Date: Mon, 26 May 2008 22:41:34 -0700
Reply-To: Scott Foss - Shazam <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Foss - Shazam <scottdaniel@TURBOVANS.COM>
Subject: Re: Master cylinder question
In-Reply-To: <002001c8bfb2$a0007e90$0201a8c0@troykv7nw3q4te>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi Troy,
by 'fad' I suspect you mean the pedal was vague or something. 'Brake
Fad' refers to when the pads and fluid are too hot, as during a long
descent using the brakes to much, and brake effectinvness ( i.e.
stopping power ) just starts going away. That's 'brake fad.'
In an extreme case the brake fluid can boil at the caliper pistons (
that's why brake fluid has a boiling point rating - Dot 4 is superior to
Dot 3 for example ) ...........but if the BF boils....you have zero
brakes, - just the mechanical parrking brake on the rear drums, which at
30 mph is about like dragging a foot on the pavement.
But really..........it's not wise, or effecient, lets' say - to change
a master cylinder without knowing what is going on the the brakes at the
wheels. especially the rear drums.
Here is what is correct, and the correct order for the rear brakes - get
the drums off, it can be very hard sometimes. If you are lucky, you
remove the two 11 mm hex head screws, whach the drum sharply ( parking
brake OFF of course ) sharply on the edge........
swinging straight toward the car, so as to impart a tilting action to
the edge of the drum - if you are lucky, it'll jump right off the flange.
On the other hand, I've strugged over an hour from that point, just
getting acces the the rear brakes.
( removing drum with the flange via the but nut is an option - but
that's pretty heavy duty work )
first thing when drum is off -
check wheel cylinder for leakage.
the rubber boot you see is just a dust seal, not the hydrualic seal.
peel back the edge of the dust boot with a tiny screw driver - if dry in
there, you're ok.
if wet..........you're leakin' baby.
next...........check thickness of the brake shoes.
it's normal from them to be more worn at th top than the bottom.
if both those are ok............I personlly will tweak up the
self-adjsut a few clicks, checking how the drum fits over the shoes each
time i turn it two clicks. Normnally this isn't done though.
But what you want is 'the shoes are adjsuted to the drums
'..............THEN .........if parking brake handle goes up to far when
you apply, only then adjust the parking brake under the middle of the
van. In all cases it is wrong to adjsut the parking brake cable without
having the shoes adjsuted up in the drums first. it's a well-working
self-adjust machansm though...........and usually you don't have to mess
with it much.
but ........
i've seen rear brakes just pathetically wasted - wheel cylinders leaking
for the last few years, shoes soake in BF etc.
so ..........you really should know what's in there, especially if the
MC doesn't come out right.
Working on customer's cars..............I would never in a millioin
years do an MC without looking in all 4 wheels first.
on the front calipers - they seldom leak......pads wear of course, discs
get tired/thin/scored/out of true etc ( rear drums have to be within
spec for thickness and roundness of course ) ...............calipers
seldom leak. but they do get seized up pistons after 15 to 20 years.
and hoses, gotta think about them. One failure mode on brake hoses is
they clog up inside and won't release pressure. Rare, but it happens.
Mostly you see the cracked outer cover on hoses.
you may not really have it bled correctly. You could try bleeding some more.
you did out to all 4 wheels, right ?
and if you have manaul trans, and since it's on the same resevoir - you
did the clutch slave cylinder too while you were at it ? ........
not expecting that but it's a great thing to do.
fwiw ............I do have a pressure bleeder. it is covered in dust,
had it 20 years.
I'm 'old fashioned' and quite 'hands on' and I 'massage ' a lot of
things to health. I only use the one person, clear plastic tube in a
bottle of old BF method..........BECAUSE............
you can feel if the MC is pumping fluid right !!
you have zero feel using any pressure method.
did the MC happen to 'pump in air' ? ............that would be a
faulty MC though, and if you have a new high quality one. ....shouldn't
be an issue.
i'll close with this ......
here is my 'ratings of importance' about parts and replacing parts :
Importance of Workmanship : 100 %
Importance of Quality of the new part : 70 %
Importance of even using a new part : Varies of course - i mean a shot
part is a shot part- but i will still say this only rates 50 % in terms
of relative importance.
there is a huge tendency to think 'part part part part'...........and
very little about 'inspect and diagnose properly'.
Or test existing components by seeing how the old MC responds to
bleeding - thats' a GREAT way to ID a tired MC btw.
And if it's 20 years old anyway- yes of course a new german high quality
one is called for - absolutely !
But a full careful inspection is where you should start - in the wheels. .
Identify the worn parts, and build from the wheesl up, and MC is last in
the chain......
or stated another way, you need to know the wheel parts of the brakes
are good to be assured of success when installing a new MC.
and I'd sure consider trying more bleeding........and hopefully after
you know the rear brakes are in mostly decent shape.
adjusting rear brakes :
you can tweak the adjuster wheel a few clicks 'tighter' yes, - hold the
pawl back with a little screw driver.
You can 'tap' on the shoes or giggle them a bit with your hands to
center them a bit - then try the drum on.
yes, pull the parking brake handle e a few times to center the shoes.
then see if you can get another two clicks out of the aduster wheel.
DO NOT make it draggy or tight !
there needs to be slack for when the drums get hot.
in normal self-adjsuting operation............the only hold the shoes
out to like 95 % ........not 98 % like we might want to make them.
so don't overdo the tightness. at all.
and hopefully..................whoever worked on the brakes last, knew
to do only one side at time............then the other side.
the self-adjusters are dedicated to each side and you sure would not
want to get them on the wrong side.
And the reason you do one side at a time is so you can go look at the
other side to see how to put the side you are working on back together
rgiht !
you should have about 1/8th inch mechanical free play or 'slop' at the
top of your brake pedal- there must be a tiny bit of free play there.
Sometiems it wears bigger. A half inch would be excessive.
A really firm and tight system.............the brake pedal will be firm
at about 2 inches down from the top. or 1/3 down from the top max, and
even that sounds bit low to me. I'd want 1.4th down from the top.
and with really good 'action' too..........how well the van slows down
in response to pedal pressure.
but if you don't know what's going on in the rear brakes.............
and you have a weird/low brake pedal..........
well, you can either try more bleeding or inspect in the brakes.
are you sure the brake line nuts are very tight at the MC ?
you MUST use a tubing nut wrench on those an open end will not do.
AND............very important - well maybe not with a pressure bleeding
method.............but for normal 'use the pedal to develop pressure
method' the MC must be 'bench bled ' first.............
AND..............this is a WONDERFUL feature of Vanagons - it's the only
car in the world were you can 'bench bleed' the MC with it mounted in
place on the vehicle by yourself !
I like that !
scott
www.turbovans.com
Troy wrote:
> Hi folks:
>
> I'll stop talking about battery woes and move on to a new subject;)
>
> Just finished up installing a new master cylinder on my 89 Westy as well as an Audiovox cruise control. Everything went fairly smoothly, and my homemade brake bleeder worked great. It was fun to finally get a chance to try it out. Puzzling thing to me is the brakes are now grabbing/engaging towards the end of the pedal travel, whereas prior to changing the cylinder out they engaged a little bit sooner, but would fade. I've got really good pressure, pedal is not spongy, so am I looking at a rear brake adjustment? Just can't figure out why a master cylinder would change where the brakes would engage.
>
> >From what I recall about adjusting the rear brakes, the star adjuster is turned until the brakes just scrape. Someone mentioned then applying the parking brake as well as pumping up the brake pedal to center the pads, and then readjusting. Is this the correct procedure? I've only ever tried this once.
>
> I like to have the brakes engage at the first third of travel instead of the last third, and I believe pedal height comes form the rear brakes adjustment, but would like confirmation of this.
>
> Thanks,
>
> Troy
>
>
>
