Topic: Master cylinder & brake piston issues

[bookah]

I had to buy a new MC after my old one broke. So I hooked this new one up, bled the brakes and noticed that the caliper is grabbing. I took the caliper apart and noticed that the piston is not retracting, and just gripping the disk. I'm assuming this is not a fuel line/bleeding issue, as much as it is an MC issue?

[mrfish2]

Sounds to me like the seal inside the caliper needs replacing if the piston isn't retracting.

[70CB750]

Most likely the caliper needs to be cleaned and lubed. Would not hurt to replace the retrcting rubber ring and polist the piston.

[bookah]

Thanks guys. I ordered the new piston seal last night. Looks like I have yet another mini project on my hands this weekend. Appreciate the quick responses!

[flybox1]

be positive the piston seal groove is clean. 
any corrosion here and it will offset the seal, not allowing the piston to ride on it properly.
also, ensure the caliper housing for the stationary brake pad sits perfectly parallel to the rotor face.  Use the caliper spacing adjuster screw here.
if its off by too much, the piston-side pad contacts the rotor face at an angle, wedging it in the caliper housing.

[bookah]

be positive the piston seal groove is clean. 
any corrosion here and it will offset the seal, not allowing the piston to ride on it properly.
also, ensure the caliper housing for the stationary brake pad sits perfectly parallel to the rotor face.  Use the caliper spacing adjuster screw here.
if its off by too much, the piston-side pad contacts the rotor face at an angle, wedging it in the caliper housing.

Thank you for the tips. I haven't taken it apart yet so I'm not exactly sure what I am up against - but I assume removing the piston is pretty straightforward?

[flybox1]

yes. 
be detailed in your cleaning of the caliper.
any pitting in the piston surface can compromise proper function.
(replacement Phenolic pistons are readily available)

read this before you assemble anything...

http://forums.sohc4.net/index.php/topic,56544.0.html

This thread has gotten very confused.  Lets' review.
There are four products needed to restore a caliper.
1. Brake cleaner
2. Brake parts assembly lube for the caliper seal only.
3. Dow corning High vacuum grease.
4. Brake fluid

Each has it own specific application and needs for the task to be performed.

#1 is used to get everything clean.  (given the confusion, it had to be said)
#2 is used ONLY on the seal and must be compatible with #4, as some of it will invade the brake fluid chamber.
#3 is NOT used on the seal, as that would put silicone inside the brake fluid chamber.  This is a bad thing as the compounds are incompatible.  It is used behind the brake pads and a thin coat is used on the parts of the calipers and piston that are exposed to the elements and subject to water ingression.  The Dow Grease will not mix with ANYTHING.  It is a simple barrier with the very important property that it will NOT melt when the parts get hot and then run/creep into the brake pad friction material and provide lubrication between pad and disk rotor.
#4 is what makes the hydraulic part of the brake function. (I hope that part is clear.)

The "Permatex® Counterman’s Choice® Ultra Disc Brake Lube" I have NOT used.
It is NOT to be used in the #2 application (directly on the caliper seal, as that would put some inside the brake fluid vessel and is clearly NOT it's intended application).

Depending on it actual composition, it may be suitable for the #3 task, IF and I stress the IF part, it will not melt/run into the brake pads.  The brake pads/rotor interface are where you WANT fiction!

Previous discussions in this forum were regarding Syl-Glyde, which I have personally tested and can pretty much guarantee that it will run/creep into the pad to rotor interface.  It only contains silicone as a minor ingredient.  The rest of this (Syl-Glyde) compound cannot take the 500F plus heat that the Dow corning grease can without doing a phase change.

The remaining question is whether Permatex® Counterman’s Choice® Ultra Disc Brake Lube will run/creep into the brake pads/rotor, especially when it gets hot, in this application on the Honda brake caliper.
I don't have any, I haven't tested it, you use it at your own risk.  I do know the Dow corning silicone grease DOES work properly and certainly appears to be the same stuff Honda used during production assembly.
I admit I am skeptical.  The last time a counterman recommended a product for #3 application, it was Syl-Glyde which, if he were still working behind the counter, I'd be tempted to make him eat.

[streak09]

Been doing a lot of searching on this topic (and now my head hurts  ). For clarification, is the brake assembly lube applied to the caliper piston, in-between the seal and piston (as well as seal groove)? Doesn't this lesson the friction between the seal and piston, which is needed to retract the piston when releasing the brake?

Also, what is the recommended way to clean the groove? Scotchbrite? steel wool? 

FYI, after digging, it looks like this is a pretty feasible source for the lube. From my research, it looks like people have a hard time finding. http://www.amazon.com/WILWOOD-290-11087-Synthetic-Brake-Assembly/dp/B005JVNNDG

[flybox1]

I purchased a small brass brush for my Dremel just get the seal groove clean.   Scotchbrite would be fine.
Follow TT's outline in my post above and you will be golden.