Changing Brake Fluid

[GreaseMonkey]

OK, my reply above was in response to WGB, I posted at the same time as Oscar, but it was not a reply to him.
Re Oscar's remarks;
gravity will work if all you are doing is changing fluid, NOT if there is air trapped.
If you imagine an air bubble in a tangle of bent pipes, it will sit at the highest point, right?
Well the brake fluid can pass below it to the bleed nipple without it moving, so leaving what may feel a better pedal because of the new fluid, but still not 100%.
Regarding DOT numbers, I don't know the specs on DOT 5, but I do know there was an industry wide warning about DOT 4 not being compatible with some recent Japanese seals and could lead to failure in Toyotas.
Yeah, great, let's put DOT 4 in every Toyota we see, sooner they're off the road the better.
Chris

 

[WGB]

Silicon brake fluid is called Dot 5 as far as I know Oscar.

Bill

 

[WGB]

But that doesn't make sense.
Why would there be "a little air trapped in a caliper" such that it needs a lilttle pedal pressure?

Because I paid my way though Uni by working for Ford Motor Company New Zealand for 4 months a year for three years as a brake bleeder on the assembly line before they promoted me to fix the cars no-one else could bleed and that is what I did to get the best pedal (Except I used someone elses wife at the time)

If, as you say it has always worked for you, great, but if you have to change a master cylinder for example, or do get air in the system you may find it is not good enaough.
Chris M.

Same Reply except that if you replace the master cylinder you don't need to worry about the state of the bore so you can safely use full pedal travel.

For the third time I agree that pressure is better but there are other options.

Bill

 

[Lukas]

Thanks for the further discussion all.

That "good fluids come in tin cans" thing sounds a little strange, surely they can make effectively waterproof plastics by now?

Anyway, does anyone have a picture of either a commerical or home-brew pressure bleeder - the part that connects to the master cylinder? I'm wondering how you attach it (and keep it attached and sealed under pressure).

Lukas

 

[GreaseMonkey]

Thanks for the further discussion all.

That "good fluids come in tin cans" thing sounds a little strange, surely they can make effectively waterproof plastics by now?

Anyway, does anyone have a picture of either a commerical or home-brew pressure bleeder - the part that connects to the master cylinder? I'm wondering how you attach it (and keep it attached and sealed under pressure).

Lukas

The one I got has a threaded end on the plastic hose which fits through the reservoir cap supplied, with seals either side sqeezed into place with a nut,
Not sure if my description sounds ok, but it is quite simple and safe.
If interested, email me and I can send a photo by return.
Chris

 

[CraigS]

I use the Motive products bleeder system and must say that it is very easy to use. I have multiple fittings for various master cylinders so it is an easy job to change the fluid annually. I recently did the Tatra and in preparation, wanted to buy a 4lt drum of brake fluid. I checked with Repco ($70), Coventry (now Bursons) $52 and of all places, I bought it as SuperCheap (Castrol) for $34. Pays to shop around.

 

[Styria]

I use the Motive products bleeder system and must say that it is very easy to use. I have multiple fittings for various master cylinders so it is an easy job to change the fluid annually. I recently did the Tatra and in preparation, wanted to buy a 4lt drum of brake fluid. I checked with Repco ($70), Coventry (now Bursons) $52 and of all places, I bought it as SuperCheap (Castrol) for $34. Pays to shop around.

Hi CraigS, that's excellent buying and thanks for the tip - we may have to bestow upon you the title of Finance Master or Purchasing Officer with all the good deals that you are unearthing. As you say, it pays to shop around.

Just have one question regarding the quantity of Brake Fluid that you have bought - I realize that you have a number of cars and you may possibly use the full compliment over a short period of time. However, buying in bulk may not be suitable for everyone as I believe that shelf life of Brake Fluid is limited as it attracts moisture. I am not sure if this is true, but that's what I have always been advised of. I personally prefer to purchase the small either 500cc or 1 litre containers. I have probably used six over a period of three years. Regards Styria

 

[BAR]

Styria is quite right, brake fluid is hydroscopic.

The amount of moisture in brake fluid definitely affects its performance. The big problem is it is absorbs moisture quickly. Over a relatively short period of time brake fluid will absorb moisture from the air. SAE field tests have shown that the average one year old car has 2% moisture in the fluid. A random test of vehicles in the U.S. showed an average water content of 2.6% for vehicles with an average age of 8 years. And 25% of these vehicles had water content greater than 4%.

As water content in brake fluid increases over time, the boiling point decreases. Fluid with a reduced boiling point (or high water content) can create vapor by boiling in the caliper, or wheel cylinder. The result is sudden brake failure. And water in the brake fluid can contribute to corrosion of parts such as steel pistons and ABS modulators.

The end result is even though DOT 3 fluid is "rated" at greater than 401oF, in the typical 3 to 4 year old car with 3 to 4% moisture content, it could boil under 300oF. And if it has got more than 4% moisture, you may as well be running straight water!

Moral: Flush your brake fluid every year or so. But only if you would like it to work well scarcely an inch away from those toasty 500oF rotors on your SHO during a couple of hard stops! Or would you rather have a squishy pedal?

Technical data courtesy of Leica Refractometers. www.leica-ead.com

Silicone brake fluid (DOT 5) should be avoided because it is not compatible with regular brake fluid, it is hard to pour without introducing bubbles and thus results in soft pedal feel, and moisture still gets into your system and will pool in low areas like your calipers and encourage rapid corrosion. STAY AWAY!

That leaves DOT 3 and DOT 4 fluids. These fluids are compatible with each other and may be interchanged or mixed with no ill effects.

Let's look at some popular brake fluids and their boiling points:

Fluid DRY WET
Castrol LMA DOT 3/4 446 311
Ford Heavy Duty DOT 3 550 290
ATE Super Blue Racing 536 392
ATE TYP 200 536 392
Motul Racing 600 585 421
Castrol SRF 590 518
Performance Friction 550 284

One could observe that based upon the above together with the heavy weight of the W116's, Castrol's SRF is the best for the model!

 

[CraigS]

Yes Styria - I do have a few cars to change, and bear in mind that the average car brake system only takes .75 litre of brake fluid. I spoke to a shop that specialises in brakes and they recommend that if sealed, it will be good for 12 - 18 months. Unsealed 6 months. Another thing to consider is that is you recycle the brake fluid that you bleed out, that you don't re-use it for a couple of days to allow the trapped air to dissipate. This is on the assumption that it is fresh brake fluid, not something that has been sitting in the car for a few years.

 

[GreaseMonkey]

Reply to Craig S and Styria; yes, brake fluid can be kept ok in a sealed container. The hydroscopic question only arises if it is exposed to air, and a master cylinder reservoir cap is vented to allow for the push and pull of the fluid in the system.
A reguler brake fluid container with a tightly screwed on top will not have this problem, so shelf life is not so critical.
C.M.

 

[Michel]

Reply to Craig S and Styria; yes, brake fluid can be kept ok in a sealed container. The hydroscopic question only arises if it is exposed to air, and a master cylinder reservoir cap is vented to allow for the push and pull of the fluid in the system.
A reguler brake fluid container with a tightly screwed on top will not have this problem, so shelf life is not so critical.
C.M.

I concur...

 

[GreaseMonkey]

Glad we cleared that one up then.
C.M.