Re: Bleeding Dual Circuit 69 Brakes Again and Again and...

[Scott Fisher <sfisher71@domain.elided>]

So... smart-ass windshield comments aside, I'm working
through the brakes on my '74 Berlina, and have some
observations that may help (even if it cheats me out
of a good price on a crack-free windshield).

--- Mitch <wolberg5@domain.elided> wrote:
> I can't believe this is still not working. I took it
> to a professional with
> vacuum and pressure bleeders and he swears there is
> no air in the system. Yet
> the pedal is still low and soft. 

So's my '74 Berlina -- that is, it takes very little
force to move the pedal, and it moves a long way
compared to my '74 Spider.  

> Its a newly resleeved MC, 

Does your car have the dual-booster, dual-MC setup?  I
know that GTVs from one year (and I thought it was
'69) have a dual-circuit system with a second master
cylinder and second vacuum booster plumbed somewhere
else in the car, like a Rover 2000TC.  Is it just
BARELY possible that your "professional" didn't bleed
both master cylinders?

> new front brake
> hoses, and I've gone through a number of quarts of
> DOT 3 fluid trying to bleed
> it myself, cracked the lines at the boosters, kept
> the engine running and so
> on and so forth. What else do I need to do?

Two things:

1 - Have you tried replacing the pads yet?  If your
pads are worn, it will take a larger volume of fluid
(therefore a longer pedal travel) to push the pistons.
 And if you HAVE replaced the pads... are they bedded
in properly?  (Check the packing materials, or see
below.)

2 - How does it actually STOP?  That is, when you
press on the low and soft pedal, does the car sort of
gradually, gently slow in a frightening manner (as
mine did before Saturday), or does it slow down right
now, with just a lot of travel on a very soft pedal?

I ask these questions because my continuing efforts to
bring my own Berlina up to regular-use standards has
reached exactly this position.  I replaced pads on
Saturday and while they're still getting bedded in,
the difference is astonishing.

I still have a fairly soft pedal with a longish
travel, but the brakes STOP the car quite effectively
now.  It's gone from about 30% as good as the Spider
to about 80% as good, and I haven't yet bedded in the
pads (and haven't even touched the rears yet, for that
matter -- I had some front pads in the spares box, so
I took ten minutes and installed them Saturday
afternoon).

I'll go over the vacuum-system diagnostics I learned
over the weekend, in a separate message.  I don't
think that's your problem, except that your vacuum may
be providing too much assist for your tastes.  (And
mine.)

Bedding in brake pads: It takes a certain amount of
use for brake pads and discs to become "bedded in,"
the term for surfaces that have adapted to each other
for most effective use.  Bedding in pads may vary from
manufacturer to manufacturer; Repco/Axxis always used
to recommend that you make a series of stops from slow
speed and low pedal pressure, gradually increasing the
speeds and pedal pressure.  

Until new pads are bedded in, they can give you a
scare because stopping distances increase, and pedal
travel can go up.  Follow your pad manufacturer's
recommendations, and reserve judgment on
braking-system performance till you've properly bedded
in the pads.

One final comment: have you tried plugging the vacuum
line at the manifold, disabling the boosters
altogether?  A couple of respondents to my question
said that they did this, and liked the feel of the
unassisted brakes better than the assisted ones. I
haven't done this yet, but I may give it a try.

--Scott Fisher
  Tualatin, Oregon
.
Yahoo! - Official partner of 2002 FIFA World Cup
http://fifaworldcup.yahoo.com
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