Dear All,

I'm recommissioning my Herald at the moment. After a certain amount of
swithering, I decided to go for silicone fluid in the brake and
clutch. The clutch, which I did first, was fine. However, the brakes
have been a real pain. After a first session, with almost a litre of
fluid through the system the pedal was still very springy. A second
session a week later improved things a bit. A third session today
shows no bubbles at all emerging, but there is still a fair bit of
spring in the pedal.

However ... I also have new shows and pads, which always adds a bit of
bounce on the Herald till things bed in

And ... I have read claims that silicone fluid is a bit more
compressible than glycol

So ... should I be worried? Have folk here had problems bleeding
silicone fluid? Experience of it giving more spring to the pedal?
Shall I just take the car out for a drive - the MOT station is 20
miles away over twisting moorland roads - and hope that everything
firms up a bit.

Incidentally, I know that I could switch to glycol, but my reasons for
silicone are fairly good, and I'd like to stick with it unless it
simply isn't going to be possible to get satisfactory performance.

Ian

PS New master cylinder, calipers, rear cylinders, hoses (Goodrich) and
most pipes.

Ian formulated the question :
> The clutch, which I did first, was fine. However, the brakes
> have been a real pain. After a first session, with almost a litre of
> fluid through the system the pedal was still very springy. A second
> session a week later improved things a bit. A third session today
> shows no bubbles at all emerging, but there is still a fair bit of
> spring in the pedal.

Does it have a servo and you are testing it with the engine running?

If so they can feel a little soft and springy with the servo working, 
try it again without. Its to do with you applying much more pressure on 
the pedal than you would when actually driving.

-- 
Regards,
        Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Ian wrote:
> Dear All,
> 
> I'm recommissioning my Herald at the moment. After a certain amount of
> swithering, I decided to go for silicone fluid in the brake and
> clutch. The clutch, which I did first, was fine. However, the brakes
> have been a real pain. After a first session, with almost a litre of
> fluid through the system the pedal was still very springy. A second
> session a week later improved things a bit. A third session today
> shows no bubbles at all emerging, but there is still a fair bit of
> spring in the pedal.
> 
> However ... I also have new shows and pads, which always adds a bit of
> bounce on the Herald till things bed in
> 
> And ... I have read claims that silicone fluid is a bit more
> compressible than glycol
> 
> So ... should I be worried? Have folk here had problems bleeding
> silicone fluid? Experience of it giving more spring to the pedal?
> Shall I just take the car out for a drive - the MOT station is 20
> miles away over twisting moorland roads - and hope that everything
> firms up a bit.
> 
> Incidentally, I know that I could switch to glycol, but my reasons for
> silicone are fairly good, and I'd like to stick with it unless it
> simply isn't going to be possible to get satisfactory performance.
> 
> Ian
> 
> PS New master cylinder, calipers, rear cylinders, hoses (Goodrich) and
> most pipes.

Personally I don't like silicon fluid not worth the expense. If you 
correctly flush your fluid every two years you should have no problems, 
except wear and tear on the system components, which is normal what ever 
the fluid you use.

Ok having had my rant, make sure that the rear brake shoes are adjusted 
fully up, this can induce soft brakes, these should also be adjusted up 
after the linings bed in.

After the system has been bleed let the car sit and check the pedal next 
day. You may check the play in the rod on the pedal and adjust that up 
as well.

r

On 27 Aug, 20:19, Harry Bloomfield 
wrote:
> Ian formulated the question :
>
> > The clutch, which I did first, was fine. However, the brakes
> > have been a real pain. After a first session, with almost a litre of
> > fluid through the system the pedal was still very springy. A second
> > session a week later improved things a bit. A third session today
> > shows no bubbles at all emerging, but there is still a fair bit of
> > spring in the pedal.
>
> Does it have a servo and you are testing it with the engine running?
>
> If so they can feel a little soft and springy with the servo working,
> try it again without. Its to do with you applying much more pressure on
> the pedal than you would when actually driving.
>
> --
> Regards,
>         Harry (M1BYT) (L)http://www.ukradioamateur.co.uk

Make sure the shoes are adjusted properly, have you tried bleeding
with the shoes backed off, then adjusting the shoes to the correct
postion?

Also make sure that all seals in the system are happy with silicone
fluid, silicone fluid is not reccomended for my Morris Minor because
it is said it can damage the seals.

On 28 Aug, 03:45, Rob  wrote:

> Personally I don't like silicon fluid not worth the expense. If you
> correctly flush your fluid every two years you should have no problems,
> except wear and tear on the system components, which is normal what ever
> the fluid you use.

Like I said, it was a close call, and if all else fails I'll go back
to glycol.

> Ok having had my rant, make sure that the rear brake shoes are adjusted
> fully up, this can induce soft brakes, these should also be adjusted up
> after the linings bed in.

They're as well adjusted as any new shoes in new drums can be - I'll
certainly expect to re-adjust them after everything has bedded in.

> After the system has been bleed let the car sit and check the pedal next
> day. You may check the play in the rod on the pedal and adjust that up
> as well.

No adjustment at the pedal or in the cylinder. However, leaving the
car to sit for a few days after the first bleed did seem to improve
things a bit - mainly, I think, by allowing microbubbles to coalesce
into bigger, bleedable lumps of air.

I've done some limited road testing and the brakes work OK, without
pulling - it's just that the pedal feels bouncier than I'd like. And,
I fear, than the MOT tester will like ...

Ian

On 27 Aug, 20:19, Harry Bloomfield 
wrote:
> Ian formulated the question :
>
> > The clutch, which I did first, was fine. However, the brakes
> > have been a real pain.

> Does it have a servo and you are testing it with the engine running?

No servo - just a bog standard Herald system.

Ian

Ian wrote:
> Dear All,
> 
> I'm recommissioning my Herald at the moment. After a certain amount of
> swithering, I decided to go for silicone fluid in the brake and
> clutch. The clutch, which I did first, was fine. However, the brakes
> have been a real pain. After a first session, with almost a litre of
> fluid through the system the pedal was still very springy. A second
> session a week later improved things a bit. A third session today
> shows no bubbles at all emerging, but there is still a fair bit of
> spring in the pedal.
> 
> However ... I also have new shows and pads, which always adds a bit of
> bounce on the Herald till things bed in
> 
> And ... I have read claims that silicone fluid is a bit more
> compressible than glycol
> 
> So ... should I be worried? Have folk here had problems bleeding
> silicone fluid? Experience of it giving more spring to the pedal?

I have got silicone fluid in my PI - it wasn't my choice, the previous 
owner put it in after a complete brake overhaul.

And at the time I bought the PI, I had a 2000 with ordinary brake fluid. 
  And there was *always* a different feel to the PI brakes.  The systems 
are pretty well identical except the PI has a vacuum storage thing and 
the 2000 didn't, and both stopped well enough to get MOTs, but the PI 
pedal never felt as solid as the 2000 one.

When I had to replace one of the brake parts for an MOT, I let the 
garage do it for the cheap retest, and provided a bottle of DOT5 to make 
sure he used the right stuff.  It got the MOT, but when I collected the 
car afterwards the pedal felt even more spongy than before.  I used it 
for a week or so, then decided I really didn't like it so took it back 
for him to bleed again.  It was better second time, but still not as 
good as it had been when I bought it.  A third bleed a month later 
finally fixed it.

Apparently, silicone fluid gets "micro-bubbles" which are too small to 
see in the bleed jar but affect the braking system.  You have to leave 
the system unused for long enough for these micro-bubbles to coalesce 
into larger ones and then bleed them out.

My advice is to leave your Herald undriven for at least a week, then 
bleed again.  Provided after that you get brakes without the pedal going 
so far down that you feel inclined to pump it, then it is safe to drive, 
it should get an MOT, and you need to do some driving to bed in the new 
pads and shoes.  Once you are happy that they are bedded in, adjust them 
then leave the car as long as is practical without using it, and then 
bleed again.  The pedal will still feel a little bit springy - it is a 
characteristic of silicone - but that last bleed should make it as good 
as it will get.  And it should then stay like that for years!

Jim

Ian wrote:
> On 27 Aug, 20:19, Harry Bloomfield 
> wrote:
>> Ian formulated the question :
>>
>>> The clutch, which I did first, was fine. However, the brakes
>>> have been a real pain.
> 
>> Does it have a servo and you are testing it with the engine running?
> 
> No servo - just a bog standard Herald system.

I was about to say that'll be the same as my Vitesse then - unless yours 
is drums all round. I never had a problem with silicon and don't 
remember any great difficulties bleeding the system. But perhaps I was 
less sensitive to any sponginess than you are.
I'd certainly recommend you persevere rather than switching back to 
normal brake fluid.

On 28 Aug, 07:16, Jim Warren  wrote:

> My advice is to leave your Herald undriven for at least a week, then
> bleed again.  Provided after that you get brakes without the pedal going
> so far down that you feel inclined to pump it, then it is safe to drive,
> it should get an MOT, and you need to do some driving to bed in the new
> pads and shoes.  Once you are happy that they are bedded in, adjust them
> then leave the car as long as is practical without using it, and then
> bleed again.  The pedal will still feel a little bit springy - it is a
> characteristic of silicone - but that last bleed should make it as good
> as it will get.  And it should then stay like that for years!

Thanks Jim - much appreciated.

Ian

Ian wrote:
> On 28 Aug, 03:45, Rob  wrote:
>
>> Personally I don't like silicon fluid not worth the expense. If you
>> correctly flush your fluid every two years you should have no
>> problems, except wear and tear on the system components, which is
>> normal what ever the fluid you use.
>
> Like I said, it was a close call, and if all else fails I'll go back
> to glycol.
>
>> Ok having had my rant, make sure that the rear brake shoes are
>> adjusted fully up, this can induce soft brakes, these should also be
>> adjusted up after the linings bed in.
>
> They're as well adjusted as any new shoes in new drums can be - I'll
> certainly expect to re-adjust them after everything has bedded in.
>
>> After the system has been bleed let the car sit and check the pedal
>> next day. You may check the play in the rod on the pedal and adjust
>> that up as well.
>
> No adjustment at the pedal or in the cylinder. However, leaving the
> car to sit for a few days after the first bleed did seem to improve
> things a bit - mainly, I think, by allowing microbubbles to coalesce
> into bigger, bleedable lumps of air.
>
> I've done some limited road testing and the brakes work OK, without
> pulling - it's just that the pedal feels bouncier than I'd like. And,
> I fear, than the MOT tester will like ...
>
> Ian

If the problem is micro bubbles, then the answer we found (on motorcycles) 
is to pressurise the system and leave it pressurised over night, the 
reduction in pedal travel the next day is quite amazing.

I use a brake pedal jack (home made from a mastic gun) to hold the pedal 
down.  Also useful for checking brake equality and brake lights !!

Mrcheerful

On 28 Aug, 14:08, "Mrcheerful"  wrote:

> If the problem is micro bubbles, then the answer we found (on motorcycles)
> is to pressurise the system and leave it pressurised over night, the
> reduction in pedal travel the next day is quite amazing.
>
> I use a brake pedal jack (home made from a mastic gun) to hold the pedal
> down.  Also useful for checking brake equality and brake lights !!

Splendid idea. I shall investigate a bodge along those lines!

Ian

Mrcheerful wrote:

> If the problem is micro bubbles, then the answer we found (on motorcycles) 
> is to pressurise the system and leave it pressurised over night, the 
> reduction in pedal travel the next day is quite amazing.

When I mentioned the trouble I'd had bleeding the front brakes of my 
Landy (notoriously difficult) to the MOT tester, he said that he always 
gravity bled them - i.e. opened the bleed nipples and just let the fluid 
run through on its own for an hour or so. I've never tried this, but 
guess it would avoid the problem of micro bubbles.

A web search suggested reverse bleeding them by forcing fluid into the 
bleed nipples via a syringe, but I'd already sorted them by then. Dunno 
if that method would help the OP.

> I use a brake pedal jack (home made from a mastic gun) to hold the pedal 
> down.  Also useful for checking brake equality and brake lights !!

Nice idea, and less hassle than searching around for a length of wood 
then trying to jam it against the seat back!

Willy Eckerslyke wrote:
> Mrcheerful wrote:
> > 
>> I use a brake pedal jack (home made from a mastic gun) to hold the pedal 
>> down.  Also useful for checking brake equality and brake lights !!
> 
> Nice idea, and less hassle than searching around for a length of wood 
> then trying to jam it against the seat back!

For checking brake lights I use a KrookLock.  Adjust to length then lock 
with the key and jam it between pedal and front seat frame.

Jim

Jim Warren wrote:
> Willy Eckerslyke wrote:
>> Mrcheerful wrote:
>> >
>>> I use a brake pedal jack (home made from a mastic gun) to hold the 
>>> pedal down.  Also useful for checking brake equality and brake lights !!
>>
>> Nice idea, and less hassle than searching around for a length of wood 
>> then trying to jam it against the seat back!
> 
> For checking brake lights I use a KrookLock.  Adjust to length then lock 
> with the key and jam it between pedal and front seat frame.

I've got a mirror on the garage wall. Just back up and have a look.

-- 
Pete M - OMF#9

BMW 325i SE Touring
Range Rover V8 Turbo

"Wait! We can't stop here, this is Bat Country"

On 27 Aug, 18:19, Ian  wrote:
> I'm recommissioning my Herald at the moment. After a certain amount of
> swithering, I decided to go for silicone fluid in the brake and
> clutch. The clutch, which I did first, was fine.

Bigger pipes on the clutch. Silicone is a problem because of surface
tension issues meaning that bubbles won't come off the pipe surface as
easily, especially if there's more pipe area / volume. The trick is:

* Don't put bubbles in there. Use fluid that has sat in the bottle and
settled out, then pour it gently.

* Pressure bleed it gently, rather than pogoing on the pedal. The
Gunson pressure bleeder is cheap enough and works fairly well. Run it
from a spare tyre at no more than about 15psi. It also doesn't work on
Alfa Romeos or other cars where the fluid-loss warning switch fits
through a notch cut in the reservoir next (remove the switch, slip a
collar of bike inner tube over it).

I have four Gunsons, as it's the only way I could ever bleed my
fscking Rangie.

On Thu, 28 Aug 2008 08:29:59 -0700 (PDT), Andy Dingley
 wrote:

>On 27 Aug, 18:19, Ian  wrote:
>> I'm recommissioning my Herald at the moment. After a certain amount of
>> swithering, I decided to go for silicone fluid in the brake and
>> clutch. The clutch, which I did first, was fine.
>
>Bigger pipes on the clutch. Silicone is a problem because of surface
>tension issues meaning that bubbles won't come off the pipe surface as
>easily, especially if there's more pipe area / volume. The trick is:
>
>* Don't put bubbles in there. Use fluid that has sat in the bottle and
>settled out, then pour it gently.
>
>* Pressure bleed it gently, rather than pogoing on the pedal. The
>Gunson pressure bleeder is cheap enough and works fairly well. Run it
>from a spare tyre at no more than about 15psi. It also doesn't work on
>Alfa Romeos or other cars where the fluid-loss warning switch fits
>through a notch cut in the reservoir next (remove the switch, slip a
>collar of bike inner tube over it).
>
It also doesn't work on Toyotas which have a pop-on rubber reservoir cap
:-(
-- 
Regards,  Chris    (Please take out my car to reply by plain text email)     
------1967 Riley Elf------1978 Mini 1000------1971 Mini Clubman------
--1972 Mini Clubman estate--1979 Ford Capri--1984 VW Type 25 camper--

On Thu, 28 Aug 2008 13:08:45 GMT, "Mrcheerful" 
wrote:

>Ian wrote:
>> On 28 Aug, 03:45, Rob  wrote:
>>
>>> Personally I don't like silicon fluid not worth the expense. If you
>>> correctly flush your fluid every two years you should have no
>>> problems, except wear and tear on the system components, which is
>>> normal what ever the fluid you use.
>>
>> Like I said, it was a close call, and if all else fails I'll go back
>> to glycol.
>>
>>> Ok having had my rant, make sure that the rear brake shoes are
>>> adjusted fully up, this can induce soft brakes, these should also be
>>> adjusted up after the linings bed in.
>>
>> They're as well adjusted as any new shoes in new drums can be - I'll
>> certainly expect to re-adjust them after everything has bedded in.
>>
>>> After the system has been bleed let the car sit and check the pedal
>>> next day. You may check the play in the rod on the pedal and adjust
>>> that up as well.
>>
>> No adjustment at the pedal or in the cylinder. However, leaving the
>> car to sit for a few days after the first bleed did seem to improve
>> things a bit - mainly, I think, by allowing microbubbles to coalesce
>> into bigger, bleedable lumps of air.
>>
>> I've done some limited road testing and the brakes work OK, without
>> pulling - it's just that the pedal feels bouncier than I'd like. And,
>> I fear, than the MOT tester will like ...
>>
>> Ian
>
>If the problem is micro bubbles, then the answer we found (on motorcycles) 
>is to pressurise the system and leave it pressurised over night, the 
>reduction in pedal travel the next day is quite amazing.
>
>I use a brake pedal jack (home made from a mastic gun) to hold the pedal 
>down.  Also useful for checking brake equality and brake lights !!
>
The same thought occurred to me; Minis are buggers for it. Wedge the
pedal down overnight, the difference is amazing. Like another poster
here, I've made use of a Krooklock for the purpose.
-- 
Regards,  Chris    (Please take out my car to reply by plain text email)     
------1967 Riley Elf------1978 Mini 1000------1971 Mini Clubman------
--1972 Mini Clubman estate--1979 Ford Capri--1984 VW Type 25 camper--

On 28 Aug, 21:48, Chris Bolus  wrote:

> The same thought occurred to me; Minis are buggers for it. Wedge the
> pedal down overnight, the difference is amazing. Like another poster
> here, I've made use of a Krooklock for the purpose.

Krooklok went in at 10pm! Rebleeding sometime this evening.

Ian

In article ,
   Willy Eckerslyke  wrote:
> I was about to say that'll be the same as my Vitesse then - unless yours 
> is drums all round. I never had a problem with silicon and don't 
> remember any great difficulties bleeding the system. But perhaps I was 
> less sensitive to any sponginess than you are.
> I'd certainly recommend you persevere rather than switching back to 
> normal brake fluid.

I'm not convinced. Provided you change ordinary brake fluid regularly -
perhaps every couple of years - the parts should have a long life. And
changing the fluid and the subsequent bleeding forces you to examine the
condition of the hoses and pipes.

-- 
*When the going gets tough, use duct tape

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Dave Plowman (News) wrote:

>> I'd certainly recommend you persevere rather than switching back to 
>> normal brake fluid.
> 
> I'm not convinced. Provided you change ordinary brake fluid regularly -
> perhaps every couple of years - the parts should have a long life.

But realistically, how many of us want to change the fluid that often?
Now that he's bought the stuff, and the cost factor is gone, I can't see 
any reason not to stick with it. I'm certainly not convinced that the 
system will feel noticeably different once properly sorted, and am also 
dubious that the trouble he's been having so far is down to the type of 
fluid.

> And
> changing the fluid and the subsequent bleeding forces you to examine the
> condition of the hoses and pipes.

ISTR the OP said he'd fitted steel braided hoses, so inspecting _them_ 
won't tell him much anyway.

"Dave Plowman (News)"  wrote in message 
news:4fd65f45c1dave@davenoise.co.uk...
> In article ,
>   Willy Eckerslyke  wrote:
>> I was about to say that'll be the same as my Vitesse then - 
>> unless yours
>> is drums all round. I never had a problem with silicon and 
>> don't
>> remember any great difficulties bleeding the system. But 
>> perhaps I was
>> less sensitive to any sponginess than you are.
>> I'd certainly recommend you persevere rather than switching 
>> back to
>> normal brake fluid.
>
> I'm not convinced. Provided you change ordinary brake fluid 
> regularly -
> perhaps every couple of years - the parts should have a long 
> life. And
> changing the fluid and the subsequent bleeding forces you to 
> examine the
> condition of the hoses and pipes.

I'm with you. I really can't see the point of changing to a 
silicone based fluid. DOT 5.1 has many of the advantages of DOT 5 
IMO, without any of the potential problems.
AIUI DOT 5 is not compatible with glycol based brake fluid, so 
unless a glycol based system is completely purged of any traces 
of the old fluid, any remaining 'could' cause problems.
There could also be a problem with the seals themselves on an 
older system, as apart from the incompatibility of the fluid 
itself, early seals were not chemically resistant to silicone 
based fluid, meaning all the seals had to be changed for ones 
that were.
Having said that, AFAIK all later manufactured seals are 
compatible with both types of fluid, but if the seals have been 
replaced with NOS seals it could still be worth checking.
Mike.

Mike G wrote:

> I'm with you. I really can't see the point of changing to a silicone 
> based fluid. DOT 5.1 has many of the advantages of DOT 5 IMO, without 
> any of the potential problems.

We keep hearing about the potential problems, but always from people who 
have never apparently used the stuff.
I agree that it'd be a mistake to switch to it from conventional fluid, 
but on a rebuilt system where all the seals have been replaced, I really 
can't see why not. That's what I did with my Vitesse and it's been 
perfect. Cost-wise, what's an extra 15 quid when you're probably 
spending 100+ quid on parts anyway? And if it's really an issue, you'll 
save by not having to replace the fluid every few years anyway.
Spongy pedal feel? Not in my experience.

Advantages - knowing your brake system will come apart when you want it 
to without revealing a mess of rusted calliper pistons, etc; No damage 
to paintwork from spills so your carefully restored bulkhead can stay 
looking that way.

> AIUI DOT 5 is not compatible with glycol based brake fluid, so unless a 
> glycol based system is completely purged of any traces of the old fluid, 
> any remaining 'could' cause problems.

Officially, it shouldn't happen as the DOT ratings insist that all 
fluids can be mixed. But, I agree that it's best avoided.

> There could also be a problem with the seals themselves on an older 
> system, as apart from the incompatibility of the fluid itself, early 
> seals were not chemically resistant to silicone based fluid, meaning all 
> the seals had to be changed for ones that were.
> Having said that, AFAIK all later manufactured seals are compatible with 
> both types of fluid, but if the seals have been replaced with NOS seals 
> it could still be worth checking.

AIUI, seals are only prone to damage from silicon fluid if they've 
already been exposed to conventional brake fluid, so _unused_ old stock 
ones are OK.

The funny thing with all this, is that if we'd we always used silicon 
fluid, the huge disadvantages of glycol based fluid would see it used 
only by genuine racers and the Max Power brigade while the rest of us 
would avoid it like the plague. And newsgroups would be full of doom 
mongers telling everyone to stick to DOT5!

Willy Eckerslyke wrote:

> We keep hearing about the potential problems, but always from people who 
> have never apparently used the stuff.
> I agree that it'd be a mistake to switch to it from conventional fluid, 
> but on a rebuilt system where all the seals have been replaced, I really 
> can't see why not. That's what I did with my Vitesse and it's been 
> perfect. Cost-wise, what's an extra 15 quid when you're probably 
> spending 100+ quid on parts anyway? And if it's really an issue, you'll 
> save by not having to replace the fluid every few years anyway.
> Spongy pedal feel? Not in my experience.

Nor mine  "Slightly springy" is how I would describe it, but it is only 
noticeable if you regularly alternate between a car with silicone fluid 
and one with glycol fluid.  If you only drive the DOT5 one, you stop 
noticing anything after the first few days and it always feels perfectly 
normal after that.

And let us not forget that the OP has *already* renewed his entire 
braking hydraulics and filled it with silicone, so changing back is not 
a realistic option.  The merits of one over the other is only of 
academic interest to most.  Whatever the system is filled with, it will 
stay filled with unless and until there is cause to do wholesale 
replacements.

Jim

Willy Eckerslyke wrote:


> The funny thing with all this, is that if we'd we always used silicon 
> fluid, the huge disadvantages of glycol based fluid would see it used 
> only by genuine racers and the Max Power brigade while the rest of us 
> would avoid it like the plague. And newsgroups would be full of doom 
> mongers telling everyone to stick to DOT5!

If I assemble brake components I use a liquid silicon, and run a normal 
glycol brake fluid. - Calipers, master cylinders and rear cylinders.

So I have a mix to start.I have no problem with mixing the two.

Where does the problem start with the mixture and why does one have to 
ensure the integrity of the fluid, where does it start to fail and how?

r

"Willy Eckerslyke"  wrote in message 
news:6hqbvkFn877fU1@mid.individual.net...
> Mike G wrote:
>
>> I'm with you. I really can't see the point of changing to a silicone 
>> based fluid. DOT 5.1 has many of the advantages of DOT 5 IMO, without any 
>> of the potential problems.
>
> We keep hearing about the potential problems, but always from people who 
> have never apparently used the stuff.
> I agree that it'd be a mistake to switch to it from conventional fluid, 
> but on a rebuilt system where all the seals have been replaced, I really 
> can't see why not. That's what I did with my Vitesse and it's been 
> perfect. Cost-wise, what's an extra 15 quid when you're probably spending 
> 100+ quid on parts anyway? And if it's really an issue, you'll save by not 
> having to replace the fluid every few years anyway.
> Spongy pedal feel? Not in my experience.
>
> Advantages - knowing your brake system will come apart when you want it to 
> without revealing a mess of rusted calliper pistons, etc; No damage to 
> paintwork from spills so your carefully restored bulkhead can stay looking 
> that way.
>
>> AIUI DOT 5 is not compatible with glycol based brake fluid, so unless a 
>> glycol based system is completely purged of any traces of the old fluid, 
>> any remaining 'could' cause problems.
>
> Officially, it shouldn't happen as the DOT ratings insist that all fluids 
> can be mixed. But, I agree that it's best avoided.
>
>> There could also be a problem with the seals themselves on an older 
>> system, as apart from the incompatibility of the fluid itself, early 
>> seals were not chemically resistant to silicone based fluid, meaning all 
>> the seals had to be changed for ones that were.
>> Having said that, AFAIK all later manufactured seals are compatible with 
>> both types of fluid, but if the seals have been replaced with NOS seals 
>> it could still be worth checking.
>
> AIUI, seals are only prone to damage from silicon fluid if they've already 
> been exposed to conventional brake fluid, so _unused_ old stock ones are 
> OK.
>
> The funny thing with all this, is that if we'd we always used silicon 
> fluid, the huge disadvantages of glycol based fluid would see it used only 
> by genuine racers and the Max Power brigade while the rest of us would 
> avoid it like the plague. And newsgroups would be full of doom mongers 
> telling everyone to stick to DOT5!

There is one major disadvantage with Silicon fluid though. It's not 
hygroscopic.

This means that any moisture that gets in to the system, will gather, and 
eventually work it's way to the lowest point in the system, which is 
typically the brake calipers/cylinders. Where it'll then sit, until the 
brake caliper/cylinder reaches the boiling point of water, then boil in to 
steam, giving you some nice brake fade until things cool down again.
However, flushing the brake fluid out won't get rid of that water sitting in 
the bottom of the caliper/cylinder, as the bleed nipple is at the top.

Hygroscopicity is the main advantage of conventional brake fluids. It may 
sound like a major weakness, but the fact it absorbs water is an advantage. 
Rather than the above scenario, any moisture gets absorbed into the brake 
fluid, where it gradually lowers the boiling point of the entire system 
(unless of course the brake fluid becomes saturated), and by routine 
maintenance (ie changing the fluid every two years), the brake fluid boiling 
point should never drop below critical levels. Plus 90+% of any moisture 
should get flushed out with a fluid change.

On 29 Aug, 09:20, Ian  wrote:
> On 28 Aug, 21:48, Chris Bolus  wrote:
>
> > The same thought occurred to me; Minis are buggers for it. Wedge the
> > pedal down overnight, the difference is amazing. Like another poster
> > here, I've made use of a Krooklock for the purpose.
>
> Krooklok went in at 10pm! Rebleeding sometime this evening.

I gave it almost 48 hours, and there is a distinct improvement. It's
getting to the stage where "new shoes" explains most of the
springiness. I'll give it another go later in the week, but I think
it's just about MOT-able.

Here, by comparison, is how to bleed DS brakes. Attach tupe between
caliper bleed nipple and LHM reservoir. Open nipples. Start engine.
Apply brakes for ten seconds. Repeat for other caliper. Repeat for
rear brakes using a can to collect the LHM. In practice, it's only the
front ones which generally need doing. Total time ... ten minutes.

Sigh.

Ian

On 30 Aug, 17:06, "moray"  wrote:

> There is one major disadvantage with Silicon fluid though. It's not
> hygroscopic.

The same goes for LHM, and I'm not aware of any dreadful problems
caused by moisture in Citroen (and other) systems using it.

Ian

Ian  gurgled happily, sounding much like they
were saying:

>> There is one major disadvantage with Silicon fluid though. It's not
>> hygroscopic.

> The same goes for LHM, and I'm not aware of any dreadful problems caused
> by moisture in Citroen (and other) systems using it.

Indeed. It's a bloody big ADVANTAGE, not a disadvantage.

"Ian"  wrote in message 
news:8fc745a6-65bf-4241-89d9-5e681d29cc8e@c65g2000hsa.googlegroups.com...
> On 30 Aug, 17:06, "moray"  wrote:
>
>> There is one major disadvantage with Silicon fluid though. It's not
>> hygroscopic.
>
> The same goes for LHM, and I'm not aware of any dreadful problems
> caused by moisture in Citroen (and other) systems using it.

Modern hydraulic power brake systems will still work with air in the system, 
albeit with a delay in the time taken for them to apply/release while any 
air/vapour is compressed/expanded. This is due to the fact the pump pressure 
acts directly on the braking system, and doesn't rely on a fixed 
displacement once the pedal is pressed.

On Sun, 31 Aug 2008 11:30:53 +0100, "moray"
 wrote:

>
>"Ian"  wrote in message 
>news:8fc745a6-65bf-4241-89d9-5e681d29cc8e@c65g2000hsa.googlegroups.com...
>> On 30 Aug, 17:06, "moray"  wrote:
>>
>>> There is one major disadvantage with Silicon fluid though. It's not
>>> hygroscopic.
>>
>> The same goes for LHM, and I'm not aware of any dreadful problems
>> caused by moisture in Citroen (and other) systems using it.
>
>Modern hydraulic power brake systems will still work with air in the system, 
>albeit with a delay in the time taken for them to apply/release while any 
>air/vapour is compressed/expanded. This is due to the fact the pump pressure 
>acts directly on the braking system, and doesn't rely on a fixed 
>displacement once the pedal is pressed. 
>

Modern?

-- 

Ian D