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

[Chris Dreike]

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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