Topic: Front wheel does not spin after reinstalling brake caliper.

[jcupit01]

Hey all,

I have a 75 CB550k1 that I have been rebuilding over the winter.  One of the first things I did was rebuild the master cylinder and replace the pads.  I thought everything was together fine and it sat while I did the top end rebuild.  Taking it out for a test run I noticed it was struggling to get going, turns out the front wheel spins very little, there is active resistance.   I loosened the caliper bolts and it spun great, so obviously the brakes are screwy.

It does not matter what the caliper adjuster screw is doing or where it is set, as soon as I tighten the two caliper bolts the wheel locks up again.  I bled the lines to zero bubble and  I inspected the pads and all looked normal.  The only thing I can think of is that the aftermarket pads I got are too thick or the caliper is not retracting correctly and maintaining a grip on the rotor.  Any thoughts appreciated.

Thanks

[cmonSTART]

I've found too-thick pads before, but rarely. 

The caliper should be free to slide on a couple shoulder bolts I think.  These might be gunked up a bit.  Or, the caliper itself might need rebuilding. 

[OpTiCz]

I had the same issue.
For me, the white ring behind the pad had come off center. Can you post a pic of the pads currently seated?

Sent from my SGH-T989 using Tapatalk

[camelman]

I concur with the nylon ring issue. It needs to rest around the raised bump on the back of the active pad.

[SohRon]

Did you open up the fluid return hole in the MC? That will cause the brake to freeze up. And check that nylon ring (you did install it, right?). One way to test the fluid return is to apply the brake, then release it. Immedietly open the bleeder on  the caliper and if you get a stream of fluid, your return hole is blocked.

Push the moving pad back into the caliper, so that the pad face is even with or below the caliper face, then adjust the gap between the fixed pad and rotor to .006"; that will at least get you started out right at the caliper end, and hopefully you can trace it from there.

[scottly]

Make sure the caliper arm pivots freely on the pin.

[ekpent]

Piston or pad is sticking in the caliper. Whack it with a rubber mallet and see if it free's up till you hit the brakes again.

[phil71]

isn't there a drag adjust, that would possibly be way out of spec once new pads are installed?

[ADW]

Did you open up the fluid return hole in the MC? That will cause the brake to freeze up. One way to test the fluid return is to apply the brake, then release it. Immedietly open the bleeder on  the caliper and if you get a stream of fluid, your return hole is blocked.

DING DING DING! We have a winner! At least in my case...72 CB350F did exactly the same thing after my complete winter redo on it. Was fine for the first couple rides then front was super tough to turn. Ended up using a wire brush wire (stiff, yet small) to poke through the MC fluid return hole and that fixed it.

SohRon...when you say "open up the fluid return hole..." is there a known procedure/recommended size or something? I've had this happen a couple of times now so if there's a piece of "tribal knowledge" that many agree on as to how to open up that hole a touch without screwing anything up I'd love to hear it!

[SohRon]

There is no "accepted" procedure for clearing the return port hole; people use guitar strings, dental pics, random stray wire, etc, when it gets plugged. It definitely requires attention whenever the MC is rebuilt or otherwise renewed, and I would suggest that, if it does clog, it's a good indication that a system flush and MC rebuild is in order.

[ADW]

There is no "accepted" procedure for clearing the return port hole; people use guitar strings, dental pics, random stray wire, etc, when it gets plugged. It definitely requires attention whenever the MC is rebuilt or otherwise renewed, and I would suggest that, if it does clog, it's a good indication that a system flush and MC rebuild is in order.

OK, I thought maybe when you said "open" the return hole you meant people were enlarging it a touch so that it didn't plug so easily.

[SohRon]

OK, I thought maybe when you said "open" the return hole you meant people were enlarging it a touch so that it didn't plug so easily.

No, not at all. That hole is as small as it is for a reason. so we don't want to mess with it. Cleanliness is the word of the day!

[bollingball]

There is no "accepted" procedure for clearing the return port hole; people use guitar strings, dental pics, random stray wire, etc, when it gets plugged. It definitely requires attention whenever the MC is rebuilt or otherwise renewed, and I would suggest that, if it does clog, it's a good indication that a system flush and MC rebuild is in order.

Just for grins if you open your house door do you make a bigger hole or turn the door knob to get in?

OK, I thought maybe when you said "open" the return hole you meant people were enlarging it a touch so that it didn't plug so easily.

[jcupit01]

Some excellent suggestions here.  I will address the MC return hole today, will try the little test.  I took apart the caliper last night and verified correct assembly.  My manual, stated that the piston should be able to be pushed back in "by hand".  Well this definitely was not the case as I had to crank on a "C" clamp to get it back, it was not going easy for sure.

THanks for the help!

[crazypj]

Caliper needs a re-build.
 The seal grove has corrosion in ity and is pushing seal onto piston too tight
 It needs doing every couple of years

[jcupit01]

A rebuild normally entails replacing seal and not the piston right?  I have not torn it apart yet so I cannot speak for the condition of the piston in it's entire length.  I do know a new piston is about $90 new and would rather just get a new seal.  When I drained this caliper last fall, the gunk that came out of it was a brown sludge like I have never seen before.  Obviously this Caliper was ignored for pretty much the entire life of bike.

Also the bleeder valve seems to be broken, at least the nipple is busted. Will replace that as well.

[LesterPiglet]

Be gentle with that nipple. Don't want that snapping off.

[jcupit01]

Lol, it is already snapped off.  I got the bike with it like that.   

[crazypj]

A rebuild normally entails replacing seal and not the piston right?  When I drained this caliper last fall, the gunk that came out of it was a brown sludge like I have never seen before. 

Your probably going to need a new piston. There will be a ring of pitting where the seal touches it.
 Don't buy stock Honda, get either the stainless steel one or the phenolic (on e-bay) about $50.00

[RAFster122s]

There is a member here on sohc4 forums out of texas who has phenolic pistons available to members at a price better than 50.  Dont recall his name, he's in the services section of the site.  He modifies the lincoln ls pistons to fit our bikes...

[jcupit01]

Okay, I am not sure how to remove this piston from the caliper.  I fully extended the piston and gently tried to pull it out but no good.  Ideas or can you point me to a thread that covers this?  I did a search with no good results on this topic.

[70CB750]

Grease gun to the bleader, plug the brake line and pump it out.

[RAFster122s]

You can thread the grease gun in partway at the brake hose/line connection by hand and then pump it out. Works well for me. Since you dont force it it wont messup the threads.

[ekpent]

You can se an air compressor also if you don't want to make a mess or don't have a grease gun Handy.
  But a word of WARNING-Secure the piston with a loosely fit c-clamp,wrap in a good rag and wear good gloves. When the piston lets go it can shoot out like a bullit 

[cmonSTART]

You can se an air compressor also if you don't want to make a mess or don't have a grease gun Handy.
  But a word of WARNING-Secure the piston with a loosely fit c-clamp,wrap in a good rag and wear good gloves. When the piston lets go it can shoot out like a bullit 

I cover the whole works up with an old towel or anything handy to keep the piston from flying away.  It makes an nice little pop, too!

[SohRon]

If it's that loose, a gentle blast from an air gun will do it and you won't have to deal with cleaning up all of that grease; just point it into a corner or something as they can pop out pretty forcefully...
 
That slot that the seal sits in is basically square-bottomed. There's a groove that runs down the middle of the slot that must be cleaned out as well; take a small screwdriver or other metal implement and make sure that slot and groove are clean, clean, clean.

There are a several things that happen with this seal. First off, debris can get under it, build up, and cause the seal to squeeze the piston so tightly it cannot move. Second, that seal flexes and is an important component in retraction of the moving pad, so crud that makes its way into the slot can freeze the seal up so that it can't flex.  Both of these scenarios will lock up the piston. In addition, the seal itself can harden with age and use and not grab the piston correctly, allowing the piston to over-extend itself so that it drags on the rotor. Lots of folks use their old seals but, really, they're cheap and there's no real reason not to replace it when you can, IMHO.

The piston needs to be lubed to work properly, and to ease insertion during installation. Some use brake fluid to grease it up, but that's not recommended. Instead, a thin coating of Dow Corning High Vacuum Grease should be applied to the piston when inserting it into the seal. This stuff is very easy to find on the 'net, which is where I got mine. Highly recommended repeatedly on this site by some real authorities.

Make sure the return fluid port in the MC is clear, as I mentioned in an earlier post. It runs right around .017"- .018" in diameter (just a hair under half a millimeter), so it's amazing it doesn't clog up more often than it does. If it's plugged, high-pressure fluid from the caliper can't return to the reservoir after braking, so the piston is unable to retract, leaving the pads clinched on the rotor.

Next, check that the hose running from the MC to the 3-way joint isn't excessively long and runs in as straight and direct a route from Mc to joint as is possible with no loops, twists or kinks that can either stem fluid flow or trap air in the system.

Once everything is clean and shiny, start your installation by setting the gap between fixed pad and rotor (as outlined above) before you attempt to bleed the brakes, as this setting determines the extent of piston travel. Two Tired has an exemplary write-up covering brake bleeding in the FAQ section of this site that is well worth reading and following for a professional brake servicing procedure.

Good luck!

[crazypj]

SohRon, the seal grove has an angle on the bottom.
I forget how much, maybe 3~5 degrees?
When the seal is fitted, the 'outside' edge is almost flush with bore but the 'inside' edge is noticeably higher.
 You need to be a bit careful cleaning it out

[MCRider]

SohRon, the seal grove has an angle on the bottom.
I forget how much, maybe 3~5 degrees?
When the seal is fitted, the 'outside' edge is almost flush with bore but the 'inside' edge is noticeably higher.
 You need to be a bit careful cleaning it out

I never knew that. So its the groove itself and not the ORing that has the tilt? In other words, fool proof?

[SohRon]

Right, the bottom of the slot is slightly tilted; this helps facilitate flexion of the seal. There's a "U" shaped groove cut into the middle of that that, IIRC, helps hold the seal in position. I was just giving a thumbnail and didn't get into details...   

[MCRider]

Right, the bottom of the slot is slightly tilted; this helps facilitate flexion of the seal. There's a "U" shaped groove cut into the middle of that that helps hold the seal in position. I was just giving a thumbnail and didn't get into details...   

Interesting I never knew that, thanks. 

[jcupit01]

Well the brake is back together and except for a little fine tuning on bleeding it is great.

I used the compressor on the caliper to pop the piston,  it popped with 100psi out, just took about 10 seconds.  The pop still startled me even though I was expecting it

The piston actually looked pretty darn good.  The major issue was UNDER the old seal.  A whole bunch of dirty gritty nastiness that took a bit of brake cleaner, toothbrush and a light touch with a dull screwdriver to clean up. 

After cleaning, installed a new seal, used brake fluid to reseat piston.  Gapped the back pad and tightened it all up.  Just a little spongy but it does not death grip the rotor and it is a very smooth pistony (made that one up) operation. 

Operation complete and successful and I can ride my newly rebuilt 75 cb550k!

Thanks for your help, I am sure I will be back.