Well, I feel like a dummy. Bled the brakes before using only the bleeders down on the wheel, by the calipers. This time I used the bleeder up top on the hand brake lever assembly. I got bubbles. Now the front brake is good as new. Be interesting to see if problem recurrs. Hope not. Anyhow, I'll not be needing a rebuild kit or new assy.

Lesson I keep learning over and over: try all the easy stuff first!

 

I found bubbles in mine as well as a mix of good and spent-looking fluid -- mostly good in the cylinder and mostly spent in the lines (bike was purchased used and had received a "full service" including fluids prior to my purchase). I usually do it all over again myself, anyway, but took my time getting around to it with this bike (too much fun riding and modding).

 

My '17 GT gets soft lever and requires a quick bleeding at the m/c every once in a while. A buddy's old Brembo-equipped Tuono V2 Factory would require bleeding at the m/c once a month to maintain lever pressure. No leaks, just air incursion.

 

For ten years I had no brake problems, never had to bleed the brakes at all except every two years when I changed the fluid. Now that I have deleted the ABS I have no more problems.

 

Check caliper mountings and make sure calipers are not moving excessively when lever is actuated. Loose caliper or missing hardware or missing brake pad(it can happen) can require more hydraulic travel than your master can generate and allow excessive lever travel. Smaller bikes can be tested for master cylinder internal leakage by removing single caliper and clamping brake pad or flat metal plate to retain caliper piston(s). Once piston travel is prevented the lever is held tight for a time. If lever sinks slowly and no external leaks are apparent, you have internal master cylinder leakage and will require rebuild or replacement. Multi piston opposed twin calipers could make this method unworkable. You can be fairly certain if your calipers are not moving excessively and lever sinks with no external leakage you can probably safely expect your master has failed and leaks internally. Your ABS would likely not cause internal pressure drop.

 

Mine was rebuilt as a recall during the warranty period (2yrs) even though no problem had surfaced. Must be some reason for the recall.

 

I just had the same thing happen to my 2017 SDR. This whole riding season was a total waste. Broken radiator, leaking clutch slave, lost the friction material on a front brake pad, then the front brake master.

Thank god this thing wasn't expensive...

 

Did you do the work on the master cylinder, or did you have a shop do it? Do you recall part number for MC repair part? My lever slowly "leaks down" as I squeeze and hold it, so I'm pretty sure it's the MC. I'd prefer to buy a rebuild kit vs. a new MC due to the cost.

 

Clogan~ For reference - I rebuilt my '15 front master cylinder with KTM's kit (part number #: 61302032000). It may be different for the GT's however this may help. Note: I also replaced the slave with a Rekluse version.

 

Thanks for the lead, but it appears that your part is for a 12mm piston. I'm pretty sure (not positive) mine is either 15mm or 16mm.

 

FWIW, the good folks at KTM World, where I often buy parts, tell me that there is no rebuild kit from KTM for my bike. They recommended buying the entire front brake lever/reservoir/bracket assembly, costing $400 or so. Before I do that, I may just try to disassemble mine (if disassembly is possible), clean it, and put it back together. Seems prudent before spending $400.

Wonder if Brembo sells rebuild kits?

Anyhow, most folks are closed today for the New Year's weekend. Guess I'll wait until next year.

 

Sorted! Great! I missed this whole thing but I did want to chime in. First, I have swapped out a stock m/c on an Aprilia with a Brembo RCS and, HOLY COW!, it was great. A really good m/c is absolutely amazing. Second, do you know of the trick for removing bubbles from the lines by zip tying the lever to the bars overnight? I have to do that regularly with both the front and the rear brakes on my GT to keep the lever/pedal feeling firm so I don't think you are all alone on this.

 

Interesting you should mention the zip ties. I'll make a note of that.

My bike had been sitting up for a bit over a month, while we enjoyed the holidays and endured an unusual cold snap. I typically ride at least weekly, so I wonder if the 30-day lay up had anything to do with the brake getting so mushy? Hmmm...

 

Well actually I now use a strip of double sided velcro and wrap it around the lever and the handlebar with a little tension and leave it overnight. It works great and I can get a consistently firm lever but the mushiness always seem to come back. I have noticed that my brakes get mushy if the bike sits for a while.

 

If mc doesn't have a rebuild kit those mc are usually simpler in design using parts that don't necessarily want to pull apart easy ...
What I mean is, it is what it is , inside .
I have 2 wrecked brembo street bike version mc because of design and no rebuild kits . Offroad mc often come with rebuild kits....

One supermoto guy told me once that there is a reason why street get non maintenance /rebuild mc .

 

Reviving old thread. Anyone have any success bleeding the system? Mine constantly loses pressure. I can blead the MC like once or twice and get fully pressure again.

 

Never a good idea to revive a dead thread. Best to start your own thread with all relevant details for best success. Your solution is to reverse bleed air out of master by compressing caliper pistons a bit to force air back out. This will work temporarily. Rebuilding master cylinder can help for awhile but new replacement master cylinder is the permanent fix

 

I replaced the stock m/c on my SDGT with a Brembo RCS Corsa Corta. I still get air in the lines! This leads me to believe that whatever the problem is, it's not the m/c. Also, the RCS is awesome!

 

Do the levers hit the switch gear housings? Guessing no

 

A friend (who is a master mechanic and engine builder) had to bleed his Aprilia Tuono V2 Factory front master once a month to maintain braking pressure. Never did figure out why in several years of ownership. Evidently, some manufacturing defect causes some Brembo mc's to suck air. Possibly the splitter block under the bottom triple clamp has a porosity issue?

 

I have a theory. I suspect warm brake fluid cools and shrinks fluid displacement and draws air into master cylinder as fluid cools. Just a theory

 

According to this, your theory is plausible. If the ventilation of the reservoir is blocked or restricted, the4 resul;ting vacuum wi9ll tend to pull air in from wherever it can. Racebikes use socks around the res to soak up spillage, that, without ventilation, could not happen.

Do I need to change my brake fluid? - BG Find A Shop

As vehicle owners, we assume our vehicles will be reliable. We trust that the brakes will stop the car, every time. Most people don’t really question how the

bgfindashop.com

.

 

Didn't know that was the reason race bikes used socks. I thought it was just to cover up the clear reservoir. Sounds like I'll end up doing a bleed. It's just weird that for the first year and a half there was no issue and now out of nowhere just sitting in the garage there's no pressure. It usually just takes one crack on the bleeder to get pressure back up.

 

In the garage I can pull a soggy lever enough to hit the cluster but in use there haven't been any issues. When the brakes are well bled I have to pull hard to get the lever touch the cluster. There is enough adjustment in the lever to adjust any issues away and less lever travel is needed so it works out. Again, the RCS is awesome. Even with a soggy lever there haven't been any issues.

 

This **** is driving me crazy with my '14 SDR. Lever goes right to the bar, but if you pump it a couple of times it's completely fine. Then let it sit a few minutes it's back down to the grip again. I've replaced the entire master cylinder with a brand new $400 OEM one, flushed out the lines, tapped all the fittings and junctions, no bubbles at all from anywhere when bled either at calipers or MC.

Sucks when you're riding, because you never know how much pressure you have to give to get a given amount of braking force - it's super sketchy and feels dangerous. I can feel the lever sinking toward the bar while braking down a hill, for instance.

On the one hand, there's absolute zero leakage of brake fluid anywhere, so how can it be anything but fluid bypassing the piston in the master cylinder? There's nowhere else for the fluid to go, and the level in the reservoir never goes down. But on the other hand, it's a brand new OEM M/C straight from KTM, so how is it gonna be failing like that?

 

This **** is driving me crazy with my '14 SDR. Lever goes right to the bar, but if you pump it a couple of times it's completely fine. Then let it sit a few minutes it's back down to the grip again. I've replaced the entire master cylinder with a brand new $400 OEM one, flushed out the lines, tapped all the fittings and junctions, no bubbles at all from anywhere when bled either at calipers or MC.

Sucks when you're riding, because you never know how much pressure you have to give to get a given amount of braking force - it's super sketchy and feels dangerous. I can feel the lever sinking toward the bar while braking down a hill, for instance.

On the one hand, there's absolute zero leakage of brake fluid anywhere, so how can it be anything but fluid bypassing the piston in the master cylinder? There's nowhere else for the fluid to go, and the level in the reservoir never goes down. But on the other hand, it's a brand new OEM M/C straight from KTM, so how is it gonna be failing like that?

This is exactly what happened to me on my 2015. I put on a brand new master cylinder $600 but still wouldn't hold pressure. Before I bought the master cylinder I had a KTM dealer power bleed the system including the ABS unit but it didn't work and they (like me) believed the mastercyclinder was fcuked.
After I installed the mastercyclinder with no success I pulled apart the brake calipers and replaced all the seals again it didn't work. I really didn't think the seals were a problem as there was no fluid leaks anywhere but I thought I would eliminate that possibility.
I then did something that I should have done first up that would have saved me a lot of time and money, lesson learnt. I bought two long banjo bolts then uncoupled the brake lines from the ABS unit and joined the lines together using the longer bolts. After bleeding the brakes they became rock hard and stayed that way.
So it was the ABS unit all along but did not show up any faults and the KTM dealer didn't pick it either.
A new ABS unit here in Australia cost $3500 but there was none in the country. After putting down a $500 deposit I waited three months and it still hadn't left Europe because of the financial problems KTM are having. The dealer couldn't tell me when it might turn up so I got my deposit back. I now ride the bike without the ABS and traction control, that's not an issue for me but I guess it will be if I ever sell it.

 

More than likely loose caliper mounting or possible brake hose failure. Hope you checked master cylinder lever free play. Too tight or zero clearance will also cause your symptoms.

 

Everything with the M/C seems reasonable and when it's not being spongy it's exactly expected. It's just sometimes it decides to sink right down to the bar. I'm curious what you mean by caliper mounting - do you mean the caliper being oriented so that weight or stress tends to push the pistons back into the pots? I guess this is a possibility worth looking into.

 

Be sure to adjust master cylinder lever free play exactly as specified in your service manual. This setting is critical to brake operation. Your master cylinder converts your lever pressure to hydraulic pressure and it's transmitted to calipers where it's hydraulic pressure is converted to mechanical pressure again. Your caliper mountings or rotor mountings or anything mechanical can cause excessive travel/movement to dissipate more hydraulic pressure/stroke. Imagine your master having the ability to generate 1 inch of movement to fully lock calipers normally but wear or damage has now required 2 inches of movement. Your lever needs to travel further. Loose wheel bearings, loose caliper mountings can all cause this additional travel. Lift front wheel off ground. Watch caliper movement when applying brake and rotating front wheel. Observe any excessive movement or travel.

 

I had a similar issue with my BMW S1000's rear brake. Replaced MC but didn't sort the issue. Took it to dealer to get bled using BMW computer where it was diagnosed as a bad ABS pump. At ~$2k, told dealer no way. Bought new rear brake line and bypassed the abs pump which worked fine.

You can try KTM shop for bleed but will likely have same issue. Maybe it's the ABS pump and you want to retain ABS so you buy new pump. But you also have an option to delete ABS with new brake lines directly from MC to calipers for a fraction of the price.

Good luck.

 

Just as an experiment I loosened the caliper mounts to avoid any pressure that would tend to push the pads apart. Zero movement of the calipers when the brakes are applied, which is disappointing since it's one of the few other plausible explanations, heh. Lever free play is adequate, there's zero pressure on the piston until there's a bit of lever travel, and when there's sufficient pressure, the full travel of the lever ends well short of the bar.

It's just that after no lever squeeze for a minute or two, the first pull is very soft. The second pull is firm and behaves exactly as it should. It's almost as if the pads got slightly pushed apart in between, but I'm confident they're not.

The shop seemed pretty convinced it's a master cylinder problem, but.. this is a brand new one, new brake fluid, bled at the calipers and the master, etc.

 

Just as an experiment I loosened the caliper mounts to avoid any pressure that would tend to push the pads apart. Zero movement of the calipers when the brakes are applied, which is disappointing since it's one of the few other plausible explanations, heh. Lever free play is adequate, there's zero pressure on the piston until there's a bit of lever travel, and when there's sufficient pressure, the full travel of the lever ends well short of the bar.

It's just that after no lever squeeze for a minute or two, the first pull is very soft. The second pull is firm and behaves exactly as it should. It's almost as if the pads got slightly pushed apart in between, but I'm confident they're not.

The shop seemed pretty convinced it's a master cylinder problem, but.. this is a brand new one, new brake fluid, bled at the calipers and the master, etc.

Unfortunately the last piece of the puzzle is the ABS pump. If it's piston/seal is leaking you'd never know it externally as the fluid would just bypass it.

Hopefully a good bleed with the dealer tool sorts it for you but go in prepared for the worst.

Good luck!

 

The front brake line goes from the MC to the ABS pump, another line runs from the pump to the splitter under the lower triple clamp and then down to the two calipers. If there is any kind of foreign material or debris in the brake fluid it can foul the ABS pump seal.

What year is your bike? Has the brake fluid been flushed at interval spec'd in manual? If not, debris can foul up the pump. That was the issue I had with my 2014 S1000. As I mentioned, I bypassed the ABS pump as I was not willing to spend $2k for a new one. Bike was less than a month out of a 3 year warranty which just added salt to the wound.

Anyway, hope you get it sorted.

 

Mine went away after I flushed my fluid. I don't know if it was a coincidence or what.

 

Yeah it makes sense that crud could foul the seal in the ABS pump. I'm still not really grasping where fluid bypassing that seal would go though, other than to the calipers. Anyway, the bike has had all its services and fluids changed on time. I'm half tempted to bypass the ABS pump just as a diagnostic but I don't really have a place to tear the bike apart to get at it. Can't really ride it much now though as the master cyl doesn't seem to hold pressure for long.