Replacing clutch, brake fluid

When using a hand vacuum pump to remove the old fluid how does one know if the fluid is removed at the piston/s below the bleed screw? Doesn't the fluid flow follow the most direct route from the reservoir to the bleed screw?

When using the pump how much should the bleed screw be loosened to allow fluid to flow? Does air enter around the bleed screw threads?

Since the bleed screw is far below the reservoir is it possible to introduce air into the system at the bleed screw -- assuming the reservoir opening is always covered with fluid and also that the pump never applies positive pressure?

I don't know.

I just bleed until nasty brown fluid stops coming out. And everything works great after that.

It's that simple.

I use my vacuum pump to evacuate almost all the fluid in the reservoir and wipe it down. I then add clean fluid and use the pump to bleed the system. I will cover the reservoir and pull the lever a couple of times while a vacuum is drawn on the caliper/cylinder. For you first timers: Never squeeze the levers with the reservoir uncovered. It is such a bitch to clean the ceiling and the whole motorcycle before the brake fluid peels off all the paint.

Once the bleed screw is open ¼ to ½ turn it doesn’t make much difference if it opened more, it just lets more air past the threads. Air does enter around the threads. In the end it doesn't matter as long as you close the bleed screw before all the vacuum has bled off. I pump up to max vacuum then close the bleed screw, this also helps to draw the leftover fluid into the bleed jar instead of dribbling all over the place. I've wrapped the threads with Teflon tape and that helps. I've used plumbers putty to seal around the screw and that almost always stops the air infiltration.

Secret weapon #1: Good Wife keeps the reservoir topped off so all I have to do is keep vacuum on the bleed screw. When I cover the reservoir to pump the brakes I have Good Wife hold the cover in place so I don't have to use the screws. There may be an opportunity to start kids on a learning experience here too.

Secret weapon #2: I made my own bleed jar from a glass peanut butter jar with barb fittings and O rings from a hardware store. By seeing the fluid being evacuated you can tell how you are doing. When done, it lets you look in amazement at the collection of water, dirt and debris that you just removed. I’ve drawn max vacuum on the jar many, many times over the years and never imploded it but the metal cover does draw down.

(A surprising set of questions from Mr. Mesh! )

CM,

A gravity bleed for the clutch application works great! Should not need a vacuum assist. Just keep the drain tube over the bleed outlet and close it before your Reservoir gets too low. Re-fill. Pump it up, hold pressure on the lever. Release at drain tube. Repeat until no more air comes out.

WW

SkooterG said:

I don't know.
I just bleed until nasty brown fluid stops coming out. And everything works great after that.

It's that simple.

Click to expand...

Samo - samo here...

Never really thought about air seeping in at the bleed screws - I just keep a vacuum on it until I wrench 'em down.

...and no - I don't torque 'em either, being the "mechanical rebel" that I am...

Oh - I do both front brake calipers at the same time... Multi-tasking!

Constant Mesh said:

Since the bleed screw is far below the reservoir is it possible to introduce air into the system at the bleed screw

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Physics dictate that if bleed screw is below reservoir, no air should enter the system, but that's not always the case. I WOULD NOT bleed any braking/clutch system by gravity alone (just opening the valves without doing anything else). Use vacuum, or preferably, the pedal/levers.

I also recommend always finishing a bleed job with the LEVER/PEDAL after vacuum. Vacuum is a negative pressure, as you know, and it can leave a bit of air after closing the valve. Even just one pedal/lever pump at the end will eliminate any bubbles with positive pressure. I however, don't fully depress the clutch lever first, as you can't feel when pressure is gone. I always put pressure on the lever until I feel resistance (clutch never disengages), then open the bleed valve just enough to allow fluid out as you continue to depress the clutch lever, and close the valve right before you hit the grip. Easier done than said, believe me.

My clutch bleeding procedure is as follows: Start with lever fully depressed, then open valve. I do this twice. This is the best way to get the most fluid out of the slave, but you can't feel when the pressure is gone, so I only do it at the beginning. Then I use vacuum but only on cars, which have a lot more fluid volume. On motorcycles, I can suck air with the reservoirs at half level, so I prefer to work the levers; it's almost as fast anyway. And I finish the job with positive pressure, as described on the pharagraph above.

As for the 'squirting', I always do my brakes/clutch without the covers, and never have a drop leaked, but you have to VERY slowly start depressing the lever until the peep hole is covered. I still put rags around the reservoirs just in case. And DON'T let the reservoir level get too low folks; better safe than sorry.

But I agree with ionbeam you should cover the reservoirs until you're more familiar with the procedure. I also use a 60cc syringe for the job since I always do it by myself.

ALWAYS CHECK YOUR CLUTCH/BRAKES BEFORE OPERATING your motorcycle folks. Give the brakes a strong squeeze, and make sure you have no leaks.

Bleeding brakes on this bike is a piece of cake compared to the servo system on my BMW; it had 11 valves to bleed :blink: .

Hope this helps, and go have some fun .

JC

You can count on getting tiny air bubbles past the threaded bleed nipples.

Don't worry.

If it REALLY bugs you, you can evacuate the entire system, then remove the bleed nipples and using Teflon tape wrap the nipples threads.

That will keep the tiny bubbles from showing.

However brake fluid will attack and eventually erode the tape. The next time you bleed the system you will have to repeat the process. Its a Pain. Do like the others. Bleed until clear. DO NOT pump the levers with the caps off!

OK, a final 'Trick'. Sometimes the levers wont feel real firm, after bleeding. heres a TRICK to use.

After bleeding to the best of your ability, squeeze the lever (with the reservoir full, and cap on), half way and hold it in place with a zip tie or tape. Over nite. In the morning pump the lever and it should pump up hard.

A simple technique for replacing clutch and brake fluid --- vacuum pump not required.

https://www.motorcyclecruiser.com/tech/brak...n/photo_01.html

A simple technique for replacing clutch and brake fluid --- vacuum pump not required.

Click to expand...

But what you wrote in your first post was:

When using a hand vacuum pump to remove the old fluid

Click to expand...

If you asked about simple fluid replacement the answers may have been different. In any case, this thread has presented a range of options. There are many options -- traditional 'pump the levers'; speed bleeders; gravity; vacuum pump, and various combinations.

I just replaced all the brake lines on my 07', with the all the piping and and volume I can't imagine using anything but a good vacuum pump to do the job.

i replaced the brake/clutch fluids this past saturday....i used a vacuum pump i picked up from harbor freight (sale).

the brake fluids looked pretty clear, had just a tint of color. the clutch fluid was very dirty, almost black.

why would the clutch fluid be so dark after 10,000 miles?

Good, detailed vacuum brake bleeding instructions.

https://www.mityvac.com/user_manuals/MV6830.pdf

"During the bleeding process, as brake

fluid is being vacuumed through the bleed

screw, air will also be sucked into the bleed tube

from around the bleed screw threads. This can

give the misconception that air is bleeding from

the lines, however it is normal and does not

indicate a malfunction. To prevent or reduce this

introduction of air, coat the bleed screw threads

with silicone grease prior to bleeding."

A small quantity of silicone grease can be purchased at ACE Hardware and many other vendors.

https://www.acehardware.com/product/index.j...095667&sr=1

One of these 1/2 fl. oz. packages is available at my local ACE for $2.29. This waterproof 450 degF grease is also recommended by Yamaha for greasing the clutch and brake lever pivots.

SkooterG said:

I don't know.
I just bleed until nasty red fluid stops coming out. And everything works great after that. Cuz I pass out. Cheap high.

It's that simple.

Click to expand...

Fixed, as Quality is Job 1!