Bleeding brakes question for the brake gurus...

[Pilot]

Some car manufacturers recommend changing the brake fluid periodically, such as every 24-months. I assume that recommendation is made because DOT 3 & 4 brake fluids absorb water which in turn can rust things. But I don't see any recommendation to do so in Toyota's MR2 maintenance or owner's manuals. Any opinions on whether or not it is advisable to change the brake fluid in an MR2 on a periodic basis? t?

[GrandpaGofast]

Can't hurt.
GP

[traintech86]

its not very expensive and it shouldn't take to long so why not?

[Pilot]

I had a mechanic argue with me that bleeding brakes can cause problems in the long run as the new fluid cleans-up the system and leaks can develop. I wonder if that is true...

Besides, who needs good brakes anyway.

[como]

Originally Posted by Pilot

I had a mechanic argue with me that bleeding brakes can cause problems in the long run as the new fluid cleans-up the system and leaks can develop. I wonder if that is true...

Besides, who needs good brakes anyway.


http://www.aa1car.com/library/no_brakes.jpg

on the same argument, new oil cleans up the engine seals and can cause leaks to develop.

[traintech86]

well tbh clean sounds like a good idea to me. if there is a leak, i'd want to know about it and replace it.

[kbrew8991]

If changing your brake fluid causes leaks to develop you needed to fix those parts anyway

Brakes = safety equipment in my mind, so yes, change the fluid with a bit of regularity

[como]

safety equipment is for the birds

[Pilot]

Easy job on the MR2, I generously pre-soaked the bleeders with penetrating oil the day before. The brake fluid looked really bad--you could see the water contamination. I like to think the brake system is happier.

I took a quick look at the clutch hydraulic assist cylinder fluid by using a turkey baster to remove what was in the reservoir--which is also DOT 3--it was even worse, looked like 90W black syrup. Flushed it using basically the BGB procedure, rubber hose over the drain fitting into a cup with some fluid (near the transaxle), assistant would pump clutch pedal 3-times and advise when holding pressure on the pedal, I would loosen bleeder until clutch pedal was reported to be on the floor board, close the bleeder and repeat. It took about 1.5 cups before it was coming through clean. Because the clutch reservoir is so tiny, would refill after every 4 pump/bleed cycles to avoid sucking air into the system. Took about 15-minutes. After seeing the syrup that came out, was definitely worth the few minutes and $2.00 worth of brake fluid.

[mr.ac]

yep, if your brake fluids are black its time for a change. hell if you don't want to do it, take to a shop. $30-40 tops and in about 30 mins tops. Its pretty simple.

[ToyotaTechGeek]

depends on climate. in high-humidity environments, it's wise to change the fluid once the oil begins to darken as most brake fluids are barely golden in colour. there are test strips available to test the fluid for the 'geeks' out there. when changing the fluid, it's wise to use a good fluid like Castrol LMA (which is low moisture activity). also, don't go thinking that buying the huge gallon jug of 'brand x' fluid is great either. technically once the seal is broken on the bottle, the brake fluid is 'contaminated', so buy several of the smaller bottles if you plan to keep some around. i buy the medium sized bottle if i buy off-the-shelf. i usually use the Castrol LMA or Valvoline/Pyroil fluid to flush my lines before i fill with ATE Super Blue or Motul. i recently brought a few small bottles of the AmsOil synthetic (non-silicone) fluid to try in my truck.

[mrclean]

I had a car with 10 year old hydraulic clutch fluid in it. Even though the clutch worked fine, I pulled in fresh fluid just in case. Sure enough, within one drive the new fluid completely destroyed the seals in both the master and slave.

So, if you're planning to bleed a car with really stale fluid, be ready to do all the hydraulic parts too and start completely fresh, otherwise you might just leave it as-is if its working.

[Pilot]

Originally Posted by mrclean

I had a car with 10 year old hydraulic clutch fluid in it. Even though the clutch worked fine, I pulled in fresh fluid just in case. Sure enough, within one drive the new fluid completely destroyed the seals in both the master and slave.

So, if you're planning to bleed a car with really stale fluid, be ready to do all the hydraulic parts too and start completely fresh, otherwise you might just leave it as-is if its working.

I suspect your seals were on the very edge of failure.

For over a decade, my mechanic has claimed it is a bad policy to replace brake fluid--but I have done it on all my old vehicles and have yet to have a problem.

[CJMR2T]

YES, you should change the fluid periodically. I personally change mine once a year. It is recomended for a street car that it be changed every 12,000 to 15,000 miles.

Brake fluid is Hydroscopic thus like you said, it absorbs moisture. The Moisture lowers the boiling point of the fluid. Brake fluid becomes compressable once it contains moisture and or boils which causes a spongy peddle for starters. Whats even worse is that once it becomes compressable, the same peddle effort gives less line pressure and thus less clamping pressure (i.e. less brakes)... This obviously is a safty issue.

DOT 3 fluid typically has a dry boiling point of 370*f, at just 2% moisture content by volume, the boiling point is lowered to about 320*f, and at 3% will bring it down to about 290*f so at just 3% your down 80*f which is significant.

DOT 4 is a bit better because of two aspects, for starters it starts out with a higher dry boiling point (typically about 450*f) and it absorbs moisture at a slower rate which is good. The problem with DOT 4 though is it looses boiling point faster at the same percentage of DOT 3. At 3% moisture content DOT 4 typically below 300*f but the higher dry point and slower absorbsion rate makes if a superior fluid to DOT 3

Any1 who says that changing the fluid is a bad idea should not be working on brake systems and or probably cars for that matter. I have never once had a leak form because of changing the fluid even on cars that i know have never had it changed or not had it changed in many years. Also these "mechanics" should sit down with brake system engineers and try to argue with them. Or even better, contact the NHTSA (National Highway Traffic Safty Administration) and see how many accidents and deaths are out there that have been proven to be cause by sudden brake failure due to boiled brake fluid.

Rust from brake fluid having to much moisture in it is what causes the seals to go out 90% of the time. Under the pressures that the systems typically operate at, sludge build up that would supposedly seal small slits and what not keeps the all sealed as the pressure would blow it out. There is a reason why the o-ring are Square and cut and not round that seal the pistons and I'll bet that anyone who says changing the fluid is a bad thing probably can not tell you the correct two main reason why they are square cut.

For the safty of yourself and other that are either in the car with you and others that are on the same road as you at any given time, change the fluid and bleed the brakes well.

[kbrew8991]

"dot" rating is just a number - for street use you'll be ok shopping that way, but if you aren't you'd better research that brand's boiling point

- KB, Motul 600 user, 595* boiling point

[CJMR2T]

DOT is not just a number it is a direct specification to the minimum dry and wet boiling points of the fluid along with other minimum specification of the particular fluid.

Now yes, you can find higher rated fluids, but they also fall under a higher DOT spec. (i.e. DOT 5)

Side note, do not run regular DOT 5 as it is a silicone based fliud and will give a very spongy peddle as it is compressable. It is not hydroscopic thus will not absorb moisture, but its solely intended for application that very rarely get driven like a high end show car etc... Its to prevernt rusting thus preventing maintance for something that never gets used.

DOT 5.1 is what you want to use if your something with a high boiling point most all your race type fluids fall under DOT 5.1 catagory. All fluids that have a DOT 5.1 rating will have a minimum dry boiling point of 518*f. Again, this is a minimum... Manufactures do make them higher then that but they still fall under the DOT5.1 classification.

If you race, then yes you want to shop by temp specs but you have to watch. A lot DOT5.1 fluids have very fast moisture absorbsion rates thus requiering more frequent change intervals. The best fluid you can by is Castrol SRF (590*f dry and 518*f wet). Even at 3% moisture content it still meet the minimum dry boiling point for a DOT5.1 fluid. No one else even comes close to that. The down fall to that is its EXTREMELY expensicve. It typically runs about $80+ a liter... not cheap...