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Discussion Starter #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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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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^ These are the same questions I have.
 

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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.
 

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Discussion Starter #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.
 

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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.
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.
 

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Discussion Starter #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.
 

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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.
 

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Discussion Starter #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 ?
 

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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 ?
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?
 

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Discussion Starter #12
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?
Yes, it was replaced under the suzuki recall kit, its new master together with the reservoir. And after I found the new recalled MC got issue, I ask the mechanic to borrow me his working MC. Turns out both MC are spongy after sitting for few days. We replace all the brake fluid to new motul Dot4 fluid when bleeding, by pumping the lever. The brake lever was rock hard or back to normal after bleeding. But after a few days sitting, it went spongy and I have to bleed again. There is air in the MC, no air on both calipers.
The only possible solution in this ordeal, is take another MC and test it. But I dont have any other MC to test. The next thing to do would be rebuild the MC, replace the line, rebuild the calipers, do all that until the issue stop. Am I going to the right direction ?
 

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Yes, it was replaced under the suzuki recall kit, its new master together with the reservoir. And after I found the new recalled MC got issue, I ask the mechanic to borrow me his working MC. Turns out both MC are spongy after sitting for few days. We replace all the brake fluid to new motul Dot4 fluid when bleeding, by pumping the lever. The brake lever was rock hard or back to normal after bleeding. But after a few days sitting, it went spongy and I have to bleed again. There is air in the MC, no air on both calipers.
The only possible solution in this ordeal, is take another MC and test it. But I dont have any other MC to test. The next thing to do would be rebuild the MC, replace the line, rebuild the calipers, do all that until the issue stop. Am I going to the right direction ?
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.
 

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Yes, it was replaced under the suzuki recall kit, its new master together with the reservoir. And after I found the new recalled MC got issue, I ask the mechanic to borrow me his working MC. Turns out both MC are spongy after sitting for few days. We replace all the brake fluid to new motul Dot4 fluid when bleeding, by pumping the lever. The brake lever was rock hard or back to normal after bleeding. But after a few days sitting, it went spongy and I have to bleed again. There is air in the MC, no air on both calipers.
The only possible solution in this ordeal, is take another MC and test it. But I dont have any other MC to test. The next thing to do would be rebuild the MC, replace the line, rebuild the calipers, do all that until the issue stop. Am I going to the right direction ?
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.
 

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Discussion Starter #16
I'd just take or back to suzuki
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.
 

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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.
+1 on the Brembo ! 300.00 to have a better end result. Brakes!
 

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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.
 

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@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?
 

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Discussion Starter #20
@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?
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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