NC700X front brake master cylinder question

[TacomaJD]

Anyone ever pulled apart the front brake master cylinder on their bike? My 2013 model front brake lever feels funny and I do not need to encounter a problem with front brakes while on track. It stops good, but almost feels like it has a catch in it. I'm wondering if I may have gotten air in the lines when I done a fluid flush last year, but I'm also wondering if the master cylinder could be failing or dirty. It's not a hard catch, it's difficult to explain. It's like the lever gets hard sometimes and brakes don't grab as good.

I currently have the brakes apart, going to clean the pistons thoroughly, grease the pin, do another fluid flush/bleeding, but I'm also wondering if the oem master cylinder can be taken apart and possibly cleaned, or is it a closed mechanism that you pretty much throw away and replace if needed? I've never messed with master cylinders too much, so this is a bit of a new problem for me.

A new oem master cylinder on Pro Caliber's site is $200......I can get a Brembo master cylinder for $90 more. But I'm not sure what mm the Brembo would have to be to replace the oem one.

Any general info you guys could share would be appreciated.

 

[670cc]

This is not much of an answer but a wild hunch guess from a distant memory is that there is a check valve or port of some sort in the master cylinder, which upon getting stuck or blocked, causes a hard brake lever or brake drag.

I’m not in a place where I can check my service manual, but perhaps it has a section on master cylinder maintenance or rebuild.

 

[TacomaJD]

Thanks for that. I picked up some new dot 4 and brake cleaner after work today, but ended up mowing rather than working on the bike.

When it does what it does, it will do it while sitting still, so I should be able to tell fairly easily if a thorough bleeding helps anything. If not, then I guess I will have to resort to monkeying with the master cylinder, if not replacing it. I hope to go to the track either the 26th or 27th so I need this sorted by then.

 

[davidc83]

Sometimes your condition is caused by moisture (water) in the brake line...with all the heat and humidity we have had this year in the ohio/tennessee river valleys, I wouldnt be surprised....I had the condition, changed the brake fluid/bled the lines, and the condition was resolved...had the same issue on my C50 Boulevard, replaced the fluid and bingo, problem resolved...

 

[TacomaJD]

Sometimes your condition is caused by moisture (water) in the brake line...with all the heat and humidity we have had this year in the ohio/tennessee river valleys, I wouldnt be surprised....I had the condition, changed the brake fluid/bled the lines, and the condition was resolved...had the same issue on my C50 Boulevard, replaced the fluid and bingo, problem resolved...

I flushed fluid front and rear last summer before my first track day on that bike, it started doing this within a few months during the fall. It stays in an insulated garage at home and didn't really get ridden very often on the street, although it did get a little wet once on a deals gap trip back over the winter, but it wasn't torrential. Either way, I'm 99% sure moisture isn't the culprit.

Another factor, I flushed the fluid, then a few weeks later I swapped out oem pads for some EBC HH pads. The oem pads weren't in terrible shape, so I just put the EBC's in, compressed the pistons, mounted caliper back on and tore out. Once I started noticing the front brake lever feeling funny, I thought well maybe the reservoir is too full now that I put thicker pads in the caliper, so I removed the cap, and took out some of the brake fluid, problem still exists. Although I haven't bled them since. It doesn't do it all the time, but it is frequent enough to be an issue. It hasn't caused an issue yet, but it has me paranoid enough about it to try and remedy it because it could be very dangerous if it fails. I may get a chance to dig further into it tonight or this weekend. Will report back with my findings/results after close inspection and thorough flush and bleed.

 

[dduelin]

Sounds like a loose bit of trash or glop blocking the compensation port.

 

[dduelin]

Sometimes your condition is caused by moisture (water) in the brake line...with all the heat and humidity we have had this year in the ohio/tennessee river valleys, I wouldnt be surprised....I had the condition, changed the brake fluid/bled the lines, and the condition was resolved...had the same issue on my C50 Boulevard, replaced the fluid and bingo, problem resolved...

The reason vehicle manufacturers give time and mile recommendations for replacing brake fluid is prevention and safety. Brake fluid 100,000 miles old is on borrowed time.

 

[brb]

Brake fluid is hydroscopik, will absorb moisture(unless its dot5). That allows any moisture to dissapate thru entire system. I can suggest a few pointers on brake work for all bikes and cars. Never compress the caliper and push old fluid back to master. You should open the bleeder first(use a small clear line that goes into a bottle) and check that it flows by itself that is known as a gravity bleed. That shows that the brake hose is not internally compromised and the compensator hole is open(some mechanics will pinch the hose dont know of any MFG that recommends that). Then as you compress the caliper all that dirty fluid does not go up to the master. Calipers get very hot and just like a hot pan on the stove can scorch the fluid that can restrict caliper action. Next compress the pistons they should move with very little pressure(that shows that the rubber seals are working right that is what allows the piston to retract after release of master). Clean all sliding and lubricate with the correct high temp grease. Install new pads reassemble caliper (check MFG recommendations thread lock usually called out)and when pumping up master use small pumps the seals in the master under normal use move in the first half of master bore if you pump further than that the seal will go into the "gray"area of master and can cause a problem. I learned a few of these tips over the years was a Honda Motor Cycle tech in the 80s and ASE master tech 90s now I inspect aviation assys.

 

[Wedders]

Sorry if I’m stating the obvious but anything wrong with the fluid will usually cause a spongy brake lever. I would consider something mechanical.

 

[wheel_of_steel]

Anyone ever pulled apart the front brake master cylinder on their bike? My 2013 model front brake lever feels funny and I do not need to encounter a problem with front brakes while on track. It stops good, but almost feels like it has a catch in it. I'm wondering if I may have gotten air in the lines when I done a fluid flush last year, but I'm also wondering if the master cylinder could be failing or dirty. It's not a hard catch, it's difficult to explain. It's like the lever gets hard sometimes and brakes don't grab as good.

I currently have the brakes apart, going to clean the pistons thoroughly, grease the pin, do another fluid flush/bleeding, but I'm also wondering if the oem master cylinder can be taken apart and possibly cleaned, or is it a closed mechanism that you pretty much throw away and replace if needed? I've never messed with master cylinders too much, so this is a bit of a new problem for me.

A new oem master cylinder on Pro Caliber's site is $200......I can get a Brembo master cylinder for $90 more. But I'm not sure what mm the Brembo would have to be to replace the oem one.

Any general info you guys could share would be appreciated.

Hey TacomaJD, yes, master cylinder rebuild kits exist, as do caliper rebuild kits. Sometimes aftermarket companies like all balls offer them, sometimes it's genuine only. My 700SA might run a different master cylinder to your 700X, but I have used honda part number 45530-KVY-911 to successfully fix my dragging front brake. That part number is item number 20 on this diagram: https://bluecitymotorcycles.com.au/...l=4847&assembly=68772&accessory=&adrAssembly=

I'm not sure about diagnosing your problem. I bought my 2012 in 2018 and it only had 15,000 km on it, and original brake fluid. So there were a few problems with various rubber parts on the bike that had hardened from lack of use and deteriorated fluids.

 

[phoenix02]

Brake fluid is hydroscopik, will absorb moisture(unless its dot5). That allows any moisture to dissapate thru entire system. I can suggest a few pointers on brake work for all bikes and cars. Never compress the caliper and push old fluid back to master. You should open the bleeder first(use a small clear line that goes into a bottle) and check that it flows by itself that is known as a gravity bleed. That shows that the brake hose is not internally compromised and the compensator hole is open(some mechanics will pinch the hose dont know of any MFG that recommends that). Then as you compress the caliper all that dirty fluid does not go up to the master. Calipers get very hot and just like a hot pan on the stove can scorch the fluid that can restrict caliper action. Next compress the pistons they should move with very little pressure(that shows that the rubber seals are working right that is what allows the piston to retract after release of master). Clean all sliding and lubricate with the correct high temp grease. Install new pads reassemble caliper (check MFG recommendations thread lock usually called out)and when pumping up master use small pumps the seals in the master under normal use move in the first half of master bore if you pump further than that the seal will go into the "gray"area of master and can cause a problem. I learned a few of these tips over the years was a Honda Motor Cycle tech in the 80s and ASE master tech 90s now I inspect aviation assys.

I think you're onto something here. I hate to start a new thread and spread this info out among several posts. I compressed my front caliper and did not open the bleeder valve. Now I can't get a hard lever. I have run a whole can of new DOT 4 through it, took the master cylinder plunger out to make sure the seal wasn't folded back, power bled it at the caliper and still nothing. I am not familir with the compensator hole. Is there a check valve in there? I must have run some dirt into it, wherever it is. I have removed the little sheet metal deflector inside the reservoir and can see the hole through clear fluid. It looks like there is a black line across the hole, like it's a flathead screw. I'm planning on pulling the master again, pulling the plunger and blowiing out the hole. Am I focusing on the right area?

 

[phoenix02]

I think you're onto something here. I hate to start a new thread and spread this info out among several posts. I compressed my front caliper and did not open the bleeder valve. Now I can't get a hard lever. I have run a whole can of new DOT 4 through it, took the master cylinder plunger out to make sure the seal wasn't folded back, power bled it at the caliper and still nothing. I am not familir with the compensator hole. Is there a check valve in there? I must have run some dirt into it, wherever it is. I have removed the little sheet metal deflector inside the reservoir and can see the hole through clear fluid. It looks like there is a black line across the hole, like it's a flathead screw. I'm planning on pulling the master again, pulling the plunger and blowiing out the hole. Am I focusing on the right area?

Follow-up. I cleaned out the reservoir and the two ports with brake cleaner and blew it out. I power bled it again and could not get it to firm up very much. I took it down the street to the carwash to get all the brake fluid off and the brake immediately firmed up. Go figure. No power brake system here but for some reason, that's what it did. I may never know what the problem was but for sure I will open the bleeder next time I compress the caliper pistons to get clearance on a brake disc.

 

[brb]

The compensation port is the hole in the master that allows the fluid in the master to supply the cylinder piston. When the brake lever is released this port opens up and allows the pressure to lower by allowing it to return to the reservoir. This port along with the rubber bladder in the cap(which by the way has a hole in it. the system is vented to the air that is how moisture gets in) allows the fluid to compensate for the brake pad material wear. With brake hoses especially rubber its good to bend and move the hoses it allows any air to move up to the master. Most likely the air self bleed thru this port when you rode it. As far to the original post goes every master I have come across can be disassembled. If you do be sure to have new seals to install and do not scratch the inner bore.

 

[T S N]

When mine feels funny/crunchy, I pull the pivot pin on the handle and lube the pin and the part that pushes the piston. Done it 4 times in 76000 miles.
Fluid gets changed every time I remove a wheel.