Author Topic: Delayed Brake Bubbles?  (Read 519 times)

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Offline Old Steve

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Delayed Brake Bubbles?
« on: September 06, 2017, 02:34:50 am »
I got a new rear tire, and had the dealer flush the brake and clutch fluid at the same time. I rode home (about 20 miles), and everything was great. Two days later, on the weekend, I took about a 30 mile ride to some local low-grade twisties to scrub off the new tire. Again everything was great. Then she sat for a week while I was traveling. When I got back, the front brake lever sank to the grip with almost no resistance. I tried pumping, fast & slow... just **SQUISH**.
Looking through these forums, I figured it was a bad master cylinder, but decided to try bleeding anyway. Sure enough, I got air out of the bleed valve at the master cylinder. Just in case, I bled the two calipers too, and after that, the brakes seem fine.
My question is, why did the air take so long to affect the brakes, or do you think something else is going on?

Offline MAN OF BLUES

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Re: Delayed Brake Bubbles?
« Reply #1 on: September 06, 2017, 03:26:36 am »
Dunno...
Good possibility the tech didn't completely flush the system, and or never made sure the bleeders sealed tight.. and it sucked some air back in... or, he used a can of fluid that had been opened, and sat on the shelf since the last brake job he did...3 monthes ago...

Keep an eye on it, and make it a point to let the dealership know what you had to do to fix the job you paid them to do... :-[

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW

Offline gPink

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Re: Delayed Brake Bubbles?
« Reply #2 on: September 06, 2017, 08:50:12 am »
Dunno...
Good possibility the tech didn't completely flush the system, and or never made sure the bleeders sealed tight.. and it sucked some air back in... or, he used a can of fluid that had been opened, and sat on the shelf since the last brake job he did...3 monthes ago...

Keep an eye on it, and make it a point to let the dealership know what you had to do to fix the job you paid them to do... :-[

They also put your life at risk....just sayin'

Offline Old Steve

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Re: Delayed Brake Bubbles?
« Reply #3 on: September 06, 2017, 02:11:45 pm »
Dunno...
Good possibility the tech didn't completely flush the system, and or never made sure the bleeders sealed tight.. and it sucked some air back in... or, he used a can of fluid that had been opened, and sat on the shelf since the last brake job he did...3 monthes ago...

Keep an eye on it, and make it a point to let the dealership know what you had to do to fix the job you paid them to do... :-[

They also put your life at risk....just sayin'

Yup - both of those actions had occurred to me; I just added another item to the list of things that the dealer is not allowed to do to my bike.

MOB:
I hadn't thought about the possibility of old fluid, but I suppose that could explain the initial good performance and then later failure. I think I'll be doing a full flush this weekend.

Offline RWulf

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Re: Delayed Brake Bubbles?
« Reply #4 on: September 06, 2017, 06:25:22 pm »
If you are sure that everything was working correctly on your
ride home and the short ride two days later then you can rule
out air in the lines and bad fluid. You would have noticed something
wrong. The bleed screw at the caliper could have leaked under
pressure when braking, this i think you would have noticed. The
master cylinder is under a slight bit of negative pressure from the
weight of the brake fluid. If said bleed screw is loose or was loose
you have found your problem.
It is also possible the wrong brake fluid was used but not likely.

Offline barberman

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Re: Delayed Brake Bubbles?
« Reply #5 on: September 21, 2017, 06:05:13 pm »
I found the bleeders tend to leak air in if not cranked down pretty well. I used Teflon tape and curred the issue. Seems to me the threads are a bit rough in the reservoir castings.

Offline MAN OF BLUES

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Re: Delayed Brake Bubbles?
« Reply #6 on: September 21, 2017, 07:54:19 pm »
I found the bleeders tend to leak air in if not cranked down pretty well. I used Teflon tape and curred the issue. Seems to me the threads are a bit rough in the reservoir castings.

Never use teflon tape on any brake fitting... ever....
Pieces can become sheared off, and disloged, and allowed to migrate in the system blocking the already tiny ports within the master cylinders on both brake and clutch reservoirs... requiring complete disassembly, and met8culous cleaning efforts, to correct the issue.. I've disassembled both, and will tell you its a p.I.t.a. job, and afterwards the bleeding is 5x harder to achieve a  good lever feel...

Bleeder valves threads have absolutly nothing to do with the "sealing" , the seal is the conical tip of that valve, pressing into a conical recess... its a face seal.
If either surface, the needle or the seat is compromised, or scratched/nicked, it results in a poor seal.. often time "overtightening" excessivly causes damage by "smearing" the sealing surfaces, causing voids in the contact area..

Just never use teflon tape, please....

Also not, some bleeders, such as "speed bleeders" by design, utilize an adhesively bonded sealant on the threads, mostly the outer 1/2 of that threaded area.. this is not done to seal fluid, this was done because they found during "speedbleeding with a mity vac pump" air got sucked in along the threads... first edition speed bleeders were all like that, and people began using "tape" to prevent that... the manufacturers saw a lot of complaints, and as a stopgap measure began adding that thread sealer to prevent complaints and liabilities...

Once a speed bleeder with this captive sealant is installed, I recommend not doing repeated removals of that bleeder, loosen/tighten ok, but repeated removals may dislodge that material also, and allow migration.

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW

Offline barberman

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Re: Delayed Brake Bubbles?
« Reply #7 on: September 23, 2017, 07:00:35 pm »
Thanx for the info there "M.O.B. " I'll take tape off, next change.   I was having issues with fluid changing from clear to beer color in as little as two weeks. just bought bike and figured water/vapor was culprit. after five complete flushes it stays clear now. When bleeding (clutch mainly) I noticed just a light turn down was letting in very tiny bubbles, so i tightened normally. I made it sound too much in initial comment , sorry. Thanks for technical detail