Topic: Brake Fluid - What are you guys using...

[NEFaurora]

Here's a good explanation.... that's why I'm sticking with DOT 3 fluid...

https://techtalk.mpbrakes.com/brake-fluid/can-i-use-dot-5?hs_amp=true


)

Tony K.

[69GT350H]

Here's a good explanation.... that's why I'm sticking with DOT 3 fluid...

https://techtalk.mpbrakes.com/brake-fluid/can-i-use-dot-5?hs_amp=true


)

Tony K.

I'm installing a totally new brake system. No water, no old brake fluid. Dot 5 should be good for me then? Driving will include some fun sport activities. I am expecting higher temps.

Per the mentioned article, where does this water come from that can turn into vapor?

Boiling point ranges
Dry boiling point   Wet boiling point
DOT 3   205 °C (401 °F)   140 °C (284 °F)
DOT 4   230 °C (446 °F)   155 °C (311 °F)
DOT 5   260 °C (500 °F)   180 °C (356 °F)
DOT 5.1   260 °C (500 °F)   180 °C (356 °F)
DOT 5 - Wikipedia https://en.wikipedia.org/wiki/DOT_5

Per Wikipedia and http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm, DOT 5 fluid has a higher dry/wet boiling point than both DOT 3 and 4. DOT 5 does a better job at keeping water intrusion out of the rubber hose than 3 or 4.

The only issue I can see is that the DOT 5 silicone fluid is that it is more compressible than glycol fluid, especially at elevated temperature. In a test (http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm), at 400 °F wheel cylinder/caliper temperature, pedal travel increased by 13.5 mm to 18 mm (0.5 to 0.7 inches) in two sample systems. The brakes with silicone fluid continued to operate at this temperature in spite of the compressibility. Nothing was said about the DOT 3 fluid when it reaches 400 °F wheel cylinder/caliper temperature, as 1 more degree would be boiling point and that would make that cylinder/caliper fail.

Is there any fault in what I am reading, that DOT 5 IS a better choice then DOT 3/4 based on the documentation I have provided?

[Bob Gaines]

I'm installing a totally new brake system. No water, no old brake fluid. Dot 5 should be good for me then? Driving will include some fun sport activities. I am expecting higher temps.

Per the mentioned article, where does this water come from that can turn into vapor?

Boiling point ranges
Dry boiling point   Wet boiling point
DOT 3   205 °C (401 °F)   140 °C (284 °F)
DOT 4   230 °C (446 °F)   155 °C (311 °F)
DOT 5   260 °C (500 °F)   180 °C (356 °F)
DOT 5.1   260 °C (500 °F)   180 °C (356 °F)
DOT 5 - Wikipedia https://en.wikipedia.org/wiki/DOT_5

Per Wikipedia and http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm, DOT 5 fluid has a higher dry/wet boiling point than both DOT 3 and 4. DOT 5 does a better job at keeping water intrusion out of the rubber hose than 3 or 4.

The only issue I can see is that the DOT 5 silicone fluid is that it is more compressible than glycol fluid, especially at elevated temperature. In a test (http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm), at 400 °F wheel cylinder/caliper temperature, pedal travel increased by 13.5 mm to 18 mm (0.5 to 0.7 inches) in two sample systems. The brakes with silicone fluid continued to operate at this temperature in spite of the compressibility. Nothing was said about the DOT 3 fluid when it reaches 400 °F wheel cylinder/caliper temperature, as 1 more degree would be boiling point and that would make that cylinder/caliper fail.

Is there any fault in what I am reading, that DOT 5 IS a better choice then DOT 3/4 based on the documentation I have provided?

Regardless of what fluid you use air along with moisture is introduced through the master cylinder vent system made into the cap. Read reply #6 for general conscience and best usage per driving style.

[69GT350H]

Regardless of what fluid you use air along with moisture is introduced through the master cylinder vent system made into the cap. Read reply #6 for general conscience and best usage per driving style.

Offline Building 3
Sr. Member
****
Posts: 318
View Profile  Personal Message (Offline)

Re: Brake Fluid - What are you guys using...
« Reply #6 on: March 29, 2018, 12:29:21 PM »
Quote
I have used DOT 3 in my older and classic cars.  I use the brake strip testers each year to see if there's any deterioration. Never seen any deterioration, but I still change the fluid every 5-6 years. The cars only get 300-700 miles or so a year and are in a heated garage. No track time.  For my daily drivers I change the fluid every two years.
Report to moderator     Logged
1966 289 C code auto convertible December 1965 scheduled build at Dearborn.

1966 289 C code auto convertible
October 1965 scheduled build at Metuchen.

Reply #6 does not tell me much. Now Reply #7

I and others have used the Dot 5 for years in the vehicles that do not get used as much as a daily driver because the fluid is more maintenance friendly. The fact that the silicone does not absorb water into the system keeps the brake calipers and wheel cylinders ,proportioning valve etc. from freezing up internally from rust . Regular brake fluid absorbs water faster and must be changed frequently to keep rust from forming on the internal metal surfaces. Another plus is if or when it break fluid leaks somewhere it will not eat the paint  . The Dot 5 is not good if you are doing open track with the car. I don't use Dot 5 in any car that I would vintage race. Those type use vehicles should have brake fluid flushed every 6 months or so.  Dot 5 has a lower boiling point and gives a softer pedal feel. Given your driving habits and expectations and it sounds like the dot 5 would be what I would suggest using.

Dot 5 does NOT have a lower boiling point. It is higher. And at 401 deg when the Dot 3 is boiling, Dot 5 is still working, though with a slightly lower pedal. Why not change it out every 6 months?

[Bob Gaines]

Offline Building 3
Sr. Member
****
Posts: 318
View Profile  Personal Message (Offline)

Re: Brake Fluid - What are you guys using...
« Reply #6 on: March 29, 2018, 12:29:21 PM »
Quote
I have used DOT 3 in my older and classic cars.  I use the brake strip testers each year to see if there's any deterioration. Never seen any deterioration, but I still change the fluid every 5-6 years. The cars only get 300-700 miles or so a year and are in a heated garage. No track time.  For my daily drivers I change the fluid every two years.
Report to moderator     Logged
1966 289 C code auto convertible December 1965 scheduled build at Dearborn.

1966 289 C code auto convertible
October 1965 scheduled build at Metuchen.

Reply #6 does not tell me much. Now Reply #7

Dot 5 does NOT have a lower boiling point. It is higher. And at 401 deg when the Dot 3 is boiling, Dot 5 is still working, though with a slightly lower pedal. Why not change it out every 6 months?

I misspoke on the lower boiling temp but regardless when you are operating at those temps you would be typically track racing where it is not typically desirable. For context I am re posting my previous post for context.

I and others have used the Dot 5 for years in the vehicles that do not get used as much as a daily driver because the fluid is more maintenance friendly. The fact that the silicone does not absorb water into the system keeps the brake calipers and wheel cylinders ,proportioning valve etc. from freezing up internally from rust . Regular brake fluid absorbs water faster and must be changed frequently to keep rust from forming on the internal metal surfaces. Another plus is if or when it break fluid leaks somewhere it will not eat the paint  . The Dot 5 is not good if you are doing open track with the car. I don't use Dot 5 in any car that I would vintage race. Those type use vehicles should have brake fluid flushed every 6 months or so.  Dot 5 has a lower boiling point and gives a softer pedal feel. Given your driving habits and expectations and it sounds like the dot 5 would be what I would suggest using.

  The silicone is typically shunned by the vintage race crowd because of the soft pedal . You are expected to change the conventional brake fluids every 6 months on a track car because of contaminants (moisture etc) in the fluid that could compromise the performance since this a safety issue for the driver and others around the drivers car. Most likely the silicone brake fluid would be expected to be done the same way ,that is if it was even used in that situation .  There is nothing that is written that says that you are prohibited from using the Dot 5 silicone fluid in spirited driving it but it will not perform as good as the Dot 3/4 in those spirited driving situations. It is your choice what you use.

[sgl66]

You are expected to change the conventional brake fluids every 6 months on a track car because of contaminants (moisture etc) in the fluid that could compromise the performance

Is it common practice to remove the calipers to drain the fluid or is there some other trick? The bleeder valves up top on 65/66 only let out air and excess fluid pumped in but do nothing to drain any cr@p or old fluid at the bottom of each caliper

[Bob Gaines]

Is it common practice to remove the calipers to drain the fluid or is there some other trick? The bleeder valves up top on 65/66 only let out air and excess fluid pumped in but do nothing to drain any cr@p or old fluid at the bottom of each caliper

For the purposes of this discussion on the track cars the fluid is typically flushed without removing the calipers . When it is changed that often you don't typically get the build up of debris associated with corrosion breaking off from surfaces inside the system .Or it is just faster and gets most everything out anyway.   

[gjz30075]

  I use the brake strip testers each year to see if there's any deterioration.

I don't know what's in my brake system , ie, DOT 3/4 or 5.    It doesn't remove paint, but neither did my Valvoline Synthetic DOT 3/4.    I need
to determine, absolutely, what my system has.   What kind of indication will these testers give if the system is DOT 5?

[BKnapp]

I think you can try taking a teaspoon of fluid from the master cylinder and mix it with a clean glass of water. If the fluid mixes in with water it is conventional 3 or 4. If it is dot 5, it will not mix with water and will probably float to the top...that’s my understanding anyway.

[67gtasanjose]

Regardless of what fluid you use air along with moisture is introduced through the master cylinder vent system made into the cap. Read reply #6 for general conscience and best usage per driving style.

This introduction of "air along with moisture" issue can be addressed on non-driven cars should a person wish to do an undetectable modification to the cap.

I mention "non-driven" because of a very slight issue of safety and any related liabilities associated with the nature of  any potential of an "accident" caused because of brake failure and  how lawyers look for loopholes to assign blame. This "modification" could actually be done to "driven" examples too but for reasons stated already, perhaps not such a great idea.

So, how does the moisture get past the cap? Through the vents designed in the cap, right? Why are the vents needed then? Because of FLUID DISPLACEMENT, right? Where does the fluid go? Leaks? Not likely on a show car, right? Displacement into the wheel cylinders or calipers when braking is temporary and as soon as the brakes are released, returns to the Master cylinder, right? So why the REQUIREMENT of the vents? Easy answer is so that a vacuum does not develope within the master cylinder and by nature, air will seap in by ANY means possible and that is obviously worse than any introduction of moisture. Hence, the vents were designed to remove ANY CHANCE of this  air entering in (air entering in past the wheel cylinder seals or the master cylinder piston-end seals are a few examples of "where" air can enter in that come to mind). A "Trailer Queen" would not likely ever see such a condition while a driven car has a POSSIBILTY only so this "idea", by default has flaws in it. Then you add the very fact that none of us will live forever and the car will one day be sold so even a "trailer queen" could one day be driven. Basically, the master cylinder cap has a diaphams that allows for the NORMAL displacement but if a leak were to occur anywhere in the system at all, if the diaphams was fully extended, it COULD cause a brake failure that MIGHT not have happened if the cap was designed to vent air into the reservoir....hence the vents.

Clear as mud? If you are worried about moisture getting in, you could consider this idea to modify your cap regardless WHAT fluid you choose. Most of us are not likely to do this but it can be done. Just an idea.

[sgl66]

For the purposes of this discussion on the track cars the fluid is typically flushed without removing the calipers . When it is changed that often you don't typically get the build up of debris associated with corrosion breaking off from surfaces inside the system .Or it is just faster and gets most everything out anyway. 

The point I was trying to make is how do you "flush" the fluid out of the lower 80+% of a K/H caliper? The inlet hose, transfer tubes and bleeder are all up top so there is no way to push the old fluid out that I know of without removing the caliper, turning it upside down and letting gravity do its job. K/H should have put the transfer tube at the bottom like Brembo

[Morsel]

Sorry to beat a dead horse with this older post, but I'm getting close to doing my brake fluid now and I just want to confirm one last time. As I mentioned the calipers came from Jim Cowles who only uses Dot 5 bake fluid in his rebuilds. So I was originally just going to go with his recommendation on using it until I started hearing people voicing their opinions about it being "a softer pedal". So what exactly does this mean, is it spongy and not as snapping coming back into position after a hard brake or is it just a slightly different feel? I do only drive the car about maybe 200 miles a year at most, but when I do drive it, I do drive it rather aggressively at times, I mean it is a K-Code, so you got to drive it hard sometimes I'm fine with a different feel of pedal, but I just don't want it to be "less performance and a liability" of any kind.

If people think I should be using Dot 3 and bail the Dot 5 entirely, as mentioned by the pervious post, how would I go about flushing the calipers to remove the Dot 5 that's in it? They are not on the car currently, and I don't really want to break them apart again, but I guess if that's the only way to flush and get the old dot 5 out, I guess so be it. The rest of the lines and master cylinder are completely clean...

Thanks,

Jason

[67350#1242]

Moisture entering the system through the MC cap vents probably isn't a big issue since the vents are actually above the gasket.  The diaphragms in the gasket make up for pad wear and minor leakage - so the top side is necessarily open to the atmosphere but bottom side is sealed.
I think the only way to make sure no old fluid or moisture is in the calipers is to pull them apart - you cant get everything out of there otherwise.
I would also be wary of relying on a flush to remove everything in the system.
With DOT 5 any water entering the system will seek the lowest spots since the fluid floats on top of water. The lower part of the caliper would be one collection spot.  I am still on the side of using DOT 5 because I think it is the best option for seldom driven non racetrack vehicles.

[Morsel]

Moisture entering the system through the MC cap vents probably isn't a big issue since the vents are actually above the gasket.  The diaphragms in the gasket make up for pad wear and minor leakage - so the top side is necessarily open to the atmosphere but bottom side is sealed.
I think the only way to make sure no old fluid or moisture is in the calipers is to pull them apart - you cant get everything out of there otherwise.
I would also be wary of relying on a flush to remove everything in the system.
With DOT 5 any water entering the system will seek the lowest spots since the fluid floats on top of water. The lower part of the caliper would be one collection spot.  I am still on the side of using DOT 5 because I think it is the best option for seldom driven non racetrack vehicles.

Well not worried about my lines and flushing them to remove the old Dot 3 because they are all new including the freshly rebuilt master cylinder, and the except the front lines and proportioning valve which I did clean, I removed the fittings and ran alcohol through the lines using a vacuum brake bleeder several times and also ran it through the proportioning valves and then they've been dry now for about a month, so hopefully I'm good and the system is completely clean.

I guess I'm going to stick with the Dot 5 and give it a try, sounds like most are happy with it and I don't really want to take apart my calipers that Jim did.

Thanks,

Jason

[Bob Gaines]

Well not worried about my lines and flushing them to remove the old Dot 3 because they are all new including the freshly rebuilt master cylinder, and the except the front lines and proportioning valve which I did clean, I removed the fittings and ran alcohol through the lines using a vacuum brake bleeder several times and also ran it through the proportioning valves and then they've been dry now for about a month, so hopefully I'm good and the system is completely clean.

I guess I'm going to stick with the Dot 5 and give it a try, sounds like most are happy with it and I don't really want to take apart my calipers that Jim did.

Thanks,

Jason

Don't worry .The soft pedal statement is more in reference to extreme braking in comparison to the Dot 3. I doubt you will notice any difference in pleasure driving.