CB650F Rear Brake Trouble

mikegml · Jan 24, 2026

I changed the pads front and rear on my 2018 CB650F and then thought I’d bleed the brakes. It’s only done 5k but assumed the fluid would benefit from changing. Started with the rear first. Using a non return tube which is one I’ve used many times I quickly emptied the rear line without fluid being drawn down from the brake reservoir and ended up with the line full of air. I continued trying to draw fluid down from the reservoir but it wouldn’t have it. I ended up using a syringe to reverse fill the rear line and started to get some feeling back into the line. Took her out for a test ride and it was crap. I assume still too much air in the line, lot of travel in the brake lever, and feeble braking power. Didn’t touch the front brakes which work great.

Can’t understand why fluid isn’t being drawn down from the reservoir to the rear line? Observing the fluid level (cap off) it’s not going down at all. Also tried allowing air to escape from rear line with a tube extending above the brake piston height but still not got real good pressure to rear. Bit baffled.

miweber929 · Jan 24, 2026

It should bleed if everything is done right, however note you have an ABS bike so there is still some fluid in the pump. If the fluid has never been changed there may be a buildup or slight blockage.

I’d try a manual bleed where you loosen the bleeder, push down on the pedal, hold it there and snug the bleeder back up. Do that over and over to get the fluid moving and refill the reservoir as needed. I’ve had stubborn brakes where I’ve had to manually do them and once you get going they’ll bleed with a speed bleeder.

mikegml · Jan 24, 2026

I did try the old fashioned way, but not much. I'll have another go.

Brammers · Jan 24, 2026

If you have air in the ABS unit, it can be a PITA to get out.

At least the rear has shorter lines.

Another vote for doing it "the old way".

J

mikegml · Jan 25, 2026

Might be next week before I get a chance to tackle it again, but I'll see how it goes.

JDude · Feb 7, 2026

This might be to late and possibly incorrect so take accordingly, don’t you have open the electrical circuit to open the abs module to have the brake fluid pass through it?

mikegml · Feb 7, 2026

JDude said:
This might be to late and possibly incorrect so take accordingly, don’t you have open the electrical circuit to open the abs module to have the brake fluid pass through it?

It's not too late. I played around with the brakes last week and improved the feel (not so much travel in the pedal) but still don't think it's right. Due to work and the fact it's not stopped raining here in the UK for 3 weeks I've not had time to take it for a test ride so can't confirm, but it doesn't feel solid enough to me. When you say 'open the circuit' do you mean turn on the ignition? The fluid seems to bleed from the pedal to the nipple without any problem as it is.

miweber929 · Feb 7, 2026

mikegml said:
It's not too late. I played around with the brakes last week and improved the feel (not so much travel in the pedal) but still don't think it's right. Due to work and the fact it's not stopped raining here in the UK for 3 weeks I've not had time to take it for a test ride so can't confirm, but it doesn't feel solid enough to me. When you say 'open the circuit' do you mean turn on the ignition? The fluid seems to bleed from the pedal to the nipple without any problem as it is.

I think he’s saying activate the ABS pump. Usually that’s done by software only a dealer or major repair shop has access to.

JDude · Feb 8, 2026

Mike is correct, I’m not sure if it’s software but something opens the abs units passages to allow the fluid to flow freely. Maybe there is some difference between the 2018 and 2019 abs modules.

mikegml · Feb 9, 2026

Surely you don't need to take the bike to a dealer to carry out a simple brake bleed job? Won't have time to mess around with the brakes till next week.

Brammers · Feb 9, 2026

You don't. I've changed the brake fluid several times on my abs 650f without issue.

Abs units can be a pig to bleed if you get air in them though.

J

mikegml · Feb 13, 2026

Brammers said:
You don't. I've changed the brake fluid several times on my abs 650f without issue.

Abs units can be a pig to bleed if you get air in them though.

J

Yeah, just bonkers. Bled a few bikes without trouble. Can't understand it because the rear brake line (haven't touched the front) is so short, only about a foot long. Might have a chance to play around with it tommorow.

Brammers · Feb 13, 2026

It's the abs unit, it's a sod.

I've had luck by putting a syringe on the bleed nipple and sucking rather than pushing the fluid.

Also, push fluid backwards too... Sometimes that helps move the air pocket.

J

mikegml · Feb 13, 2026

Brammers said:
It's the abs unit, it's a sod.

I've had luck by putting a syringe on the bleed nipple and sucking rather than pushing the fluid.

Also, push fluid backwards too... Sometimes that helps move the air pocket.

J

I did exactly that. Both ways, sucking and pushing, that's what improved it, but as said it's still not right. seems pretty solid but only after quite a lot more lever travel than normal.

Brian C. · Feb 14, 2026

I recently replaced the front and rear pads on mine and bled both systems to refresh the fluid.
I actually used this bleed kit to get the job done. It was cheap enough, and although the seals aren't the best quality, I found that using a small cable tie to tighten the connections worked to prevent leaks.
It might be worth a try if you're struggling! I'd definitely recommend performing a complete bleed so you’re pulling fresh fluid all the way from the reservoir through to the caliper—it’s the best way to ensure you've cleared any trapped air from the system I think.
It did seem to retract the pads slightly so i had to pump them back out initially and I was concerned there had been an issue, but once this was done the system has been fine for me ever since.

mikegml · Feb 14, 2026

That looks pretty good for a cheap price. I'll maybe order that if I don't sort it out soon.

mikegml · Mar 2, 2026

For what it's worth I've sorted my rear brake woes. It only took about 15 mins. I did it the old fashioned way. I junked the one-way brake bleeder which I thought was working and just did the simple "loosen nipple with spanner, pressure on brake pedal, feel the fluid flowing through, tighten nipple before pedal was at full travel and repeat" and 'voila' within 2 minutes pedal felt solid with little travel. TFFT, thought it was gonna be a right pig to sort.

Pete Croney · Mar 29, 2026

A top tip is to syringe the reservoir to empty before you start, then refill. Any new fluid pulled through is then fresh.

Brammers · Mar 29, 2026

Pete Croney said:
A top tip is to syringe the reservoir to empty before you start, then refill. Any new fluid pulled through is then fresh.

Good tip! I always do this, but forgot to think of it!

J

mikegml · Mar 29, 2026

Good tip that, never thought of doing that. I'll try and remember that one.