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#Post#: 102522--------------------------------------------------
Re: Bleeding brakes
By: fuckwit Date: September 6, 2017, 3:38 am
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[quote]cars with servos used different brake linings from those
without servos.
Hmmm! S3s were fitted with servos. S2s did not, normally, have
servos. But did the cars leaving the factory have different
brake linings? All you can buy nowadays is "one size fits all"
brake shoes. Not only that, HMG in their wisdom banned asbestos.
I read that modern cars wear their discs out, because asbestos
free-brake pads require greater pressure for the same stopping
power. Discuss.
[/quote]
Entirely my point, there's so many factors to take into account,
and no easy way to verify the effect or even the existence of
many of them, for braking becoems such a complex subject, it's
easier to disappear up your own jacksy looking at it. Most
definitely the lining-material varies batch to batch, and the
current one size-fits-all, can't be good where linings should be
softer for some applications. And who knows what we are really
getting anyway?
And agreed, to improve mechanical-advantage by decreasing the MC
size or increasing the swept-volume of the wheel-cylinders or
calipers is the way to go. Here drum have several limitations
over discs. They need more piston-travel for a start.
Increasing tyre diameter has an undesirable effect, but will
increase the footprint, which whilst this will not increase tyre
to surface grip because of area, does allow the tyre distortion,
like a rucked-up rug to better deal with the surface.
The major advantage of discs they require far less
caliper-piston movement, yet have more space for larger
pistons, so there's a double -wahmmy, all upping the
mecahnical-advantage along with the ability to be off as
quicklly as they're on, and along with no self-servo effect,
this gives greater pedal-feel, and abilty to deal with modern
systems like ABS. The only return spring on discs is hte
piston-seal, and thus they're fast. Discs win here too.
We could go on forever...
#Post#: 102523--------------------------------------------------
Re: Bleeding brakes
By: Namrac Date: September 6, 2017, 3:46 am
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Thanks guys for the suggestions. Have had to leave vehicle for a
week due to other commitments but in the meantime had new rear
pipes made up as existing pipes looked rough and flexible hose
was seized into union so had to be cut off. Now it's stopped
raining am going to fit and bleed again. Watch this space.
#Post#: 102524--------------------------------------------------
Re: Bleeding brakes
By: w3526602 Date: September 6, 2017, 4:57 am
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Hi,
First ... having reread my mail above, I did not key any of the
"GAY" words in relation to the Green Bible. Is there a
homophobic program playing pranks on me?
I'd agree with fitting discs, but the expense puts me off. There
is also a problem with standard wheels not fitting over some
callipers.
My Reliant Scimitar GTE used TR6 front suspension, with (I
think) Jaguar XJ6 callipers. The GTE weighed about 25cwt, (about
the same as a Land Rover 88") and in my case, was geared to pull
30mph in overdrive top, and red-lined at 6,500rpm. I suggest
those brakes worked a lot harder than most Land Rover brakes. Of
course, the GTE was on 14" wheels, so the Principle of Levers
worked in it's favour ... but the smaller discs worked against
it.
How much do new Jaguar callipers cost? How much do 2nd hand Jag
callipers cost, and how much to have them fitted with stainless
steel sleeves? The calliper carrier bracket on the GTE was not
exactly impressive to look at, probably not expensive to hack
out of ingot in a Mumbai back street workshop. What are the
chances of a Discovery hub and disc fitting a Series stub?
Well, I can dream, can't I?
602
#Post#: 102525--------------------------------------------------
Re: Bleeding brakes
By: Namrac Date: September 6, 2017, 11:47 am
---------------------------------------------------------
Finally replaced rear copper pipes and flexible pipe, bled using
the one man bleeding device which seemed to get all the air out
and have now got good brakes. Yippee. I think some of the old
wheel cylinders must have been seized since God was a lad. I
ignored the suggestion in Haynes to start bleeding at the front
and followed what I've always done and started from the rear
nearside, furthest away from the master cylinder. After all
that's where all the air was in the new pipes. Now just to sort
out the wandering steering which I found was due to both
nearside track rods ends being seized, and they are only 2 years
old! Still, that's another topic, but an easy fix.
Thanks all of you for your suggestions, although I think I'll
stick to non-servo drums. I also drive Austin Sevens and Morris
Minors so used to not over-fierce braking.
#Post#: 102526--------------------------------------------------
Re: Bleeding brakes
By: w3526602 Date: September 7, 2017, 1:29 am
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Hi,
Ah ... Austin 7 brakes. Fond memories of my first four-wheeler,
1934 Austin 7 for £10 (but this was circa 1956/1957, when HMG
said we need not waste our petrol ration on driving lessons,
just tie on the L-plates, and drive ... unaccompanied). I had
three lessons with BSM before my test, so they could teach my
how to go round corners without screeching the tyres. I took my
test in a 1935 Austin 10 ... which also had interesting brakes,
Austin 7s were the first car with ABS. No matter how hard you
pressed the pedal, everything flexed ... and slackened the
cables. But if you were going backwards, and pressed the pedal,
everything flexed the other way, and your knee smacked you in
the face. I think it was Bowden Cables who made a kit for
sorting Austin 7 brakes, after which they could stop.
602
#Post#: 102557--------------------------------------------------
Re: Bleeding brakes
By: NoelC Date: September 22, 2017, 7:32 am
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[quote author=fuckwit link=topic=9867.msg102508#msg102508
date=1504394694]
Er, but I'm afraid I have to put you task here, even in
contradiction of yourself. If, and I quote: 'A servo does reduce
pedal effort, however it does not improve the performance of the
brakes. Just means you don't have to push as hard.',
Ahem, so we push not so hard for the same braking effect? It
must lead us to ask... For the same pedal-effort where would the
force be off to then? Perchance, a day at the races?
[/quote]
What I'm getting at is the limiting factor in all of this is
tyre adhesion. My 2A 109 with gradually increasing pressure on
the pedal will slow down and lock all 4 wheels on dry tarmac. My
3 109 with a servo does exactly the same, with less pressure on
the pedal. Stick both on a rolling road brake tester and the
efficiency is no different as both vehicles exceed the adhesion
limits of the tyres, hence stating a servo doesn't improve the
performance of the braking.
It's all too common in series circles to moan about crap brakes
and then think fitting a servo will somehow uncrapify them when
it's not the case. I'll always argue that if your non-servo
series won't manage the effort to lock all 4 on a dry road and
it does when a servo is fitted you're either (a) a weakling or
(b) the servo has treated the symptom not the cause.
#Post#: 102563--------------------------------------------------
Re: Bleeding brakes
By: fuckwit Date: September 25, 2017, 5:20 am
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[quote author=NoelC link=topic=9867.msg102557#msg102557
date=1506083557]
[quote author=fuckwit link=topic=9867.msg102508#msg102508
date=1504394694]
Er, but I'm afraid I have to put you task here, even in
contradiction of yourself. If, and I quote: 'A servo does reduce
pedal effort, however it does not improve the performance of the
brakes. Just means you don't have to push as hard.',
Ahem, so we push not so hard for the same braking effect? It
must lead us to ask... For the same pedal-effort where would the
force be off to then? Perchance, a day at the races?
[/quote]
What I'm getting at is the limiting factor in all of this is
tyre adhesion. My 2A 109 with gradually increasing pressure on
the pedal will slow down and lock all 4 wheels on dry tarmac. My
3 109 with a servo does exactly the same, with less pressure on
the pedal. Stick both on a rolling road brake tester and the
efficiency is no different as both vehicles exceed the adhesion
limits of the tyres, hence stating a servo doesn't improve the
performance of the braking.
It's all too common in series circles to moan about crap brakes
and then think fitting a servo will somehow uncrapify them when
it's not the case. I'll always argue that if your non-servo
series won't manage the effort to lock all 4 on a dry road and
it does when a servo is fitted you're either (a) a weakling or
(b) the servo has treated the symptom not the cause.
[/quote]
Agreed I see you point. Yet, I've got a stonking servo on there
and this gives me 'feel' far over even a stock servo would do,
now I won't profess to be the world's best driver, but light
pressure and/or slightly more pressure for lock-up gives a more
modern 'feel', which even those with less ability can deal with.
Maybe you're simply a better driver, but if I using more than my
toes to brake, I can't 'feel'. If I'm 'gorillaing' the pedal to
stop, I'm just not good enough to have what finess I can muster
easily. I want my brakes to have the feel of modern cars, and
with proper servo assistence, a bias valve, and the pistol-poor
limits of the tyres, they pretty much do. I could not get near
that without a servo.
And if it's me on the road at the same time as you, even if you
don't need one, with my own limitations, for all but the
strongest and most talented, I reckon we'd all be better to hope
we've got servos.
#Post#: 102571--------------------------------------------------
Re: Bleeding brakes
By: NoelC Date: September 29, 2017, 3:48 am
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I think driving style comes is to a degree dictated by what
you're used to. My working week comprises driving a range of
buses and coaches dating from the 1950s up to brand new, a
non-servo series stops like an F1 car in comparison. :smilewide:
I don't consider myself a better driver than anyone else, just
more used to driving large heavy things that don't stop well. I
did have to deliver a Green Goddess to a customer on bar grips
on wet roads a year or so ago - that was an interesting
experience. That'd let go at 15mph on a roundabout.
#Post#: 102603--------------------------------------------------
Re: Bleeding brakes
By: w3526602 Date: October 13, 2017, 1:01 am
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Hi,
A servo utilises atmospheric pressure acting on a diaphragm.
Atmospheric pressure is decreed by Mother Nature. The area of
the diaphragm is decided by the bloke in a white coat, wielding
a pencil.
The amount of servo assistance is limited by both these factors.
There will come a point where applying more pedal pressure will
make no further difference to the servo assistance.
If you want real servo assistance, think about the little
hydraulic pump bolted on top of Citroen BX engines. I think I
read something about 3000psi. That's a frightening amount to
push through a rubber hose.
602
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