Hello Guy,
Nope, you've missed it entirely. I too thought that the problem would
be with the primary seal in the bore. However, that seal provides
compression and is not really designed to keep all the fluid in the
MC. Let me explain.
First this is a newly brass sleeved unit, bead blasted and restore to
better than new condition. It was fitted with a new seal kit as well.
It has not been used to do more than bleed the system.
Now the problem.
If you look at how these are constructed, you will see that the bore
has two diameters. The main aft bore is where the two braking pistons
operate. The larger forward bore contains a stationary seal where the
forward portion of the piston exits the MC. This is where the pedal
pushrod makes contact to operate the internal workings of the MC. If
you look inside a disassembled unit, you will see that there is a
3/16" hole drilled just before the mouth of the smaller bore. That
hole leads right up to the fluid reservoir. So, even if the primary
seal in the smaller bore kept out ALL the fluid (which it doesn't),
it wouldn't make any difference because the reservoir is supplying
fluid in _front_ of the primary anyway. This is necessary to keep
atmospheric pressure of the fluid and I'm told this design would not
operate were there not fluid in this location.
In order for the fluid not to leak then, the stationary secondary
seal must seal at the outside diameter AND the inside diameter where
the piston passed through the secondary seal. Since the last time I
searched for this piston, I was not successful in finding one, I made
some attempts to repair the gouges in that "outside" portion of the
piston, but was not completely successful. Seems now the only
solution is to replace it or perhaps find a Redi-sleeve for it. I
don't think they make anything that long though.
Gerard
>Gerard,
>
>Just an idle train of thought....
>
>The 'rubber' lumps/cups (seals) in the brake cylinder provide the seals for
>the fluid within the m/cyl casing (or bore). The pistons provide the
>mechanical means to assist in locating the seals and push them about within
>the bore.
>Doesn't this mean the pistons do not provide the seal? Therefore scoring on
>them does not give an area where the fluid can leak, it leaks past the
>seal - not the piston.
>Scoring/wear on the pistons comes from metal to metal contact i.e.. they
>have been rubbing on the bores of the m/cyl casing. So, this is where the
>leaks are, between the rubber lumps and the bore. The scoring on the
>pistons is just showing that there has been contact with the body of the
>m/cyl casing and may be indicative of where that contact was.
>
>Should the questions be -
>Why is the piston coming into contact with the bore?
>What has caused it to become misaligned?
>Is the piston harder than the bore - so wear in the bore is more than that
>showing on the piston?
>Has any-one got a spare tandem (dual line) master cylinder used on the
>latest Spridgets to replace this one with a worn larger front bore?
>
>
>A Hhhmm! moment or two.
>Please bin this idle train of thought if it does not agree with your needs.
>:-)
>
>Guy R Day
>
>
>----- Original Message -----
>From: "gerard" <pixelsmith@gerardsgarage.com>
>To: <spridgets@autox.team.net>
>Sent: Thursday, July 03, 2003 11:56 PM
>Subject: Call for MC part, i.e. new piston.
>
>
>> If anyone has either a source for a new master cylinder piston or a
>> very good used one, please let me know.
>>
>> The part I am specifically looking to find is the front piston that
>> passes out through the front of a tandem (dual line) master cylinder
>> used on the latest Spridgets. This is the type used in conjunction
>> with the pressure failure assemblies.
>>
>> I have a badly scored one that I believe is preventing a proper seal
>> in the larger front bore, hence a slow leak.
>>
>> Any and all suggestions/assistance welcome.
>>
>> Thanks!
>>
>> Gerard
>
>>
>
>
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