Topic: Dual Disc CB550 Brakes locking

[timmangan]

I recently ( two days ago) converted my CB550 to a dual disc front end.

I had a spare 550, so I reversed the caliper, put the disc on, switched over to CB650 brake lines (also spare parts bike), kept the CB550 master cylinder and figured it should be good to go.

However, the wheel wont move. When I loosen the two bolts on the new caliper it loosens it up, but when its tightened down it gets stuck.

I have put some washers in to space it out so the inside pad has a little more room, but nothing seems to get the wheel going.

Any ideas?

[timmangan]

[bryanj]

Caliper you fitted has a sticking piston?

[timmangan]

I will throw some grease in it tonight to see if thats the case, but the brake pad closest to the wheel is the one that seems to be getting pulled tight against the disc.

I have been trying to space out the mounting bracket to move it over, but nothing seems to work.

Ill try the grease, any other thoughts?

[Muckinfuss]

I wouldn't use grease.  It's a contaminate to brake fluid and you'll create more problems than you want to solve.  Right out of an automobile owner's manual:  "Do not allow petroleum base products to contaminate the brake fluid- all brake seal and components could be damaged causing partial or complete brake failure." 

if this was my problem, I'd pull the newly installed caliper and block the piston so it can't move.  Apply the brakes and see if the problem is still there.  If so, you might have a master cylinder issue.  Reverse the test to verify that the newly installed cylinder is indeed in the lock up.  If both are locked...master cylinder is suspicious.  Could be a contaminate in the uber tiny return hole.  If the original is locked, but not the new....work on the original.  If new, but not the original.....you get the idea.

[timmangan]

yep, that would suck. Any ideas on how to lube that puppy up?

[Muckinfuss]

brake fluid is a lubricant in its own right.  until you know the problem...see my edit to the other post....you can't fix it.  I don't know how good the parts are that make up your new system,.....but the pistons, if metal, should be nice and shiney....the seals not swollen...the inside of the caliper as clean as you can make it.  Once convinced that all is sanitary and as matched as possible, then assemble in stages until the problem surfaces, if it does at all.......the last thing changed is where your culprit lives.  Again, brake fluid is the only lubricant needed inside the disc brake system.

Maybe you've already done this research, but something sticks in my head that I came across someone who successfully did what you're doing and they had to flip the right side lower leg around so the caliper was on the backside.  I've never done the brake thing, so I could be mixing up things I've picked up along the way, but check this out also.   http://www.dotheton.com/forum/index.php?topic=52168.0

[timmangan]

Sweet mate, that updated post I think will get me there.

Thanks again

[alacrity]

Some basic hardware questions I would ask (myself).
are the two discs of identical thickness?
are there new and identical pads in both calipers?
are there new and identical pistons and seals in both calipers?
Did you test to see if the piston would move in and out in both calipers prior to installation?
Are you certain you have the pads and pistons installed correctly?

Figure out which side is locking/sticking.  If the system is still all together, loosen the caliper mounting bolts on one side (releasing the pressure) and see if the wheel turns. If the wheel is locked, retighten and loosen the other side.  IF one side is the culprit, it's probably a hardware problem.  If both sides are "locked" you have a fluid prob (most likely).

Did you test for fluid flow into and through both calipers? (put a rubber tube on each and have each drain into a separate measuring device - like a grad.cylinder, keep refilling the MC reservoir as you slowly pump the fluid through.  Both receptacles should fill at an identical rate.  This is also a good way to be sure your lines are generally clear and clean. Obviously you will have to bleed both sides afterward.

[timmangan]

Hey Alacrity,

The discs and calipers are both of cb550's, the discs are the same, I will double check on the calipers.

They have different pads because they came off different bikes.

Pistons and Seals im assuming (It is just an assumption) that they are both factory.

The left side was fully functional prior to installation, the right side, not certain. I will know once I pull it apart tomorrow afternoon.

Pads are installed correctly, I assumed the piston on the new caliper was, the old is for sure.

When I looses to calipes main bolts the wheel moves, when tightened, no more movement.

[bryanj]

You one of two problem:-

(1) you have not spaced the caliper enough for the inner pad to clear the disc

(2) The piston is sticking in the bore and not retracting enough to free the disc


Either of these will go away when you loosen the two caliper bolts

[timmangan]

Bryan, I did realize that the caliper mount was a lot further over than it seemed to be, I put spacers in between the bracket and the fork, but didn't fix the problem.

What seems strange though is that the tensioner screw is quite undone, but the mount doesn't spring back as far it can, it just seems to get stuck as well, and even with pressure applied it doesn't move.

I think ill be taking the caliper apart tomorrow afternoon to see whats happening inside.

[bryanj]

Does the caliper arm move freely on the pivot?

[alacrity]

Imho you are playing russian roulette here. Id you dont have 100percent fresh parts in this critical system, or at least if you haven't pulled it all apart down to the last washer and spec'd/mic'd everything, (including checking both discs for proper min diameter and flatness- in spec "runout", you just have no idea what you are trusting your life to.

The fact that you are assuming parts are OEM but you don't in fact KNOW what they are, what condition they are in, if they are installed correctly or if they are working as a designed and engineered system scares me.  It should scare you. It means you aren't in control of the situation-- or your destiny.

i would go back to the start.  U had a functional braking system.  Disconnect and remove the "new" caliper, rotor, brackets and banjo fittings.   Take it all apart.  Measure everything properly.  Test the caliper actuation and piston return.   And then if its all great, and you find you have matching "mirror" twins for parts and function, put fresh matching pads in both calipers. You don't want a different coefficient of friction or heat rating or any other characteristic from one side to the other.  They have to act in perfect sync.  You wouldn't put a flip flop on your left foot and a hiking boot on your right foot and then go for a run, would you?

[Ewan 500K1]

looks like you may have the mudguard mounting bracket in the wrong place on the right hand side. It should go between the fork and the pivot mounting bracket. (see picture) Looks like you have it on top of the mounting bracket. Try changing it and see it that solves it for you. Also see the adjuster screw in the attached picture, when correctly set up the adjuster screw doesn't protrudes through its hole at all on the right hand side.
Distance between the inner pad and the disc should be 0.006 inches, so you need to get a set up in place that achieves that.

[flybox1]

this happened to my on my dual disc conversion.
your caliper faces are NOT square to your rotor face.  use a couple of straight edges to confirm.
if they are not perfectly parallel, your piston(pad first) will be pushed against the rotor on edge, which causes the piston to be pressed into the piston bore at an angle,  locking it in place, and locking your pads against the rotor.
you need to get the pads out, calipers back on the forks without the pads, and make sure the caliper faces are perfectly parallel to the rotor.
shim and adjust the slave pad adjuster as needed.

[timmangan]

Flybox1, how straight to they need to be? Mine look straight to me but these things are not moving.

Of the bike the pads move back and forth freely, on the bike they move forwards but just won't come back, almost like they are locking in place.

But they do look straight.

When you say straight, do you mean parallel with the disc? Mount parallel to disc, caliper parallel to disk (I'm assuming of the mount is parallel the caliper will be also).

Do I need to mess with the tensioner spring at this point?

[SUELZER]

I'm getting ready to do the conversion on my 550. Was able to dig up some stuff from way back.

Great step by step walk through
http://www.salocal.com/sohc/tech/dual_disks/dual_disks.htm

The thread I pulled the above link from
http://forums.sohc4.net/index.php?topic=53532

Hope you can find a solution to your problems

[scottly]

In addition to the fender brace, the axle is installed incorrectly: the end with the nut should be on the other side.