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Old 23rd August 2018, 19:40   #1
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Default Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

Here is a D-I-Y of cleaning / replacing the front disc brake master cylinder components of my bike.

Model : Yamaha Gladiator
Mfg. Year : 2006
Odo reading : 57000+ kms

Caution :

1. Some of the parts are delicate. Carefully handle them. What started out as a small cleaning job turned out to be a replacement exercise, because of my carelessness.

2. The nuts and bolts on my bike have a tendency to break, loose thread, bolt heads deform etc. The air bleed screw head got deformed - due to few cycles of tightening and loosening during this exercise, and had to be replaced (Yamaha OE part - cost Rs. 27/-).

3. The old fluid in the rubber hose, caliper and the master cylinder was full of muck, foul smelling and dirty grey (couldn't take any pictures because of pretty dirty fingers!). Since the quantity of fluid was very less, ~50 ml, I dumped it into a drain. Not sure this is the right thing to do. How does one go about disposing off old oils / fluids?

4. The caliper pistons of the Gladiator (KBX - Kalyani Brakes brand; though you can spot the name in 'brembo' in one of the pictures) is housed in a sealed unit which can't be dismantled like some others (the one on Apache for instance, has two screws on the body to enable dismantling of the caliper assembly)

5. Disc brake fluid is hygroscopic. Those with sensitive hands, take care. Use latex gloves. My finger tips looked as if they belonged to a 90 year old - even on the next day morning - after I finished the work

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-18.-hygroscopy.jpg


Sorry about the picture qualities - shot on my mobile and the exercise started late in the evening and was concluded at about 9.30 pm.

Parts required (apart from air bleed screw) -

1. Master Cylinder Kit - Yamaha OE - Rs. 190/-

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-2.-master-cylinder-kit.jpg

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-3.-master-cylinder-kit-items.jpg


2. DOT 3 Brake Fluid - TVS Girling - 250ml - Rs. 85/-

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-17.-master-cylinder-fluid.jpg

3. The only acceptable fluid for internal cleaning is the brake fluid recommended for the system or a "Disk Brake Cleaner" which comes in an aerosol can.

Background :

1. Brake was working fine, but there used be an occasional squeal / screech even with disengaged brake lever (when pushing the bike of its stand); pads were replaced about a year ago and have been used for 2,000+ kms and disc (rotor?) appears to be OK (no deep scouring marks).

2. Front wheel didn't 'feel' as if it was spinning freely.

3. Bike is getting old.

4. Last serviced about six months ago. Instead of leaving some of the jobs to the service station during the next service, planned to get my hands dirty.


Going about it :

1. Remove the rubber cap on air bleed screw on the caliper and attach a plastic tube, so as to let the fluid flow into a plastic bottle. This will prevent spillage and proper collection (and disposal) of the used fluid.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-1.-bleeding.jpg


2. Remove the mirror (eagle eyed readers may notice from the subsequent pictures that the mirror isn't the OE. I prefer the ones Bajaj uses on Discover / Pulsar).


3. Remove the cover of the brake fluid reservoir, loosen the air bleed screw and drain the fluid. Ideally the fluid would flow out smoothly on depressing the brake lever, without removing the cover. However, even after pumping the brake lever several times the fluid outflow was not smooth, and had to remove the cover to check the level of fluid inside.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-4.-master-cylinder.jpg


This picture was towards the end of the job - which is why the fluid is pink and clean!.


4. Once the fluid is completely emptied, remove the bolt at the top end of the hose i.e. the bolt which connects the hose to the master cylinder, which has a brass washer. Take care of this washer (easy to slip and miss) and keep the bolt dust and dirt free, as the brake fluid flows through this bolt. I used WD40 to clean out the bolts, air bleed screw, master cylinder etc. and a little kerosene to clean remaining muck in the cylinder.

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If you look closely, you can see that the plastic window to indicate the fluid level is damaged. Actually, it was a plastic tube initially, which got corroded by the brake fluid (about five years back).

Also, look at the pin-hole near the inlet / outlet for fluid flow, which can get blocked by dirt while undertaking the cleaning exercise. Make sure that the entire cylinder is cleaned thoroughly.


The whole master cylinder assembly costs Rs. 1,100/-. So take adequate care while removing the bolts and cleaning the cylinder.


5. Loosen the two bolts to remove the gear level assembly clamp and the screw + nut for removing the gear lever.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-5.-mirror-holder.jpg

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-6.-brake-lever.jpg


6. Remove the plunger from its bracket - this is the metal thingy with a spring enclosed in a rubber boot. This is part which the gear lever pushes so as to operate the hydraulic circuit and activate the brake.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-7.-brake-plunger.jpg


All the parts disassembled ...... but the toughest and critical part yet to come!

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-9.-components.jpg


7. The tricky part is now to remove the snap ring (circlip). It needs a special tool to aid its fitting / removal - I used forceps and (nose) pliers for removing it. Removing it easy - fitting it back is tough. (In fact, I couldn't use the new one while re-fitting, as it wouldn't snap into place. Finally, gave up and used the old one).

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-8.-assembly-full.jpg

8. Once the snap ring is removed, you can pull out the piston assembly (is it the correct name for this part?) from the master cylinder.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-10.-components-replacement.jpg

Pictures of the old and new side by side. Hard to tell the difference? Well, the one on the left is the old one. I had inadvertently cut one of the sealing rings while trying to dismantle it for cleaning. This part and the spring can be cleaned and re-used. Ensure that the parts are dried before re-assembly - use the brake fluid as a sort of lubricant while re-assembling.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-11.-components-defective.jpg

9. Now that I had a new set, cleaned the master cylinder assembly to remove the accumulated dirt and muck, using WD40 and kerosene. There was still some left, and didn't want to scrape the inside of the reservoir. (Probably have to soak it in kerosene overnight next time?). Dried it using a nice clean cloth and rinsed it out using some brake fluid - poured the fluid while holding the two open holes (for bolt and piston) with my finger. Fitted the rubber washer and cap on the reservoir and gently shook it, still keeping both the holes closed.

Re-assembled the piston.

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-12.-assembly-start.jpg

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-13.-assembly-part.jpg


10. Like I said earlier, re-fixing the snap ring was tough. Once the snap ring is in place, gently test the smooth action of the piston inside the cylinder. You wouldn't want to complete the fitting to find out that the piston wasn't doing its job, do you?!

Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components-14.-circlip.jpg


11. Voila! All that remains to be done is now to fit the entire assembly back by working in reverse order of the above steps.


12. Once the assembly is completely fitted, pour new fluid into the reservoir and close it. Keeping the brake lever depressed, loosen the air bleed screw - whatever fluid was left over in the hose and within the caliper piston unit should flow out. Once the flow stops, tighten the air bleed and then release the brake lever. This is essential to ensure that air isn't sucked inside once again. Repeat the exercise till the fluid flows out cleanly, without any air bubbles. It may take three to four cycles, and needs to be done patiently. Once done, tighten the air bleed screw and put on its rubber cap. Keep an eye on the fluid level in master cylinder during this exercise.

13. In my case, the fluid within the caliper piston assembly was also dirty and I had to remove it (from the fork) to ensure that both the caliper pistons were working smoothly (by activating the brake level while preventing one of the pistons from moving - did this one by one on both of them, to check that they were moving with each action of the brake lever).

14. Fitting completed, spin the wheel to ensure that the brake works smoothly. Else, you may have to bleed the brakes again to expel any trapped air.

15. Left the bike overnight (which is why I preferred to start the work late in the evening) and rechecked the master cylinder next day. There was some drop in the fluid level, which I topped off.

Phew! Writing and editing this thread was more strenuous than the actual job..

Hope I have done justice to both -D

Last edited by Samurai : 30th August 2018 at 13:04. Reason: point 3 changed as requested
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Old 28th August 2018, 04:24   #2
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Default re: Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

Thread moved from the Assembly Line to the D-I-Y section.
Very informative, thanks for sharing!
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Old 28th August 2018, 12:23   #3
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Default Re: Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

Adding a few thoughts;

Quote:
Originally Posted by vrprabhu View Post
1. Some of the parts are delicate. Carefully handle them. What started out as a small cleaning job turned out to be a replacement exercise, because of my carelessness.
Using the right tools is key, but since I have a tendency to go ape-crap crazy I make sure to stock spare fasteners before going in for the rebuild;

1. The MC Cap screws, you can get a pair for under 10/- from Bajaj Spares, the same cost 100/- per piece when bought from Hero/Honda as the earlier batched were made in Japan and imported to India.

2. Spare Banjo Bolts, a pair costs under 40/- with copper washers included from Bajaj Spares.

3. Caliper Drain Nipple, now this as the name suggests is as sensitive as a nipple, I always get a spare, they come in two sizes and cost under 20/-.

In your case you could get a new Window kit for 30/- from Bajaj Spares, it includes the inspection window, its clip and O ring, which is convenient if you ask me.

Spares for such components are mostly common across motorcycles, hence the chances of compatibility issues are non-existent.

Quote:
2. The nuts and bolts on my bike have a tendency to break, loose thread, bolt heads deform etc. The air bleed screw head got deformed - due to few cycles of tightening and loosening during this exercise, and had to be replaced (Yamaha OE part - cost Rs. 27/-).
I presume you were using a ring spanner or open C spanner, I'd suggest you limit usage to only bleeding and not tightening and undoing with torque as in such cases the fastener causality rate is pretty high. Settle with 'long reach' '6 Point' box spanner sockets, they're fairly cheap, I got a set from Aliexpress a few months ago, they work flawlessly.

Quote:
3. The old fluid in the rubber hose, caliper and the master cylinder was full of muck, foul smelling and dirty grey (couldn't take any pictures because of pretty dirty fingers!). Since the quantity of fluid was very less, ~50 ml, I dumped it into a drain. Not sure this is the right thing to do. How does one go about disposing off old oils / fluids?
Thumb rule of motorcycling is that you change brake fluid (and pads, in my case) once a year irrespective of use, else there'd be gunk build-up which would render your MC and Caliper hard to service.

Quote:
4. The caliper pistons of the Gladiator (KBX - Kalyani Brakes brand; though you can spot the name in 'brembo' in one of the pictures) is housed in a sealed unit which can't be dismantled like some others (the one on Apache for instance, has two screws on the body to enable dismantling of the caliper assembly)
The design is called a 'floating caliper' as it is not hard fastened to forks, you can undo both bolts and pull the caliper and mount off the motorcycle, once off you can slide the mounting bracket off, there are rubber jackets here that you may consider replacing.

In older motorcycles you might need to use a bit of persuasion to get the caliper to slide off the bracket studs, penetrating oils would help.

Quote:
5. Disc brake fluid is hygroscopic. Those with sensitive hands, take care. Use latex gloves. My finger tips looked as if they belonged to a 90 year old - even on the next day morning - after I finished the work
Which is why you should always use a fresh bottle, in spite of me telling innumerous times I have friends that store the remaining fluid to be used the following year or for top-up's.

Speaking of which, topping the brake fluid is a strict 'NO', reduction in fluid quantity means either than the pads have worn or that there is a leak, in which case you should either change the pads along with the fluid or you should change the brake line along with the fluid.

Last edited by ashwinprakas : 28th August 2018 at 12:25.
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Old 28th August 2018, 14:07   #4
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Default Re: Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

Quote:
Originally Posted by ashwinprakas View Post

1. In your case you could get a new Window kit for 30/- from Bajaj Spares, it includes the inspection window, its clip and O ring, which is convenient if you ask me.

2. I presume you were using a ring spanner or open C spanner, I'd suggest you limit usage to only bleeding and not tightening and undoing with torque as in such cases the fastener causality rate is pretty high.

3. Thumb rule of motorcycling is that you change brake fluid (and pads, in my case) once a year irrespective of use, else there'd be gunk build-up which would render your MC and Caliper hard to service.

4. The design is called a 'floating caliper' as it is not hard fastened to forks, you can undo both bolts and pull the caliper and mount off the motorcycle, once off you can slide the mounting bracket off, there are rubber jackets here that you may consider replacing.

5. Speaking of which, topping the brake fluid is a strict 'NO', reduction in fluid quantity means either than the pads have worn or that there is a leak, in which case you should either change the pads along with the fluid or you should change the brake line along with the fluid.
Thanks.

1. Will try this and update the status here.

2. I used the socket type tool. The problem was the air bleed screw was slightly rusted, and may be that hastened the damage.

3. I do change the brake pads - depending on the kms run and not an annual basis (hardly runs about 3000 kms a year now). But I am not sure whether the service centre really replaces the entire fluid, even though they charge for it :-(

4. I will try this. Since the mounting bracket was sitting snug, didn't want to fix what ain't broken! I presume that once I remove the bracket, I will be able to clean the caliper bolts and replace the rubber jackets as well?

5. You are right. But, in my case, apart from the slight brake pad wear, the calipers had to be forced back during the re-fitting. Hence, definitely there would be some air in the system, which would have slowly escaped into the reservoir. Touch wood, there are no problems and the brakes are working fine. (Did a 100 kms round trip on Sunday - action was smooth and no squeals at all)
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Old 29th August 2018, 20:08   #5
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Default Re: Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

Quote:
Originally Posted by vrprabhu View Post
3. I do change the brake pads - depending on the kms run and not an annual basis (hardly runs about 3000 kms a year now). But I am not sure whether the service centre really replaces the entire fluid, even though they charge for it :-(
From my experience at the service centers at Kollam, Bajaj does it the right way, Hero and Honda do blasphemy by soaking the MC dry and pouring in new fluid , Yamaha is in a way better because they don't do it at all.

The more you depend on service centers the more likely you are to take the DIY route, because some of their practices are outright unethical.

Quote:
4. I will try this. Since the mounting bracket was sitting snug, didn't want to fix what ain't broken! I presume that once I remove the bracket, I will be able to clean the caliper bolts and replace the rubber jackets as well?
Yes you can, it is recommended to use copper grease on the studs before sliding the caliper back in place.
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Old 29th August 2018, 23:22   #6
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Default Re: Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

A few thoughts, if I may:

First, if one squeezes the brake lever and the brake operates to stop the wheels rotation and, if releasing the brake lever that applies the brakes allows the wheel to turn freely, there is usually nothing wrong with the master cylinder. A slight "drag" on the brake disk that you can hear but it doesn't seem to be restricting the wheel rotation is normal.

It is a good idea however to lightly squeeze the brake lever that actuates the master cylinder and hold it for 20-40 seconds. If it slowly moves because the pressure seems to become less, the master cylinder has an internal leak. This is usually because one of the rubber piston seals has worn.

If the master cylinder shows no signs of an internal leak and it applies and releases the brake as it should, leave it alone.
The old adage, "If it ain't broke, don't fix it." applies.

The master cylinder has nothing to do with sounds coming from the disk or drum, like the brakes squealing.

If the brakes feel "spongy" or squishy when the lever is pulled it is almost always due to air which has somehow gotten inside the brake system.
This does not require repair to the master cylinder.
It does require fully bleeding the brake system to remove the trapped air.

_______________
Washing dirt and grime off of the outside of the master cylinder with kerosene or other petroleum solvents is fine however they should not be used for cleaning any part of the interior of the master cylinder or the wheel cylinders.
The only acceptable fluids for doing this internal cleaning is the brake fluid recommended for the system or a "Disk Brake Cleaner" which comes in an aerosol can.
Use the clean brake fluid to wash away any accumulated dirt or deposits inside the master cylinder.

This Disk Brake Cleaner is also the only type of cleaner I recommend for removing oils or brake fluid from the brake disk or brake pads.
It does not attack the rubber parts like many petroleum fluids do and it will not harm painted surfaces.

Speaking of painted surfaces, Dot 3, Dot 4 and Dot 5.1 ALL will eat paint like it's candy.
Go to whatever lengths it takes to make sure these fluids do not get on painted surfaces.

______________

Bleeding old fluid out of the master cylinder and replacing it with new fluid at least once a year is a good idea.
When doing this pay attention to vrprabhu's caution about closing the wheel cylinder bleed valve before releasing the squeeze on the master cylinders brake lever.
Please note: The bleed valve takes very little torque to close it tightly. Do NOT apply a lot of force when you tighten this valve.

Another tip about bleeding the wheel cylinder.
Place a snug fitting rubber tube on the bleed valve and place the lower end of it in a jar which is partially filled with brake fluid. Make sure the lower end of the tube is below the fluid in the jar.
Doing this will eliminate the possibility of air accidentally being sucked back up thru the bleed valve and into the brake system.

________________

ABS brakes use a special control valve assembly to control the brakes.
These usually have a number of complex passages inside of them and if air happens to get inside it can be difficult to remove with normal bleeding methods.
Some of these ABS systems have complicated methods that must be used to get all of the air out of the system.
My suggestion is, if your motorcycle or car has a ABS system, it is best to take it to a dealer or someone that specializes in ABS systems to get it repaired.

Last edited by ArizonaJim : 29th August 2018 at 23:24.
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Old 30th August 2018, 12:39   #7
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Default Re: Motorcycle DIY: Cleaning / Replacing the Disc Brake Master Cylinder Components

Quote:
Originally Posted by ArizonaJim View Post
A few thoughts, if I may:

1. A slight "drag" on the brake disk that you can hear but it doesn't seem to be restricting the wheel rotation is normal.

If the master cylinder shows no signs of an internal leak and it applies and releases the brake as it should, leave it alone.
The old adage, "If it ain't broke, don't fix it." applies.

The master cylinder has nothing to do with sounds coming from the disk or drum, like the brakes squealing.
_______________

2. .. kerosene or other petroleum solvents is fine however they should not be used for cleaning any part of the interior of the master cylinder or the wheel cylinders.

Go to whatever lengths it takes to make sure these fluids do not get on painted surfaces.

______________

3. Another tip about bleeding the wheel cylinder.
.. make sure the lower end of the tube is below the fluid in the jar.
You are absolutely right and thanks very much!

Let me elaborate on the above three points (i.e. my experience) -

1. There was a slight drag. But, the wheel was spinning smoothly. The brakes were functioning fine. In fact, the brake action is pretty sharp (the front forks dive quite a bit when applied fully, and this usually results in the 'T' joint bearing taking a beating - have replaced that bearing four times, almost every alternate year after the original one gave up in the fourth year of ownership. I have heard this complaint frequently from Gladiator owners. Probably some design flaw, I guess. Going off topic, let us have a discussion on that separately)

Actually, the action of brake lever didn't 'feel' right, as though there was a resistance to (or friction in) the movement of the lever. With the bike parked, I could hear a squishy sound when the brake lever was operated.

Let us say I have a nut tightened on bolt. A well oiled thread will enable the nut to be removed with minimum effort. A rusted nut will need quite a bit of force to unbolt. Any situation in between the two, will need a little effort. This was the position of the brake lever.

And, like ashwinprakas has posted above, I was not sure whether the brake fluid was really replaced in the last couple of services...... hence, this exercise.

BTW, I too agree with the 'don't fix what ain't broken' adage, but when it comes to me, hindsight is an exact science and probably I am a fool who is yet to learn from his previous misdemeanours!


2. Absolutely right. But I had to make do, and since I had to carry out the fluid refilling and bleeding exercise completely after refitting the brake (almost two cycles of filling the fluid and bleeding), it would have flushed the master cylinder clean (now, in hindsight, may be after a month or so, will reopen the reservoir to check what condition the fluid is in :-) )


3. Now that is common sense and proves what I said (about myself) in para 1 above right But I think this needs to be added in the opening post, and will request mods to edit it appropriately.
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