[T2] Can disc master cylinder be used with drum brakes?

[Chris Dreike]

One more piece of info. I went through about of quart of fluid trying to
get all the air out of the calipers. There may still be a little left.

Chris

On Thu, Jul 2, 2020 at 2:29 PM Chris Dreike <cdreike at gmail.com> wrote:

> I recently installed EMPI drop spindles on my 71. I purchased the calipers
> from EMPI and I also installed new rotors purchased locally. Of course
> these are 73+ parts.
> I am having a problem with the calipers dragging intermittently. I
> installed a new MC and booster, there are new hoses all around as well as
> new wheel cylinders and shoes in back.
> Any idea on the intermittent dragging? It drags hard enough to heat up the
> rotors something fierce and I can feel it in the throttle. It needs more
> gas.
> Could I have a residual valve causing the problem?
>
> Thanks,
> Chris
>
> On Thu, Jul 2, 2020 at 2:06 PM Al Brase <alribee at gmail.com> wrote:
>
>> Personally, I've managed to live pretty well in years past with a 1969 and
>> 70 and all drums. I currently have a ratty 70 Westy that I might just
>> adopt
>> as a forever car because it will be too much work to make it a flipper.
>> So, I might end up wanting front discs on it. I rather like the wide 5
>> look. So maybe I'd investigate a conversion or is it possible to home
>> build
>> such a thing?
>> I certainly have all the bits to completely change to a 1978
>> undercarriage,
>> but maybe I'll save that and hope a later model rust free shell comes into
>> my life. I actually CUT UP a very rusty 1978 Champagne Edition once and
>> save nearly every single piece. Missing front seats and rear hatch at this
>> point is all. I'd hoped to find a better CEII,with a sunroof, but now
>> about
>> 10 years too late!
>> So, I guess that is a two subject post reply.
>> Sorry for the thread hijack.
>>
>> On Thu, Jul 2, 2020 at 12:28 PM david raistrick <keen at icantclick.org>
>> wrote:
>>
>> > so the residual valves on all the bus MCs that I've seen (keep in mind
>> it's
>> > been a lot of years now since I last dug into this) are external.  so
>> > they're easy enough to remove (or gut).
>> >
>> > you definitely need residual valves on the drums - but any VW bus master
>> > from any era is going to have that already because everything was always
>> > rear drum.   even if you use a rabbit MC, it's also going to have rear
>> > drums, so it'll have residual valves.   you'd be up into A4 golf land
>> (99+)
>> > to get a 4 wheel disc MC that wouldn't have resid valves...
>> >
>> >
>> >
>> > for front discs - I don't really think a residual valve is a good thing
>> at
>> > any level.  there are no springs pushing things back, so you'd just be
>> > using that residual pressure to hold the pads against the disc....
>> >
>> >
>> > as for 1 2 or 4 piston calipers - for a bus, it really doesnt matter
>> > (really).  (if you've got a 2liter in a split and you're heavy on the
>> loud
>> > pedal, it might matter....but not really).    1 piston calipers are
>> always
>> > floating calipers, though - so that's actually a real positive for daily
>> > driver types.   what it means is that the caliper slides on a bracket
>> and
>> > -always- self centers (as long as the slides dont bind from lack of
>> > maintenance and lube).    4, and usually 2 piston calipers, are fixed
>> > calipers - you HAVE to shim and adjust them to center and square.   if
>> > you're off a little bit, you'll get reduced brake force on the inside or
>> > outside pad and uneven wear.
>> >
>> > but our choices are limited (unless you're designing a kit yourself), so
>> > it's kind of a "take what you can get" set of options.
>> >
>> >
>> > I think the most important part of any disk brake selection is going to
>> be
>> > wear-item availability.  pads and disks and caliper piston seals.    So
>> a
>> > caliper that has fitment to a known vehicle (98 golf, etc) or from an
>> known
>> > aftermarket mfr (wildwood, etc) is really important - both from a long
>> term
>> > ownership standpoint and from a "can I adjust this with different pad
>> > compounds if I dont like it".       Discs are harder - but a full size
>> or
>> > cut-down 944 disk, or a mustang 2 disk that has a machined seal surface
>> are
>> > things you -can- buy again and get any machine shop to make fit for you
>> > later.   well, the full unmodifed 944 disc doesnt even need that. :)
>> >
>> >
>> > I dont recall that EMPI had an option when I last looked - so not sure
>> what
>> > they're using.  Send me a link and I'll take a look when I get a chance.
>> >
>> >
>> >
>> >
>> >
>> >
>> > On Thu, Jul 2, 2020 at 12:35 PM Warren McKean <
>> warren.p.mckean at gmail.com>
>> > wrote:
>> >
>> > > David,
>> > > Thank you for this info. I read your analysis of the 4 disc conversion
>> > > kits plus other sites on the internet. There seems to be some
>> agreement
>> > > that either a 2 lb residual valve or no valve is recommended for discs
>> > and
>> > > a 10 lb residual valve is recommended for drums. Since I will have
>> front
>> > > discs and rear drums I would need a master cylinder with no residual
>> > valves
>> > > and install a 10 lb valve in the brake line to the rear drums. What do
>> > you
>> > > think?
>> > > Do you have an opinion of the advantages of getting a 1,2, or 4 piston
>> > > caliper? And did you look at the EMPI kit?
>> > > Warren
>> > >
>> > > On Wed, Jul 1, 2020 at 12:56 PM david raistrick <keen at icantclick.org>
>> > > wrote:
>> > >
>> > >> yes.
>> > >>
>> > >> but you can also use the drum master for the disks.   for aftermarket
>> > >> disk conversions, this is usually the better choice anyway.  (I've
>> > written
>> > >> a lot about this in the past....)
>> > >>
>> > >>
>> > >>
>> > >> On Wed, Jul 1, 2020 at 3:47 PM Warren McKean <
>> warren.p.mckean at gmail.com
>> > >
>> > >> wrote:
>> > >>
>> > >>> Gents:
>> > >>> I have a 1970 Baywindow (bought new). I plan to upgrade to front
>> disc
>> > >>> brakes soon, but have an immediate need for a master brake cylinder.
>> > Can
>> > >>> I
>> > >>> use the brake cylinder that will be necessary for the front discs
>> with
>> > my
>> > >>> existing front/rear drums? Also, since most folks install discs in
>> the
>> > >>> front only, does the 1971 brake cylinder have a retention valve in
>> the
>> > >>> rear
>> > >>> hydraulic line?
>> > >>> Warren McKean
>> > >>> 1970 Camper
>> > >>> _______________________________________________
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>> > >>
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