| Re: [GMCnet] update on master cylinder replace [message #198353] |
Wed, 13 February 2013 16:02  |
KB
Messages: 1262
Registered: September 2009
Karma:
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Senior Member |
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I think I said it correctly. Drum brake wheel cylinders may (and
that's the question) need different valving in the master cylinder than
disc brake calipers do. Disc brake calipers have o-rings. Drum brake
wheel cylinders have cup seals. So a master cylinder designed only for use
with disc brakes may not be a good thing to use with drum brakes.
Or at least that's the theory/question.
The point I was trying to resolve is what master cylinder to use
when you have drum brakes but expect to upgrade to disc brakes.
thanks
Karen
1973 23'
1975 26'
KenH wrote:
> I'm confused by that statement/question: You speak of disc master
> cylinders and wheel "cylinders" rather than "calipers". Calipers do not
> need residual pressure valves unless the master cylinder is located below
> the calipers, as on some hot rods. And the purpose is not to retract the
> pads but to prevent them from retracting too much when the fluid runs back
> to the master cylinder. Normally, caliper pistons are retracted by the
> hysteresis of their rubber seals, by disc run-out, and by play in the wheel
> bearings.\
> On Mon, Feb 11, 2013 at 3:17 PM, KB wrote:
>
>> > As long as I'm bothering the experts with silly questions... :-)
>> >
>> > If I understand it, one should not use master cylinders designed for an
>> > all-disc
>> > system on a vehicle that has drum brakes, because some (most? all?) wheel
>> > cylinders need residual pressure to retract fully and keep the cup seals
>> > closed.
>> > Most disc-disc master cylinders don't include the necessary valve(s).
>> > This could
>> > result in dragging brakes and/or air in the wheel cylinders.
>> >
>> > Any truth to this??
>> >
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Karen
1975 26'
San Jose, CA
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