brake fluid confusion

[Elanconvert]

david .....I sympathise...

as a fellow confused classic owner, I have a foot in both camps, and equally undecided........
rebuilding a ginetta g4, I have gone with silicone [all new seals, pipes, etc.] for brakes and clutch....will I regret it? possibly...

the elan''s brakes are fine at present, but fluid will be due for replacement next spring........do I replace with dot4.....probably........

fred

[TroonSprint]

so much for hoping someone would suggest a product and then 20 replies saying "agreed"!

That's the mark of a true optimist!

Mike

[pharriso]

is draining down MC and then pushing a fair amount of new fluid through each bleed nipple and acceptable way of flushing through?!

Yes, As I said starting with the caliper furthest away from the master cylinder....

[rgh0]

From wikipedia article

https://en.wikipedia.org/wiki/Brake_fluid

Dry boiling point Wet boiling point Viscosity limit Primary constituent
DOT 2 190 ?C (374 ?F) 140 ?C (284 ?F) ? Castor oil/alcohol
DOT 3 205 ?C (401 ?F) 140 ?C (284 ?F) 1500 mm2/s Glycol Ether
DOT 4 230 ?C (446 ?F) 155 ?C (311 ?F) 1800 mm2/s Glycol Ether/Borate Ester
LHM+ 249 ?C (480 ?F) 249 ?C (480 ?F) 1200 mm2/s [6] Mineral Oil
DOT 5 260 ?C (500 ?F) 180 ?C (356 ?F) 900 mm2/s Silicone
DOT 5.1 260 ?C (500 ?F) 180 ?C (356 ?F) 900 mm2/s Glycol Ether/Borate Ester
Wet boiling point defined as 3.7% water by volume.

The different viscosity and major components can affect how brake systems work. The LHM+ is the citroen style fluid.

Current standard components for an Elan appear to work Ok with DOT 3 / 4 / 5.1
Use of DOT 5 has been known to give problems in some cars and be Ok in others
I used it for a few years in my PLus 2 but i did not like the soft pedal and the brake booster tended to have a slow action and then come in suddenly so i changed back to DOT 4 which rectified these problems

I run DOT 5.1 in my Elan with no problems but its cost is much higher and only really warranted or needed on a track car.

Most cars that specify DOT 3 can also use DOT 4 or 5.1 but not all. My Toyota Landcruiser specifies DOT 3 and I used DOT 4 once for a routine change as that was what I had in the garage for the Lotus and I thought it should be OK. I found that the brake pedal started sticking and the antilock brake system warning light was coming on. I changed back to DOT 3 as specified and all the issues went away. Maybe a viscosity issue or a seal compatibility issues with the different composition of DOT 3 to 4.

While silicone DOT 5 fluid is not hydroscopic like the other fluids, water still gets into the wheel brake calipers overtime as it gets passed the seals as the pistons move with ever brake application in miscrosopic amounts and it sits as free water in the caliper cylinders and causes corrosion. Only really a problem if you drive your Elan in the rain but it can happen.

cheers
Rohan

[elj221c]

While silicone DOT 5 fluid is not hydroscopic like the other fluids, water still gets into the wheel brake calipers overtime as it gets passed the seals as the pistons move with ever brake application in miscrosopic amounts and it sits as free water in the caliper cylinders and causes corrosion. Only really a problem if you drive your Elan in the rain but it can happen.

https://en.wikipedia.org/wiki/Hygroscopy

[nomad]

Just to add to this now age old argument......
I flushed the lines with alcohol on my 72 MGB, rebuilt all cylinders, and used the then new Silicone fluid back in the mid 1970's. The car was only a few years old and all the brakes were corroded and definitely in need of a rebuild.
A friend now owns that car and I don't believe he has ever even bled the system. No brake issues what so ever. Car has way over 100K on that brake rebuild.

Compressible fluid.....come on! how much can it compress?

It is somewhat higher viscosity, however, and cars I now have it in seem to have a different brake feel so I may be leaning toward the flush every couple of years camp.

Kurt
26/3754

[mbell]

One interesting thing I've seen commented against the SIlicon fluid is when burnt it generates a sand type material. So a faulty brake booster leaking fluid into the intake could cause some significant engine damage unlike standard DOT3/4/5.1 fluids.

[patrics]

So Why aren't silicone fluids used in industry?
Silicone fluids are not used because they simply don't meet basic performance requirements.
The often quoted 260 degC boiling point is completely irrelevant because the fluid becomes highly compressible above 100 degC - and this is the main Achilles heal of the product.
There are other issues like:
It is a poor metal to metal lubricant especially with aluminium alloys
Viscosity and foaming issues make it unsuitable for use with ABS systems.
The viscosity also gives bleed issues.
Some will say that it doesn't absorb water is an issue because when water gets in to the system it stays as water and thus the system then has a boiling point of 100 degC and a freezing point of zero. This may be true but Rolls Royce used a mineral based system for decades without issue.
They adversely effect the paintability of metal surfaces and are difficult to remove.
The problem with SBR rubber seals was always demonstrated by placing a piston seal in a beaker, filling half with silicone and half with traditional fluid, leave it overnight and then lift the seal out. At the point where the two fluids met the seal would pull apart like chewing gum

Positives!
They offer good corrosion protection as they are non conductive electrically
Being non hygroscopic they are good for long term storage

If you have silicone fluid and don't experience problems then that great keep using it.

General
The main entry for water in to a brake system is via the flexible hoses
For obvious reasons I wouldn't use a bleed system that applies compressed air over a hygroscopic fluid.
As far as choice is concerned I don't think DOT 3 is available in Europe any more.
Super DOT4 and DOT 5.1 are the same thing
The latest iso rating for brake fluids like DOT 5.1 is now called Class 6


Regards
Steve

[rgh0]

While silicone DOT 5 fluid is not hydroscopic like the other fluids, water still gets into the wheel brake calipers overtime as it gets passed the seals as the pistons move with ever brake application in miscrosopic amounts and it sits as free water in the caliper cylinders and causes corrosion. Only really a problem if you drive your Elan in the rain but it can happen.

https://en.wikipedia.org/wiki/Hygroscopy

from the artcile

The similar-sounding but unrelated word hydroscopic is sometimes used in error for hygroscopic. A hydroscope is an optical device used for making observations deep under water.

Good thing I is an engineer and not an english teacher

cheer
Rohan

[Gordon Sauer]

That's great, Rohan, I'm always amazed by what you add to these things. I'll have to go back and change my placard on my SM which uses LHM which is non-hygroscopic and in 25 years of showing the car nobody has ever pointed out my mistake thanks Gordon Sauer

[Elanconvert]

Good thing I is an engineer and not an english teacher

cheer
Rohan

rohan
I know which bucket of your knowledge I would like to have!!!

fred

[Craven]

Hi,
A high percentage of fire following an accident is caused by highly flammable brake fluid leaking on to hot surfaces.
The non-flammable nature of silicone brake fluid is a huge plus when considering its use in our somewhat fragile and FIBREGLASS cars.
Ron.

[gus]

>>>>Do not use Silicon brake fluid... it will soften the seals.<<<

total baloney

I have run silicone fluid in my car for over 30 years and do not have a soft pedal and have not had seal failures, ever

you must change fluid occasionally as since it does not absorb water water can separate out and cause rust spots where it sets. I would think running a pint thru every 5 years would do it.

I see this come up on this list every once in a while, silicone is far more reliable than older types and I won't go back.

[Chancer]

Whilst I have had exactly the same exp?riences as you Gus I am always open to hear of contrary exp?riences however most often its just very opinionated stuff like you quoted without a real explanation, the world is flat because I say its so and you are a heretic etc.

So I was very pleased to read the very informative and unopinionated posting by Patrics, I can identify with all of it, I have suffered the spongy pedal in the paddock yet I know the temps were well below the rating of the fluid, I have had no corrosion problems for 2 d?cades but the system was filled from new with silicone fluid and new brake lines, I am pretty sure that the calipers retained their original seals though which had been exposed to normal brake fluid.

I want to change the brake fluid on my road car, she will soon be 14 years old and more than 300000 miles, I would have used silicone fluid but given the ABS and just maybe a risk to the seals I will use normal stuff.

[Lyn7]

Hi guy's, been watching this thread for a while, it seems to be a divided camp as usual. My contribution is, I have been using Silicon brake fluid for more than 30 years and cannot attribute any fault to it. The first car I used it in was the Elan and I would have been one of the first users at it was not available retail (in the UK) at the time. I have been using it ever since. I have used it in other car of other makes, no problem. I appreciate all the theory but in practice it is fine in my experience. You pay your money and make your choice!
Cheers Lyn....