Rear brake locked?
 

How does the rear master cylinder adjustment bolt and lock but work. I was riding home from work and my rear brake locked up? As soon as I loosened the lock but it came free again but I'm not sure how that affects anything? The lock but I had right against the rear set threads but is this how it goes?

I'm referring to the 10mm nut right against the boot (what's it for?) and the 12mm lock nut(does it go against the rear set threads or the 10mm nut?)


Attachment 16665

you may need to either rebuild the slave or at the least,take it apart and clean it out and put new fresh fluid.
if it locked up,chances are there is sludge and moisture/bad seal,worn out cylinder etc etc......
i have a friend that has a 900rr and did the same thing.i cleaned it,new guts and fresh fluid,and its better than it ever was,hope this helps.
K L Rear Brake Master Cylinder Rebuild Kit Honda VTR 1000 F Super Hawk 1998 2004 | eBay
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Check to see if the caliper axle is seized.

well its unlocked now. its because when i installed the new rearsets the other day, i adjusted the top (10mm) nut wayyyyyyyyyyyyyy up because i thought thats how u adjust the lever which im not exactley sure what that does but it made my brakes stick. i loosened it back down to what seems to be a normal position so and it seems to work much better. im still not sure what that nut actually does which is what im trying to find out. it seems to be some adjustment in terms of how hard the brakes bite but i could be wrong. anyway im hoping that doesnt happen again because it suckedddd! fortunatley it didnt start locking up until i was like half a mile from my house. weird though but ill find out if its still an issue tomorow when i hit the canyons (hopefully its not)

I know you are having fun learning on this bike, but PLEASE make sure your rear brake works properly before riding at 10/10 tomorrow. I would hate to hear you crashed and messed up the bike or worse yet, yourself.

Just going off the picture, as I never adjusted mine. That said, the nut you are talking about is the either the jam nut or the nut attached to the bolt. You loosen the jam nut, then turn the other nut to adjust the brake lever where you want it, then bring the jam nut down and tighten it (the jam nut is tightened against the other nut to prevent it from moving, hence the name). They have no effect on the "bite" of the pads.

What I'm guessing happened, is that you loosened the jam nut all the way up, and when you hit the brakes, the jam nut was shoved inside the master cylinder and it got stuck inside there, keeping the brakes locked. You can fix it by simply pulling up on the brake lever.

When you adjust the linkage you have to make sure that the master cylinder is fully extended. If not the brake pads will not retract fully, the drag will heat up the caliper and brake fluid and eventually create enough pressure to lock up the brakes. When everything cools down the brakes will release. When the master cylinder is fully extended the brake line and caliper are vented to the master cylinder reservoir. When you apply the brakes the first movement of the master cylinder closes off the vent port so the system can build pressure. Make sure your linkage allows the MC to extend fully or you may end up on you're arse.

A common way for rear brakes to "lock" is that they begin to drag. This usually happens from a cocked pad misinstalled or knocked out of line in some way.

It can also be a maladjusted lever as stated or jammed lever.

The bike easily overcomes this drag and rides on, but building friction heats the rotor then caliper to the point that the fluid boils and creates huge pressure to apply the brake.

I have seen it done on the racetrack on every kind of bike up to an Aprilla RSV.

As stated. Be aware of how dangerous this situation is. Motorcycling is treacherous with a perfect bike but this is a way to have a single vehicle crash for no reason.

Ride like an old lady til you are sure all is well. Ask many questions but dont get on a bike with a brake adjusted to drag (like you just did).

You only get so many passes that dont end badly.

definitely good to hear peoples opinions on causes. so to let you guys know it was a progressive thing. i could feel it dragging more and more as i rode, not a bite all of the sudden. plus my work is literally 2 minutes from my house so it all happened relatively fast. definitely see the safety risk which is why im just gonna cruise around with my buddy on his harley today rather than wearing my leathers and riding at 10/10. im bringing tools with me should any problems arise. i would never just go out there and push it with an issue happening the night before. i like to just take it easy after ive installed new parts or made adjustments until im sure everything is correct and safe. ill let you know if it happens again while im out today.

also the top nut in the picture, closest to the MC is not part of the bolt (which is what i had originally thought) it goes up and down on the bolt just like the lock nut does so thats why i said in an above post that it must adjust something. the way to adjust the pedal is by threading the bolt into the housing of the rearsets more or less to move the pedal up and down. but the nut right under the boot rotates independantly of the bolt some what im reallly trying to figure put is what that bolt does? but after searching ALOT on here, the web, through the service manual, and parts fiche's i still cant figure out ALTHOUGH it does seem to be an adjustment on the brakes as in making them a more frim or a more plush feel? thats why i said i think they have to do with bite. but thats why im asking you guys because i really dont know

it's a free play adjuster, thats all...It does not change the force applied.. for more "plush" or less braking.

That said, in the OEM pedal, MC design,, the push rod (the thing with the adjuster nut) is set an a 90 deg angle to the MC.. It may be just the picture you posted.. but it looks like the aftermarket rear sets have that push rod going into the MC at an angle.

Perhaps it is driving the MC piston at an angle into the MC bore and causing it to bind?

not it has all to do with the bottom 12mm lock nut although im not sure why. but im under the impression that the nut goes agaisnt the rear set threads to keep the bolt from moving. but thats what causes the brakes to drag, as soon as i loosen that nut it frees up so maybe the lock nut goes against the 10mm adjustment nut at the top?

The lock nut in stock location, assembly, is tightened down against the U shaped clevis the pedal attaches to.
https://www.superhawkforum.com/forum...1&d=1391381573

If locking the nut against the rear set clevis causes the rear brake to lock... and keeping it loose does not.. Is locking it changing the angle just enough to cause it to bind?

i dont think it has anything to do with the angle. i agree the picture it looks like its not straight but as soon as you start to depress the brake the angle changes and its goes in straight. i juts dont see how that one nut could cause the brakes to drag? i think it might have to do with how much of the bolt is showing, considering thats how u adjust the lever height. but what it seems to be is that if you try to adjust it so the lever is higher side then when the brake goes to return, it cant fully extend becuase of the way the rearset is made causing the brake to drag a little, heat up, and eventually lock.

She it, I shouldn't have read this post.

I went for a 150K ride yesterday and the back brake was dragging.


No amount of fiddling would free it up, then eventually it freed itself.






I certainly don't want to experience a wheel lock up whilst charging hard.


Will investigate tomorrow night and report findings.


One thing that concerns me is the amount of flex in the rearsets.


Hope this has nothing to do with it.

yea its been really bugging me. and i agree the rearsets do have some flex especially the brake when you get on it hard. and for me the dragging and locking is only an issue when that lock nut is tightened down against the rear set. i did a litte more fiddling last night to try and resolve the problem so we will see if i have corrected it. i think it has to do with coming the bolt coming out of the MC at a bad angle. in the stock setup it comes straight out of the MC but the closest it can get to straight with the new rearsets is with the pedal adjusted adjusted at a steep angle. how do you have yours adusted?

I had a GSX400 that was doing the same thing, aftermarket rear sets, the previous owner that had installed them didn't shim the master cylinder properly and same thing, the angle looked off at rest but as soon as it moved it seemed to go back to the correct 90* angle... ehh wrong, the shaft of the bolt was just bending under the pressure where it meets the piston, this is bad mkay.

A couple of shims later behind the master cylinder where it bolts to the rear set and problem was solved, the brake even returned properly without a return spring.

whats a shim?

Shim, Spacer, washer :)

ahhh so your telling me ive been confused on countless posts all because of a synonym? geesh. anyway how would that affect the angle? i dont think its a poor angle as a result of the MC being too far to the outside of the bike ( which is why you would "shim" the MC if my thinking is correct) I think the bad angle is a result of the threads for the bolt on the MC not being far back enough which results in the bolt being pulled towards the front of the bike as the brake pedal returns to its normal position

At least we know what we are dealing with now. The piston inside the master cylinder is binding, causing it to stick or "lock". Sounds like it would be a simple fix. Either shim the master cylinder at the mounting bolts or you might have to slot the mounting holes for the master cylinder to move fore and aft. I don't have a set of these Danmoto's, so I'm just guessing how everything is mounted.

Just visualize the master cylinder in the correct position. If you can't visualize it, then use a straight edge, like a small 12" ruler. Then do whatever modifications necessary to get it to that position.

pleased to say that i believe the issue has been sorted out. i just got back from about a 50 mile cruise up the coast and no drag, sticking, or locking at all. remember that the last 2 times the dragging/locking happened it happened within a mile or so of the start of the ride. what seems to be the issue was my attempt to have the pedal in the same position as the stock rear set since thats where i was use to it. the dan moto site does say that these rear sets have a steeper angle on the pedals to support the more aggressive knee angle. so i think i was trying to put things in a posistion they werent meant to be. i do think if they had a little more product testing the could have sorted things out a little better. i will say though that after the ride this morning, the steeper angle is actually a little more comfortable once you get use to it.

I have a huge foot so I like the steeper angles.. you wouldn't believe how much farther down the shifter peg is from the brake lever on my hawk. I wish I could adjust more of an angle into the brake lever lol

And I couldn't tell from the photo what needed to happen to make the Brake master cylinder right, I was just stating my experience and how I solved it so that the Op and others could have that information and learn from it if there problems are similar so they know where to start looking to solve it

Will try adjusting my lever down to night and see what that does.

Everything is way out of line and the rod enters the master cylinder at a ridiculous angle.

Now to work out how to get it straight.


Will take it all apart and start again and try and get the rod straight by adjusting and shimming.

I wonder if sailorjerry had the same issue? If he hasn't, I sure hope his rear brake doesn't lock up in the future.

You would think Danmoto would've designed these rearsets a little better. The rear master cylinder working properly should've been a given in the design.

I very much agree that there was poor product testing BUT the website says the pedals are angled steeper to suit the more aggressive knee angle so I think have been use to the stock setup on the hawk we are trying to put the lever at an angle it wasn't designed to be at. So although you can put it in a similar place as stock it's meant to be angled more downward, and when you do angle it down the MC is straight

Mucked around with mine last night.

Angle of m/ cyl rod is much better but still not perfect.


Will play with it tomorrow.

I'm also going to put some spacers where the Mc bolts on because it puts the bolt going into the MC at a very slight angle which prolly contributes to the dragging but after I readjusted my pedal to a steeper angle I havnt had anymore issue

On mine the M/C mounting plate moves.

Prick of a thing but will play with it more until it's right.


I want to ride tomorrow and it must be right otherwise I will be on edge and won't be able to enjoy the ride.


Not like when I was younger, as long as the wheels turned it was ridden.


Sometimes knowledge is a dangerous thing EH!

Played and played till I was happy.

Have been for a ride of approx 120 Klms.


Didn't have any probs, so now I am happy as well.


More of an adjustment thing on my part than a bad design I think.


The mounting plate was moving because the little screw that goes into it from the back was loose.