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Front Brake Issues

17K views 62 replies 18 participants last post by  oomh 
#1 ·
Hi everyone,
Hope you are well. My K9 750 suffer from spongy brake after recall done. After numerous time of bleeding the brake as per the manual with fresh dot4 brake fluids, there is always air on the master cylinder after sitting for few days. I have change the brake pads (SBS HH race pads) recently and clean the piston too. Now here is the weird part, I have also swap out a good condition master cylinder (borrow frm the mechanic) and still having air in the master cylinder after sitting for a few days. Ohh, there is no leak on the caliper and master cylinder if you are wondering.
Hope you guys can help me out, the mechanic is pointing at brakes lines and rebuilding the caliper next. I dont want to spend cash on something that does not fix the issue.
*I did run some search and cant find what Im looking for, hence looking for some kind soul for wisdom.
 

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#2 ·
Hi and welcome,

How are you determining there is 'air in the MC'? Are you using a clear tube and seeing the bubbles bleed out when you bleed the MC? Then you state the MC is not leaking, as in not leaking brake fluid?
You did bleed both sides of the wheel and the MC?
I actually use a clear tubing like they usually use on fish tank air lines to actually 'see' what is coming out when I bleed my motorcycles brakes.
 
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#4 · (Edited)
First off, realize that you should be replacing brake lines every couple of years, so replacing lines is NOT a waste of money. In fact, it's regular maintenance. You can alleviate this by buying SS lines.

Second off, it sounds like you're doing it wrong. Maybe you should tell us your technique, because either your technique is off or you're incorrect about your parts not being faulty.
 
#5 ·
Hi, I use a clear aquarium tube n a bottle to catch the dot 4 fluid. I saw a huge air coming out from the MC only. Nothing or no air when I bleed from the caliper. Technique I use: Pump, pump pump, squeeze the brake lever, slowly crack the bleeder about 1/6 open, still squeezing the lever, then close the bleeder. I did this to MC, follow up by left caliper, then right caliper and back to MC.
I didnt see any air from the caliper, but when I bleed the MC there is air. I take it to the mechanic after I cannot figure it out anymore, same thing, air in the MC. No leaks mean no brake fluid leaking. All this is the post recall MC and SBS brake pads.
Now, we thought it was the MC, so the mechanic borrow his working condition MC and install it on my ride. Same thing happen, front brake went spongy, bleed the MC, and the calipers again. Only found air in the MC. So, my thoughts either the mechanic MC is faulty or something wrong with my line or caliper or rotor ? Remember that, the brake went spongy when it is sitting, it was perfectly fine when we tested while riding. Tested mean we brake the crap out of it, endo, hard braking, u name it.
Looking for some solution out of this ordeal. Thanks guys.
 
#6 ·
When it goes flat have you tried just bleeding from the master cylinder and seeing if that solves the problem? Then do the same for each caliper, and the one with air in it may be your culprit.
I'm assuming there are no obvious leaks.
 
#7 · (Edited)
Well, that is what I've done before, I found there is air in the MC only, the caliper are fine. After bleeding, it will last a few days before going spongy and about a week to go all flat, lever (at setting #1) hitting the throttle. Are you saying the mechanic MC is also bad ? I understand that the mechanic rebuild that MC before. Yea, there is no sign of brake fluid leaking anywhere.
 
#8 ·
Are you getting air out every time you bleed? Only from the MC? Only from the calipers? To me it sounds like you have a bad MC. Tell me after it sits can you pump the lever and get a solid lever and it be fine until you let it sit a few hrs? If yes the MC is the culprit.
 
#10 ·
Hi Jet, yep only the MC have air when I bled it, caliper is fine. It will lose pressure with lever @ setting 1 touching the throttle after sitting for a few days. Nope, pumping the brake lever would not change anything or do any better. Again, I checked and re-torque the lines and calipers, no visible leaks. I am going to clean the caliper piston again soon.
If you think it is likely the MC, I am going to dissemble my recall MC and rebuild it. Will that be a good call ?
 
#11 ·
So I went back and read your post. Am I correct you replaced the MC that was replaced under the recall with another? And have the same issue? If so I guess its possible to have two defective MC’s but highly unlikely. Who is doing the bleeding and how much fluid are you bleeding out? Half a bottle full bottle? Are you just pumping the lever or vacuum bleeding? After you bleed it do you ever get a rock hard lever?
 
#16 ·
Was this done at a authorized Suzuki dealer if so I would take it back and have them fix or replace the defective part, which sounds like the MC. If you’re only getting air bubbles from the MC I wouldn’t mess with the calipers if its not broke don’t fix it.. take the bike back and leave it for a couple days or how ever long it takes for the problem to show up so they can exactly what is happening. Or get a Brembo and be done with it.
Cant afford a Brembo : ( The dealer did ring up Suzuki Japan and they claim the new MC is working fine before they ship it here and install it to my bike. I already explore and talk to Suzuki Japan, and they would not going to replace or trying to fix the issue. I am from south Asia btw.


I've had good luck pumping fluid into the caliper bleeders. If there are 2 calipers, usually I tape/wrap the lever to the bar and pump into the left caliper and crack the right hand bleeder till no air comes out, and that usually gets the air bubbles out of the calipers. Sounds like you may be able to skip that part but if it has dual front calipers, make sure there is no air trapped at the junction where the caliper lines meet. Next, release the handle and shut the right caliper bleeder then keep forcing fluid into the left caliper bleeder until no more bubbles come out in the m/c reservoir. Sometimes a small air bubble gets trapped at the m/c banjo connection but just pull the lever while very quickly cracking and tightening the banjo bolt one time and that should get you pretty close.
As I mentioned before, there was no air coming out from the caliper. If there is air, I would know what the calipers are out and need to be rebuild. Air was coming out from the MC alone. We didnt try to bleed from the MC banjo tho. Will give that a try.

Thanks everyone for giving your view, appreciate it. Will report back.
 
#18 ·
He shouldn't have to spend money on aftermarket parts for a botched job. Especially when the factory MC is more than sufficient for even club racing.
 
#19 ·
@oomh

Reading your last posts, you say that the system bleeds well and the lever is firm when you're done.

When it goes soft after a couple of days, can you pump it back up with the lever only and it is good again for a day or so?
 
#20 ·
After it was sitting a few days, it went soft and pumping the lever does not help. I bought some SS lines from local shop, and going to install it in OEM routing. Question is, the right line is longer by 15cm and I have to route it to the left, go down under the steering stabilizer and back to the right caliper. Would that create any issue ? I check the steering free play is ok, it was not kink at all, just need to route it longer.
I draw some illustration below. Thanks.
 

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#21 ·
Bummer. I was hoping you would say that the brakes would pump back up. I don't have any guesses.

As long as the brake line is not interfering with anything, it should not matter. It's just not a very nice installation. I'm guessing the lines were not made for the bike?
 
#26 ·
I have to vote for a bad master cylinder too. I had one just like that. Good hard lever after bleeding, let sit for a week, and lever went soft again. Replaced master after much bleeding and fiddling and problem went away. The master cyl was a Nissan purchased used. I replaced the stocker, bled it out and the problem was gone. I finally replaced the stock master cylinder with a Brembo 19 rsd. Set on the 19 by 18 setting, and the brake modulation is much improved. I am using stainless lines, Brembo master, and EBC HH pads. Far better set up than stock.
 
#29 · (Edited)
The recall work was done in mid Nov 2018, and after 1 month the problem occur. I did try my best to talk to the dealer and Suzuki Japan. The dealer said they cant do anything because Suzuki Japan would not send any new part in because according to them, the recall MC is new and should not have any issue. My bike does not have warranty anymore, does recall MC have any warranty ? I am not saying the recall MC is bad because the mechanic MC is also having this issue when he install it in my ride.
 
#30 ·
Yes the recall MC should have a warranty.
Let me see if I understand you when you say the mechanic can put your MC on a different bike and not have the same problem, and put a different MC from the recall one on yours and have the same problem? And you say you didnt have this issue before the MC change? Obviously there is no leaks?
 
#32 ·
It almost sounds like the original problem that the recall was to remedy, corrosion of internal metal parts causing off gassing and a spongy lever. But this seems to happen much quicker and dramatically.
 
#33 ·
I don't think they tried to put HIS replacement master on another bike. That said, On a car, you MUST bleed the master at the line connections. I am fairly certain it should be done on a bike as well. I am thinking either this master is bad, OR it is NOT being bled completely, or properly...
 
#36 ·
Yep, we both keep track on the fluid and check whether there is leak, no leaks. The mechanic MC is working condition when he install it in my ride. But we did not try it on other bike with my recall MC, so there is a question mark here. He is sure that his MC is working well and I should look else where to solve my issue. Do u guys recommend to rebuilt the MC if there is still issue after the lines ?
 
#37 ·
Hi guys, some updates. I manage to get spare MC frm a friend and change the lines to SS. Will monitor these change from here. Strangely, the recall MC was not able to pump and bleed properly, there is little fluid push out after an hour bleeding it. I dissemble the recall MC and there is some white spot inside the MC. I wondering what cause that. I looked at the piston set, the spring seems to be corroded, the rubber look ok and the surface inside the MC is smooth. when I took out my recall MC, I checked using brake fluid checker and the fluid was contaminated. Not sure if I buy a new piston set for recall MC, would it solve the issue not pumping ?
 

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#40 ·
exactly same problem on my L5 gsxr600 , i'm waiting for another MC , will rebuild it and will see , how it will works .

good OEM pads , good rotors , good brembo calipers , stock lines . and bleeded with motul rf660 3 times , like manual said , but always get spongy after few days . in first dayt after bleeding it's just perfect !
 
#41 ·
Hi, if most of your parts are good, I guess the only thing you should be looking at would be MC. Can you update us what is the outcome after the rebuild. Unfortunately, after I changed to SS lines, my friend MC also went spongy. I am still waiting for the piston set to go into my recall MC. It is quite skeptical, but I think I have to rebuild the caliper next, that the only thing left to do after all this trouble. Sigh......
 
#47 ·
Hi everyone,

Hope you are well. My K9 750 suffer from spongy brake after recall done. After numerous time of bleeding the brake as per the manual with fresh dot4 brake fluids, there is always air on the master cylinder after sitting for few days. I have change the brake pads (SBS HH race pads) recently and clean the piston too. Now here is the weird part, I have also swap out a good condition master cylinder (borrow frm the mechanic) and still having air in the master cylinder after sitting for a few days. Ohh, there is no leak on the caliper and master cylinder if you are wondering.

Hope you guys can help me out, the mechanic is pointing at brakes lines and rebuilding the caliper next. I dont want to spend cash on something that does not fix the issue.

*I did run some search and cant find what Im looking for, hence looking for some kind soul for wisdom.
I have the same issue with mines I track my 2012 gsxr600 and my brake was always soft ish but it had braking power I went to tech my bike at a different organization at the same track they fail my front brake for being to soft they bled my lines and it got alot better it's been sitting for a week and went to move it it's the same spot where it was before bled it again to have air coming out the MC now it's back firm soo I'm assuming master cylinder is leaking pass its seal.

Sent from my SM-G965U1 using Tapatalk
 
#48 ·
Maybe next time listen to the guys when they tell you to take it back to Suzuki since they did the recall and after the recall it did not fix the soft brake issue.You went through all that trouble only to state the following:

"Strangely, the recall MC was not able to pump and bleed properly, there is little fluid push out after an hour bleeding it. I dissemble the recall MC and there is some white spot inside the MC. I wondering what cause that. I looked at the piston set, the spring seems to be corroded, the rubber look ok and the surface inside the MC is smooth. when I took out my recall MC, I checked using brake fluid checker and the fluid was contaminated."

Obviously the replacement MC from Suzuki was defective and they would have or should have covered it under warranty...........
 
#49 ·
Forget the OEM master cylinder ditch that thing. Brembo master that corresponds to the piston size of your calipers (17RCS or 19RCS), stainless steel braded lines, good pads like Vesrah, Motul fluid and change out the bleed screws with Speed Bleeders (makes bleeding brake fluid so much easier). Your bike will bike will stop like a bullet hitting an AR500 plate.
 
#51 · (Edited)
R6/R1 master would be better than oem gsxr but it would work best with R6/R1 monoblock calipers if you can find the set off someone for cheap. Just be aware of the piston size in the calipers as some are smaller or larger diameter if your going to mix a different bikes master with your bikes calipers because this effects the way the piston size in the master cylinder pushes fluid to caliper which in the end creates the lever feel for the brakes (soft or firm). That's why you see 15, 17, 19 version masters.
 
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