Why are brake systems so old fashioned?

[JohnD]

This is another for the Common Room of Sideways University!

I wondered if the brake fluid we use is the same as the fluid used in the hydraulic systems on diggers and bulldozers etc.  They do the same job, but they are not the same!     When hydraulic brake systems came in on cars, about WW1, they could not use mineral oil as that would rot the seals in the cylinders, so they use glycol based fluid.   The more massive systems on diggers etc. came in about WW2  when seals that could resist a mineral oil based fluid became available.

So we use brake systems whose operating fluid is over a century out of date!  AND it destroys paintwork!

Is this just the inertia of the motor industry, or are there other reasons?

John

PS DoT 5 brake fluid is silicone based and doesn't rot paint, I know.

[PeteStupps]

An interesting question John. I do not know the answer but some lazy googling returned these plausible-sounding theories:

1. That hygroscopic is preferable to hydrophobic in braking systems, because brakes get very hot when you need them most, and any water in a mineral oil line would collect at the bottom, i.e. caliper, and boil. I've heard this in relation to silicone fluid but don't know how much is truth vs myth.

2. An almost inverse argument, that mineral oil thickens more significantly at low temperatures, which renders it less efficient or effective. So your Swedish Volvo drivers would have sluggish brakes in winter.

 

[yorkshire_spam]

Pete is on the mark - temperature! The hydraulic oil used in diggers etc doesn't need to tolerate anything like the temp range that a braking system does. 

 

Edit - also to add the pre-war Rover that I helped my dad restore had rod-operated brakes, with wiffle-trees. That was a pain to set-up and needed very regular adjustment. By comparison hydraulic breaks feel positively modern and wonderful. 

Edited September 12, 2024 by yorkshire_spam

[JohnD]

A very good point, YS!  Especially if there is water in the fluid, which will, of course, boil at about 100C causing vapour bubbles and brake failure.   You prompt me to find out about brake fluid and oil boiling points, and a Google finds that  DoT 5/5.1 boils at 260C.   As a comparison, engine oil boils at about 300C, so in fact mineral oil sounds better, and of course it is hygrophobic, unlike a glycol based fluid.

Then, several manufacturers that sell hydraulic brake systems for bicycles  promote mineral oil fluids!   I found a table of their boiling points:

So that, given the right mineral oil fluids, they should be as suitable for car brakes as bikes! 

So I must repeat my question, why is car brake fluid still made from glycol?  Nearly a hundred years after a better fluid was developed?  Is Dot5 the answer?

John

PS It's not cost.  Shimano mineral brake fluid can cost the same as DoT5.

Edited September 12, 2024 by JohnD

[yorkshire_spam]

45 minutes ago, JohnD said:

So I must repeat my question, why is car brake fluid still made from glycol?  Nearly a hundred years after a better fluid was developed?  Is Dot5 the answer?

I think it's mostly "inertia" from a society/industry point of view, but also a simplicity thing. To most people in the car world, brake fluid is brake fluid. A previous owner used 5.1 in my Dolomite when they recommissioned it, I'd like to switch to .4. Why? Because it's what all my other cars have, I won't get confused and end up mixing them, it's cheaper, easier to get. If the Dolomite went to a garage for brake work I'd be paranoid that they'd refill with the wrong type (even though there's a tag on the master cylinder cap to remind them!) 

[Escadrille Ecosse]

Those bicycle hydraulic oils are all synthetic. And bicycle brake systems are sealed and have a tiny capacity.

They also don't have ABS.

Ask why Rolls Royce stopped using mineral oil.

I suspect the main reason is moisure tolerance and long service intervals. And the fact that a satisfactory glycol based fluid is cheaper than a satisfactory synthetic oil based fluid.

Plus the ABS 'thing'.

[Nick Jones]

Citroen have used mineral oil in brakes for years in their fully hydraulic cars. Also some of the high end German cars from late 80s/90s with hydraulic assisted brakes not vacuum servo.

I suspect a lot of it is historical and not mending what’s not broken, but the main argument seems to be that while the absorbed water in the hygroscopic DoT 3/4/5.1 does lower boiling point and increase cotton to an extent, its not nearly as bad as the free water that would collect In hydrophobic mineral oil or DoT 5 systems. 

[JohnD]

Thanks, all!    I've asked Shimano if they have any views on using their product in a car.

[Nick Jones]

The issue with converting a car to mineral oil would be the system seals. The DoT fluids require EPDM rubber to survive. EPDM hates mineral oil and will swell and go soft within hours. Mineral oils require NBR (nitrile) material but I doubt seals for most car braking systems would be available in it. Nitrile wouldn’t last long with DoT fluids.

Fully synthetic oils might be different but I wouldn’t chance it.

[zetecspit]

4 hours ago, JohnD said:

Thanks, all!    I've asked Shimano if they have any views on using their product in a car.

Let's be honest. They won't be saying yes, give it a try. At best they will refer you to your car manufacturer, but if I was them I wouldn't respond at all. Or say "can't help"

I am not sure what you are trying to achieve either? Nothing wrong with dot4 fluid, or if you really need high temp, dot5.1

I did find this though

https://epicbleedsolutions.com/blogs/faq/whats-the-difference-between-dot-4-and-dot-5-1-brake-fluid?srsltid=AfmBOoo5s0a6M1k2gttlOLFXmSyB_SbnV0W9ROylyepkSIXBRQIKw7me

[Escadrille Ecosse]

5 minutes ago, zetecspit said:

Let's be honest. They won't be saying yes, give it a try. At best they will refer you to your car manufacturer, but if I was them I wouldn't respond at all. Or say "can't help"

I am not sure what you are trying to achieve either?

My thoughts too

[JohnD]

Im always interested in questions, and asking them!    I'm not about to fill my brakes with mineral oil, but it might arise one day.

John

[PeteStupps]

9 hours ago, JohnD said:

I'm not about to fill my brakes with mineral oil, but it might arise one day

Fair enough. Could also try putting dot4 in your gearbox

 

[Escadrille Ecosse]

1 hour ago, PeteStupps said:

Fair enough. Could also try putting dot4 in your gearbox

 

GL4 is just so yesterday...

[mossmonaco]

from 'Pooh and the art of motor car maintenance'.....

 

I fill my brakes with honey,

I got it from my wife.

The pedal feels quite funny,

I'll have a quite short life.

 

[mossmonaco]

As I understand it, If you use a mix of mineral and glycol based brake fluids your down-hill performance may be substantialy increased. 

 

[zetecspit]

20 minutes ago, Escadrille Ecosse said:

GL4 is just so yesterday...

I have filled my sprint gearbox with an MTL oil. It is a 75-80 GL4. We shall see how it performs when the car is on the road. 

With that I am working on the notion that oils have developed and improved over the decades. Also that GL4 is required for the brass synchros to work correctly. This all came about after I rebuilt our Honda Jazz gearbox. EP80 would be fine, so I thought.Nope, horrible gearchange, so bought the correct oil which is also a 75-80 GL4 spec. All issues disappeared.

[Escadrille Ecosse]

9 minutes ago, zetecspit said:

I have filled my sprint gearbox with an MTL oil. It is a 75-80 GL4. We shall see how it performs when the car is on the road. 

Yes. Been using that in the Scimitar gearbox after the rebuild. The Rover 5 speed which has history in that respect. After the 'recommended' ATF, straight 90 hypoy, and 75/90 multigrade and the semi synthetic. The MTL GL4 seems the best so far.

But even though all of them (with the exception of the ATF) are GL4, still not going to try honey yet.

[JohnD]

36 minutes ago, mossmonaco said:

from 'Pooh and the art of motor car maintenance'.....

 

I fill my brakes with honey,

I got it from my wife.

The pedal feels quite funny,

I'll have a quite short life.

 

LLOL!

[RogerH]

Brakes have not changed a great deal in the last 100 years. 

Why should they.

Most early cars did not have front brakes

And then when they did the rear brakes remained with rods not oil

The early fluids work perfectly well for what was expected.

But then performance/expectations changed

So better (similar) fluid was produced.

As technology rolled on more problems were created.  ABS cannot tolerate air in the system   So DOT 5.1 arrived and it works very well (even as a paint stripper)

Cost is a serious factor when you are making millions and millions Rodney.   You quote Mineral versus DOT 5  - BUT Dot 5 is far more expensive than Dot4.

As for temperature  all post WW2 aircraft used mineral oil (usually DTD585) and it gets pretty cold at 30,00ft - and it works very well.

That was supersededadded to by ester based oils in aerospace partly for its fire safety (Skydrol was one of the first)  These are very very excellent paint strippers

If you compare what is available they all have a place and they all do it well - but do not put them in the wrong place.

The only fluid that is used in the wrong place today is DOT 5  silicone.  But if the ignorant (unknowing)  want to use then carry on.

 

Roger 

 

 

 

 

 

 

[PaulAA]

31 minutes ago, RogerH said:

These are very very excellent paint strippers

So, instead of mineral oil, maybe Nitromors? It's definitely hygroscopic...

35 minutes ago, RogerH said:

The only fluid that is used in the wrong place today is DOT 5  silicone.

It is indeed.

[zetecspit]

Anybody remember the "crimson" brake fluid used in the 60s/70s?

If somebody mixed that and "normal" brake fluid you get a hard jelly. I once bought a herald where this had happened, goodness knows how as it was in the mid 90s.

Solution was to junk the entire hydraulic system. (easy then as I broke up several heralds in that period  so spares were plentiful)

Maybe the manufacturers learnt a valuable lesson.

Edited September 13, 2024 by zetecspit

[Escadrille Ecosse]

[mossmonaco]

In the late 70's my first car was an obscenely high-milage  herald. I paid 18 quid for it (about what it was worth), welded/brazed the chassis, wrapped the lower part of the doors in ally sheet to avoid the jagged rusty flappy bits, and MOT'd it I was assured that the lurid purple brake and clutch fluid in it was courtesy of a BAC Lightning jet. (some years later it was confirmed that while it quite possibly was fluid from a lightning, it wasn't brake fluid from a lightning. The previous owner was an airman at RAF Binbrook). I had brake failure twice, each time as a result of a hard line bursting where it passed inside one of the chassis members. After the second time I replaced all the brake lines, but a positive outcome was that I learned how to best cope with brake failure.

In about 1980 I was with a girlfriend who was driving a knackered mini van down a long hill when she shouted 'The brakes arent working';I heaved on the handbrake and I got her to pump the brakes, change into second, turn the ignition off (it didnt have a servo or steering lock),  weave, and kerb the tyres. We were still rolling fairly quickly when we got to a garage island at the bottom of the hill, so we rolled into the forecourt and did a couple of circuits of the garage. 8 of us got out (6 in the back), and after a brief negotiation she sold the mini to the garage for 50 quid and we all hitched back to uni.

 

[PeteStupps]

13 minutes ago, mossmonaco said:

In about 1980 I was with a girlfriend who was driving a knackered mini van down a long hill when she shouted 'The brakes arent working';I heaved on the handbrake and I got her to pump the brakes, change into second, turn the ignition off (it didnt have a servo or steering lock),  weave, and kerb the tyres. We were still rolling fairly quickly when we got to a garage island at the bottom of the hill, so we rolled into the forecourt and did a couple of circuits of the garage. 8 of us got out (6 in the back), and after a brief negotiation she sold the mini to the garage for 50 quid and we all hitched back to uni.

Blimey!