New sponginess + travel to RR brakes

All,

I got a break in the weather yesterday to run the FJR, and I was surprised to find the rear brake lever very spongy, and it traveled MUCH more than ever before. I only went a short distance, then came back to evaluate. The pedal travels a LOT, and appears to be actuating the plunger into the RR master a LOT further than it should or used to. It does operate the RR brake, but is is only lightly engaging it. I cannot see any leak in the system, and I checked and topped off fluid level. The brake pads are good- 3/4 material left.

It feels like fluid is bypassing a seal, and instead of pushing through the lines and exerting force on the pads, seems to be in some sort of closed recirculating loop. I am looking for ideas on where to look. My first guess is the RR master cylinder, and should I look to rebuild or replace? Next place I suspect is the rear or linked front caliper, but is seems less likely because there does not appear to be a leak.

Ideas on where to check, and if I should rebuild or replace the rear MC are appreciated. Back to winter doldrums

Bleed your rear brakes. The rear master Cylinder is on the right, behind the side panel with "FJR" on it, underneath the seat. Bleed the right lower front caliper first, as this is the linked caliper. Then bleed the rear.

While you're at it, you should do the fronts and the clutch.

Bleed first. Lower front right first, then rear. If not that then I would consider master cylinder.

I ride a Gen 1 and have not yet experienced this kind of symptom. My first thoughts are to bleed the rear system and restore with new DOT fluid careful to avoid any possibility of getting air bubbles in the line.

Air compresses, fluid doesn't, so I am suspecting air in your rear system somewhere...

You haven't had a wheel off have you? I've had a similar experience, and with no other point for air to enter the system am wondering if I damaged a caliper seal with dirt or crud during a tire change.

Listen to HRZ and RK above. Bleed the rear brakes beginning with the RF caliper and more than likely, the rear brake will come back better than before.

For whatever reason, linked brakes on GEN IIs & GEN IIIs are prone to get soggy rear brakes. My '15 has the same symptom now and needs a good bleed.

--G

Thanks for the ideas. I did bleed everything as suggested, but MAYBE just a little improvement. The fluid is nice and clear now . I have not had a wheel off, I rode it about a week before this happened and it was ok. It does "work", but still not right.

I took it for a quick low speed ride, and while I didn't test fully, it seemed like the abs stopped working. I was able to chirp the rear brake, and I did not get the abs activated pulse I am used to.

I'll test some more this weekend, focusing on abs. The brake system seems fairly complex, and I will make sure that this experience was not just a low speed test anomaly. Does the computer store any abs failure codes or anything? Hmmm.

After that? I guess I start tearing into it component by component.

ABS won't work at very low speeds ( < 5mph???), make sure you're fast enough.

Any chance your master cylinder is going bad?

My rear brake suddenly got softer a year or more ago. Took it to the dealer, since it's still under warranty, they charged me a bunch to do a multi-step bleeding. Made no difference. Pedal still softer than original. I have trouble with the idea that a closed hydraulic system suddenly needs bleeding -- how did air get in? In my case, I've had the rear wheel off multiple times, with the associated movement of the caliper pistons, which I have not rigorously cleaned, so I could see a path there (though I still doubt it). But without moving the pistons, as in your case, I don't understand where the air would have come from.

"Any chance your master cylinder is going bad? "

Now that's an interesting question.

Not sure if the '08 store an ABS code but the '14 displays a code 16.

Do you have an ABS test wiring connection? On Gen III it is mounted at the front left of the top part of the battery?

Finally got around to bleeding / flushing the brakes on my '15A today.

Both front linked and rear calipers had a couple bubbles in addition to discolored fluid. After the bleed / flush, rear brake is back to a normal hard pedal. Rear linked brakes last bled in June '15.

--G

Just did the same on mine, got air out of the front caliper. Very odd. It's never been bled before and has 33k on it. Sat for 2 months (longest stretch it has set) and spongy rear brake. How does air get in the system like that?

On a 2008 with 33k miles, i would make sure all hydraulic lines are thoroughly purged with fresh fluid. You're way overdue. Not sure how air gets in- I guess the seals aren't perfect and may allow air in; especially when they dry out a bit. Doesn't really matter unless it recurs regularly. Then you would be looking to replace seals.

kleake posted: Just did the same on mine, got air out of the front caliper. Very odd. It's never been bled before and has 33k on it. Sat for 2 months (longest stretch it has set) and spongy rear brake. How does air get in the system like that?

Click to expand...

Just guessing ... as brake fluid volume changes with temperature, air may be able to leak in where seals are slightly imperfect. (ie, air gets sucked into the line as shrinking brake fluid draws a vacuum in the lines.)

It doesn't take much air to make brake action spongy. If temperatures undergo a few 'radical' cycles before you ride again, you could have enough air in the lines to be noticeable.

I used to have the same thing happen to my St 1300 every couple of years. I think it is related to linked brakes and miles.

I'm so glad to ride a superior Gen I. Either I don't have the problem, or I just don't give a shit.

While ya at it, clean up the calliper pistons, lube the 2 slider pins, remove, clean and lube the brake arm pivot and finally bleed out the ABS solenoids. And buy a manual.

What is this thing you speak of, Ken, bleeding out ABS solenoids?