[Spridgets] Caliper pistons

[an5.sprite at gmail.com]

Peter,

Thanks for the explaination.
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Peter Caldwell <peter at nosimport.com>
Sender: spridgets-bounces at autox.team.net
Date: Tue, 31 Aug 2010 08:20:13 
To: David Ambrose<stargazer1 at cox.net>; <spridgets at autox.team.net>
Subject: Re: [Spridgets] Caliper pistons

At 04:57 PM 8/30/2010, David Ambrose wrote:
>  On 8/30/2010 2:12 PM, corvallis at peoplepc.com wrote:
>>I will guess the pistons were already in poor shape when previously
>>installed. I just rebuilt one of mine and those seals are near identical.
>>You have to pull the old ones out and remember the order, and know to
>>compare on reassembly. ...bill in corvallis
>Just did this job a couple months ago. The grooved seal is on the 
>outside. It's responsible for retracting the piston just a bit when 
>you let off the brakes.
>
>Cheers,
>Dave Ambrose
----------------------------------
Uhh.... no.

The outer seal IS grooved, or actually a double lip. It's sole 
function is as a dust excluder... retained by that pesky steel ring.

The inner seal does the work. If you look closely in the groove in 
the the bore, you'll see a slight step towards the outside. This 
step, in combination with the square section seal, is responsible for 
the seal deflecting under pressure, and importantly, relaxing with no 
pressure dragging the piston inwards very slightly. Brakes stick "on" 
when the piston is rusted enough to scratch the rubber and not 
deflecting, but scoring the seal. (among other causes)

The outer excluder should not "see"  any fluid. Best if it is lubed a 
bit at installation with some special brake grease, or brake fluid, 
at installation.

Peter C. 
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