Sign in to follow this  
Followers 0
dabar

Brake fluid change

47 posts in this topic

Hi,I went to the dealership the other day and they told me that it is time to change my brake fluid. Right now I'm at 40 000Km, they said I should do it now but I can wait until my next B-Service. They told me all of this without even looking at the car. How much does this usually cost? Thanks! :doublethumb:

Share this post


Link to post
Share on other sites

Mine was about $85 or so all in, not too bad.

Share this post


Link to post
Share on other sites

... They told me all of this without even looking at the car...

Yes, it's a scheduled maintenance item when you reach 36,000km.

s m a r t regards,

Bil :sun:

Share this post


Link to post
Share on other sites

I've been thinking of bleeding mine myself, long before 40,000 km, and put in DOT 4 (silicone). I've done my other cars and a motorcycle. At least DOT 4 doesn't take off the paint if you miss when topping up the reservoir.

Share this post


Link to post
Share on other sites

When the dealer did mine, he broke a bleed screw and had to replace a front caliper. Ended up all warranty as replacing a caliper requires you to flush the brake fluid.

Share this post


Link to post
Share on other sites

Dot 4 is not Silicone, Dot 5 is. Here's an article about the perils of changing...

Battle of the DOTs

DOT 3-4 Verses DOT 5. Which brake fluid should I use?

From Oak Okleshen #35 "With regards to the DOT 3-4 verses DOT 5 brake fluid controversy, here is an article sent to me by Mr. Steve Wall. It is one of the most professional treatments I have seen on the subject".

[i had to condense this article from 6 pages to 1 due to space limitations -ed]

Brake Fluid Facts

by Steve Wall

As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:

Fluid compatibility with the brake system rubber, plastic and metal components.

Water absorption and corrosion.

Fluid boiling point and other physical characteristics.

Brake system contamination and sludging.

Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.

First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry.

Fluid Compatibility

Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.

Water absorption and corrosion

The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.

Fluid boiling point

DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.

DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.

With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.

Brake system contamination

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

New developments

Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage.

--------------------------------------------------------------------------------

Share this post


Link to post
Share on other sites

I've been thinking of bleeding mine myself, long before 40,000 km, and put in silicone.

:tremble: don't, you'll damage the car.You cannot properly bleed the smart yourself, only what is in the pipes and tank.Smart use the Star machine to open the ABS pump and pulse it to clear the fluids, even then it won't be clean enough to add silicone.

Share this post


Link to post
Share on other sites

When I recently did my brake job...I had to bleed about 5ml from each side to get the piston back into place.I did not top up because the fluid level was still where it should be...Did I damage my car/brakes by opening that bleed screw?Eddie

Share this post


Link to post
Share on other sites

No, that should be OK. No air can get in if you do it carefully, as I'm sure you and Derek did.

Share this post


Link to post
Share on other sites

When you fit new pads you usually have to lower the fluid level a bit - the new pads are thicker so the pistons don't go out so far - hence less volume in them. It is not a bad idea to give your bleeders a love tweak now and again to keep them from freezing in - procedure is to have some one apply a bit of pressure to the pedal to keep some pressure on the line. If you are bleeding - you let fluid come out to displace the air - refilling the master cylinder. Usually the bleeder is low in the circuit as well - helps flush crud out. If you do this - insert disclaimer here - harm death - bring the video camera - make sure you know what you are doing - tighten them well - wipe them off first - don't strip or break the bleeder.Some cars are real @#$%& - you have to either pressure bleed (put a pressure feed on the master cylinder or vacuum bleed (draw vacuum to bring the air out) them. I'm hoping the smart is not one of those. Some cars had an issue with the pressure switch (i.e. there is a switch - if one part of the circuit has less pressure (leak) then the other it comes on) - getting them to reset could be fun too.The new DOT 5.1 is of interest - but only if you are racing or towing - the smart is pretty well braked so normal DOT 3 or 4 should be more than fine. Looked into Silicone when it first camed out - more issues than it was worth - plus with DOT 3 or 4 - you can change the fluid a couple of times for the same cost.Cheers,Cameron

Share this post


Link to post
Share on other sites

Whenever I've changed pads, I've never had to drain off any fluid, but only because I had not topped it up as the pads wore.....Ideally the bleed screws should be at a high point in the caliper, to encourage bubbles to get out. I'm not sure where the smart's are....But that's less of a concern with power bleeding equipment. Bleeding by pumping the brake pedal should be a last resort, as it often leads to master cylinder seal failure, especially in higher km cars.

Share this post


Link to post
Share on other sites

Hi Mike - I meant lower in relation to most of the other components.The trick to bleeding brakes without issues is gentle pressure - if you stomp them like a mad kangaroo - expect issues - you can also get a bleeder bottle to do it one handed - or a little vacuum pump - if it fits the bleeders. Done it litterally a hundred times with out any issues.If the MC is that close to failing - best do it too - 'cause in an emergency you tend not to moderate your effort on the brake.Cheers,Cameron

Share this post


Link to post
Share on other sites

I use a power bleeder myself, but if you have to pump the pedal because you don't have one of these, only use the range of travel that the pedal normally would move in.Going beyond that can rip the seal to shreds. The cylinder bore is polished where the normal range of piston/seal travel is, but it can be corroded beyond. So a perfectly good seal that could last another decade in normal use can be ruined by pushing the pedal in too far when purging the brake fluid.

Share this post


Link to post
Share on other sites

I did not have Derek on hand as this was on the Sunday when I finally got that gator socket to remove the E18 bolts...What I did was keep pressure on the piston, then opened the screw a touch with my pocket gerber...As a tiny amount of fluid came out... I was able to squeeze the piston back into place. Closed the screw, then used the backing plate of the pad to get it the rest of the way.Eddie

Share this post


Link to post
Share on other sites

Should be good.

Share this post


Link to post
Share on other sites

When changing pads, just open the brake fluid tank by removing the cap and push the caliper piston in by hand, that way you don't have to bleed any fluid.

Share this post


Link to post
Share on other sites

Nope, brake fluid doesn't retain a great deal of moisture thesedays, not as bad as it used to, just undoing the cap, pressing the caliper piston in and tighten the lid on again won't introduce any water at all.

Share this post


Link to post
Share on other sites

I was referring to giving the bleeders a occasional opening - not about retracting the pads for doing the bleeding thing. The salt they use on the roads in places here does wonders to ensure parts act as one. Opening the bleeder once in a while rather than after several years - keeps them so you can open them when you have to. C Clamp and a stickof wood work good if the caliper is less than friendly (or truck sized). Mainly the storage of brake fluid Eddie that causes moisture issues - only buy quantities that you will use within a short while (i.e. a year or so) and make sure the lid is on tight.Cheers,Cameron

Share this post


Link to post
Share on other sites

I agree that changing brake fluid on a regular schedule is a good idea.Nowhere in my '06 warranty booklet(checked "additional work") or owners manual does it state anything about changing it.Bill,where did you find the recommended frequency of 36,000kms? Is there also a time component or just mileage? Just curious.

Share this post


Link to post
Share on other sites

Check the back section of the service manual...there's a section about extra work to be done on the A/B services and at what interval.Eddie

Share this post


Link to post
Share on other sites

Hey Eddie! Actually there's nothing in that section. Already checked. They talk about fuel filter, antifreeze intervals but nothing on brake fluid. You've got an '06 too. If you find that info let me know.

Share this post


Link to post
Share on other sites

What I have always been told on Mercedes was change fluid every two years. I did mine at 75K as that was where I was at 2 years old.

Share this post


Link to post
Share on other sites

If you look on the last page of the "Service Sheet for smart fortwo coupe/cabriolet" under "every 2 years" it says

Replace brake fluid

Roy

Share this post


Link to post
Share on other sites

I was referring to giving the bleeders a occasional opening

Oh ok, sorry.Just opening the bleed nipples is a bad idea. Although it is a good idea to open them once a year to stop them seizing up.Best idead is to pump the foot pedal until it's solid, hold the pressure on it while someone opens the nipple.As soon as your foot touches the floor get them to close the nipple BEFORE raising your foot again.Repeat with the other 3.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0

    Chatbox
    You don't have permission to chat.
    Load More