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Sudden rear brake failure

L

lloydcliff3210

Member
Member
Hi Everyone, wondering if this situation is familiar to anyone and what to do about it... I decided it was time replace my front and rear brake fluid. Bled the front out no problem then moved to the rear when the problem begain.

For context the rear brake has been working just fine. The fluid level was good and the fluid looked clean albeit a little dark. Here is the sequence of events:

1. Removed the cap on the rear resorvoir and topped it up a little
2. Pumped the rear brake and held the pressure (good firm feel to it)
3. Opened the bleeder screw on the rear caliper and got a good squirt of fluid as the pedal went fully down.
4. Held the pedal down and tightened the bleeder screw
5. Released the pedal

Thinking all seemed as it should I then went to repeat the cycle but found the pedal had lost all pressure and just moved freely up and down with no resistance other than the spring. I tried bleeding the usual way even though there was no pressure but the pedal is not pushing any fluid out to the rear caliper. I then tried attaching a Mity Vac to the bleeder screw and built up some pressure with the pump. I opened the bleeder and got a slow but steady flow of fluid being pulled out by the vacuum. I kept topping up the rear resorvoir and flushed about 10 oz of clean fluid through. Still absolutely no pressure at the rear pedal.

I guess I've somehow blown the seal in the rear master and fluid is just flowing past the piston (?) but what is wierd is the total lack of rear pedal pressure, you would think that even a piston with no rubber seal should have some resistance (?) Could this be some wierd ABS thing? Any thoughts very welcome. The bike is a 2008 C14 ABS with 10,000 miles.
 
In desperation, l have dismantled it, cleaned it and reassembled - and it is still working, but a repair kit would be better.
 
Freddy said:
The master cylinder piston is seized in the bore.
Click to expand...
I am a brake novice, so forgive my ignorance. As I am reading the original post, the brakes worked well until the OP replaced the fluid. If the master cylinder piston is seized I don't understand why there were not braking issues before trying to replace the fluid and they were only manifested after an attempted fluid change.

Apologies if I missed something in the original post. This also has particular meaning to me as I am rebuilding my calipers after an unfortunate interaction with road material in Idaho.
 
If the system has not been flushed periodically as recommended by Kaw, crud accumulates therein and the piston seizes when pushed full stroke.
 
Freddy said:
If the system has not been flushed periodically as recommended by Kaw, crud accumulates therein and the piston seizes when pushed full stroke.
Click to expand...
This seems a very plausible explanation in this case. The rear brake pressure has always been good so minimal piston travel during normal use. When I cracked the bleeder the piston travelled further into the bore than it had for a long time. I suspect the "unused" part of the bore might be corroded and caused friction that shredded the rubber seal on the piston.

I wonder if there is now risk of the particles flowing back into the ABS module? Will a resorvoir --> caliper flush correct that or might a reverse flush (i.e. push fluid in through the caliper) be better I wonder?

I picked the bike up last year so no idea about its past maintenance history. I have ordered a rear master kit and will update this thread on actual findings when I inspect it. Thank you for pointing me in the right direction!
 
Freddy said:
If the system has not been flushed periodically as recommended by Kaw, crud accumulates therein and the piston seizes when pushed full stroke.
Click to expand...
Freddy, by the way I am also Australian. Have lived in the US for 16 years and am a citizen now but originally came from Perth. Sorry about the rule change!
 
ha ha. I'm in Geraldton.

I dont know what's happened in the last 2 days, but l can now post replies. I see I'm now a member here - l don't know how that happened.

I repair these early ABS units and sell them on ebay on an exchange basis. They have 2 modes of failure: solid pedal with total rear brake failure; or locked on / binding rear brake. It's caused by crud getting into the tiny valves in the ABS unit.
 
Last edited:
Freddy said:
ha ha. I'm in Geraldton.

I dont know what's happened in the last 2 days, but l can now post replies. I see I'm now a member here - l don't know how that happened.

I repair these early ABS units and sell them on ebay on an exchange basis. They have 2 modes of failure: solid pedal with total rear brake failure; or locked on / binding rear brake. It's caused by crud getting into the tiny valves in the ABS unit.
Click to expand...
I used to be involved in the Lobster industry before moving to the US and have spent a lot of time in Geraldton, Jurien, and many other fishing towns up to Exmouth. I'll bet I don't recognize Geraldton! Curious if you think there is anything I can do to minimize the risk of the ABS unit failing due to particicles from the rear brake failure?
 
Douglasjre said:
What do you use the rear brake for?
Click to expand...
At very low speed "dragging" the rear a brake a little while slipping the clutch is a good technique at very slow speed. I do use the back brake in most stopping situations, I just tend to manually apply an 80 / 20 rule (i.e. 80% front.) But... for the most part I just have a hang up about things not working the way they should on my vehicles - its an OCD thing!
 
In my course at RaceTrack we discuss rear brake use in extraordinary detail. We then send you out on the track to practice it
 
Murph said:
I got a lesson from a Suzuki factory rider coach years ago...he told me they only put rear brakes on street bikes so you wouldn't roll backward lighting a cigarette at a stop sign... :ROFLMAO:
Click to expand...
Seriously though... I don't get this no back brake thing. The Concours is a heavy bike. If you stop purely with the front brake the front forks tend to dive. I'm fat and old, and don't need my nuts crushing on the tank. Using both brakes delivers a much more dignified stop IMHO!
 
abs is a wonderful thing....back in the day, the oss end on most bikes had a tendency to lock up, and try to come around on you...let off of it and you went high siding...
 
Murph said:
abs is a wonderful thing....back in the day, the oss end on most bikes had a tendency to lock up, and try to come around on you...let off of it and you went high siding...
Click to expand...
Agreed! Older riders tend to know how to "simulate" ABS when using the rear brake (or they know to just keep it locked if the rear wheel starts to skid). ABS has come a long way but the first generation ABS on the 2008's worries me a little.
 
I had the same problem and reported on this thread:

ABS?? No Rear Brake after Cable switch, new fluid and pads​


Mech said it is the worst corrosion he has ever seen in a piston.

After a good cleaning and rebuild using the following parts from ebay, my brakes were bleed and had full pressure in 2 minutes.

Here are the parts I used:

Kawasaki OEM Brake Piston 43020-1057

OEM Kawasaki 92033-0079 - RING-SNAP 20.9X24.6X1

I hope this helps.

Dimitrius
 
dsamudio said:
I had the same problem and reported on this thread:

ABS?? No Rear Brake after Cable switch, new fluid and pads​


Mech said it is the worst corrosion he has ever seen in a piston.

After a good cleaning and rebuild using the following parts from ebay, my brakes were bleed and had full pressure in 2 minutes.

Here are the parts I used:

Kawasaki OEM Brake Piston 43020-1057

OEM Kawasaki 92033-0079 - RING-SNAP 20.9X24.6X1

I hope this helps.

Dimitrius
Click to expand...
Hi Dimitrius, yes it is helpful, thankyou. I have not dismantled mine yet to see what the full extent of the problem is. I have ordered a seal kit that includes the rubber parts but reading your post makes me wonder if I might find damage/corrosion beyond just deteriorated rubber. In your case if the piston was so badly corroded it needed replacing what was the condition of the cylinder bore?
 
lloydcliff3210 said:
Hi Dimitrius, yes it is helpful, thankyou. I have not dismantled mine yet to see what the full extent of the problem is. I have ordered a seal kit that includes the rubber parts but reading your post makes me wonder if I might find damage/corrosion beyond just deteriorated rubber. In your case if the piston was so badly corroded it needed replacing what was the condition of the cylinder bore?
Click to expand...
According to my Mechanic, it took a bit, but he cylinder bore came clean. The piston was not salvageable. The piston was so bad, he could not even get it clean enough to use as an emergency spare.

I'm the second owner, and I willing to bet the brakes, forks, and radiator had not been maintenanced at all. The air filter had been changed for a K&N, but it was another "the dirtiest I've ever seen" for my Mechanic. So, I am guessing the brake fluid could be years old.

Hope this helps,
Dimitrius
 
dsamudio said:
According to my Mechanic, it took a bit, but he cylinder bore came clean. The piston was not salvageable. The piston was so bad, he could not even get it clean enough to use as an emergency spare.

I'm the second owner, and I willing to bet the brakes, forks, and radiator had not been maintenanced at all. The air filter had been changed for a K&N, but it was another "the dirtiest I've ever seen" for my Mechanic. So, I am guessing the brake fluid could be years old.

Hope this helps,
Dimitrius
Click to expand...
Yes, very helpful. Thanks Dimitri!
 
Hi Everyone, Thank you for the valuable inputs you provided. I wanted to close out the thread by sharing what I found when I pulled the master cyclinder apart.

As predicted by Freddy the piston was stuck in the master cylinder bore. The cause of the sticking was a brown paste that had become semi hard and "glued" the piston to the side walls. The source of the paste was the mixing of water and brake fluid. There is a rubber boot at the lower end of the master that provides a seal over a metal washer that is held in place by circlip, and which holds the pedal actuator in the bore opening. The rubber seal when new is a tight fit and likely does a decent job of keeping water out of the bottom of the bore. However on mine the seal had become lose over time and allowed the ingress of water past the washer/circlip and into the lower bore. The water mixed with the residue of brake fluid on the bore walls. Over time this became a sticky paste that trapped the piston when it moved down into that area.

I do not refute that regularly flushing the brake fluid will reduce the occurance of this (and other) problems but in my case the root cause was a worn rubber seal and not the brake fluid itself, so it is unclear if a regular flushing regimen would have helped in this situation.

Upon dismantling and cleaning I found that the master cylinder casing and bore cleaned up well with no evidence of scoring in the bore. The piston was very crusty and probably not servicable, and the rubber boot at the bottom was unservicable.

I replaced the following parts to fully repair the master cylinder and return the bike to service:

1. Piston (inc. 2 x piston rubber seals, and piston spring) 43020-1057
2. Rubber boot (lower) (See below)
3. Rubber boot circlip 92033-0079
4. Rubber o-ring (seals where reservoir tube enters master) 92055-0741
5. Circlip retainer for reservoir tube 92033-1186
6. Banjo bolt washers 49091-0001
7. Pedal linkage split pin 550 (I did not use an OEM part)

I could not find the rubber boot as a separate part number but found an aftermarket version in this kit from Boss Bearing (18-1003) on ebay, otherwise you can buy the entire linkage assembly. Note that the Boss Bearing kit includes other parts needed but I went OEM on everything else.

I thoroughly cleaned:

1. Master cylinder casing and bore
2. Plastic "L" shape pipe from reservoir
3. Pedal linkage assembly (particularly the "ball" end that fits into the piston socket end)
4. Pedal linkage sealing washer that sits between the lower rubber boot and bore (I should have replaced this)
5. Banjo bolt (I should have replaced this)
6. Brake line banjo fitting (master to ABS line)

Lastly, I flushed two bottles of fluid through the system for good measure and bled it out.
 
This is a good write up, thanks. The rear master may be the last item I haven't cleaned or rebuilt. It's now added to the winter list.
 
lloydcliff3210 said:
Hi Everyone, Thank you for the valuable inputs you provided. I wanted to close out the thread by sharing what I found when I pulled the master cyclinder apart.

As predicted by Freddy the piston was stuck in the master cylinder bore. The cause of the sticking was a brown paste that had become semi hard and "glued" the piston to the side walls. The source of the paste was the mixing of water and brake fluid. There is a rubber boot at the lower end of the master that provides a seal over a metal washer that is held in place by circlip, and which holds the pedal actuator in the bore opening. The rubber seal when new is a tight fit and likely does a decent job of keeping water out of the bottom of the bore. However on mine the seal had become lose over time and allowed the ingress of water past the washer/circlip and into the lower bore. The water mixed with the residue of brake fluid on the bore walls. Over time this became a sticky paste that trapped the piston when it moved down into that area.

I do not refute that regularly flushing the brake fluid will reduce the occurance of this (and other) problems but in my case the root cause was a worn rubber seal and not the brake fluid itself, so it is unclear if a regular flushing regimen would have helped in this situation.

Upon dismantling and cleaning I found that the master cylinder casing and bore cleaned up well with no evidence of scoring in the bore. The piston was very crusty and probably not servicable, and the rubber boot at the bottom was unservicable.

I replaced the following parts to fully repair the master cylinder and return the bike to service:

1. Piston (inc. 2 x piston rubber seals, and piston spring) 43020-1057
2. Rubber boot (lower) (See below)
3. Rubber boot circlip 92033-0079
4. Rubber o-ring (seals where reservoir tube enters master) 92055-0741
5. Circlip retainer for reservoir tube 92033-1186
6. Banjo bolt washers 49091-0001
7. Pedal linkage split pin 550 (I did not use an OEM part)

I could not find the rubber boot as a separate part number but found an aftermarket version in this kit from Boss Bearing (18-1003) on ebay, otherwise you can buy the entire linkage assembly. Note that the Boss Bearing kit includes other parts needed but I went OEM on everything else.

I thoroughly cleaned:

1. Master cylinder casing and bore
2. Plastic "L" shape pipe from reservoir
3. Pedal linkage assembly (particularly the "ball" end that fits into the piston socket end)
4. Pedal linkage sealing washer that sits between the lower rubber boot and bore (I should have replaced this)
5. Banjo bolt (I should have replaced this)
6. Brake line banjo fitting (master to ABS line)

Lastly, I flushed two bottles of fluid through the system for good measure and bled it out.
Click to expand...
Excellent write up. By any chance did u take some pics.

This would make a great and IMPORTANT write up for an upcoming issue of the Concourier magazine. That way every member would get word of the issue. Especially if they aren't forum conscious
 
Konehead34 said:
Excellent write up. By any chance did u take some pics.

This would make a great and IMPORTANT write up for an upcoming issue of the Concourier magazine. That way every member would get word of the issue. Especially if they aren't forum conscious
Click to expand...
Thank you. Sadly I did not think that far ahead. It was trial and error for me so I was concentrating on not making a mistake and didn't think to take pics.
 
I know old thread, but my rear brake has locked up, I tried bleeding over the weekend with no luck

I'm thinking it's the same locked up master cylinder as here

I'll try pulling that off and see what I find, hopefully this doesn't involve the ABS module
 
You've probably read the whole thread.

If this fails: I'll try pulling that off and see what I find, hopefully this doesn't involve the ABS module
refer to reply 11.
 
this thread and the other one about brake failure has me worried. On my other bike I do full change of fluid every couple years. But I bought used 2015 Connie earlier this year and I don't think the fluid ever changed. What is best way to go forward? If concerns about getting any debris into ABS, should I push fluid from the bleeders instead of usual direction? I usually just take out a lot of fluid in master cylinder, fill with fresh fluid, then follow routine outlined by OP while topping off with fresh fluid till I get fresh fluid in drain bottle. Of course what happened to OP was not just debris.
 
l repair the gen 1 ABS units, which seem more prone to failure from crud in the rear master cyl. I recommend you buy an aftermarket rear m/cyl, fit it and then strip the original one for alook inside. ebay has cheap m/cyls listedfor ZX14. They are good quality.
 
This is the rear m/cyl I supply with exchange gen 1 ABS units. Use the original K clevis yoke.

www.ebay.com

Rear Brake Master Cylinder For Kawasaki ZR550 ZX1400 ZR750 ZR400 ZR-7 ZR250 | eBay

Kawasaki ZR250 Balius-II 1991-2007. Kawasaki ZR400 Zephyr 400 1989-2008. Kawasaki ZR550 Zephyr 550 1990-1998. Kawasaki ZX1400 Ninja ZX-14 2006-2011. Kawasaki ZX1400 Ninja ZX-14R 2012-2014. Kawasaki ZX1400 ZZR1400 2006-2014.
www.ebay.com

Here's some pix of what comes out of rear m/cyls.

1697889152023.png
1697889199126.png
1697889278308.png
 
Last edited:
I bought a new, cheap one with a reservoir and hose.
Twelve years old, it was time.
The bottom line is to change your fluid every year,

and this would not happen:unsure:

I admit I neglected it, also.

www.ebay.com

Rear Brake Master Cylinder For 2008-14 Kawasaki Concours 14 ZG1400A ABS, ZG1400B | eBay

Kawasaki ZG1400 Concours 14 2008-2014. Kawasaki FX400R 1986-1990. Kawasaki GPZ550 1984-1988. Kawasaki GPX600R 1988-1997. Kawasaki GPZ600R 1987-1989. Kawasaki GPX750R 1987-1990. Kawasaki KDX125 KDX125SR1990-1999.
www.ebay.com
 
cuda said:
I bought a new, cheap one with a reservoir and hose.
Twelve years old, it was time.
The bottom line is to change your fluid every year,

and this would not happen:unsure:

I admit I neglected it, also.

www.ebay.com

Rear Brake Master Cylinder For 2008-14 Kawasaki Concours 14 ZG1400A ABS, ZG1400B | eBay

Kawasaki ZG1400 Concours 14 2008-2014. Kawasaki FX400R 1986-1990. Kawasaki GPZ550 1984-1988. Kawasaki GPX600R 1988-1997. Kawasaki GPZ600R 1987-1989. Kawasaki GPX750R 1987-1990. Kawasaki KDX125 KDX125SR1990-1999.
www.ebay.com
Click to expand...
I have bottles of old brake fluid in one of the garages that I point out to visitors when I am telling them brake fluid needs to be changed on a regular basis. I still have doubters.šŸ™„
 
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