rear brake caliper-84

[bigbore2]

Trying to push in the pistons on my rear brake caliper.  using a c clamp and pushing in on one side , no go-----after putting in the brake plate as a cover to push down on both sides of piston at the same time, no go.  Do I need to drain fluid out of lines, caliper etc to get the piston to compress?

Pistons were way extended out as i had worn completely thru the pads and only had the metal plates hitting on the disc, to my suprise.
Bike got hit by neighbor with her car on this side.

[Harvy]

Piston might be cocked on an angle...... you may need to pop them out first, rather than trying to get them to retract. When they are out, check the cylinder walls carefully before replacing the pistons.
All this means that you have to completely remove the caliper of course.

Harvy

[ribbert]

As Harvy said, it is likely cocked to one side. A C clamp can exert way too much force and is difficult to get an even pull in that application.
If your brakes had worn down to metal they are obviously working which suggests the pistons were not stuck until you tried to force them back.

How much are they still protruding by and do they appear "square" to the naked eye?

Depending on how hard you turned the C clamp, they could be quite firmly wedged in there.

Noel

[FJ1100mjk]

+1 on removing the pistons. Sounds like it may have been quite some time since they were. Simply changing pads, maybe what's only needed though.

On old neglected calipers, I have found where the aluminum corrodes where the grooves are for the piston seals and wipers. Between that, and old, hard seals and wipers, there's just going to be problems with the piston trying to extend and retract.

I was surprised by how good the OEM brakes are if the calipers are rebuilt, new EBC HH pads installed,  and removal of the old pad glaze from the rotors is performed.

Good luck!

[bigbore2]

yea, forgot to mention, I rebuilt them 3 yrs ago.

just got my compressor fixed, if I need to pop them out.

I was just trying to avoid draining the fluid, if possible.  Guess that will be necessary.  Rubber gloves, anyone?

thanx, guys.

[Steve_in_Florida]

yea, forgot to mention, I rebuilt them 3 yrs ago.

just got my compressor fixed, if I need to pop them out.

I was just trying to avoid draining the fluid, if possible.  Guess that will be necessary.  Rubber gloves, anyone?

thanx, guys.

There's nothing magical or scary about brake fluid. Just keep it off the paint and plastic. Keep water handy, and apply it quickly to avoid damage to the cosmetics.

In fact, you may want to pop the pistons out with the fluid, rather than the air. Fluid is easier to control. Remove the caliper from the swing arm and wrap it in a rag, leave the hose attached, and squeeze the brake handle. This will pop the piston out in a controlled manner. You might lose a finger or an eye with air pressure. (Claims that they will grow back are bunk!)

If you ever suspect your fluid is contaminated with water, simply flush it out with fresh fluid. It's cheap and available. Really.

Steve

[bigbore2]

thanx Steve.

I should just be able to separate the 2 halves keeping fluid in and get my c clamp in the middle of the piston, not on the edge to push it back. If it is not cocked too bad.
Just trying to do it without draining fluid, just to see if I can do it that way.

Or am I missing something about trying it that way?

[bigbore2]

WELL, I am missing a channel for fluid between the 2 halves.  I am used to looking at one sided piston brake calipers, like on a car.

Separated the 2 halfs and the piston went in easily like they are supposed to. 

[FJ1100mjk]

Welll, there ya go. Good going. 

[bigbore2]

So FJ1100mjk, how do you remove the pad glaze from the rotors?

[FJ1100mjk]

I've been using one of these http://www.brushresearch.com/brushes.php?c1=6 to do the job. You have to take the rotor off of the wheel to clean both sides of tbe rotor. Clean the rotor screws' threads (screws and internal threads on wheel) real good, and apply the appropriate strength threadlocker to the screws before reassembling them.

Others may chime in about their methods of removing the old friction glaze, but the above works for me. Some may even recommend just throwing the pads on without removing the glaze.

Good luck!

[ribbert]

So FJ1100mjk, how do you remove the pad glaze from the rotors?

The same way you remove it from your car rotors.

Noel

[X-Ray]

I always thought the way to "de glaze" discs was to get them machined, which would also give back a nice flat surface. Tell you what, learn something every day 

[ribbert]

I always thought the way to "de glaze" discs was to get them machined, which would also give back a nice flat surface. Tell you what, learn something every day 

The bike discs are a bit thin to machine Ray.

Just as an aside, if you haven't had a chance to compare lately, new rotors are so cheap for cars, you wouldn't bother machining them anymore. I fitted a new sets of fronts to a BMW recently, a bit over $100 for a pair of brand name rotors.

Noel

[Flying Scotsman]

I would machine them.Surface grind them a few thousandths per side.A flex hone would be fine though.