For FMJ vehicles, Chrysler only recommends inspecting the brake fluid – but says nothing about changing it.
DOT 3 is what FMJ cars were built with. DOT 4 is a slightly better fluid than DOT 3 (higher boiling point) but for all practical purposes, DOT 3 and DOT 4 are the same thing. DOT means US Department of Transportation – which is who classified the names/numbers.
If pricing brake fluid and you can find DOT 4 for same price as DOT 3 – get it, otherwise it really doesn’t matter to most of us.
Brake fluid has a high boiling point – but if brakes do get hot, air bubbles will form causing a temporary spongy brake petal and reduced braking pressure until parts cool down. DOT 3 and DOT 4 brake fluid also tends to absorb water moisture from the air – which is why all brake components as well as bottles should be keep airtight.
When brake fluid absorbs water moisture, it lowers the boiling point of fluid down. Here are the boiling points of brake fluid:
DOT 3 new - 400’ F (205’ C). with 3.7% water moisture absorbed – or referred to “wet” – 285’ F (140’ C).
DOT 4 new – 445’ F (230’ C), wet – 310’ F (155’ C).
DOT 5 new – 500’ F (260’ C), wet – 355’ F (180’ C).
DOT 5.1 new – 500’ F (260’ C), wet – 355’ F (180’ C).
This is DOT 4 fluid - but marketed to those who don't know the difference between the two.
A new can of DOT 3 or DOT 4 brake fluid opened and left open can absorb about 10-15% of water out of the air (more so when humid out, less so in Phoenix AZ) which makes the fluid useless – so keep those bottles tight!
A new (unopened) bottle of fluid should last forever.
DOT 3, DOT 4 and DOT 5.1 are all Glycol-based (the same item used in coolant). Also, DOT 3, DOT 4 and DOT 5.1 fluids will eat paint and other metal coatings right off in no time – so be careful not to spill any on a freshly painted car or part!
DOT 5 is Silicon based and it will not damage paint. It will not mix with any other fluid type (not without causing problems). DOT 5 fluid is not to be used with ABS (Anti-lock braking systems) for ABS solenoids/valves will aerate the fluid – which leaves a spongy brake petal. I hadn’t seen anyone add ABS on to an FMJ car . . . yet.
Now getting back to the question about changing brake fluids. Most car manufactures recommend changing brake fluid (depending on brand) every two to three years. The reason why is water moisture absorption (which happens) – but more so the byproduct of “wet” brake fluid boiling. When you get brakes to boiling temperature (which is drastically lower when “wet”) – not only do you have gases (boiled fluid) as well as water moisture in the shape of steam.
What happens when water moisture (steam in this case) when it contacts un-protected steel or iron?
Where is this hot fluid being heated at? (at the brake calipers and wheel cylinders).
Those locations are where RUST (yes, I said that four letter word) happens at. I have taken apart brake calipers where the iron caliper housing was so rusty (internally), it looks like it was used to distribute salt/brine for the Wisconsin street department. The caliper pistons were made of Stainless Steel, which was either highly polished or in some cases, had a layer of chrome on the stainless piston. Even so, rust still happened, so someone came up with the idea of using plastic (phenolic – spelling?) for caliper pistons, thinking it “can’t” rust. Well, guess what: the plastic won’t rust but the iron housing will and can/will lockup up after a while.
Brake wheel cylinders don’t have the froze up problem (as much) but the problem they experience is rust still happens but this time, rust will start to eat away at the rubber hydrolytic cups causing them to leak. Rust can act like a sandpaper and the rubber will lose every time.
A way to check that is to pinch back the rubber boot whenever you have a brake drum off. If nothing comes out – GREAT! If fluid comes out, or if you have a trail of fluid running out before boot was pinched back, then, um, NOT GREAT (insert frown, here).
In my opinion and even though Chrysler says otherwise, I HIGHLY recommend EVERYONE to change brake fluid out every two to three years. Just bleed (correctly) until you see new fluid at each wheel. It doesn’t matter if car gets driven or not. This also applies to any carline (and to motorcycles, etc.) as well.
Even aluminum brake master cylinders are subject to corrosion – but not to the same extent as iron/steel is.
BudW
DOT 3 is what FMJ cars were built with. DOT 4 is a slightly better fluid than DOT 3 (higher boiling point) but for all practical purposes, DOT 3 and DOT 4 are the same thing. DOT means US Department of Transportation – which is who classified the names/numbers.
If pricing brake fluid and you can find DOT 4 for same price as DOT 3 – get it, otherwise it really doesn’t matter to most of us.
Brake fluid has a high boiling point – but if brakes do get hot, air bubbles will form causing a temporary spongy brake petal and reduced braking pressure until parts cool down. DOT 3 and DOT 4 brake fluid also tends to absorb water moisture from the air – which is why all brake components as well as bottles should be keep airtight.
When brake fluid absorbs water moisture, it lowers the boiling point of fluid down. Here are the boiling points of brake fluid:
DOT 3 new - 400’ F (205’ C). with 3.7% water moisture absorbed – or referred to “wet” – 285’ F (140’ C).
DOT 4 new – 445’ F (230’ C), wet – 310’ F (155’ C).
DOT 5 new – 500’ F (260’ C), wet – 355’ F (180’ C).
DOT 5.1 new – 500’ F (260’ C), wet – 355’ F (180’ C).
This is DOT 4 fluid - but marketed to those who don't know the difference between the two.
A new can of DOT 3 or DOT 4 brake fluid opened and left open can absorb about 10-15% of water out of the air (more so when humid out, less so in Phoenix AZ) which makes the fluid useless – so keep those bottles tight!
A new (unopened) bottle of fluid should last forever.
DOT 3, DOT 4 and DOT 5.1 are all Glycol-based (the same item used in coolant). Also, DOT 3, DOT 4 and DOT 5.1 fluids will eat paint and other metal coatings right off in no time – so be careful not to spill any on a freshly painted car or part!
DOT 5 is Silicon based and it will not damage paint. It will not mix with any other fluid type (not without causing problems). DOT 5 fluid is not to be used with ABS (Anti-lock braking systems) for ABS solenoids/valves will aerate the fluid – which leaves a spongy brake petal. I hadn’t seen anyone add ABS on to an FMJ car . . . yet.
Now getting back to the question about changing brake fluids. Most car manufactures recommend changing brake fluid (depending on brand) every two to three years. The reason why is water moisture absorption (which happens) – but more so the byproduct of “wet” brake fluid boiling. When you get brakes to boiling temperature (which is drastically lower when “wet”) – not only do you have gases (boiled fluid) as well as water moisture in the shape of steam.
What happens when water moisture (steam in this case) when it contacts un-protected steel or iron?
Where is this hot fluid being heated at? (at the brake calipers and wheel cylinders).
Those locations are where RUST (yes, I said that four letter word) happens at. I have taken apart brake calipers where the iron caliper housing was so rusty (internally), it looks like it was used to distribute salt/brine for the Wisconsin street department. The caliper pistons were made of Stainless Steel, which was either highly polished or in some cases, had a layer of chrome on the stainless piston. Even so, rust still happened, so someone came up with the idea of using plastic (phenolic – spelling?) for caliper pistons, thinking it “can’t” rust. Well, guess what: the plastic won’t rust but the iron housing will and can/will lockup up after a while.
Brake wheel cylinders don’t have the froze up problem (as much) but the problem they experience is rust still happens but this time, rust will start to eat away at the rubber hydrolytic cups causing them to leak. Rust can act like a sandpaper and the rubber will lose every time.
A way to check that is to pinch back the rubber boot whenever you have a brake drum off. If nothing comes out – GREAT! If fluid comes out, or if you have a trail of fluid running out before boot was pinched back, then, um, NOT GREAT (insert frown, here).
In my opinion and even though Chrysler says otherwise, I HIGHLY recommend EVERYONE to change brake fluid out every two to three years. Just bleed (correctly) until you see new fluid at each wheel. It doesn’t matter if car gets driven or not. This also applies to any carline (and to motorcycles, etc.) as well.
Even aluminum brake master cylinders are subject to corrosion – but not to the same extent as iron/steel is.
BudW
It's something I knew, just sort of forgot over the years. Hey, there's only so much room in the brain and with all the crap you need to know to work on the modern automobile 5 days a week, some of the older info has to be deleted to make room, lol.
