Topic: Brake Pads stuck after rebuild

[samfig]

Hey.

I just finished rebuilding the Master Cylinder, replacing some hoses, cleaning the front caliper, replaced the piston seal, and bought new pads.  I left the wheel on and simply just connected the two sides of the brake on the arm and the pads immediately touched the disc.  Tightening the two sides to the arm, the way it is intended to be, results in the pads having a death grip on the disc.  I loosened the spring and it is essentially at it's loosest point. 
Here is what I did that might help you diagnose this:
1.When I rebuilt the piston I put a little grease on the piston and on the piston seal.   
2. When I bought all the parts (from VintageCB750.COM) I ordered the pads too, which are NHC brand.  Could it be that I need to remove the paint from the sides of the pucks to create more space?
3.  The puck on the inside, held by the cotter pin, seems to be pretty thick in this picture.  Is it too thick of a pad?

Any help would be much appreciated.

[MickB]

Sam I had the same thing, I solved it by sanding down the pads by a mm or so on both pads.

[samfig]

Here are some pictures of of the parts.

[samfig]

the pads and the grease I used.

[Phinn]

The pad on the piston side should fit into the caliper freely. I needed to sand down the edge of the pad's metal holder quite a bit, and also give the mating surface of the caliper a very light sanding with very fine wet sandpaper, to get them to fit. Too much of a gap and water will intrude. Too little and the pad will bind and won't retract. If you have to use a clamp to get the pad to seat on the piston, it's too tight.

I used silicone grease. It's in the hardware store, with the faucets.

[ekpent]

Lot of the new pads are not drop in ready. As Phinn mentioned they need to  be tweaked to slide in and out easily by hand before officially buttoning it up.

[jonda500]

As well as needing to slide in and out easily, like MickB mentioned, sometimes they are too thick and need some material removed from the friction pads.

My last set were just a little too thick, the wheel turned but was somewhat hard to turn - I fixed it by riding it around the block a few times doing heavy brake applications until the wheel spun freely.
John

[strynboen]

that silocone ..is it rek to be used at the inside of the piston.?.hvere it komes in kontakt vith fluid..some types can be used both inside and autside..but not all types..
but the problem you have now,,, is not related to the silicone greese.
.its probly, paint vho blokes for free movent(return)of the piston

[RAFster122s]

The silicone grease you used will contaminate the brake fluid. It should be used on the edges of the pad and back of the pad in a thin layer, very thin.
If it migrates under high temps the caliper will generate then it will get on the pad surface and you know what that spells.
The Dow High Hacuum grease does not migrate and that is what most recommend for our sohc/4 brakes.

Odds are your pad edges (metal painted area) need to be sanded to fit.  There have been several cases of the replacement pads being too thick and have to be sanded back as was mentioned. The pads should be able to slide into and out of the caliper without any sticking/binding. So, sand the edges until it can do so. The Dow grease  will not melt and migrate/run onto the pad surface.  More is not better when lbing the edges. The piston and rubber seal are best lubed with Brake Assembly Lube or brake fluid. You don't apply silicone grease here or you contaminate the brake fluid.

The other thing that could be at play is the alignment of the caliper, but...if it came off the bike and didn't bind previously then it is the pads.

[Phinn]

Be sure to test fit a new puck, BUT ONLY DO SO WHEN THE PISTON IS INSTALLED.

My first attempt at fitting a sticking pad/puck turned into a disaster because I did it without the piston in. (I had thrown the old piston away and ordered a phenolic one, which hadn't arrived yet.) When I pressed the pad in, it got stuck in the caliper and would not come out. I drilled holes in it and tried to fish it out with hooked tools, wires, lever it out with giagantic screws ... everything short of explosives.

I couldn't squeeze it out because without the piston in place, air, grease and brake fluid just ran out uselesslly, even before I drilled holes in it. Total nightmare.

I took it to a machinist who used some kind of slide hammer. Don't do what I did. File, grind or sand down the edges of new pads until they fit and move freely.

[samfig]

Thanks for all the info and advice, guys.  I put a very light coating of that line pictured above on inside of the piston as well as the seal (like I saw Dino do on his build).  I don't think it's the same stuff so hopefully i didn't compromise the system fluid. 

I also just sanded the paint off the metal portion of the pad and ensured it moves freely, so I'm good there.  I didn't do so for the other pad and just reassembled the caliper and I've got some movement with the wheel!  It isn't moving completely uninhibited but I can push the bike back and forth at least. 

It seems like booth sides are still touching the disc so is my next step to sand down the pad portion a bit?  If so, any advice?

[Phinn]

Be sure that the caliper arm moves freely. It pivots left to right, on a pin, to adjust to pads of varying thicknesses. That pivot pin is sealed with an o-ring above and below, but they always fail. You have to pull the pin out and re-grease it and clean out the holes.

Then, the adjuster bolt will turn the arm to get the rear static pad to line up properly with the rear (right) side of the rotor. If that rear pad is binding the rotor, it's a problem with the caliper arm, not the pad.

But really, don't take any chances with silicone inside the brake fluid area of your caliper. Blow out the piston, clean everything and start over.

[RAFster122s]

The pads will lightly press against the disc, the rubber seal in the piston side flexs when the brake is applied and then pulls the pad back slightly when the pressure is released. It will lightly run against the disc. The spring and shoe are to align the disc and caliper so it is centered on the disc. Personally, I would clean the caliper with brake cleaner after disassembled and flush the system. But, it is up to you ultimately.
A 1/4 oz of the Dow High Vacuum petcock grease (lab equipment) is available on ebay for about $10 or less if I recall correctly. It's the stuff to use when you break the system down and flush your fluid. Should do that every two years (min) or every year if you are fastidious about your bike.  Personally, I don't skimp on tires or brakes as both affect your life directly.  Gear being a third item to invest in...

Sounds like you are good. The static side will touch the disc and as your brakes wear you adjust the spring and bolt through the brake arm to ensure it remains centered.  BTW, the pivot joint is another place to apply the Dow grease and replace the o-rings there as well. The Dow grease keeps water out as well as lubing that joint and it has a very wide range of temps for use.

EBC pads are known for brake squeal, in case you go with EBC.

Good luck Sam and enjoy riding the bike!

David

[samfig]

Thank you all for all the help!  I ended up checking the caliper arm, which was moving fine, and then decided to sand the backing and the friction part of the static brake pad (the inside one).  It worked like a charm!  The bike is  rolling nicely now.

I am going to take apart the caliper and remove the grease I applied to the seal and piston, just to be safe.  Do you guys think it would be necessary clean the MC out as well?  I can't imagine that the fluid makes a full rotation from the caliper up through the MC.  What are your thoughts?

[ekpent]

Technically I think the fluid in the line remains fairly static when working correctly and does not flow from top to bottom. Maybe TT will chime in to correct me though

[strynboen]

just pump some fluid through..it vill vash all up.
..its a good idea to pump the resuair almost emty..dry up vith some paper ,,and fill nev fluid inn..and themn pump atleast 1 dl through the system..then all is super klean and the system only holds new fluid..do it evrt 3 year..then korosion dirt and  vater is removet aut of the system

[Stev-o]

Maybe TT will chime in to correct me though

Dont hold your breath, Eric!