Synthetic Brake Fluid

[Bruce2]

How about "spongy pedal" syndrome?

You get used to it.

Push the pedal, the car stops. Why does a spongy pedal change anything?

Many, many people have driven my car. Not one person has said anything about the brake pedal, so the difference must be negligible.

[ProctorSilex]

How about "spongy pedal" syndrome?

You get used to it.

Push the pedal, the car stops. Why does a spongy pedal change anything?

Many, many people have driven my car. Not one person has said anything about the brake pedal, so the difference must be negligible.

When I reassembled my steering rack for manual steering, it opened up a whole realm to me. There are faster drivers than me who have no problem with power steering. I need the car to scream at me while others understand what the car wants from a gentle whisper. A firm pedal is a Holy Grail to a dolt like me who needs every iota of input I can get.
It comes down to the driver's needs for the application and the consistency. If your soft pedal is consistent and it works for you, then there is nothing wrong with it.

[Bruce2]

I've never heard anyone who has a good reason why a hard pedal is needed.

[Ol'fogasaurus]

A soft pedal is/used to be an indication of something out of adjustment, an imbalance side to side or front to rear or something wrong with the braking system. With power brakes the feeling went away somewhat. I won't drive a car with manual brakes that has a soft pedal.

Lee

[Bruce2]

A soft pedal with paint stripper usually indicates air in the system.

If there's no air in the system, why is a hard pedal better than a soft one?

[Ol'fogasaurus]

A soft pedal with paint stripper usually indicates air in the system.

I don't understand that sentence at all. The only thing I can think of with paint stripper would be if the brakes failed and you ram into something.

If you are talking about a system flush then this follows some other rules of thumb such as: you never put anything in your ear that is smaller than your elbow. Never cut the cheese and a dark room until you have turned on the lights to see if there is anyone sitting in the dark to surprise you. Never put anything in a safety device that doesn't belong there (and brakes would fall under safety device). If in doubt then replace it with the proper component, material or with the proper properties.

If there's no air in the system, why is a hard pedal better than a soft one?

(sigh) Assuming that there is no air in the system, the MC is ok especially with a dual chamber MC, a soft pedal usually means that the brake shoes themselves are not adjusted correctly, the soft lines are bulging or that there could be an improper balance to the system front to rear. A dual chamber MC where one of the chambers isn't functioning can also cause a soft pedal and poor braking. Almost every time I have experienced a soft or spongy pedal there was something wrong with or in the braking system, the same with a brick hard pedal that didn't move of move much.

Like steering, there is a lot of information that comes up through the brake pedal (less with power or power assist brakes). Even now, when coming to a stop I lightly press the pedal to make sure the brakes are there and their conditions. This is after a few incidents where the brakes went away while driving (Part failure. I did not do the brakes if you were going to push that against me).

[RHough]

Could it be that soft and hard are subjective terms?

If there is no air in the system and the only difference is DOT5 fluid or DOT4 fluid the only change in brake pedal "hardness" or "softness" would be fluid compressiblity . Hard to imagine that the fluid compressibility would be noticed before rubber hose flex, brake shoe flex, caliper flex, and pedal flex were felt.

Anyone care to measure pedal travel vs force at the pedal for DOT4, then change the fluid for DOT5 and retest? That would give an objective measure.

If none of the people that have driven the car have noticed a "soft" pedal, it is reasonable to conclude that using DOT5 in a street car would not be a problem unless the rubber parts react badly to it.

I think the horse is dead?



Randy

[Ol'fogasaurus]

" ....unless the rubber parts react badly to it."

That is one major part of my concern if the system is being flushed. Over most of my 34 years at my job I had to spend hours on end, maybe full days in a row going through processes and procedures line by line then those processes and procedures that were internal components/inbedded of the original document. Sometimes you had to go through several layers of this before you might find a problem or got to the bottom of things.

One of the common themes in them was do not inject substances that did not belong there in the first case. Some chemicals might not affect the soft parts immediately or at all but a supposedly same product by a different manufacturer may have a change or two in its' make up which might, even over a long period of time, cause problems even though it has been supposedly been removed and/or neutralized.

Again, it is better to error on the side of caution than to go out in a blaze of glory.

By-the-way, one of the sidelights of going through the processes and procedures was that it was easy to get side tracked when you ran into something unusual/interesting. Two if of the interesting things I remember was running into was explosive welding and the welding together of steel and AL. Ya never know what's out there.

[Piledriver]

If DOT5 is the silicone oil I think it is, it's EXTREMELY compatible with ~all common rubber seals/orings etc.
(Polydimethylsiloxane, sometimes called by trade name dimethicone, used for oring lube, the active ingredient in gas-x, and as a primary constituent of the "butter" topping on some theater popcorn )

The only thing I really have against it came up recently at work: we have a process chiller that uses a thinner version of silicone oil as the working fluid, and the system got contaminated with water, and as the water does NOT mix, it stays free in the bottom of the system to do its worst. ~$15Ks worth...

[Ol'fogasaurus]

I wasn't so much concerned with the synthetic brake fluid as I was with the flush. I did some looking around on brake fluid and I couldn't find anything about brake fluid causing problems (as that is a prerequisite they have to follow) with soft items other than DOT 3, DOT 4 and maybe DOT 5.1 might be hard on paint.

Remember that materials of some after market goods are always in a state of flux depending on who is making them for whom to sell, contract language or not. A good example might be the brake light switch: each time an importer changes countries for cheap labor there is a problem with leaky/substandard switches. By the time they get it right the cost of them goes up so the contractor goes looking for another source of cheap labor.

As far as a spongy/soft feeling pedal or, in my case, a turning brake: if that is what DOT5 gives you it would certainly bother me to no end.

Lee

[Bruce2]

Anyone care to measure pedal travel vs force at the pedal for DOT4, then change the fluid for DOT5 and retest? That would give an objective measure.

You don't need to do such a detailed experiment. Just get in a car with DOT5 and push the pedal. In my car, when I push the pedal under normal traffic type conditions, the pedal is about 4-5" off the floor. If I push it with all the strength of my leg, I can push it another 2-3".

[RHough]

Anyone care to measure pedal travel vs force at the pedal for DOT4, then change the fluid for DOT5 and retest? That would give an objective measure.

You don't need to do such a detailed experiment. Just get in a car with DOT5 and push the pedal. In my car, when I push the pedal under normal traffic type conditions, the pedal is about 4-5" off the floor. If I push it with all the strength of my leg, I can push it another 2-3".

Is that different than with DOT4?

The only way to have an objective measurement is to reduce variables. No objective conclusion about the effect if the brake fluid can be made by comparing your car's brake pedal to another car.

The point I am trying to make is there seems to be a logic disconnect here.
If DOT5 fluid is more compressible than DOT4 fluid it is logical to assume that *all other things being equal* that the pedal travel will increase. From this it is *not* logical to conclude that because a car has DOT5 fluid in it the brake pedal must be soft. The only way to come to that conclusion would be to show that DOT5 fluid is so compressible that it gives a soft pedal effect before rubber hoses, caliper flex, shoe flex due to poor adjustment and any of the other things that contribute to brake pedal feel.

Here is something to consider; If the compressibility of DOT5 fluid makes it unsafe to use in systems not designed for it there would be a metric ton of warnings and disclaimers and it would probably not be for sale to the general public.

It is pretty well documented that DOT5 does not absorb water like DOT3 & 4 do. Moisture will collect in low points of the system.
I find mentions that DOT5 holds tiny air bubbles in suspension and being careful not to aerate the fluid during bleeding can be an issue.

In either fluid, water degrades brake fluid performance and the systems should be flushed any time moisture is present. This performance degradation is independent of component damage from moisture.

If you have a few drops of water in a brake caliper full of DOT5 and you get the brakes up to 400°F the water won't have an effect into that corner. However when you release the pedal and the system pressure drops the water will vaporize and act exactly like an air pocket in a poorly bled brake system and the pedal travel is increased going into the next corner. After everything cools the brakes will be fine again and unless the bleeders are at the point where water collects, bleeding the brakes won't show anything. Flushing the system usually restores the performance until it is contaminated with water again. Just like a DOT4 system.

I've got no horse in this race. I won't condemn DOT5 fluid based on this thread. I doubt that a mechanically sound brake system on a street car would know the difference between clean DOT5 or DOT4 fluid. It would be an interesting data point to see if any difference in pedal travel or feel could be measured between the two.

The main reason I run DOT4 is that if I need to add fluid it is available everywhere. DOT5 would require I carry fluid since you cannot top up a DOT5 system with DOT3 or 4.

If your brakes are in good condition and properly adjusted I doubt you have a "soft" pedal due to DOT5 fluid.

Cheers,

Randy

[Ol'fogasaurus]

Well said Randy. I had found the water vs. DOT 5 issue in some the research I did not mention it as I felt that I was going into another level and would start something else. I forgot about the "vaporizing" bit which is important.

Those of us who go off-road and maybe don't go real fast would still be concerned with the soft pedal/handle issue when on the steep faces of hills/dunes. You don't want to be in an emergency situation requiring a quick brake or maybe more so turning brake actuation and blooding the guy's nose in the back seat as you continue to pull to overcome the compression of the fluid .

Anyway, I think we may have beat this pretty much to death but it is still a good subject to have around.

[Jim Ed]

I read on another forum that O Reilly auto parts DOT 3 synthetic brake fluid is the same formula as the old conventional DOT 3 and that they re-named it to DOT 3 synthetic brake fluid to increase sales.
I still will not take the chance after using Valvoline Syn_Power synthetic brake fluid DOT 3 & DOT 4 after the way it made the hoses swell up.
I went to Carquest auto parts yesterday.
They had plenty of DOT 3 that did not say 'synthetic' on the label so, i bought some. I think Auto Zone still might have some too.

[Piledriver]

Yep, the whole "synthetic" thing with brake fluid is kinda weird, it's not like they tap trees for it like maple syrup (Yum!)
Technically, one could say it's all synthetic, as ethylene glycol or silicone-oozing trees are scarce.