Strange Brake Problem ??

[Yorick]

Just flushed the front brake fluid and de-glazed the pads. Took it for a spin and lots of hard braking. Front wheel was sticking a bit at first as maybe not put the brakes back in same way. After lots of hard braking, the front freed itself. But another problem arose.

After loads of super hard braking, the lever came right back to the bar After 2 or 3 pumps it came straight back. Enough to lift the back wheel.

So assumed it was the Dot 4 from a full, but already opened, bottle.

So bought half litre of Dot 5.1 and all was OK on ride to shop.

Flushed it again. 7 or stupid heavy braking from 100, and then it happened again. But again it worked after a quick pump. One time it worked, even though the lever came almost right back to the bars. When I got home after slow last mile, I checked the temps
Piston 130c
Disk 170c

I don't think I'd ever brake that hard and as often on track, but it's got me worried. Still gonna go to the trackday but will take it steady

Any ideas ?

[weeksy]

Abs pump still on it?

[Yorick]

Abs pump still on it?

Yeah, all standard. I could feel and hear the front wheel squealing

[weeksy]

Don't they need a different bleed with vacuum or computer?

[A_morti]

Something obviously isn't right, and you need to fix it before riding round a track or they'll be scooping you up.

On the principle of "the last thing you touched is probably the problem", your issue will have been caused by flushing the fluid. In these hard braking scenarios you described it's activating the ABS, but there's air in there rather than fluid.

Most likely this will need to be rebled by the dealer who has the special tool to pulse the ABS pump, which is how it has to be bled.

If you changed the fluid spec, that could also be an issue, IDK enough about it.

[A_morti]

You'll probably be fine to ride it to the dealer as long as you don't need the ABS on the way.

[Yorick]

Just been Googling and it's the same way, with or without ABS.

My first thought was moisture in the first fluid I used, but the new 5.1 should have cured that.

[KungFooBob]

Bleeding abs and Non-abs is the same... If you don't want to flush the abs valve block.

You need to cycle the pump to get the old fluid out, there's probably a good amount of old dot4 still in there and now mixing with your new 5.1.

[A_morti]

Did you undo any brake lines? Even loosen the banjo bolt. This can cause an air leak which would be resolved by replacing the copper washers.

[Yorick]

Bleeding abs and Non-abs is the same... If you don't want to flush the abs valve block.

You need to cycle the pump to get the old fluid out, there's probably a good amount of old dot4 still in there and now mixing with your new 5.1.

I've seen 4 or 5 replies on the Gixer forums saying that it's straight forward.

[Yorick]

When I flushed the new Dot 5.1 through, the left leg chucked out clean fluid. But right had lots of bubbles. Just flushed the right again and even more bubbles. Hmm
Not sure how bubbles only affect it when system is super hot.

So gonna tie the lever back over night and take some brake fluid with me.

And lots of water to cool the system on the day.

[Yorick]

Did you undo any brake lines? Even loosen the banjo bolt. This can cause an air leak which would be resolved by replacing the copper washers.

Nope. All secure.

[A_morti]

I've seen 4 or 5 replies on the Gixer forums saying that it's straight forward.

Until/unless you get air into the ABS block. Not sure how that'd happen if you didn't disturb the lines nor activate the ABS inadvertently while bleeding it. Mixing the fluids might be relevant though.

[A_morti]

When I flushed the new Dot 5.1 through, the left leg chucked out clean fluid. But right had lots of bubbles. Just flushed the right again and even more bubbles. Hmm
Not sure how bubbles only affect it when system is super hot.

So gonna tie the lever back over night and take some brake fluid with me.

And lots of water to cool the system on the day.

I'd say more likely the bubbles weren't there when you finished bleeding it, but got into the system either by it either getting hot and something expanding allowing air in, or by the ABS activation.

[Yorick]

I've seen 4 or 5 replies on the Gixer forums saying that it's straight forward.

Until/unless you get air into the ABS block. Not sure how that'd happen if you didn't disturb the lines nor activate the ABS inadvertently while bleeding it. Mixing the fluids might be relevant though.

Dot 4.0 and 5.1 are all OK.

The first flush was with Dot 4.0 so no change first time.

[Count Steer]

When I flushed the new Dot 5.1 through, the left leg chucked out clean fluid. But right had lots of bubbles. Just flushed the right again and even more bubbles. Hmm
Not sure how bubbles only affect it when system is super hot.

So gonna tie the lever back over night and take some brake fluid with me.

And lots of water to cool the system on the day.

I'd say more likely the bubbles weren't there when you finished bleeding it, but got into the system either by it either getting hot and something expanding allowing air in, or by the ABS activation.

Well, it certainly sounds like something was binding when the pads went back in, followed by lots of v heavy braking so things certainly got hot. Maybe the second flush didn't get rid of the bubbles, particularly if the braking was heavy enough to activate the ABS it might complicate the flushing? I note the bubbles were mainly in one side on the second flush...wonder if that was the side that was binding?

[mboy]

It’s worth noting that DOT4 and DOT5.1 ratings are fairly arbitrary. There’s DOT4 fluids out there (CL Brakes DOT4, Castrol RBF660 etc.) with higher boiling points than typical DOT5.1 fluids.

With your disc and piston temps nowhere near the typical boiling point of cheap DOT4’s even, I’d suggest something else is awry. Just pointing out that for track use certainly, go on the individual temp ratings of a fluid rather than just whether it is DOT4 or DOT5.1 as this can be strangely misleading.

[Yorick]

Well. On way down through Fuertaventura today, I braked hard about 10 times from 100 -30 one after another. Not quite as hard as yesterday, more normal track braking.

All was well and disk, pads and caliper were all above 200c.

So the berserk braking yesterday wasn't atypical, hence boiling the fluid.

I'm happy now and I'll be taking it steady tmrw anyway.

I'm gonna bypass the ABS and fit HEL lines to make sure

[Skub]

I'm gonna bypass the ABS and fit HEL lines to make sure

Check the legalities of disabling the ABS for the road,where you are. ABS has been mandatory fit on new vehicles for quite some years now and while turning it off is a bit of a grey area legally,it may be different if you are involved in an accident and the bike was found to have a non working ABS.

[Yorick]

I'm gonna bypass the ABS and fit HEL lines to make sure

Check the legalities of disabling the ABS for the road,where you are. ABS has been mandatory fit on new vehicles for quite some years now and while turning it off is a bit of a grey area legally,it may be different if you are involved in an accident and the bike was found to have a non working ABS.

I'm gonna keep the old pipes it in situ for the ITV (MOT)
But I'll feel safer with it bypassed. Gonna order Monday. Under £200 HEL.

The ABS light comes and goes for fun. It's got leccy gremlins so can't trust it