Topic: 77 CB550F Front Caliper

[meltshow]

I brought home a '77 CB550F about three weeks ago. After going through everything else, it's time to tackle the front brake. The diaphragm and plastic ring in the master cylinder were shredded (replaced those) and the cylinder pretty much dry. The brake pads are stuck gripping the rotor pretty well, but working with the adjustment screw down on the caliper isn't relieving that pressure. I've read some of the threads on working with a stuck piston and just want the straight talk: am I better off replacing the piston, seal and pads or should I go through the rigamarole of trying to save what I've got? The pads I'm seeing here on the bike are barely worn, for instance.

Meanwhile, the PO had removed the front fender and only replaced one of the two bolts on at the swiveling joint. It didn't seem...right and sheared completely off when I attempted to remove it (it had an 11m socket head!). It's in a awkward spot so using an easy-out won't be possible even after removing the front wheel. Something tells me I'll have to remove the wheel and caliper assembly to take care of it. Ideas?

Bear with me, this is the first time I've worked with actual hydraulic brakes...my past experience is with standard-issue CT-90 type drum brakes.

[harisuluv]

The front brake didn't activate and then seize over time onto the rotor.  The brake seized, then someone at some point used pumped the lever and then it pushed the essentially seized brake so it death gripped the rotor.  If your master cylinder is working, you now have the best working tool to get the pistons out so the whole assembly can be cleaned, inspected and serviced (if not damaged).

If someone were to go to a shop with just the calipers, they would just attach them to a grease gun and pump them out (essentially what the master cylinder would do but without all the grease).

The adjustment screw isn't going to relieve any of that pressure.  It only controls the adjustment or alignment in relation to the rotor. 

At the very least you will need a new piston seal.  Maybe a new bleeder screw, pads, or a new piston if it's too pitted.

Basically you can't assess what to replace until you inspect it.  You can't inspect it til you get it apart.  Probably the easiest way to do it instead of trying to get the caliper off right away would be to take the wheel off.  It is going to be a lot easier to remove the wheel off the caliper than the caliper off the wheel.  The caliper is bolted on so it's stationary.  The wheel you can unbolt and then also turn it while pulling it. 

Don't unhook the master cylinder yet, you will probably need to use it to get the pistons out.

[Powderman]

If the caliper is seized on the rotor and you can't get the pivot arm off the broken stud, how will you remove the wheel from the caliper or vice versa? Wouldn't it be easier to just remove the 2 caliper bolts and split the halves, drop the wheel out, remove pivot arm. Then proceed to the bench for caliper overhaul. The fork can be turned now to access the broken bolt.

[Stev-o]

Good advice ^^^.  Remove the caliper w/o removing the brake line and pump out the piston.

Once out, post a pic of the piston if you need us to access it. It's stainless so may be alright with a good cleaning.
This is very basic brake service, you can do it!

Good time to inspect the brake hoses too, if you see cracks time to order some new from Shawn:

https://slingshot-cycles.com/

[meltshow]

Thanks guys! Now I have a plan! That does wonders for my mind. I should mention that the front wheel does rotate with effort. The pads haven't clamped down like a vise grip quite yet.

So depressing the brake lever with the rotor out of the way should allow the piston to pop out?

[Stev-o]

So depressing the brake lever with the rotor out of the way should allow the piston to pop out?

Yes, just be sure to keep fluid in the MC.

Guessing the inside of that caliper will be pretty filthy.

[meltshow]

Update: I got the piston out just fine. It's a little pitted but not terribly so. Can these be polished with a little steel wool? The piston seal is pretty much even with the inside of the caliper though and the caliper was indeed filled with a great deal of blackish brown gunk. I'll update with some pictures this evening. Should there have been a cotter pin holding in the wheel-side brake pad? It popped right out.

The real headache now is getting out the stud...it's in there good enough that an easy-out isn't taking. I'm going to have to drill it out and rethread. Sigh. But progress!

[Powderman]

Show a pic of the broken bolt. Is there room to tack weld another bolt or nut to it and then back that out? PB Blaster and then heat on the fork leg will help ease the bolt out.

[Stev-o]

the 750 brake pads have the cotter pin.  What stud??

[Powderman]

the 750 brake pads have the cotter pin.  What stud??

"Meanwhile, the PO had removed the front fender and only replaced one of the two bolts on at the swiveling joint. It didn't seem...right and sheared completely off when I attempted to remove it (it had an 11m socket head!). "

[Stev-o]

the 750 brake pads have the cotter pin.  What stud??

"Meanwhile, the PO had removed the front fender and only replaced one of the two bolts on at the swiveling joint. It didn't seem...right and sheared completely off when I attempted to remove it (it had an 11m socket head!). "

swiveling joint?!

[calj737]

Stev-o it's a 550, not 750.  I think the PO replaced the caliper adjusting arm pivot bolt with an aftermarket socket head (11mm socket, from what the OP said). I'm a bit confused too, be nice if the OP would post some pictures!!!!

[Stev-o]

Should there have been a cotter pin holding in the wheel-side brake pad?

I know its a 550 cal, he asked about a cotter pin and I responded the 750 has one [not the 550]

I think we are all confused!

[meltshow]

I'm back! The broken stud has been sorted out and the caliper's been given a thorough cleaning. Here are a couple of shots of the piston, hopefully showing enough of the wear for you to get a grasp of how it looks.



As for the cotter pin, you can see it in online parts fiches. What else would be keeping the the brake pad attached to the far side of caliper?



An extra image of the glorious goop that awaited me when I first opened things up:

[calj737]

The cotter pin is #3, it passes thru the static pad, thru the caliper, then is splayed outside the "inside" caliper bracket. It does restrain the pad to the caliper body. Cotter pin/Roll pin, it is the part in question.

Melt - Inside the caliper is the seal (replace it) and seal groove. The groove MUST be spotless clean. Debris, gunk or corrosion will prevent the seal from properly functioning in retracting the piston and you will also suffer fluid leaks. If that piston has any pitting (difficult to say from the picture) replace it. Do NOT skimp on safety parts. You can obtain a phenolic piston and avoid future corrosion issues.