Brakes still feel a bit meh

[-Cappo-]

I had 2 x K6 and the brakes were immense on those. Are the K7 brakes different?

On other bikes I’ve had a lot of success with tying the lever back - pull it as hard as you possibly can, then pull it a bit more and use a cable tie. A detachable tie is even better as you can release and repeat. Have also used that technique on pesky hydraulic clutches.

[alan36]

Do you leave the MC cap off to do this?

[the cueball]

alan36 said:

Do you leave the MC cap off to do this?

place it over the brake fluid to stop anything dropping in, but don't tighten it down.

[Wildfire]

There was a big recall of the GSX-R MC's a while ago IIRC.

If could be MC. On the racebike, I had no end of issues with the lever feeling a bit soft and pulling back quite far. Stopped etc. I just wasn't happy with the feel. New MC and it was a different bike.

Maybe try a MC seal kit first?

[mikey_b]

ssray said:

Tie the brake lever back overnight, it allows tiny bubbles to escape

How? Pulling the lever back pushes the piston in the master cylinder into the barrel, sealing off any escape route for bubbles into the fluid reservoir. So where exactly do these bubbles escape to?

[bogie]

I had a similar issue develop over 6 months or so, 10 yr old bike at the time, with 30k miles on it. Brake lever would occasionally pull 1/2 way back before doing anything. Would bleed ok and feel firm initially then over the course of a ride the issue would come back. Already changed the pads. Master cylinder is integrated with the lever, OEM Brembo. It was due a big valve service couple of months later so I bought a master cylinder rebuild kit for £15 and had the garage tech fit the new parts and bleed again at service time. Its been great since.

[-Cappo-]

mikey_b said:

How? Pulling the lever back pushes the piston in the master cylinder into the barrel, sealing off any escape route for bubbles into the fluid reservoir. So where exactly do these bubbles escape to?

I don't know the science - I do know it (often) works!

[OutInTheShed]

-Cappo- said:

mikey_b said:

How? Pulling the lever back pushes the piston in the master cylinder into the barrel, sealing off any escape route for bubbles into the fluid reservoir. So where exactly do these bubbles escape to?

I don't know the science - I do know it (often) works!

It does often work!

I think having the fluid under pressure for a long time, the air is in smaller bubbles and slowly migrates to the top, instead of being a big bubble trapped by surface tension on in a pipe or hole?

[2ndclasscitizen]

It works because the system is not perfectly sealed. Keeping the pressure on by tying the lever back forces all the little bubbles out past the seals over that period of time, but when you release it is too quick for much to come back in the other way.

[arandomstranger]

Braided brake lines should make a night and day difference on an older bike.
As for the tie back brake lever thing...that's gotta be an old wives tail surely? As someone said, all that does is close the free passage of bubbles back up into the reservoir thus stopping the air escaping...completely the opposite of what is trying to be achieved. That said...I will try it because I've heard it mentioned so many times.

[John D.]

It does work.

[aterribleusername]

arandomstranger said:

Braided brake lines should make a night and day difference on an older bike.
As for the tie back brake lever thing...that's gotta be an old wives tail surely? As someone said, all that does is close the free passage of bubbles back up into the reservoir thus stopping the air escaping...completely the opposite of what is trying to be achieved. That said...I will try it because I've heard it mentioned so many times.

What happens is it closes the reservoir off from the system as you say but it also seals the fluid in down to the calliper at high pressure. This makes the air in it into small bubbles that can the travel up to the lever easier overnight (hence why you hold it closed with a cable tie). By the morning all these little tiny bubbles have congregated together at the high point, which should be the lever. When you release the lever this trapped air burps out to the reservoir and fluid comes in to replace it. It's also why it can sometimes need to be done twice or three times to get all the air out. Using brake fluid that has been standing for a while in the bottle without being shaken also helps as even if it looks fine it can hold air in tiny bubbles you can't really see.

[Stevemr]

I find it also helps, after leaving it overnight with a bungee tying it back to, hold it on hard then release it very quickly and repeat a few times which jars the master cylinder a bit and you can see the air bubbles trickle out.

Edited by Stevemr on Tuesday 1st September 22:34

[arandomstranger]

Interesting...thanks for the explanation.

[alan36]

Contacted Suzuki and the MC was replaced back in 2015. Think I will try new braided lines and a MC seal kit.

[Steve Bass]

-Cappo- said:

mikey_b said:

How? Pulling the lever back pushes the piston in the master cylinder into the barrel, sealing off any escape route for bubbles into the fluid reservoir. So where exactly do these bubbles escape to?

I don't know the science - I do know it (often) works!

Because bubbles rise when the fluid is under pressure better when in a viscous fluid. So pulling the lever pressurises the line. The bubbles then rise to the highest point and are expelled when you release the lever under the self filling process that's the same as what happens when the pads wear.Now you know