Subject: And now for something completely different....
Author: Tom Bowes
Date: Sep 12, 2001, 7:14 PM
Post ID: 1708217476
First of all, congrats to Ian for making the cover of the September
MGNOC newsletter.
A few thoughts on brake cables and petcock gaskets.
The last time we discussed the petcock gasket problem I thought I had it
beat by using Viton for the gaskets. I am sorry to say that, alas, once
again my efforts have failed. After about a month with the new Viton
gaskets I started having fuel starvation problems at speeds over 65 MPH
or when going up hills. Subsequent inspection of the gaskets reveals
that they have torn in between the holes for the fuel passages and
partially blocked the channel in the petcock rotor.
This leads me to think that the problem is one of the mechanical
strength of the gasket material, rather than the chemical makeup of it.
Viton is supposed to nearly impervious to fuels and petroleum based
solvents, and therefore should not have been adversely affected. So,
"what's the problem?", I ask rhetorically. My guess is that the large
amount of spring pressure on the rotor, and the lack of lubricating
properties in gasoline simply put too much mechanical strain on the
material and cause it to fail.
I had an original petcock gasket that I had removed, which I took to the
local rubber supplier. The owner looked at it and said that he guessed
that it was made out of vinyl, and not one of the fancier sort of
elastomers. I asked him if they had any, and he graciously provided me
with a sample. At present I am experimenting with a viton gasket,
lubricated with silicone grease, in the left petcock, and a vinyl
gasket, also lubricated with silicone grease, in the right petcock. So
far the vinyl gasket seems to be doing the trick, but I have as yet to
get the bike up to freeway speeds to really try it out. Stay tuned, more
info to follow.
Brake cables.......I had installed a front brake cable (aftermarket) on
the bike when I had originally rebuilt it. Gary Cheek took it for a ride
and commented on how much firmer the feel was on the brakes for his
Eldo. After some comparison he figured out that the original brake
cables have a larger core wire, larger jacket, and a different rate of
twist to the core wire than do the aftermarket replacements. The net
result is that the aftermarket cable appears to be made from the same
stuff as the original clutch cable. The core wire is thinner and has a
higher rate of twist, thus making it far more stretchy than the original
cable. I found an original cable and swapped it for aftermarket one.
What a difference! Previously, I could pull the brake lever all the way
to the grip with no sensation of the pressure increasing once I reached
a certain point. This means that the cable was stretching. With the new
cable, the pressure increases linearily with increased pulling force and
will not allow the lever to reach the grip. For some of you who are
struggling with anemic front brakes this may be a contributing factor.
Tom
'70 (July '69) Ambassador
99.8% Complete, 10% Left To Go
'82 V50-III
Shelby Township, Michigan