) the cylinder is a small rod. It runs
through the center of the piston. In the piston is a gripper assembly
consisting of steel fingers that holds onto the rod. This assembly in the
piston moves back and forth a fraction of an inch and is spring loaded.
When hydraulic pressure is released the spring pulls the piston back just
far enough to keep the pad clear of the rotor. As the pad wears the spring
assembly will bottom out and slide along the rod. Unlike most disk brakes,
ours keep the pads from dragging on the rotor. Actually, there are a number
of brake setups like the one on the Roadster. It is a licensed copy of
Dunlop. In fact, Dunlop seals will interchange making them easy to come by.
When removing the piston it is imperative that the piston come straight out
to prevent bending the rod. It is best done with pressure. Compressed air
can be used but GREAT care must be exercised. The piston can come out at
warp speed and cause serious injury. I recommend that you use a grease gun.
Messy but safe as the piston will simply pop out gently.
To replace the piston simply lubricate the cylinder and seal with brake
fluid and press straight in until it bottoms out. Replace the dust seal,
reassemble the caliper, and slide the pads into place.
BTW, if you have never bled the front brakes beware: they are a licensed
SOB to get thoroughly purged. Due to the large size of the pistons air
bubbles will cling to the surfaces. You must beat on them with a suitable
bludgeon to break the bubbles loose. A rubber or plastic hammer works well
for this operation. It will take multiple attempts and can get frustrating.
However, time and patience will prevail. Sooner or later you will get all
of the air out.
I would also suggest getting a set of 'Speed Bleeders'. They make things a
LOT easier.
Best regards,
Fred Schroeder
Denison, TX
SRL311-13359
TDROC
Reg e-mail sitsinwest@texoma.net
Home page http://home.texoma.net/~sitsinwest
----- Original Message -----
From: "Joe Jackson" <rimshot@a-znet.com>
To: <datsun-roadsters@autox.team.net>
Sent: Saturday, April 26, 2003 10:58 PM
Subject: Frontbrake caliperpiston operation
> Had our last snow this week in upper NY State ,garage temperature now
livable,
> power back on and fallen trees cleared after ice storm so am back at
> my resuscitation efforts to revive a dead 67.5 SPL 311..New rings rod
> bearings; starter,fuel and oil pumps and ignition made workable. now
> brakes--drums and rotors out for turning;little wear,only some illimois
rust
> after 15 years rest (linings ,pads almost like new). Will someone educate
me
> re front "self-adjusting"? (The basic hydraulic actuation is pretty
> elementary) Motorbooks Manual says".......move progressively along the
> post...friction stops,which grip the post,provide a positive datum to
which
> the piston returns" (friction stops ?). Later ,before putting in pads,
"...the
> pistons must be returned to the base of the bore."( How??). I have removed
the
> piston-cylinders to free up the pads,but not dissembled them. Thanks for
your
> help
>
> Joe Jackson
> Baldwinsville
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