Brake bleeding problems - silicone fluid

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Hugo
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#21 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Sat Mar 31, 2018 7:08 pm

cactusman wrote:
Sat Mar 31, 2018 5:05 pm
....Dot 5 will not absorb moisture. I can't see why it would attack seals as it is pretty inert, non flammable and won't eat paint....
1) Are these DoT numbers the same in the UK as in the US? I have a feeling they are not.
2) I don't think anybody suggested silicone fluid attacks seals. I do know from my own experience that it will leak past worn seals in situations where the old-fashioned stuff will not (although Angus seems to think this is 'utter rubbish' for some reason).
3) Does conventional brake fluid attack modern (2K) paint? I thought it did not?
4) I never knew the old stuff was infalmmable - got to go & set fire to some now!
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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#22 Re: Brake bleeding problems - silicone fluid

Post by cactusman » Sat Mar 31, 2018 7:26 pm

Dot numbers are the same here and the US so far as I know.
Old seals leak whether silicone or glycol imo.
Can't comment on two pack paint and glycol
Glycol based fluid is extremely flammable...spray on a hot exhaust manifold and it will spontaneously combust. Never spill brake fluid on hot exhaust parts...bizarrely fuel spilt on a hot exhaust will probably not inflame. Car fires post accident are often caused by severed brake lines spraying glycol based fluid onto hot exhausts or by electrical short circuits and rarely by fuel leaks....although once a fire has started if it gets to the fuel then whoosh.
Julian the E-type man
1962 FHC
1966 MGB....fab little car too

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#23 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Sat Mar 31, 2018 8:07 pm

Well, that's a new one on me. I do know that the temperature at which diesel will spontaneously combust is lower than that of petrol/gasoline. My neighbour in Florida was convinced that the spare can of gasoline I keep in my trunk was going to combust in the Florida heat, till I reminded him of my Harley, which carries its fuel in a tank exposed to the sunlight sitting on top of a very hot engine. I think the relevant temp is around 600 degrees F.
I had a crazy girl driving for me a few years ago - one night she lobbed a lit cigarette into the fuel tank of one of my buses. I only learned of it when I found the butt on top of the fuel filter when I changed it!
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Series1 Stu
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#24 Re: Brake bleeding problems - silicone fluid

Post by Series1 Stu » Sat Mar 31, 2018 8:56 pm

cactusman wrote:
Sat Mar 31, 2018 5:05 pm
A minor point but dot 5.1 is not silicone based. It is still glycol based and is equally good at stripping paint. I know...I use it in my mg. Silicone fluid is dot 5. No point one.
Yep. Well aware of this. I see no point in using silicone based brake fluid, especially since it's easy to avoid spilling it on an E Type's paintwork.

I was particularly advised against using it in the clutch system. Can't remember why.

I just remember that it has no lubricating properties and, unlike glycol based fluid, does not tend to swell the seals.

As for the original post. My money is on the master cylinder shuttle valve not flipping properly.

Regards
Stuart

If you can't make it work, make it complicated!

'62 FHC - Work In (slow) Progress
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#25 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Sat Mar 31, 2018 9:14 pm

Series1 Stu wrote:
Sat Mar 31, 2018 8:56 pm

I was particularly advised against using it in the clutch system. Can't remember why..........
I just remember that it has no lubricating properties
There might be a connection between these two, since the clutch seals have much further to travel than brake seals, so if lubrication is an issue, it will affect the clutch seals more than the brake.
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Jeremy66
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#26 Re: Brake bleeding problems - silicone fluid

Post by Jeremy66 » Mon Apr 02, 2018 3:32 pm

I’m trying to eliminate any other problem parts of the brake system so I made a by-pass pipe and connected the master cylinder directly to the rear brakes only (no servo) and bled them. The pedal consistently travels half way before resistance is felt, an additional half pump of the pedal immediately after this brings the resistance to the top of the pedal - where I would like it.

If I then leave the pedal alone for a few seconds and apply the brakes again sure enough it travels half way in its stroke before resistance is felt.

I’ve tried pumping them up and leaving the pedal under pressure over night with a block of wood incase their is air trapped anywhere but the result upon removing the block the next day is the same.

Does this sound right or does it sound like a problem with the rear cylinders which are new repro units rather than reconditioned originals like I’m used to.

Thanks

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#27 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Mon Apr 02, 2018 3:51 pm

If you had drum brakes this might be an adjustment issue. But discs rule that out. So there's air in there somewhere.
Try clamping off the rear flexi hose & see what that does. At least it will tell you where the air is. In fact you could bleed it in stages - just crack open each joint from front to back & bleed it.
Brake bleeding is really mind-over-matter. I always do mine single handed, without the use of any tools or gadgets, not even a bottle. Never have any problems. Mind you, I haven't yet done the brakes on my E Type, so I may yet have to eat my words, as it looks like a horribly complicated system.
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#28 Re: Brake bleeding problems - silicone fluid

Post by mgcjag » Mon Apr 02, 2018 4:05 pm

Hi Jeremy.....how are you actually bleeding the brakes....you need to open a valve, fully press the pedal, close the valve without releasing pedal.....then release pedal.....repeat......is this how you are doing it.... Steve
Steve
1969 S2 2+2 & Building a C type replica

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#29 Re: Brake bleeding problems - silicone fluid

Post by Jeremy66 » Mon Apr 02, 2018 4:13 pm

It’s intereating you mention adjustment as I’m the making along the same lines. I bought my rear cylinders second hand but new, the previous owner having upgraded, when they arrived he left a note saying not to forget to adjust them or they would drag. You can’t adjust them! When I stripped them down to clean out the fluid and check the seals three of the pin assemblies retained in the cylinder body cane out as well. I put this down to poor manufacture and an overly tight spring loaded bush in the piston, the idea being that as you apply the brakes, the piston presses the pad up against the disk and then when you release the pressure the piston is retracted back in to the cylinder slightly by the spring loaded bush assembly gripping on the pin fixed to the cylinder.

I polished the pins (which were rough) and pressed the pins back in to the cylinders, I then tested the cylinders to make sure they moved under pressure and then retracted slightly.

I’m wondering if the repro cylinders are of a poor design and retract too much, effectively moving the pads too far back from the disk akin to pad knock back when you have a loose wheel bearing. Hence the need for an additional half pump to get the pedal to get pressure at the top of its travel.

I’ll try to bleed it further as you suggest and then rig the master just up to the front brakes, if they give a good pedal it must be the rears, if they act in the same way as the rears it must be master cylinder related.

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#30 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Mon Apr 02, 2018 4:16 pm

I would just open the valve & keep pumping. You might have to hold the pedal down at the end while you close the valve. Also - here's thought - you do have an in-obstructed flow from the reservoir to the m/cyl I presume?
Here's an article I just found from an earlier post - worth reading right through - especially the part about what happens if and when silicone fluid gets ingested into the engine!
One query though, I seem to remember from my schoolboy physics that you can't compress a liquid. So how come silicone fluid is 'more compressible' than the old stuff?

Damn, I can't copy & paste to this page - the article was from 'Lyons' on 23 Oct 2011 titled 'Silicone brake fluid warning'. Apart from the compressibility issue, he says that, unlike glycol which just burns when it gets ingested by the engine, silicone fluid burns to make 'something indistinguishable from sand'. Not nice.
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#31 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Mon Apr 02, 2018 4:17 pm

You have springs in your rear calipers? Are these the old Dunlop type? Just clamp off the flexi hose - that will soon tell you whether that's where the problem lies. If you get a good pedal, you have a problem with the cylinders.
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#32 Re: Brake bleeding problems - silicone fluid

Post by PeterCrespin » Mon Apr 02, 2018 4:50 pm

Gfhug wrote:
Sat Mar 31, 2018 5:07 pm
If one wants to change to silicone fluid what is the suggested way of doing it and clearing out DOT4?

Geoff
Do what your favourite coach operator seemingly did: Drive a Public Service Vehicle with a 'dangerous'/probably illegal mixture of incompatible hydraulic fluids until everything cures itself and we all live happily ever after.
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#33 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Mon Apr 02, 2018 5:38 pm

An interesting observation, but quite without merit. I had a coach with a hydraulic throttle. Switched to silicone fluid & it started leaking. Switched back to the old stuff & it stopped leaking. Nothing remotely dangerous, let alone illegal, in that.
I think the two types of fluid are immiscible rather than incompatible, by the way. I don't think that actually matters too much.
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#34 Re: Brake bleeding problems - silicone fluid

Post by Tallpaul3200 » Mon Apr 16, 2018 2:33 pm

My experience with dot 5 silicone brake fluid is from karting from what I know dot 3&4 would swell the seals and.5 when added would leak so very possibly cars that have had dot 3&4 cannot go with dot 5 without replacing all seals that have come in contact with the 3&4

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#35 Re: Brake bleeding problems - silicone fluid

Post by cactusman » Mon Apr 16, 2018 4:11 pm

Hugo is probably right. DOT 5 will not mix with 3 or 4. To me the point of using silicone fluid is to avoid the hygroscopic nature of the glycol based fluid that absorbs moisture. This both lowers the boiling point of the fluid and causes corrosion of metal parts in the brake system. Silicone does not take up moisture so both issues go away. Adding silicone fluid to a system that retains some old fluid is defeating the object. Really if you are going the silicone route all the cylinders needs thorough cleaning and new seals fitted. All the pipe work should be drained and somehow rinsed through with silicone. Only then is it worth filling with silicone fluid....and silicone is known to give a more spongy feel than the glycol based stuff. Personally....stick with the DOT 4 stuff and rinse through annually as part of the service. The cost of a litre of fluid is not high.
Julian the E-type man
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1966 MGB....fab little car too

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#36 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Mon Apr 16, 2018 6:35 pm

The fact that silicone fluid is not hygroscopic is not necessarily an advantage - water will get into the system in the same way it does with the old stuff, but instead of mingling with the fluid it will pool at the lowest points, where it can do even more harm.
If you have one of those diaphragm things under the lid of the reservoir like modern cars do then you might be ok, but otherwise I wouldn't trust the stuff.
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#37 Re: Brake bleeding problems - silicone fluid

Post by mark10337 » Thu Apr 19, 2018 10:54 am

Chris Vine on his restoration pages, links to an interesting article by Chris Jackson that was published in the eType magazine.

http://etype.chrisvine.com/wp-content/u ... 0Fluid.pdf
-Mark

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#38 Re: Brake bleeding problems - silicone fluid

Post by Mich7920 » Thu Apr 19, 2018 12:55 pm

So I do it again,
20 years using Silicone into brakes and clutch and no problem !

Mich
Michel
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#39 Re: Brake bleeding problems - silicone fluid

Post by mgcjag » Thu Apr 19, 2018 1:18 pm

Hi Mark...Im glad you posted that artical....i had it but couldnt find it...it certainly expels all the myths about silicone fluid.....Steve
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#40 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Thu Apr 19, 2018 2:26 pm

This seems to be turning into an argument between two camps, each of which is becoming ever more eager to prove the other wrong. This is irrational.
Clearly some people have had problems with silicone fluid (myself being one of them). Others have not. Why should that be contentious? Supporters of silicone fluid almost appear to have an agenda to push the stuff, and will not accept that others have good reason, based on their own experience, for disliking it.
In the process of this twisted debate, I have had to endure various insults, derogatory comments and snide remarks for merely stating the facts of my experience with it (it leaked!), particularly from those whose opinions I would normally respect.
I find this irrational behavior, coming as it does from a group of supposedly intelligent people, very odd.
I am perfectly happy to accept that some people have used silicone fluid for years with no problems. For some people, however, this seems to be regarded as proof that those who HAVE had problems with it are somehow deluded.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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