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

[Al Brase]

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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