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As with many things car care related, there is no hard, fast rule for when brake fluid will need to be changed. If you do a lot of stop-and-go driving or if you do a lot of sudden braking, your brake fluid (and brake pads) will likely not last as long as someone who does more highway driving. Here are four reasons why changing brake fluid is necessary:

Reason #1: Brake fluid is “hydroscopic,” which means it actively attracts moisture from the air.

This is often cited as the main reason to change your brake fluid. Because many parts of your braking system are made of metal, flushing the brake fluid can prevent corrosion and failure of those metal components.

Reason #2: As brake fluid ages and becomes contaminated with small particles, the boiling point of the fluid goes down.

This reduces your braking performance, which you might not notice for awhile, but every inch counts when it comes to braking. In extreme cases, it can lead to the brakes not working at all.

Reason #3: As your ABS and traction control systems activate, they generate heat, which further breaks down the fluid.

Although ABS and traction control are important safety systems that rely on clean brake fluid, the heat they generate shortens the life of your brake fluid.

Reason #4: Anti-lock braking (ABS) and traction control components are sensitive to moisture and small particulates from contaminated fluid.

Flushing the brake fluid can prevent it from ruining expensive brake parts. An ABS module, for example, is what activates the ABS and pulses the brakes to help you stop straight. This critical component typically costs several hundred dollars.


 

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Have to add that even if the auto maker doesn't given a brake fluid flush service interval this fluid flush/bleed should be done every so often.

Prior to my Porsche experience the brake fluid flush/bleed was done every time the brake hardware was renewed. That is I can't recall any automaker specifying a brake fluid flush/bleed service interval.

When I got my first Porsche the brake fluid flush and bleed service was specified every 2 years. I had this done on time but thought it a bit overkill-ish.

Some couple of years ago my Boxster clutch developed some untoward behavior. A clutch that was easy to engage smoothly and move the car off from a stop -- even on an upgrade -- smoothly and quickly and yet with minimal clutch slippage was no longer operating this way. At first I thought it was me but even when paying close attention the behavior was the same. A grabby clutch with the car often taking off like I was a beginner driver in my first manual transmission equipped car.

Also, the shifting action deteriorated. Every shift up (or down) no matter how much I focused on my clutch/shift coordination was a crunch fest.

Given the number of miles (~275K) on the clutch and transmission, even though the transmission had received fluid services at least on the factory's schedule, I figured one or both the clutch and transmission were just showing their age.

Not sure what my next step was going to be but all I could think about is at least a clutch job then if the transmission didn't improve perhaps a transmission rebuild. Except for a failed throw out bearing at over 150K miles in my Mustang I never had a clutch or transmission problem in any car.

Talked to the SA about the behavior. He asked me when I had last had the car in for a brake fluid flush and bleed. Porsche cars, at least the ones I have owned, have a clutch hydraulic system that shares fluid with the brake system so his question made sense. I of course thought within 2 years but I had been dealing with taking care of my elderly parents and had just last track of time.

The SA looked it up and found the last fluid service was 2.5 years prior. He suggested rather than a clutch job a brake (and clutch) fluid flush and bleed. I'm always willing to throw a rather inexpensive fluid service at a symptom before I start throwing expensive parts (a clutch job would have been a $3K job easy and a transmission rebuild that much or more).

After the brake fluid flush and bleed the improvement in clutch behavior and transmission behavior was nothing short of miraculous. The clutch action was back to its normal smoothness. The shifting had lost its crunchiness.

Had I not experienced this for myself I would have not believed it, that the fluid could deteriorate in just 2.5 years to the point the clutch action was affected.

I don't know why the clutch action was affected. Certainly the fluid did not get hot enough that water in the fluid boiled. (This can happen on the track and a brake pedal that goes to the floor can be the result.)

The brakes as best I could tell didn't manifest any issues before the brake fluid service and afterwards I felt no change.

But the point is the brake fluid had degraded in 2.5 years to the point its function as a vital fluid had deteriorated and it was no longer able to perform its function. Had I not had this fluid service done I could have spent money on a clutch job maybe even a transmission overhaul for naught. As it was I drove the car to 317K miles with no issues from either the clutch or the transmission other than at the end of my time with the car it was clear the clutch was worn out. This was highlighted by the amount of force it took to work the clutch pedal. But the clutch still engaged smoothly and the transmission shifted as smoothly as it had been since I bought the car.

One has to wonder had I not had the clutch to let me know the fluid was bad had I continued to run this fluid what effect it might have had on the brake system. I might add other than pads and rotors the brakes required no other attention in 317K miles. The master cylinder was fine as were all the caliper pistons, seals, lines, and even the clutch slave cylinder. I attribute all of these items and their longevity to the (except in one case) regular (every 2 years) brake fluid flush/bleed services.
 

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Or cleanse it out, replace with Dot 5 and be done with it.

Not that I know how long Dot 5 itself lasts - there must still be some wear particles created in the system - but I have a few vehicles with at least 30 year old Dot 5 in them, and they work fine.
 

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Or cleanse it out, replace with Dot 5 and be done with it.

Not that I know how long Dot 5 itself lasts - there must still be some wear particles created in the system - but I have a few vehicles with at least 30 year old Dot 5 in them, and they work fine.
DOT 5 is not that easy to use, at least use right, and could be incompatible with our car braking system.

Dot 5 is silicon based and does not absorb moisture. While it can be used in place of DOT 4 fluid or DOT 5.1 fluid, both glycol ether based at least one source (Wikipedia) says the switch over is advised only after a full system restoration has been done. IOWs just a flush of a DOT 4 brake system is not good enough.

Also DOT 5 fluid is not compatible with ABS systems and should not be used with them.

Of course any top up of the fluid must be with DOT 5 fluid. (Unless you have a sticker on the brake fluid reservoir or a lock if you take the car in for any service almost certainly a tech being thorough will add DOT 4 fluid to the brake master cylinder reservoir.)

And my info is once you use DOT 5 you can't go back to DOT 4/5.1 fluid.

Thus while DOT 5 fluid may have a place in the brake fluid world it is not based on what info I have a no questions asked suitable replacement for DOT 4/5.1 fluids.
 

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I've never replaced brake fluid on anything. Never had a problem either. Only when I did a brake job was fluid bleed to get the air out of system. All this brake fluid replace stuff to me is nonsense. 2019 Charger...2019 Challenger...2018 RAM 1500...No where in any of the manuals does it say to flush brake system.
 

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Of course any top up of the fluid must be with DOT 5 fluid. (Unless you have a sticker on the brake fluid reservoir or a lock if you take the car in for any service almost certainly a tech being thorough will add DOT 4 fluid to the brake master cylinder reservoir.)
I just knew I'd open up a can of worms with bringing up Dot 5 fluid.

But at least I have the fool proof way to avoid possibly contaminating my brake fluid: I do not take my vehicles in for service.
I may visit a dealer if having a software issue, which I probably couldn't fix on my own, or if the engine or trans blows up. But until I'm in a wheelchair, my vehicles won't be subjected to "dealer service".
 

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I run Motul 5.1 in my Challenger. Flush and replace every spring wether it needs it or not. Cheaper than an oil change. I go to Brakes Plus and provide them with the Motul fluid. 30 mins. and $45 labor is no brainer.
 

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I've never replaced brake fluid on anything. Never had a problem either. Only when I did a brake job was fluid bleed to get the air out of system. All this brake fluid replace stuff to me is nonsense. 2019 Charger...2019 Challenger...2018 RAM 1500...No where in any of the manuals does it say to flush brake system.
Invariably there are people who engage in risky behavior and seem to come up unscathed. All well and good for them but their good luck is not something I want to have to count on to get me through unscathed.

I'm always leery of following advice from someone who has probably dodged a bullet due to luck more than anything. Thus I tend to follow the less risky path.

Dot 4/5.1 fluid is hygroscopic, absorbs moisture and moisture is present in air. I can't recall earlier cars but with my Porsche cars Porsche specified a brake (and clutch) fluid flush/bleed every 2 years. The brake fluid reservoir was vented to atmosphere and thus "breathed" outside air and the brake fluid over time would absorb moisture and moisture in brake hydraulic systems is not good.

Just thinking out loud: Maybe the Dodge cars do not have a vented to air brake fluid reservoir? I need to take a closer look at my Hellcat's brake fluid reservoir.

Not with my cars but over the years I've come upon cars with rotted hydraulic brake lines due to corrosion. Cast iron calibers were also at risk of corrosion. Under normal operation the brakes were fine but come time to change the pads and the pistons were pushed way back into the cylinder where they have not been for some period of time the seals would encounter rust which would compromise the seals.

Moisture in the brake fluid also lowers the brake fluid's boiling temperature. But it is unlikely a car's brakes under normal use would have the brakes get hot enough cause a problem. About the only scenario in which this might be a problem is when driving down a long downgrade and having to use the brakes often to slow the car.

However, the wrong time to wish one had flushed/bled the brakes is when one goes to use the brakes and the pedal goes to the floor.

I admitted that I believed every two years brake (and clutch) fluid flush/bleed was a bit overkill but I did it because in almost every case the factory is the authority. As it turned out the one time I (unknowingly) let the brake fluid go longer I got a first hand exposure to what brake (clutch) fluid past its change by date had on at least the clutch's operation.

Besides that I also note 15 years and 317K miles and 14 years and 161K miles on my Boxster brakes and my Turbo brakes and not one brake system (or clutch system) component failure. Not one bad brake line, caliper, or master cylinder problem.

So, if I had my doubts before I do not now. That every 2 years brake (and clutch fluid: and I note in the Dodge (at least in my Hellcat owners manual) the clutch hydraulic system is fed by a segregated volume of fluid within the brake system master cylinder reservoir which depending upon just how segregated the two fluid volumes are) fluid flush/bleed is a good thing and one I intend to follow with my Hellcat (and my JCW).
 

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About the only scenario in which this might be a problem is when driving down a long downgrade and having to use the brakes often to slow the car.
Not saying that changing the fluid is a bad thing, but what is would be to have to use the brakes often to slow the car down on a long downgrade.

Unless we're talking about loaded tractor trailers, or pickups towing something heavy, the gears are generally sufficient for maintaining speed.
Or at least I have never been in a situation when they weren't. But then I don't usually coast down hills, either.
 

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Bosch fluid, better then them all.
 

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Bosch fluid, better then them all.
Unless it's a Girling system, like in many Jeeps and Brittsh cars, in which case Castrol seems to be the only one that works well.
Not that I've tried Bosch.
 

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  • high compatibility. Use with or direct replacement for DOT 3, DOT 4, and DOT 5.1
  • Extended Service Interval (ESI): Lasts 100% longer than DOT 3, 50% longer than DOT 4, and 10% longer than DOT 5.1
  • Exceeds all DOT 3, DOT 4, and DOT 5.1 standards
  • Wet boiling point ~ 365 DegreeF/Viscosity at -40 DegreeC ~ 670mm2/s
  • Standard brake fluid has a recommended change interval of 2 years. The recommended change interval for Bosch ESI6 is 3 years.
 

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Bosch fluid, better then them all.
I tried the Bosch fluid that's supposed to replace the DOT 3.0 thru 5.1 and it was terrible. Pedal travel was mushy and unacceptably responsive. Had it flushed and filled back to Motul 5.1 two days later. Night and day difference. Will be staying with what I know works from now on.
 

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I tried the Bosch fluid that's supposed to replace the DOT 3.0 thru 5.1 and it was terrible. Pedal travel was mushy and unacceptably responsive. Had it flushed and filled back to Motul 5.1 two days later. Night and day difference. Will be staying with what I know works from now on.
That's a bit odd. I thought that most any fluid is incompressible.
 

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Not saying that changing the fluid is a bad thing, but what is would be to have to use the brakes often to slow the car down on a long downgrade.

Unless we're talking about loaded tractor trailers, or pickups towing something heavy, the gears are generally sufficient for maintaining speed.
Or at least I have never been in a situation when they weren't. But then I don't usually coast down hills, either.
There are some areas where the hills are few and far between and not steep.

(Even so in some cases there can be some real doozies. Where I worked just north of Grain Valley MO one county road heading west from the office had some hills.... Oh my! One in particular as one topped the crest looked like one was going to drive over a cliff edge. Their only saving grace was they were not that long. Steep as all get out but not that long.)

Often -- this with cars other than my Hellcat -- I have been on a number of roads -- mostly freeways -- where the downgrade was steep enough the car gained speed even in gear and with my foot off the pedal. Gained speed to the point I've had to touch the brakes at intervals to slow the car. This is in a fairly light car: My Turbo for instance which weighed in around 3400lbs.

The alternative would be to before the need arises downshift to a lower gear than 6th gear. 5th gear or even 4th gear to have the engine develop enough engine braking to keep the car from gaining speed. This is a bit of a bother as the speed limit is often 75mph and to leave the relatively low engine RPM realm of 6th gear to 5th or even 4th is a harsh change.

With the Hellcat 8th gear offers little braking benefit that even on the downgrade I encounter to and from work without a touch of the brakes every once in a while the car would gain too much speed. So it would be 7th gear or even 6th. There are some pretty severe downgrades on for instance CA 58 highway on either side of the crest/summit. Also, on I-40 between Barstow and Needles there are some pretty good downgrades. Yet another section is on I-40 west of Flagstaff. It seems like that nearly entire 140 miles between Flagstaff and Kingman is one big old down hill section. It is a nice drive, though.
 

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The alternative would be to before the need arises downshift to a lower gear than 6th gear. 5th gear or even 4th gear to have the engine develop enough engine braking to keep the car from gaining speed. This is a bit of a bother as the speed limit is often 75mph and to leave the relatively low engine RPM realm of 6th gear to 5th or even 4th is a harsh change.

With the Hellcat 8th gear offers little braking benefit that even on the downgrade I encounter to and from work without a touch of the brakes every once in a while the car would gain too much speed. So it would be 7th gear or even 6th. There are some pretty severe downgrades on for instance CA 58 highway on either side of the crest/summit. Also, on I-40 between Barstow and Needles there are some pretty good downgrades. Yet another section is on I-40 west of Flagstaff. It seems like that nearly entire 140 miles between Flagstaff and Kingman is one big old down hill section.
The idea with heavy vehicles (think tractor trailer) is indeed to be in the correct gear before starting the decent. That's because it can be tricky or impossible to convince the non-syncro trans to engage the correct gear once going too fast.
In something like a Challenger, grabbing the right gear for the downhill is about as easy as it gets. Even after having reached higher speeds.

Is it a bother to downshift? I suppose for some it can be, but I happily keep my vehicles in the correct gear for the situation, just like you're supposed to when driving, anything.

By the way, I'm painfully familiar with the I-40 hills, having driven that stretch an awful lot. Yet, that's fairly flat compared to some of the stuff we have here in the Rockies.
 

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The idea with heavy vehicles (think tractor trailer) is indeed to be in the correct gear before starting the decent. That's because it can be tricky or impossible to convince the non-syncro trans to engage the correct gear once going too fast.
In something like a Challenger, grabbing the right gear for the downhill is about as easy as it gets. Even after having reached higher speeds.

Is it a bother to downshift? I suppose for some it can be, but I happily keep my vehicles in the correct gear for the situation, just like you're supposed to when driving, anything.

By the way, I'm painfully familiar with the I-40 hills, having driven that stretch an awful lot. Yet, that's fairly flat compared to some of the stuff we have here in the Rockies.
Most familiar with I-40 having driven it a number of times. Less often did I take I-80 or I-70. While I can't recall any specific sections I'm sure there are some steep down and up grades. And on roads other than freeways no doubt plenty of steep grades.

I do recall one time on I guess it would be I-80 in Wyoming -- in my Mustang -- being pulled over for speeding. I was going 80mph but the car was coasting in gear, down a particularly steep section of highway. 'course over the speed limit is over the speed limit no matter how it happened but the trooper took pity on me I guess and let me off with a warning.

Yesterday in the Hellcat on the way home I was on a downgrade and had the Hellcat in 8th gear with my foot off the gas pedal. It took a while but the speed dropped from 75mph to 72mph in around a 2 mile in gear closed throttle coast down the grade. In my Turbo or Boxster the car would have gained speed. Do not recall what the behavior of the JCW is. I seldom coast in that car but prefer to keep applying the whip.
 

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And on roads other than freeways no doubt plenty of steep grades.
Yes, and those are the ones I generally frequent. And with most everything I drive the speed can be kept to my liking by simply downshifting.

Of course, that doesn't mean I don't come into a corner too hot on occasion and have to use the brakes for a second or so.
Still, to me gears are for maintaining speed, brakes are for when I screw up - or need to come to a complete stop.

And maybe it's because of having driven many hundreds of miles without any brakes that I generally drive as if I don't have any?
 

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To support this point - all fluids degrade over time due to stressors (heat, pressure, oxygen, contamination) from a fluid dynamics standpoint. Unfortunately, many of us from the golden era of the automobile do not subscribe to this concept, because back then we didn't know what we do now. All fluids degrade over time. You change oil for the same reason that you need to change brake fluid, transmission fluid, differential fluid and power steering fluid.

This is a big reason why I chose to spend a lot of money and buy new this time around - because I don't trust people. Your average car owner is ignorant to many (what should be) common maintenance practices that end up doing wonders to vehicle reliability.

My 07 Charger RT is still running strong, at 212k, with not a single mechanical failure except a fuel pump at 17k (was deemed bad from factory). Not one. Nothing rotted, everything solid. A big part of that, I believe, is fluid maintenance.
 
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