Mineral Oil vs Dot 5

[The Drongo]

So let's face it, DOT fluid is a pain in the ass.

 

Sucks water in, destroys seals, wrecks paintwork, wrecks your health, bla bla bla... (it is good for experiments involving chlorine though )

 

What I am trying to ascertain is whether or not one can substitute DOT for Mineral Oil (LHM) in the DOT systems?

 

Or if anyone has in fact tried and failed/succeeded?

 

I ask, because why? I recall my Dad saying on numerous occasions that LHM could not be substituted for LHS (Synthetic) in the damn troublesome heap of Citroen we used to have the pleasure of owning.

 

He was a Master Citroen Mechanic at one stage, and always used to say that he could quite easily take up plumbing if all else failed.>>> I digress.

 

I recall him saying that the seals in the synthetic system would be destroyed by the Mineral oil.

 

I know that you CAN NOT use DOT fluid in a Mineral system, but what about the other way round? I have no prob with Mineral systems. Pentosin LHM works (green) and you can even use virgin olive oil at a push (although I would imagine it is a bit heavy).

 

All I know is that the DOT fluid in AVIDS and HAYES destroys seals that are supposedly designed for DOT fluid.

 

Can I or Can't I. Anyone??

Edited April 30, 2011 by The Drongo

[Johan Bornman]

Your observations are correct. I wish I knew the answer. DOT fluid-based brakes suck.

[Colin H]

Brake fluid has the purpose of transferring the hydraulic force from the lever (master cyl) to the caliper. Any liquid will do this as liquids are not compressible. The enviorenment that the fluid operates in adds some complexity.

Firstly is resistance to heat and in particular the boiling point of the pure liquid. Also the fluid has to look after the seals and keep them flexible etc.

Brake fluid is the best liquid to do this. Works in all sorts of cars and bikes. Works well.

 

DOT is a standard to regulate the performance of brake fluid. The numbers refer to the boiling point of the pure liquid and the liquid containing moisture.In general, the higher the number the higher the boiling temp. Most traditional brake fluid is polyethylene glycol based, and is hydroscopic. It absorbs water into solution wich then turns to steam at high temp and "boils" leading to loss of pressure transfer to the caliper and a soft level/pedal. The highest spec glycol fluid is DOT 5.

DOT 5.1 was established as a standard for synthetic brake fluid based on silicon. DOT 5 and 5.1 are not compatible with each other and with the seals and should not be interchanged in a car motorbike or bicycle.

 

The best thing to do is replace and top up the fluid with what the manufacturer designed the system for.

 

Mineral oil will work, but the performance will not be what the manufacturer designed, especially in feel and performance especially at the limits, or high heat loads. Sometimes there is not viable sort cut. Buy the correct brake fluid for the designed application.

Hope this helps.

[Johan Bornman]

Colin, I think you missed the point of the question. Drongo probably knows all this stuff anyway.

[Colin H]

Point made Johan. From racing car days you should not swap fluids between silicon and glycol even with proper flushing. Have a look at http://www.afcoracing.com/tech_pages/fluid.shtml.

With respect DOT is the only worthwhile measure of brake fluid standards.

Edited May 1, 2011 by Colin H

[Colin H]

Another link http://www.apracing.com/info/info.asp?section=Additional+Information_49

[dirtrider]

We been using DOT fluid for years , why is it a problem all of a sudden ? I think Colin's story explains it very well .

[Johan Bornman]

It isn't suddenly a problem, its always been an inferior option in our bikes. Drongo made the point that DOT fluid seems to eat the very seals that are designed to work with DOT fluid. It's true. After some use, Avids start to squeak and go mushy. If you change the fluid, you'll notice that the old fluid is the same colour as the rubbers they've just digested. The problem is so prevalent, that SRAM makes rebuild kits available. You get rebuild kits for lever and calipers. The fuid even erodes the bakelite pistons, which eventually become rough and refuse to move smoothly in and out. That rebuild kit comprises a piston and square ring.

 

The rebuild kit for the lever is an elaborate (but over the top) affair of new plastic pistons, springs etc etc etc. In reality, the only parts that are eroded are the seals. The lever pivots are also crap, so including them in a kit makes sense.

 

The point is, DOT systems are not as durable as oil systems. Shimano doesn't even offer rebuild kits for their levers and calipers. With the odd exception, they last a lifetime. They don't go squeaky and the caliper pistons don't become pitted. From a longevity point of view, they are clearly superior. In 99% of the times that Shimano systems fail, you can trace the cause back to someone putting DOT stuff in there instead of oil.

 

We can argue boiling point, performance etc, but the OP lamented the durability, convenience and ease-of-use of oil systems.

 

Had I an Avid system (or any other DOT system for that matter), I would experiment with replacing the O-rings int eh master cyclinder with buna O-rings and the square ring in the caliper, with either an O-ring or quad ring and run oil in it.

[dirtrider]

Aha so then I suggest the easy route would be to get Shimano brakes .

[The Drongo]

Great! Thanks

 

Where all you gentlemen been then? (I was out for a spin )

 

Yep, thanks Colin, got all that stuff about transfer, boiling points etc.

 

Maybe I rambled on a bit.

 

My Q was simply this. Will Mineral Oil erode the system designed for a DOT fluid setup?

 

The only reason I ask, is because of the recollection I have that Mineral Oil (Citroen's LHM)could not be used in the their hydraulic suspension system designed for LHS (Synthetic) which superseded their LHV (Vegetable Oils) as it apparently destroyed the seals. This was a vehicle setup though, not the light componentry made for bicycles.

 

Yes, any liquid can be used to charge a hydraulic system in an emergency, and yes, there will be a difference in feel based on viscosity and boiling point. But just because DOT 5 has a high boiling point does not mean it is superior. It likes to absorb moisture, and water boils quick sharp. So far more regular service is necessary.

Magura will rabbit on about their Red Blood oil bla bla. Any good Quality Mineral Oil works fine - Pentosin LHM is good. (Green in colour)

But that said, in a Mineral system, in an emergency (read 'all LBS's out of stock') you are better off replacing the oil with Virgin Olive, over Mineral Oil from the Chemist. Additives in the chemist type oils (fragrances etc) are what boil and cause poor performance.

 

Without doubt DOT fluid CAN NOT be used in Shimano, Magura, Tektro or Gator. I use Nitrile gloves to work on my brakes and forks. DOT fluid stuffs them up smartly. Shimano's seals and reservoir diaphragm's are Nitrile (or were when I last checked) so it stands to reason that DOT is a no no.

 

Being that mineral oil is not aggressive, I am trying to ascertain if the DOT seals will be harmed.

 

Still trawling the interwebs. I am really after a real life test, has anyone tried it and been successful? 's what I need.

 

'cause I am thinking of trying shortly.

[The Drongo]

Aha so then I suggest the easy route would be to get Shimano brakes .

 

 

...but Avid have some seriously smart, bling, shiny brakes....

[The Drongo]

Point made Johan. From racing car days you should not swap fluids between silicon and glycol even with proper flushing. Have a look at http://www.afcoracing.com/tech_pages/fluid.shtml.

With respect DOT is the only worthwhile measure of brake fluid standards.

 

I hear you Colin. When it comes to cars and motorcycles. But then the speeds generated, and the size of the components do not allow mineral oil use, by sheer measure of the physics.

 

We are talking bicycles here. Sure, some of the DH boys clipped 78kph at World's, but the weight of the bike, and the size of the components still allow use of mineral oils.

 

Before Avid Codes came along, Shimano Saint were the brakes to ride on your front wheel only >>> Mineral Oil (although Saints are still superior)

Formula are awesome brake systems, but they suffer the same fate as all other DOT systems. Even Hope (flagship brakes) provide replacement parts for calipers and lever reservoirs because of the damage caused by DOT fluid.

 

With respect, DOT is the only worthwhile AMERICAN measure of brake fluid standards.

[The Drongo]

It isn't suddenly a problem, its always been an inferior option in our bikes. Drongo made the point that DOT fluid seems to eat the very seals that are designed to work with DOT fluid. It's true. After some use, Avids start to squeak and go mushy. If you change the fluid, you'll notice that the old fluid is the same colour as the rubbers they've just digested. The problem is so prevalent, that SRAM makes rebuild kits available. You get rebuild kits for lever and calipers. The fuid even erodes the bakelite pistons, which eventually become rough and refuse to move smoothly in and out. That rebuild kit comprises a piston and square ring.

 

The rebuild kit for the lever is an elaborate (but over the top) affair of new plastic pistons, springs etc etc etc. In reality, the only parts that are eroded are the seals. The lever pivots are also crap, so including them in a kit makes sense.

 

The point is, DOT systems are not as durable as oil systems. Shimano doesn't even offer rebuild kits for their levers and calipers. With the odd exception, they last a lifetime. They don't go squeaky and the caliper pistons don't become pitted. From a longevity point of view, they are clearly superior. In 99% of the times that Shimano systems fail, you can trace the cause back to someone putting DOT stuff in there instead of oil.

 

We can argue boiling point, performance etc, but the OP lamented the durability, convenience and ease-of-use of oil systems.

 

Had I an Avid system (or any other DOT system for that matter), I would experiment with replacing the O-rings int eh master cyclinder with buna O-rings and the square ring in the caliper, with either an O-ring or quad ring and run oil in it.

 

Give me more on this buna O-rings. Is that a brand, or what?

[Johan Bornman]

Give me more on this buna O-rings. Is that a brand, or what?

 

O-rings come in many flavours, flavours we usually all brush off as "rubber".

 

They could be made from buna (black rubberish stuff), nitirle (you know what that is), viton (a high temperature black rubbery substance, silicone etc etc.

 

The O-rings used in forks and shocks are mostly buna and this is impervious to mineral and synthetic oils.

 

O-rings are areadily available and therefore I think that if your brake system uses O-rings, then you can experiment. However, some Avids (perhaps all), have an odd piston ring that can't readily be replaced by an o-ring. Anyone with a lathe and some ingenuity will definitely like to try.