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-   -   Brake Fluid Replacement - IMPORTANT (https://www.team-bhp.com/forum/technical-stuff/60171-brake-fluid-replacement-important-3.html)

It's not a few minutes exposure. I've seen it kept open for hours.

*bump* getting the brake oil replaced next week. Can someone summarize the difference between DOT 3 and DOT 4 ; why they should not be mixed ? And what exactly do these signify?

On a related note , does anyone suggest the same for power steering fluid ? I simply top up and never recall a 'flush' (if that is even done in this case) ; I would like to read up on how this fluid works ; any precautions/ maintainence car lovers can take with regards to this fluid?

Great post and quite informative too. In all these years I have only topped up the brake fluid in the reservoir. Not sure if MASS did take care of flushing out the old fluid and replenishing it with new fluid though. After going through this thread, I am sure I want to get the fluid changed in the next service that is coming up in a few weeks.

I have the same query on DOT 3 and DOT 4 w.r.t the difference in them. Someone please enlighten.

DOT4 has a higher boiling point than DOT3. You can change from DOT3 to DOT4 since they're miscible and absolutely compatible unlike DOT5.
This was one of my "updates" before the last track day after I had the previous DOT3 fluid boiling during the previos track day.
And the DOT4 worked pretty well on the track. Showed no signs of fluid fade inspite of my late-&-hard braking. (What happened to the EBC pads is a different story :D)
Btw, changing brake fluid isn't like changing engine/transmission oil. Get it done by a very competent, experienced mech.

Thanks for the response, Mahendra. What I would also like to know is - which is better of the two ? DOT 3 or DOT 4 and if so why ? Which one do you suggest that one should go in for, for better braking?

Obviously 4 is better, with its higher boiling point amongst other things. However, for average use, it won't really make a difference. Also, DOT 4 is not easily available.

Use either... mixing is not a good idea.

Hi,

Is there any adverse effect, if the break fluide is above the max. level mark?
If yes, how should I get rid of excess break fluid? Should I use a cloth/ tissue paper to absorb the excess? It's above the filter like cap (which is just below the break fluid container's cap).

Regards,
Dev_Kudle

Tissue paper, no way! :eek:

I'd probably use a syringe, if I were you.

My brake pedal had started touching the floor since yesterday, with very weak braking action (Esteem Vxi). So much so that I suddenly wondered whether I was depressing the clutch by mistake !

A visit to the MASS has revealed a shocker.

Total loss of brake fluid in the reservoir ! There were brake fluid leakage signs near the proportionater valve, as the SA called it.

What was more worrying was the failure of the low brake fluid warning lamp to glow in this condition. The warning lamp is coming on at half ignition position, and faithfully goes off upon firing the engine, even though the brake fluid reservoir is dry !

So that's one more check for us to do while replacing brake fluid, that is, check the proper working of the "low brake oil" sensor display before topping up fresh brake fluid.

Will get the car back tomorrow after a thorough brake system check up.

Though I have been owning car from 1997, I think I have largely depended on what the SA has suggested.

This seem to be a clear miss from my end. Will attend to the brake fluid change during next service.

Thanks a ton !

My dilemma of whether to change the brake fluid now (25k km) or stretch it to 30k kms service has clearly been answered. Going to TASC first thing this weekend to get my brake pads & fluid replaced. Thanks all.

I replaced my wagon R 2007 model LPG DUO brake fluid today at 25950 km for first time . I could not find DOT3 fluid as recommended by the manual and the service station had castrol DOT4 fluid.
So i put DOT4 in the system after having done research on this thread all saying it should be ok.
Also checked elsewhere on the net, everywhere it is said a DOT4 fluid having higher dry and wet boiling point is suitable in a system designed for DOT3 fluid, as the properties of DOT4 exceed that of DOT3.
Chemically also they are similar polyglycol ether-based fluid.
But I remember reading somewhere that the borates used to improve boiling point of the DOT4 fluid can cause the rubber components viz hose, O'rings, seals to deteriorate.
Anybody with experience in long term use of DOT4 brake fluid in a DOT3 brake fluid system please enlighten us and share your experiances.

Norhog, I think that DOT 3 is now difficult to find, while DOt 4 & Dot 5 is the norm today. Of course, Dot 5 does not mix with Dot 4. I have been using Dot 4 since last few years in my car's system and I have had no problems of any oil leakage (which is your concern I guess). The system is drained every 2-2.5 years and new fluid is filled.

MAK DOT-3 HDBF (Heavy Duty Brake Fluid) is very much available in the market, you may go to any lube dealer and pick up a bottle.
However since you have already filled DOT-4, it is not necessary to replace it now.

This is sound advice, vigsom. I will add my experiences.

For cars which are a little older or have covered many thousands of km, it is good practice not to depress the pedal to the floor when bleeding the system or pushing the new fluid down the lines. A small ridge often occurs in the master cylinder around three quarters the way along its bore, the point beyond which the pedal never goes in normal use. Repeatedly pushing the master cylinder's piston and seals past this ridge may cause the seals to fail, the result being a sinking pedal or no brakes. A new or rebuilt master cylinder is the solution if this happens.

So depress the pedal to two thirds or so of its travel when bleeding, it will do the job just the same and help prevent master cylinder failure.

When changing brake pads,I clamp the hose to the caliper then open the bleed nipple before pushing the pistons back into their bores. As well as making it easier to retract the pistons, it also prevents the most contaminated and hard-worked fluid in the calipers and rubber hoses (which allow ingress of moisture) from being pushed further back into the system, maybe into ABS components. Just make sure the reservoir is well topped up before you do this.

It is better to replace the fluid more frequently than not, although the manufacturers' recommendations are sufficient. Brake fluid is an unpleasant mix which is posionous to humans - so avoid skin contact - and especially poisonous to fish, so great care must be taken not to allow it into drains. It is also highly combustible and corrosive. A little copper grease on the bleed nipple threads makes sense to make sure they don't corrode up.

Silicon fluid or DoT5 has very different properties to DoT3 or 4. It cannot dissolve moisture, so corrosion potential is higher if moisture enters the system over time - through rubber hoses, for example. It is also non-compatible with any conventional brake fluid, and will create a gloopy mess if added to a system which has previously contained non silicon-based fluid. It is also more compressible, so needs a different master cylinder bore for it to work as well as other brake fluid. Some racing teams use it because of its high temperature stability, with brake systems designed specifically for it.

DoT4 contains borate esters which improve dry and wet boiling points when new. But the fluid usually loses its properties more rapidly than a good Dot3 fluid. Remember this classification system sets minimum standards - and different brands may vary considerably. Some DoT3 fluids have higher boiling points than some DoT4s, and will degrade more slowly. Dot5.1 is a continuation of DoT3 and 4, and is not silicon-based.

The assumption is that the higher the number or more recent the product, the better it is. This is not necessarily the case. Also be aware that some 'racing' DoT4 fluids may be quite viscous and unsuitable for use in cars with ABS systems.

The fluid is so hygroscopic that moisture can enter it even when in its plastic bottle packaging. Better fluid may be packaged in metal tins.