Let us talk about disc brake fluids and some of their details. There are few other types also available apart from the most widely used DOT 3 & 4.

When we talk about high performance vehicles we also think about brakes like Mechanical linked Brakes, Hydraulic Brakes and Air Brakes. This article is completely related to hydraulic disc brake systems which is used in Indian motorcycles. Extensive usage of Disc Brakes in Motorcycle, neglected brake service due to cost of spares, lack of knowledge about servicing and so on.

Disc brake fluids
Pic source – How Stuff Works

The image describes how a disc brake works. You can read about Disc Brakes in detail in our following series..

Lets think about the material we use and get for that. Caliper & master cylinder we get from company is made of aluminum and we use DOT 3 or 4 fluid for activation and so company recommends that too.

DOT 3 and 4 only grades for hydraulic brakes? No, A total of four grades are available DOT 3, 4, 5 and 5.1.

  • DOT 3 or 4 (Glycol Based): Maximum we use these fluids in our motorcycle. Well because we know only about those two grades and we get only these two grades.
  • DOT 5 (Silicone Based): Not widely available. Not suitable for ABS
  • DOT 5.1 (Glycol Based): Not widely available but this fluid has HIGH BOILING POINT and can mix with DOT 3 or 4. So this is the best fluid for our machines.

Servicing of disc brakes?

Well, DOT 3/4 fluids are very high hygroscopic (hygroscopic means they absorb water easily and hold it in suspension). When we apply disc brake at that time it boils at very low temp due to that it expands the internal air which is in heat expansion chamber (this chamber is in the reservoir below the master cylinder cap, and above the max level of fluid).

When air get heats up due to the internal temp it also cools down. As we know when air heats up it becomes steam but after cooling it becomes water. As I told you before about hygroscopic characteristic of fluid means it can mix with water easily. Generally our mechanic says that water is entering from the hole which is given for breathing purpose. But NO, that is not the only reason. Heat, cold & moisture is the reason behind all the mess.

The material which companies generally use for caliper and master cylinder is aluminum or sort of aluminum alloy. Aluminum never gets rusted but it does get affected by water so that shows deposition of oxidation on the surface.

In the master cylinder when fluid mixes with water, it affects the master cylinder body and starts the oxidation reaction. The oxidation will never mix with fluid but floats on the surface or sticks to cylinder wall or it goes to the main track till caliper. And here you feel bad brakes. First brake fluid becomes black due to temperature & operation; secondly oxidation clogs the track. Result: Bad and hard brake lever or no brake at all.

Disc brake fluids

So first of all service the brake system thoroughly and change the brake fluid at once every year. The level given on the master cylinder is not to refill the fluid but that indicates the brakes pads wear and tear. So if the fluid is less, then change the brake pads as soon as possible.

Brake fluid generally does not decrease by itself unless there is any accident or leakage. But at normal usage pads start wearing. You can buy your preferred brake fluid from this long list available on Amazon.

Always check and get cleaned the disc unit from professional and skilled mechanic. Do not try to attempt this at home if you are unknown to any mechanical parts. This article is for awareness only.

– Chinmay Dangre

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37 COMMENTS

  1. pls tell y ma brake stuck every time no one can fined out da reason…..i need the causes..of stuck…its irritating me..pls tell mee

  2. Vivek.
    Brake stucking? Which bike?

    For all the disc.
    1. Check whether the caliper floating foundation is properly greased or not.
    2. Did u change the brake fluid?
    3. Did u check the oxidation in master cylinder?
    4. Did u mix dot3 and Dot4 fluid together?
    5. Did u check the piston assembly after opening?
    6. Did ur mechanic service the disc network ever after placing the complaint?
    7. Did u check your caliper assembly for piston back n forth movement?
    So I want to know all the details so I can properly guide you.
    or you can mail me at macasp@gmail.com

  3. Thanks for your article it was really very informative. At hero honda service center lajpat nagar Delhi. they mix dot 3 and dot4 oil. and my disc brakes are in very bad condition beacuse i think out of 2 pistons one is not fully functional and last time when they replaced the break pads and disc plate they changed the oil in top container but din’t drained out the the grey coloured (all type of mixed oil 🙁 dot3 dot4)mixture from the tube. please help and advice a good Service Center….

  4. Dear Sures.
    The holes are given for ventilation purpose. Whenever rider or driver applies the brake lever or pedal there is a instant activation of disk pads which touches the face of disc and here the friction starts. The friction as you know casues and generate tremendous amount of heat. Due to the heat the efficiency of braking becomes less. And the pads becomes less effective to catch the disc. The best ventilation increases the braking efficiency. So in simple language it is for heat dissipation. Earlier when manufacturer or the maker of disc brake launch the disc system in the market they introduce flat plain discs, these disc where not that much efficient. But today we have most efficient disc so the hole is one of the point which makes efficient braking.

    I hope I have covered all the points. IF you have any doubts then you can ask me more Q’s without any hesitation.

    Thank you.

    • Hi Chinmay i had learnt so many things from your posts Now i want to a ask you about my problem that i facing, recently i observed that when i apply disc brakes of my bike it get Jam the wheel and it took some time to move the wheel and also it creates some noise in disc brakes( caliper) when i apply lever to brake, i had consulted it with my mechanic ,he had changed its pad and oil and was working fine at that time but after a days it creating same problem …….so kindly advice.
      …ThankYou in Advance

  5. Does the caliper assembly have some play in it?

    will it mobe a little bit up and down or is it tight?

    in my bikes case its moves little in the direction of wheel rotation when I apply the break…and it makes little knocking sound..

    another Q…

    are the pads touched to thedisk?

    in my bike’s case even if I travel 1 km the disk heats up so much that the water boils if poured on it…is this right behavior?

    last Q..

    Caliper and disk are sold out as a piar or they can be different?
    eg. can I use a car disk with my bikes brake caliper?

    thanks in advance…

  6. Dear PK,
    1Q. Does the caliper assembly have some play in it?
    Ans. Yes. But not huge. just very little, coz it’s a
    semi-floating caliper.

    2Q. will it mobe a little bit up and down or is it tight?
    Ans. No

    3Q. in my bikes case its moves little in the direction of wheel rotation when I apply the break…and it makes little knocking sound..
    Ans. check the studs which are given for caliper movement if they are worn out or damaged then change it. knocking sound due to over play in studs and caliper secondary foundation.

    4Q. are the pads touched to thedisk?
    Ans. Yes.

    5Q. in my bike’s case even if I travel 1 km the disk heats up so much that the water boils if poured on it…is this right behavior?
    Ans. Wrong behaviour. Check the master cylinder for clogging. the piston is not reversing the system so the pads are holding quiet tightly to the disk. disk should not heat up without applying the brake. if at all the rider applies the brake then only disk heat up.

    6Q.Caliper and disk are sold out as a piar or they can be different?
    Ans. diff.

    7Q. can I use a car disk with my bikes brake caliper?
    Ans. do u really want answer for this?

    thanks for asking Q’s….

  7. Chinmay,
    That was a good read..
    Last weekend I removed the front brake lever and a metal part looking like a slightly long bullet made of some alloy came off with 2 pieces of rusted and broken spring along with a rubber collar. I could’nt make out what and how to get it back. I went to a local mech and he gave me a spring conical in shape. I cleaned the bullet off some sticky leftover spring bits and inserted the new spring.
    But one look at the inside of main unit, something is wrong.
    Everything is rusty and oxidation everywhere. Pressing the bullet into it is not moving anything. its all struck and terrible.
    How do I strip it and do make it grin to a pristine finish.
    Do I need to unplug the banjo bolt at the opposite end.
    Recently I had topped it with castrol universal brake fluid(Red colored) and bleeded a lot to remove all of the old fluid.
    Even now brake power very low and scary. It doesn’t feel like stopping anywhere soon..
    Thank you.

  8. Dear Rayme,
    As per the discription from your end. I feel the master cylinder is gone as well as the psitons assembly. first let me tell you the name of thespares which u ahve opend so far.
    1. bullet = piston assembly
    2. rubber coller = seals
    the oxidation is due to hygroscopic tendency of te fluid and the rust due to the spring part.
    Well after buying new spring if u think it should work then i m sorry to say that it won’. reason :- due to rusty and oxidation, inner surface of bore is now having lot of scar which will leak all the fluid so lack of pressure. secondly when u press the piston assembly in side the bore or the master cylinder i m sure u forgot to block both the ports which are visible from top side. due to that i think u have broken the seal assembly. so lack of pressure.

    Brief:-
    1. lining on bore
    2. broken piston seal
    3. oxidation
    4. rust
    5. clogged fluid pipe.
    all the above reasons are affecting on pressure.

    My direct conclusion over this case is replace the master cylinder kit. due to relay on that spare any more. in future always remember that always change the fluid 4 times in one year or atleast twice in one year.

    Since this is email or blog communication so I may be wrong coz i don’t know the exact condition and situation over there.

    you can send the pic of open master cylinder and related spares at macasp@gmail.com for my inspection.

    Thank you.

  9. Hi Chinmay,

    Thank you very much.

    Disappointingly I couldn’t figure out much of your suggestion. Was wondering, So many parts in a small unit!!
    The rubber collar is a baloon type, may be to prevent dust entering the unit from the open piston held by the round niche on the brake lever. Yea, there is lot of scar in it, but no leakage of fluid through it. Its all very stiff and heavily oxidized white in color and the rust was due to the spring which had disintegrated into bits.
    Where are the other two ports visible from top side. I just tried pushing the piston into the groove whith my thump, I noticed no movement in it. I also applied a drop of oil into the pit to smoothen out.
    I shall sent you some picture of it next week. The brand is Unicorn.
    Meanwhile I tried the carb tuning tutorial. I can’t place a screw driver to open the air screw, all cramed, the frame is obstructing it. I could only move the fuel screw, but very difficult to access the air screw area, I see lot more screws there, lil confused, I will sent you a picture of carb too.

    Thank you.

  10. i wanna kno how to tighten disc front disc brake at home.

    i hav a p150 2005 model, the disc brake play has increased, so now i need to press it almost 40 – 50% of d liver, an if anytime i do it quickly in emergency in a flash bike gets a jerk.
    so i wanna tighten d liver more so that pressing d liver almost 20 – 30% d bike wud slow down an it wud not create that jerk

  11. Hi,
    Whenever I ride my bike and I start appying disc brakes. it becomes harder and harder. Once it became so hard it blocked the front wheel and I fell down. I have a Hunl bought in feb 2009. The mechanics we have here in Delhi for HH are not very good on it. Is castrol bike zone a good option for servicing bike. PLease suggest something on disc brake problem.. Ald also I am planning to replace rear drum brakes with disc brakes. Is that a good decision.

  12. Hey Guyz,
    I want to top up the disc brake fluid of my pulsar 150cc.The user’s guide says only to use a dot3 or dot 4 brake fluid.when i went to buy it,the shopkeeper showed me a 100ml bottle of ‘Castrol Universal Brake Fluid’ and said that it was the same as Dot3 Or Dot 4.But on the bottle it was’nt written anywhere.So i am a bit skeptical on using it,and confused as to what to do.Is it the same thing ,if not what should I do?Also how do I top up the disc brake fluid? Can i do it myself or going to a mechanic is advisable???
    PLease HELP..

  13. Thank you deepak…
    Im very well improving my knowledge over the working parts of a bike through your articles… thank you very much…
    I need to know the working methodology of single cylinder and multi cylinder engines. Eventhough i know the physics behind this, i need to know what principle is employed in this, commercially?
    Thank you…

  14. Hi chinmay,
    I read al yor replies n dat gave me a good knowledge bout disc brakes n eventhough i’ve got a Q for u, the disc pad wid the piston is movable and is the other disc pad movable, if yes, please explain..
    Thanks in advance:)

  15. Dear Chinmay
    i own a honda unicorn 2010 model and i changed my discpads(3 months back) and master cylinder kit(4-5 months back),hose pipe(2 months back)but still there is extra play in disc break lever(pressed to almost 3/4th)… and the breaks are also a bit less effective…….. what is the problem????? HELP!!

  16. A nice info Chinmay…
    I own a cbz xtreme(DDS) which is one yr old till now. I changed its rear disc pads a month before. The brake lever play is good, also the wheels spins freely and oil is also changed. But the braking is so bad that if i use it smoothly it never slows down but if i give a hard pump then the wheel gets locked and i end up skidding.
    What should i do for this??

  17. Hi, great article. I have an enfield 350cc . The disc brakes seem to have gone bad. It just completely frees out on occasions of slow breaking like a brake fail. I took it to the showroom and within 10 sec the meachanic tells me it is a defect and would replacement. The cost…..Rs 4500. I just feel it so unreasonable.

  18. So my question is, is this the right approach. That is changing the whole brake assembly or something can be done to fix / repair it.

  19. Hi,
    i have honda unicorn 2007 model. bike has run 65, 000 kms so far. is it the right time to change the master cyliner. what would be the probable cost?

    regards
    ravz

  20. i have a cbz extream bike which covered 65000 km.i replaced my front disc master cylinder and also done the servicing of disc brake but after that when i applied the brake it becomes tight and tight and disc pads block the disc very tightly.what is the reason..?

  21. My front disc brake of karizma r is jam and i will release some fluid by opening a screw which is outside of disc calipers and now my disc brake didn’t workout… Pls tell me the solution to fix it

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