Since Castrol GTLMA seems to be no longer available...

[DaveW]

Eric,

I just thought a little tongue-in-cheek somewhat sarcastic humor might be appropriate. I don't really mind having my opinion questioned - I'm certainly not always right.

[E1pix]

Oh, No… except you are, *again!*

[DanW]

Eric,

I just thought a little tongue-in-cheek somewhat sarcastic humor might be appropriate. I don't really mind having my opinion questioned - I'm certainly not always right.

As many of us are married, the above statement is true.

[E1pix]

Too silly, self-deleted.

[DaveW]

In spite of Brian's posts occasionally being excessively abrasive, he sometimes does have some good insights. So I would not want him to quit posting.

[E1pix]

Fair enough, Dave.

[Hardingfv32]

I guess all of us racing folks are misguided, our experience means nothing,

On the topic of brake fluid 'lubricity', why should your opinion be valued. You have figuratively 'no milage' on your race car brake system compared to what to what has been seen by OEM manufactures.

If OEM manufactures do not have a wear problem do to poor 'lubricity', then how can you? For example, have you ever heard of any OEM specifying brake system rebuilds at a specified milage in their maintaince schedules?

I am always up for learning something about cars, So challenge my logic on this topic.

Brian

[DaveW]

On the topic of brake fluid 'lubricity', why should your opinion be valued? You have figuratively 'no mileage' on your race car brake system compared to what to what has been seen by OEM manufactures.

If OEM manufactures do not have a wear problem do to poor 'lubricity', then how can you? For example, have you ever heard of any OEM specifying brake system rebuilds at a specified mileage in their maintenance schedules?

I am always up for learning something about cars, So challenge my logic on this topic.

Brian

I'll refer to what I said before - experience has shown us racers that some brake fluids wear seals faster or slower than others, and using a fluid known for its good lubricity pays dividends in longer time between rebuilds and less repairs needed at the track.

Bottom line - It's pretty simple. Empirical evidence always outweighs theory. Theory has to be proven (or disproven) by empirical results.

Beyond that, you can argue all you want, but it won't change the facts.

[Garey Guzman]

On the topic of brake fluid 'lubricity', why should your opinion be valued. You have figuratively 'no milage' on your race car brake system compared to what to what has been seen by OEM manufactures.

If OEM manufactures do not have a wear problem do to poor 'lubricity', then how can you? For example, have you ever heard of any OEM specifying brake system rebuilds at a specified milage in their maintaince schedules?

I am always up for learning something about cars, So challenge my logic on this topic.

Brian

Very simply, race cars and street cars do not have the same design intent. Do race car brake pads last 30,000 miles? Do race car tires last 40-50,000 miles? Do race car engines last over 100,000 miles? Why are all these things so different between race cars and street cars? To equate them is irrational and doesn't take into account basic facts and differences between the design intent of two very different vehicles.

[DaveW]

...If OEM manufactures do not have a wear problem do to poor 'lubricity', then how can you?...

Brian

But OEM's DO specify lubricity requirements because they don't want to have a bunch of early (under-warranty) failures. Why do you think the BFLV fluid manufacturers emphasize their "excellent" lubricity in their specifications?

To answer my own question - it's because they know it's important and a requirement.

[FVRacer21]

I go down rabbit holes so you don't have to:

The English say Bob's your uncle, but there is a site "Bob is the Oil Guy"

I found this thread which led to this report:

Brake Fluid Standardization for Anti-Lock Braking Systems (BFABS) Benchtop Testing Report

Who knew the military did not have their own fluid (and antilock on tanks? )

The "winning" formula might be a 5.1 fluid from Bosch.

Which seems to be available from O'Reilly.

==================================================

Now GM did have a problem with lubricity - leading to squeaks

You can get their "special" fluid from Summit

ACDelco DOT 3 GMW Brake and Clutch Fluid 19299818

==================================================

My car will not be back on track until April or May - so no real life testing for now...

ChrisZ

Update - still no specifications for lubricity - will keep working....

[Steve Demeter]

I see a lot of Valvoline DOT # and DOT 4 brake fluid
https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds

Is this stuff as good as the Valvoline DOT 4, which I can not seem to find?

[DaveW]

It's the same stuff as the DOT 4. They're just labeling it that way so you know you can also use it in DOT 3 applications. DOT 4 fluid will work in DOT 3 applications. DOT 4 just calls for higher standards than DOT 3.

[tlracer]

It's the same stuff as the DOT 4. They're just labeling it that way so you know you can also use it in DOT 3 applications. That's pretty standard that DOT 4 fluid will work in DOT 3 applications. DOT 4 just calls for higher standards than DOT 3.

Not really for DaveW (and anyone else who knows this already!) but I figured this might be helpful:

DOT 3 minimum - can use DOT3, DOT 4 and/or DOT 5.1
DOT 4 minimum - can use DOT 4 and/or DOT 5.1

DOT 3, DOT 4 and DOT 5.1 (but not DOT 5) are all compatible as they are all glycol-based. Using fluid of the minimum or higher DOT number is fine, with the exception of this...

The stupidly spec'd (in my humble opinion) DOT 5 is silicone-based and CANNOT BE MIXED with anything else!

[stonebridge20]

The stupidly spec'd (in my humble opinion) DOT 5 is silicone-based and CANNOT BE MIXED with anything else!

AND.... you can not go back and forth between DOT5 and any other brake fluid unless you completely flush the system AND replace every rubber component in the system.

[DaveW]

AND.... you can not go back and forth between DOT5 and any other brake fluid unless you completely flush the system AND replace every rubber component in the system.

I wonder if Castrol SRF (DOT 4) could be used interchangeably with DOT 5 silicon-based fluids since the SRF is silicon-ester based. Castrol does not say it can, but...

From Castrol site:
Castrol SRF is the ultimate racing brake fluid. Its unique silicon ester technology absorbs less water than conventional glycol ether fluids and prevents the fluid's high-temperature performance from deteriorating. It's high boiling point, ability to withstand extreme temperatures and superior resistance to the effects of absorbed water have established Castrol SRF Brake Fluid as the world's premier fluid for the hydraulic brakes used in all forms of motorsport and racing.

Not that I'd ever try it, but I just wondered what any "experts" would say.

[Spengo]

The stupidly spec'd (in my humble opinion) DOT 5 is silicone-based and CANNOT BE MIXED with anything else!

This caused me to have a very dramatic incident once about six years ago that I am still remembered for at Spokane/Qlispe. I just buy whatever DOT4 is on the shelf these days.

[DaveW]

...The stupidly spec'd (in my humble opinion) DOT 5 is silicone-based and CANNOT BE MIXED with anything else!

The DOT 5 spec made sense when there was only DOT 3 & 4. Now that there's DOT 5.1 it's a recipe for mix-ups.

[tlracer]

I wonder if Castrol SRF (DOT 4) could be used interchangeably with DOT 5 silicon-based fluids since the SRF is silicon-ester based. Castrol does not say it can, but...

From Castrol site:
Castrol SRF is the ultimate racing brake fluid. Its unique silicon ester technology absorbs less water than conventional glycol ether fluids and prevents the fluid's high-temperature performance from deteriorating. It's high boiling point, ability to withstand extreme temperatures and superior resistance to the effects of absorbed water have established Castrol SRF Brake Fluid as the world's premier fluid for the hydraulic brakes used in all forms of motorsport and racing.

Not that I'd ever try it, but I just wondered what any "experts" would say.

Silicon and silicone are very different. The latter is polysiloxane chains, silicon is an element, classified as a transition metal. Whilst polysiloxane contains silicon, it is in a very different structure and with very different properties.

So basically, the answer from my perspective is no.

[DaveW]

Silicon and silicone are very different. The latter is polysiloxane chains, silicon is an element, classified as a transition metal. Whilst polysiloxane contains silicon, it is in a very different structure and with very different properties.

So basically, the answer from my perspective is no.

Thanks - I originally was going to major in chemistry in college, but I changed to engineering science (a course for engineering students who didn't know exactly what their major should be) as my major, so that difference was lost on me 60+ years later.

[problemchild]

About a decade ago, my customer bought a very expensive race car that had been previously prepped by a highly respected engineer. when discussing the fluids being used in the car, specifically the brake fluid, I received a lecture about wasting my customer's money running premium brake fluid in cars that did not require it. Ordinary brake fluid was fine, I was assured. So I switched to a regular inexpensive brake fluid that I can buy anywhere and mix with other brake fluids (although I don't). I have not had a single brake fluid issue in the 8 years since.

If FRP started running street tracks (like Montreal) then I may reconsider.

I mention this only because I think that whatever choice you make for FF or FC cars, you will be happy. The quality of the cheapest fluid today is probably better than most that was available 50 years ago. If you car does not have some weird harmonic frequency that shakes brake fluid into foam (I had 2 of these) then any premium fluid should do nicely. It sounds like the repackaged Castrol product will continue to serve you well. With some of these hills we travel to VIR, I am far more concerned with the brake fluid on the tow vehicle than the race cars

[Fred Michael]

I wonder if Castrol SRF (DOT 4) could be used interchangeably with DOT 5 silicon-based fluids since the SRF is silicon-ester based. Castrol does not say it can, but...

From Castrol site:
Castrol SRF is the ultimate racing brake fluid. Its unique silicon ester technology absorbs less water than conventional glycol ether fluids and prevents the fluid's high-temperature performance from deteriorating. It's high boiling point, ability to withstand extreme temperatures and superior resistance to the effects of absorbed water have established Castrol SRF Brake Fluid as the world's premier fluid for the hydraulic brakes used in all forms of motorsport and racing.

Not that I'd ever try it, but I just wondered what any "experts" would say.

Absolutely not. Nothing plays nice with Dot 5

[DaveW]

Yeah, my question was dumb, but I thought I ought to ask it to reconfirm that DOT 5 brake fluids are not compatible with anything else.

[billtebbutt]

I don't want to derail the discussion. And perhaps I am completely off base here. But it seems to me that lubricity would reduce with wear, in that as seals wore over time they would lose rubber, and that rubber would become embedded elsewhere in the seal or the bore or simply float within the brake fluid and "interfere" with the sealing function between the rubber and the bore. And that gets further complicated by brake fluid's ability to absorb water.....

So in my simplistic way of thinking, is the absolute choice of a certain fluid paramount? Or is the cleanliness of the system equally or maybe more important? Or, can we really have a discussion of one without the other?

To put it differently, would overall system performance be better with a cheap fluid (assume of sufficient grade as to not boil in a given application) that is bled after every session (yes I am being a little over the top here) vs. a more expensive higher-grade fluid that is only bled between race weekends (if that - I am assuming most of us do a bleed between race weekends). Alternatively, would a complete flush and fill with cheap fluid perform as well (or better?) than a quickie bleed with expensive fluid?

I've been to the Run-Offs precisely once, many years ago. Where my < 1 season old front MC seal failed on the warm-up lap - so this overall subject is very interesting to me.....

best,
bt

[Rick Kirchner]

WRT the differences between street and race systems and lubricity, If you look at a street system you have two master cylinders packaged in series - with a loooong piston with several seals. Its well supported and assisted by a plethora of springs and either vacuum or hydraulic assist.

Along with a long design life they are made to be serviced by people with little training and less common sense without putting the general public at risk. I wouldn't doubt if there are also platings and coatings in the bores that are not readily apparent without sectioning. In general, unless excess moisture gets inside and corrodes it solid street MCs are a lifetime part and if produced in the kind of quantities we see for racing parts they would likely be outrageously expensive.

With a race system you have a short piston with fewer seals - and the bias bar tends to impart a bit of a side load, there's much less in the way of mechanical assistance. They are nearly an expendable service part, given that whenever you get a barn find race car the first piece of advice after sending the engine off for a rebuild is to replace the MCs if not the entire brake system. You could infer from this that lubrication is more critical in a racing system.

[DaveW]

Bill,

Up to this point I've only used Castrol DOT4 (used to be LMA). With some fluids, water absorption might be an issue if the car is stored in humid, warm conditions.

I don't think lubricity would diminish with wear. Wear particles are likely rubber worn off the seals. However seal function might be compromised (rounding the sharp edges that enable sealing). So I don't really know whether bleeding (actually you'd need a complete flush to have clean fluid) every race weekend is beneficial.

I do know that if I start seeing a significant amount of black wear material in my bled fluid, that the caliper seals on that corner are about to need replacement.

Usually I only do a total flush after the car has sat for a long time (3 months or more) to make sure the fluid hasn't absorbed too much water.

I've never had an issue with the SAAB clutch slave (I do replace its seals every year), but wear was an issue with my Tilton 78-series front pivot clutch MC. After about 3 years of use (I use the clutch on every shift) the piston seal in the master wore just enough that the MC engagement point kept shifting. Link to that thread:
https://www.apexspeed.com/forums/sho...ight=tilton+78

Bottom line - flushing often can't hurt, but I don't consider it necessary.

It'll be interesting to see what others have to say.

[DaveW]

...With a race system you have a short piston with fewer seals - and the bias bar tends to impart a bit of a side load, there's much less in the way of mechanical assistance. They are nearly an expendable service part, given that whenever you get a barn find race car the first piece of advice after sending the engine off for a rebuild is to replace the MCs if not the entire brake system. You could infer from this that lubrication is more critical in a racing system.

Additionally, most race MC's are cast aluminum, not iron or steel, so developing surface roughness and wear is much easier in a race cylinder. My current MC's are Tilton 78-series front pivot so there is little to no side load, so wear due to side load is not an issue.

[Rick Kirchner]

That army report was an interesting read. A purely academic approach to fluid performance, with an occasional nod to real-life conditions.

I'm wondering where moisture gets introduced other than through the system vent - perhaps in running the calipers through cold water?

In a lot of military systems we use desiccant to maintain humidity control, with a desiccant label as a tell-tale. I'm surprised that they haven't devised a venting system through a desiccant package that is separated from the fluid itself with various pressure relief valves to minimize air intrusion. But if you pull a lot in from the calipers it seems that would not be particularly useful.

The other thing is if most fluids absorb to 3-4% then build the internal parts to handle it, and size performance to deal with it.

Surprised that they never identified the fluids used in the report, nor compared chemistries with other fluids in the same group to discuss why they picked one brand or another as representative.

The whole bit about moisture entrapment in Silicone fluid was another puzzler. If it doesn't absorb water, where is it coming from? Does anyone know why silicone fluid doesn't work well in antilock systems? Seems it would have something to do with reacting at high frequency.

Looking into my crystal ball my guess is that eventually this will turn into a new mil-spec for the fluid itself, maybe another for the packaging, which will then go out for bid. If they have half a brain they'll try to figure out how to increase the shelf life, because they WILL put an expiration date on it and a lot of it will go to HAZMAT disposal and you just would not believe the expense of that in the US government. You think that it costs a lot in the civilian world, try bumping that figure up by a factor of 3-5.

[DaveW]

That army report was an interesting read. A purely academic approach to fluid performance, with an occasional nod to real-life conditions...

This is the army report Rick is referencing which was included in one of FVRacer21's posts (#51):

https://apps.dtic.mil/sti/pdfs/AD1091780.pdf

[DaveW]

...Does anyone know why silicone fluid doesn't work well in antilock systems? Seems it would have something to do with reacting at high frequency...

See next post...

[alangbaker]

I'd guess it might be higher compressibility which would mute ABS response.

A little googling (we don't need to capitalize that anymore... ...do we?) shows that it is:

1. Less lubricity for the rapidly opening and closing metal shuttle valves.
2. Foaming caused the that self-same rapid motion. The foaming is from dissolved air.

[Rick Kirchner]

So here's a question, doubt anyone has tried this, but one could make a cap for the MC with a fitting to a vacuum pump, and then pull a vacuum to remove dissolved air and water from the system. Yes, I know it's probably easier to just change the fluid. One could also vacuum the fluid like some guys who re-sell the stuff do, but that takes a vessel that can handle the delta P.

If you tried to do this on the car, do you suppose the major issue would be pulling air past the seals? I'm guesing they seal better with pressure behind them , rather than vacuum.

[tlracer]

So here's a question, doubt anyone has tried this, but one could make a cap for the MC with a fitting to a vacuum pump, and then pull a vacuum to remove dissolved air and water from the system. Yes, I know it's probably easier to just change the fluid. One could also vacuum the fluid like some guys who re-sell the stuff do, but that takes a vessel that can handle the delta P.

If you tried to do this on the car, do you suppose the major issue would be pulling air past the seals? I'm guesing they seal better with pressure behind them , rather than vacuum.

To get dissolved air down to zero you would need to pull a full vacuum, ie. zero pressure absolute. Absorbed water would be more difficult and would possibly need to be boiled out.

However, doing either would be pointless, as once the fluid was back under normal conditions, air would begin to redissolve and water would get absorbed again. Ultimately the equipment and effort would be more than just changing the fluid for fresh!

[DaveW]

...If you tried to do this on the car, do you suppose the major issue would be pulling air past the seals? I'm guessing they seal better with pressure behind them , rather than vacuum.

That's correct - the seals would just lean out of the way and suck in more air with a high vacuum.

[Rick Kirchner]

To get dissolved air down to zero you would need to pull a full vacuum, ie. zero pressure absolute. Absorbed water would be more difficult and would possibly need to be boiled out.

However, doing either would be pointless, as once the fluid was back under normal conditions, air would begin to redissolve and water would get absorbed again. Ultimately the equipment and effort would be more than just changing the fluid for fresh!

It doesn't take near as much as you think to get dissolved air out. We used to do this to epoxies in the navy under a bell jar. The entrapped air and water boil out quickly even at partial vacuums. Pretty cool to watch.

Yes, it starts to re-absorb water as soon as its exposed again, the question is how well the system keeps the brake fluid away from moisture laden air. if you have a decent seal on the cap with just a pinhole vent, you could flood the top of the rez with dry nitrogen, or maybe something heavier like argon, before capping and it would probably help for a good long time.

[DaveW]

...Yes, it starts to re-absorb water as soon as its exposed again, the question is how well the system keeps the brake fluid away from moisture laden air. if you have a decent seal on the cap with just a pinhole vent, you could flood the top of the rez with dry nitrogen, or maybe something heavier like argon, before capping and it would probably help for a good long time.

Back ~15-20 years ago there were orange silicone seal/bellows one could put under the reservoir cap to prevent leakage and venting to atmosphere. That would help prevent moisture absorption. I have one on my Tilton clutch reservoir. I still see a few black cap seals similar in function online, but I don't know what diameter reservoir opening they fit.