brake fluid confusion

[davidc]

I've read pretty much every topic about brake fluid on this forum but and still not clear on what type to go for

plus 2 130/5 1973. can't be sure if seals have been replaced or what fluid is currently in.

i intend to blow each line through to remove all remnants of current fluid. is this OK to do? plan on just pushing the fluid out with an empty eazibleed 1 by 1 then refilling.

not sure what to put back in. no intention of racing but i'm sure there will occasionally be a bit of spirited driving

I've read about DOT 4 rotting rubber, silicon absorbing moisture in the air mineral based fluid etc...

can anyone give a suitable choice?

[661]

A good quality DOT 4 is all you need. Personally I use Motul 600 in all my cars as it works well on track cars too and I never have to worry about what I've got in each car and mixing of fluids.
I tried Silicone, hated it and would not ( personally) recommend.

[TroonSprint]

Silicon fluid doesn't absorb water - that's it's principal advantage. DOT 3 or 4 mineral fluids are the conventional brake fluids and will absorb water over a period of time, lowering the boiling point and causing corrosion in the master cylinder and brake calipers. That's why it is recommended to change mineral fluid every two years.

The boiling points of both types are similar and these boiling points drop markedly as the fluid becomes contaminated with water. Mineral brake fluid will strip paint if it is spilled. Silcon won't.

All new car makers use a mineral fluid, and for competition cars it is the brake fluid of choice because of it's high resistance to compression. I've not heard of mineral fluids rotting "rubber" seals but I have dismantled cylinders and calipers that are very rusty inside due to brake fluid not being exchanged regularly. If your car has ABS then you must use the recommended fluid. I believe silicon is not suitable for such applications.

You can read all sorts of dire warnings about using silicon fluid with tales of it's relative compressibility and the fact that if water does get in the system it can't mix with the fluid so settles in pockets. However, many classic car owners have used it for years without issue. I have silicon fluid in both my MGB V8 and my Elan Sprint and the brakes are absolutely fine for road driving. In fact I don't notice any difference from the feel or efficiency of the brakes between mineral and silicon fluids. My MGB has driven 26,000 miles over the last six years with no change of the brake fluid and no deterioration in braking performance.

At the end of the day it's your choice.

Mike

[pharriso]

The stuff I am using is marked DOT 3/4. Do not use Silicon brake fluid... it will soften the seals.

Re flushing through, just start at the corner furthest away from the master cylinder & flush through until you see clean fluid, then next closest until all have been flushed.

[PeterK]

Don't recommend blowing lines through and then refilling with new fluid, as you risk issues with trapped air.
Just empty the master cylinder (use a turkey baster or similar) and then fill with new fluid. Then bleed each wheel in turn (starting furthest away from master cylinder) until clean fluid flows out, hopefully with no bubbles.
Vacuum easibleeds can drag air in around the bleed nipple threads. After you have clean fluid flowing out, close the bleed screw and then just crack it open, or use PTFE (plumbers tape) around the threads.
Peter

[Robbie693]

When I bought brake fluid last week the two types that were on the shelf (Halfrauds) were DOT 4 but marked 'synthetic'. This caused some consternation but the only mineral fluid available was the stuff for Citroen suspensions.

Is all DOT 4 now synthetic?

Robbie

[patrics]

Hi David,
Just use a DOT4 fluid but do not blow out the pipes with an air line as you risk contamination from the compressor lubrication oil - compressed air has to be filtered to use on a brake system
You can not use - so do not use a mineral fluid - you won't be a live for long
buy a brand name or go to a car dealership - brake fluid is not cheap but a DOT 4 / DOT5.1 or class 6 is what you want.
Don't buy a DOT 5 as that is not compatible with the rubbers used in classic cars and not approved by any brake supplier or car manufacture globally.

Regards
Steve

[TroonSprint]

Don't buy a DOT 5 as that is not compatible with the rubbers used in classic cars

Well, I don't know the absolute truth of the matter and I suspect neither does anyone else. DOT 3 and 4 fluids (apologies for calling them "mineral") will work fine, but you will need to change the fluid every couple of years and you still might get corrosion of the internal components after a few years.

I know silicone has worked for me, and a pal sold his classic MG with the same silicone fluid in the brakes as he had installed 17 years previously. The brakes had needed no work in all that time other than pad replacements. In my experience components with DOT 3 or 4 in them would have corroded in that time. In the USA many classic enthusiasts seem to use DOT 5. Here's a typical quote:
"I had regular dot 3 in my 48 and about every 4 years the wheel cylenders would oxidize up and the rubbers would get all crusty.So about 8 yrs ago replaced everything and flushed all the line with alcohol and filled it with dot 5 silicone, haven't had a lick of trouble since and I have one of the best pedals I've ever had........just saying."

Mike

[nmauduit]

I run my old cars and bikes from the early 50s to the late 70s on silicone now, it does not absorb water so reduces a lot the brake failures due to corrosion over time, and since some of them do not run very regularly I find it more reliable - you even don't have to purge so often... The silicone Dot5 I use boils at 260?C, which is a bit less than some racing fluids but more than enough for me, even for spirited track days with gripping pads (my driving performances are not limited by that I'm afraid) - it even can me mixed with regular brake fluid I was told (though not at water repellent then), but on the vehicles I have converted to silicon I had new or rather new rubber kits and have rinsed with isopropyl alcohol before putting in the silicone.

works for me...

[patrics]

Mike, no offence but you don't know the absolute truth but are prepared to recommend something that every brake and vehicle manufacture says you can not use. Traditional large companies are experts in materials and chemicals it said for good reason.
If you are successfully using the fluid that's great but another person might not be so lucky - it only takes a system previously used with traditional fluid then silicon fluid and SBR rubber to have brake failure.
SBR rubber is a good and normal material to use in braking systems - I have it in my car and next time I rebuild the brakes no doubt I will use it again.

Please don't take this as a personal attack.

Regards
Steve

[Chancer]

Yes I have been bemused to read all the horror warnings of silicone brake fluid, I have used it exclusively for the last 20 years on road and race cars, Westfields, Caterham 7's, my Elan, I have never had a failure of any component nor have I ever needed to change the fluid.

The front calipers on all the vehicles were 60s/70's, the master cylinders also, the rear calipers on the Caterhams a little later being Sierra units, the Westfield had Cortina 1600E rear drums the cylinders of which on non silicone fluid would normally have lasted say 2-5 years.

The only problem I ever had was heat soak in the paddock on the Sierra rear calipers mainly due to their mounting position, if the handbrake wasnt applied the problem was minimised, a higher boiling point fluid would have helped,

As for water seperation? Well yes, but unless you leave the master cylinder cap off in a rainstorm or there is a sealing and drainage problem like on the MK1 Galaxies then water just aint going to get in as it is not hygroscopic which for me was the most appealing feature.

Has anyone oh here gt first hand knowledge of brake problems on a classic using silicone fluid?

I have not quoted DOT numbers as the 5's and 5.1's confuse me.

Editted, just read the prvious posting which I overlapped, what is SBR rubber? is the problem supposed to be using silicone on components previously exposed to normal brake fluid?

[Gordon Sauer]

Back to your question about not knowing what you have, get some painted thing you don't care about, like a little model car and put some of your brake fluid on and see if it takes off the paint. I do believe you can't mix the two of them and unless you go clean from the start you do better not go with silicone--I've always stuck with the recommended Castrol LMA ( and there has been some question before about it being synthetic but that was answered in some forum about Castrol always having always been synthetic) Gordon Sauer

[UAB807F]

Editted, just read the prvious posting which I overlapped, what is SBR rubber? is the problem supposed to be using silicone on components previously exposed to normal brake fluid?

SBR is a synthetic rubber, styrene-butadiene rubber, hence SBR. It's a common replacement for natural rubber and arguably has better characteristics. As for whether it's the rubber used for caliper & brake cylinder seals I don't know, but it is used as a general purpose rubber for lots of automotive applications.

I'm guessing here but the concern may be about absorption into the rubber although I have read comments that silicone isn't as good in lubricating modern ABS systems so that could equally be a problem for modern cars.

But most rubbers swell in fluid (even water) by absorption and that usually results in lower strength, a bit more flexible and notably swelling. If you take out some old seals that have been in service for 2-3 years in normal brake fluid and place them alongside new ones, generally speaking you'll see a slight increase in diameter by a few percent. Not much, and you might need to measure but it will be there.

Now this might come as a surprise to some, but here's what the Lotus workshop manual says about brakes....

"The brake manufacturers recommend that at intervals NOT EXCEEDING 40,000 miles (65,000 km.) or 3 years, whichever is reached first, that the braking system be completely overhauled and all washers, seals and hoses renewed"

hmmmm. how may users of silicone fluid do that now ?

Brian

(nope, I don't either, but using normal fluids I do tend to rebuild every few years and changing the caliper seals makes a notable difference)

[TroonSprint]

Mike, no offence but you don't know the absolute truth but are prepared to recommend something that every brake and vehicle manufacture says you can not use. Traditional large companies are experts in materials and chemicals it said for good reason.
If you are successfully using the fluid that's great but another person might not be so lucky - it only takes a system previously used with traditional fluid then silicon fluid and SBR rubber to have brake failure.
SBR rubber is a good and normal material to use in braking systems - I have it in my car and next time I rebuild the brakes no doubt I will use it again.

Please don't take this as a personal attack.

Regards
Steve

Steve, absolutely no offence taken. I wouldn't recommend any particular thing to anyone. Lord knows, I'm no expert in these things. All I'm trying to say is that in my quite extensive experience silicone fluid has been absolutely fine and has reduced brake maintenance to almost zero on several classics I have owned. Lots of folk seem to regard silicone fluid as dangerous, but I have yet to see a report of any brake failures brought on by it's use. What you can find is plenty of people who use it and are happy with it. My MGBGT has a 3.9 litre fuel injected V8 and is a fast car which has been driven extensively here and on the continent, and not once have the brakes given any cause for concern.

I don't know why silicone has never been recommended by any vehicle maker (except perhaps Harley Davidson - I did read somewhere that they used it!). If anyone has the slightest doubt about it they should definitely stick with conventional fluid. As an aside, silicone fluid makes your dull grey plastic parts look like new again. It did wonders for the scabby-looking rocker switches on my Sprint!

All the best,
Mike

[davidc]

ahhhh this is so confusing!!

I think i'll just cut a hole in the floor and do like the flintstones did!

from what i am reading I think your all saying if i can't be sure what fluid i have in now (thanks for tip Gordon) I should totally empty out and start again. is draining down MC and then pushing a fair amount of new fluid through each bleed nipple and acceptable way of flushing through?

i don't want to rot any rubber seals so I either stick with DOT4 or strip all bits with seals and renew.

as for comment on vacuum easi bleed mine is the one where compressed air (via spare tyre or similar) pushes air through from MC so guess this is different?

I've got no issues with having to renew brake fluid every couple of years so am currently thinking of going with DOT4 and then planning a future job of a full brake system overhaul.

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