[Motard_Blr]

Some background
My Pulsar 200 NS was overdue for service and maintenance due to me being but with work. I use my bike for my commute to work because of which I had not found the time for maintenance. The lack of time was only one reason. The other was that I was unhappy with Bajaj dealer service because of inflated bills and slow work. The service bills always seemed to be 2000+ and the job always seemed to take 2 days or more. The alternative was finding a local mechanic. I have got some small jobs done in the past from a nearby mechanic and I had seen the low quality of his work. So I finally decided that I would service the bike myself. The day for the job finally came recently when I had the weekend to myself.

I had planned on doing only the basics: flush and bleed both the brakes, replace the air filter, clean the carburettor, clean and lubricate the chain, clean the spark plug, and replace the clutch and accelerator cables. I managed to finish the jobs over the course of 2 days since I couldn't spend 1 full day to finish all the jobs.

I wanted to share my experience of brake flushing and bleeding because of trickiness of the task. The other jobs are relatively straight forward since it's mainly cleaning and replacing.

Tools used:
50 ml or preferable larger syringe (from a medical shop or pharmacy)
PVC tubing to fit the brake bleeding nipple tightly (from a hardware shop)
Thin steel wire or cable ties to clamp the PVC tube (from a hardware shop)
Spanners
Screw drivers
Clean cotton rags

Consumables used:
DOT 4 brake fluid from a sealed container. Expect to need at least 50 ml for a single brake caliper so buy at least 100 ml.
WD40 spray

The standard method of brake bleeding
The standard method involves keeping the brake lever pressed and opening the bleed screw to relieve pressure, re-tightening it and then repeating the process until the brake lever feels firm.
I learnt a few years ago that this procedure does not work while trying to bleed the brake on my previous bike, a Yamaha FZ16. I spent almost an hour trying and finally gave up and took the bike to a mechanic!
Some research told me that in most small bikes the master cylinder is too small to push enough fluid through the system with each stroke to really move an air bubble.

The reverse bleeding method
Reverse bleeding involves pushing fluid from the brake caliper to the master cylinder with a syringe.

The advantages of reverse bleeding
1. Air is less dense than brake fluid. Pushing fluid from the bottom of the system (the brake caliper) to the top (the master cylinder) works with the tendency of air bubbles to move upwards rather than fight it as with the conventional method.

2. Fluid is pumped through much faster since the syringe is much larger than the master cylinder. This makes it more likely that air moves along with the fluid and not just sit on the side of the fluid path. The faster flow also ensures that old fluid is flushed out

3. The system is pressurised during the process so air cannot enter accidentally.


The disadvantages of reverse bleeding
There might still be some air bubbles trapped in a dead zone of the caliper where the fluid do not really flow.


The process:
This video explains the process very well and this is what I used to learn how to do it.

https://www.youtube.com/watch?v=6UCNWfA7dVs

Some tips based on my experience

Tip 1: Remove all air bubbles before bleeding!
There was air in the tube so this had to be removed by pushing it towards the top of the syringe. This was done by tapping the tube for several minutes until all the trapped air moved upwards. I found that there were several small bubbles near the tip of the syringe where the tube connected to it. This required quite a bit of tapping to persuade them to move. This process of removing all the air in the tube requires patience and there are not shortcuts.

Tip 2: Keep an eye on the master cylinder while reverse bleeding to prevent overflowing!
The empty master cylinder will be filled up with fluid from the caliper so be sure to keep checking the fluid level.
The master cylinder can be emptied using a second clean syringe or a clean rag to soak up the fluid.

Tip 3: The brake bleeder valve/screw might be rusted. Clean it before getting started.
Spray WD40 or a good penetrant spray to free it up. Remove rust by rubbing with fine (120 or 160 grade) emery paper. Don't forget to clean the centre hole. To make sure that dirt in the centre hole is removed, hold the brake lever pressed and open the bleeder screw and then retighten the screw after the brake lever stops. This will cause the fluid to come out and push out the dirt. Do this a few times. The dirty fluid can be soaked up with some rags. Don't use the clean tubing and syringe as that would contaminate them.

Tip 4: While pushing in fresh fluid, don't open the bleed screw too much or press the syringe plunger too hard.
With pressure from the syringe, if the bleed screw is open too much, the fluid will leak out from the threads. So open the screw about 1/8 or 1/6 of a turn.
Excessive pressure on the syringe plunger can also make the fluid shoot out of the port in the master cylinder! So press the syringe plunger only as hard as required.
Excessive pressure on the syringe plunger can also make the tube slip off the ends!

Tip 5: You will have to stop in the middle to remove more dirty fluid from the master cylinder.
Be sure to close the bleed screw while you continue pressing the syringe plunger to ensure that the system is always pressurised.

Tip 6: Reverse brake bleeding may not be enough!
You might be wondering why I spent all this time explaining reverse brake bleeding only to say that it might not be enough. The reason is that there might be some air bubbles inside the brake caliper that might not get dislodged during reverse bleeding. How do I know this? Because even after reverse bleeding I was not entirely happy with the feel of the brake lever. It was a big improvement over the feel before bleeding but I knew that it was not how it should be. So what was the solution? Vacuum brake bleeding.

What is vacuum brake bleeding?
It is basically the opposite of reverse brake bleeding. Brake fluid is sucked from the bleed screw instead of being pushed through it.

What are its advantages?
Stubborn air bubbles in the brake caliper can be removed from the system as vacuum is more likely to dislogde air bubbles than positive pressure.


This method is also faster than the conventional brake lever pumping method.

What are its disadvantages?
The fluid moves from the master cylinder towards the brake caliper and this fights the tendency of air to rise inside the brake fluid.

It is not as fast as reverse bleeding because only a limited amount of vacuum can be applied before air starts leaking through the bleed screw threads and between the tube and bleed screw.

Any dirt in the master cylinder will be drawn downwards along with the fluid so flushing is a longer process.


Why not use only vacuum brake bleeding instead of reverse bleeding?
Because of the disadvantages listed above.

The method:
Step 1: Use the same syringe and tube as before. Connect the tube tightly to the syringe with wire or cable tie.

Step 2: Press the syringe plunger all the way in.

Step 3: Connect the tube to the bleeder screw nipple and clamp it with wire or a cable tie.

Step 4: Pull back the syringe plunger to create a vacuum in the tube and check for air leaks. If there are no air leaks, proceed as follows.

Step 5: With one hand pull back the syringe plunger and create a vacuum. With the other hand, loosen the bleeder screw with a spanner. Loosen just enough to see fluid come through. There may be very small air bubbles. If big air bubbles come through this means that outside air is leaking in. If that happens, close the bleeder screw while there is still vacuum in the syringe. Repeat from the vacuum process. If the plunger has moved to the end of the syringe, the tube has to be disconnected from the bleeder screw and the process repeated from step 3.

Step 6: Once the fluid coming through the tube no longer contains any small air bubbles close the bleeder screw.

Step 7: Check the brake lever feel. If there is still some sponginess, repeat the vacuum bleeding process.


Warnings
Brake fluid is not good for health! Use eye protection at least. Also use thin gloves if you have sensitive skin.

Brake fluid is harmful to paint so clean any spilled fluid quickly with soapy water.


Don't over-tighten the brake bleeder screw!

[Motard_Blr]

I must confess that the first post did not have any pictures because it's very hard to take photos while the work is in progress. So today I took some photos with the tools posed as they were during the actual job. My clean hands are proof of a setup and not the actual job!

First step is to check the condition of the fluid in the master cylinder:

In this photo the fluid is clean and you can clearly see the circle at bottom of the fluid reservoir. Old fluid is generally dark and murky.


The main tool: the syringe with the PVC tube attached:

I have used copper wire to clamp the PVC tube to the tip of the syringe. This tube fit wire tightly over the bleeder screw nipple so I did not have to clamp that end with wire.
This is a 60 ml syringe and this size was enough for this bike. If you want to try this method on a larger brake system (on a car or bike with dual callipers) I would suggest a 100 ml syringe.


Fill up the syringe with fresh brake fluid. Remember to use fluid from a sealed container.



The reverse bleeding setup ready to go. Syringe filled with fresh fluid, tube attached to the bleeder screw nipple and spanner in place to loosen the bleeder screw.

At this point in the job, you have to do a thorough check for air bubbles in the tube and syringe. Small bubbles hiding in nooks and crannies such as the small gap between the tube and the tip of the syringe can make the job frustrating. Be patient while tapping the tube to dislodge the bubbles.


Safety warning
Build pressure by pressing the syringe plunger slowly and steadily. This will allow you to check whether there is fluid leakage at the ends of the PVC tube. If the plunger is pressed too hard or too fast the tube can detach from the ends and brake fluid can suddenly squirt out without warning! This is why safety glasses are recommended!

If you must stop the reverse bleeding process in the middle to drain fluid from the master cylinder, remember to keep the syringe elevated above the caliper with the plunger upright to ensure air bubbles don't enter the system.

Don't forget to stop the bleeding process before the plunger pushes the air above the fluid into the caliper!

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The vacuum bleeding setup ready to go: syringe empty of fluid, tube connected to the bleeder screw nipple, plunger pulled back to create a vacuum, and spanner in place to loosen the bleeder screw.

The most important thing in this method is always maintain vacuum during both the opening and closing of the border screw. If you don't, air can get sucked in!

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I managed to do the entire job by myself but an extra pair of hands would have been nice. Do plan accordingly.

For me, the result of this hardwork is a good lever feel with no sponginess. With EBC sintered brake pads, 2 finger braking is possible.

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[saket77]

Good work there! Reverse bleed is the way to go when you open the hydraulic lines completely and empty the caliper, as quite rightly you stated that the stroke from lever is not enough to build us pressure.

However, as an alternative, you may just fill the master cylinder reservoir with fresh brake fluid and keep the bleeder valve open for 10-15 minutes. After this time, the fluid should start dripping out of the bleeder valve, courtesy the Gravity

You may then bleed the system normally.
Anyways, reverse bleeding is good procedure and I see that you have followed that. Good work and good to see such DIYs.


Thanks for sharing.


Regards,
Saket.

[GTO]

Thanks for adding the pictures! Also dropping a link to Saket's related thread (DIY: Complete Master Cylinder & Caliper Rebuild And Reverse Bleeding Motorcycle Brakes).

[Jeroen]

Good job, thanks for sharing, very well detailled step by step approach.

I have used this method on the odd cars now and then. Sometimes, even with pressurised flush system you can not get all air out. So, it’s worthwhile to try it the reverse way.

I am wondering if this reverse flush would still work on bikes/cars with ABS? I will have to try it some time.

Jeroen

[Sutripta]

^^^
If the abs system is powered off, hydraulically it should behave as if it is not there.

Re: reverse bleeding in cars, I have not found it necessary. On the other hand, on a bike, it is almost impossible to bleed normally (ie car like). Though pressurising the reservoir should work. I haven't tried that though.

Regards
Sutripta

[Motard_Blr]

Originally Posted by Jeroen

Good job, thanks for sharing, very well detailled step by step approach.

I have used this method on the odd cars now and then. Sometimes, even with pressurised flush system you can not get all air out. So, it’s worthwhile to try it the reverse way.

I am wondering if this reverse flush would still work on bikes/cars with ABS? I will have to try it some time.

Jeroen

Thank you, Jeroen!

I have no experience with ABS but I have read that reverse bleeding or flushing will work with ABS equipped brakes, too, but only on some systems. A quick search for information will show that some systems even require special electronic tools! Nothing is straightforward! The safest thing to do is to check the manufacturer service manual first.

Originally Posted by Sutripta

^^^
If the abs system is powered off, hydraulically it should behave as if it is not there.

Re: reverse bleeding in cars, I have not found it necessary. On the other hand, on a bike, it is almost impossible to bleed normally (ie car like). Though pressurising the reservoir should work. I haven't tried that though.

Regards
Sutripta

I agree - pressurising the reservoir should work. But you would need an airtight reservoir cover with some sort of fitting to connect a fluid pump.

[Sutripta]

^^^
And that's why I've never tried it!
Wonder if anyone here has?

Regards
Sutripta

[Jeroen]

Originally Posted by Sutripta

^^^
And that's why I've never tried it!
Wonder if anyone here has?

Of course!!

I have a pressurised brake bleeder on the right and a vacuum brake bleeder on the left:



Not sure if these simple sets are available in India.

These pressurised brake bleeder are very simple, but effective. You fill the reservoir with brake fluid. Take the top of the car brake reservoir off and screw the cap from the system on it. Pressurising is done by attaching the pressure line to the spare wheel. It only needs 0,2 bar or so, so you really ought to let some air out of the spare tyre first.

https://www.youtube.com/watch?v=Lz8t6ZkVSQM

We always carry one of these on class car rallies. Works on brakes and on hydraulic clutches.

To complete the story, the vacuum bleeder is technically the best. With the vacuum any tiny air bubbles will come out. The disadvantage it is slower. Both systems can be used single handed. The vacuum one being even more convenient as it has a liquid reservoir that automatically fills the brake reservoir.

[Sutripta]

Originally Posted by Jeroen

Of course!!

Was talking of motorcycles.

Regards
Sutripta