Brake Piston wont move

Im sure Im missing something really simple but Im stumped.

When I bought this bike the front brakes were off to put in new pads. I had a look at the brake caliper and noticed it was a bit sratched up with a few marks on the piston so I bought a new one on ebay. Was assured it was in working shape and it looks great but I cant seem to get the piston to move in (on either of them). When I try to put it on there isnt enough room to get the rotor in between the pads. How in the heck do I push the piston down???? I have the brake line and bleed screw removed. Im worried about hitting somthing too hard and adding yet another chink to the piston. Any tricks to this?

 

I used a big (1") open end wrench. I layed it flat against the piston with the caliper on the ground. Press down with both hands on each side firmly.

I did this to push the piston back in _after_ I had rebuilt the caliper. Yours could be totally stuck in there (as mine was) with all sorts of crud. Unless I knew that the caliper (and piston) were in good shape I'd take it apart, inspect and clean it up, put in new seals and replace. My front brake works great after doing that. It was so frozen for the PO that it warped the rotor so I had to replace that too.

I used my air compressor with a rubber tip to pressurize the caliper to pop the piston out. Watch your fingers... use a peice of rag in the caliper to cushion the cyclinder when it POPs out under pressure.

 

Is there another way to get it out without an air compressor? Dont have one yet

 

There is a brake caliper spreader tool for autos that will work also. Usualy about $10 at an auto parts store. Or you can use what others use simply because it is laying on your bench, a C clamp. Use a shop rag to keep from marring the outside of the caliper.
And be careful with that bleeder screw off, brake fluid will ruin paint.

 

If the Pistons are that tough to move ... you need to get them out and clean-up the grooves that the seals are set in.

 

Should they be able to move easily by hand?

 

No. I always have to use a tool to move them.

 

OK Im still kinda stuck on this. The caliper that came with the bike "supposedly worked" according to the PO and just needed pads. When I looked at it the piston has kinda chewed up along the top like someone used pliers to rip it out once.

So I bought a new caliper in good shape. Was told the piston moved freely. Problem is I cant seem to get either to move enough to fit the pads and all around the disk. Heck they dont seem to move at all.

Now both are dry and been sittin a bit. I dont have an air compressor (yet, still workin on the wife) and the C clamp didnt seem to work nor the side of a wrench. Can I just shoot WD40 in it? What about pourin brake fluid in the caliper, will that get it movin? Its the last major thing I need to do before I can finally test fire this sucker up and run it down the driveway. Just wanna make sure I can stop

 

what does the inside of the caliper look like? any dirt, coagulated brake fluid, gouges, roadkill?... the caliper has to be clean. the piston has to be free of any gouges or scratches (if you can feel them with your fingers, they need to be buffed out).

did you clean the channels where the rubber seals go? those are notorious for collecting crap.

my 550's caliper was very nasty after sitting for 20 years... I spent a good half an hour cleaning the inside of the caliper...

a dremel tool with a wirebrush works good, with medium-low speed and light pressure.

 

When you say the inside do you mean the bowl that is exposed when seated in the caliper? It is a bit rusted inside the the rims and that seem to be very clean. Bit of dirt is all

 

Sorry, I meant the actual caliper body, with piston removed.

 

If you do not have a compressor to blow the piston out of the caliper you can always try the brake. Put the brake line on and tighten, then put the bleeder back in not quite tight. Try to refill the master cylinder by forcing brake fluid through the bleeder and backwards through the system, (it eliminates at lot of bleeding issues). With the caliper unmounted dangle it in a cardboard box to protect the bike from brake fluid, put a thin block of wood where the shoes belong and wrap the caliper in a rag. Pump the brakes until the piston starts to move.

 

The outside edge can be tool marked or even a bit rust stained. Anything beyond that would spoil the Piston and require replacement.

Lube it.
Not with WD-40 ... with Clean Brake Fluid.

Hook it up to some High Pressure compressed air or to a Grease Gun and gett the Piston out.

Remove Piston.
Remove Rubber Seals.
Clean-out channels for seals to bare caliper.
Clean-out Piston Bore and Reservoir area using a ScotchBrite Pad.
Shine the entire interior of the caliper body to bare aluminum.
Flush with BrakeKleen Spray.
Inspect Piston for scratches and pitting.
Replace if Piston is scored beyond the "Shadow" of the Outside Seal.

Reassemble.
Lube everything with Clean Brake Fluid ONLY
Reset seals in Lubed channels.
Lube area of seals protruding from channels

Position Piston.
Piston must be Flat, true and square to the Horizontal and Vertical plane.
Remove Bleed Screw and Banjo Bolt.
Press Piston into Caliper Body using large "C"-Clamp and a Socket placed inside the Piston to apply C-clamp pressure to interior of Piston.

Tighten C-clamp while correcting the Horizontal and Vertical plane as necessary to press the Piston deep into the caliper bore.

(Tape the Caliper to prevent the C-Clamp from marring the Caliper Body.

Plenty of Brake Fluid for lube.

Go get it!

 

Great, thanks for all the tips guys. Guess I know what Im doin saturday

 

I had the same problem and I finally got the piston out with some air. Everything clean, I guess I will order a rebuilding kit for the seals...

How do I get this thing back in? What are the recommended methods?

Also, any tips in filling back the master cylinder with brake fluid? To the top?

Thank you, Gene

 

Lube everything with Clean Brake Fluid ONLY
Reset seals in Lubed channels.
Lube area of seals protruding from channels

Position Piston.
Piston must be Flat, true and square to the Horizontal and Vertical plane.
Remove Bleed Screw and Banjo Bolt.
Press Piston into Caliper Body using large "C"-Clamp and a Socket placed inside the Piston to apply C-clamp pressure to interior of Piston.

Tighten C-clamp while correcting the Horizontal and Vertical plane as necessary to press the Piston deep into the caliper bore.

(Tape the Caliper to prevent the C-Clamp from marring the Caliper Body.

Plenty of Brake Fluid for lube.

 

I had a similar problem after bringing my "new" 82' XJ650 home last year. Like you, I don't have an air compressor. I took mine to the local repair guy. He ended up using "lots of heat" and the air compressor to get the pistons out. I had to pay about $40, but I did what Rick says and it's worked great ever since. So if you have no luck due to lack of equipment and want to get to riding, maybe pay for some help.

 

Get a Zerk Fitting and put it in place of the Bleed Nipple.
Put a Bolt wrapped in Teflon Tape where the Banjo Bolt attaches.

Get a Grease Gun and pump grease into the Caliper.
The Grease gun will have the have the power to move that Piston Out.

Zerk Fittings are short money.
So is a small Grease Gun.

 

Thanks Rick, priceless advice as always!

The piston got out with the air compressor fine, will buy the clean brake fluid since seals are on the way from z1 enterprises (12bucks+8shipping). Without shipping, Old bike barn wanted 32 bucks for the same thing...eBay 22...I just hope they fit ;-)

Thank you again!

 

Rick on that grease zerk, i can't find a m8-1.25 one. plenty of m8-1 was going to try the grease zerk but i can only catch maybe 2/3 of a turn with the m8-1 threads by fingertips. i could tighten abit more before i screw the threads up. you think that might hold pressure long enough that grease might push out the piston? the piston seal seems really be stuck. i pulled the boot off and tried moving it with a 10" pipe wrench didn't budge it. stuck a c-clamp on the piston got it to move down bout a 1/16". tried the pipe wrench again moved it bout a 1/2" hit it with air moved it up bout the 1/16" it went down with the c- clamp still won't budge. found out that the master cylinder i got off ebay needs rebuilt.

 

When I get a Caliper Piston THAT Stuck ... I take a break and go to Duncan Donuts!

As I wrote some time ago ... :

If the Piston won't budge from the Hydraulic Pressure supplied by the Bike's Master Cylinder you:

Try pushing it out with a line hooked-up to a high-pressure grease gun ... or,

Bring the Caliper and the Banjo Bolt to an Automotive Brake Specialty Shop.

(Have a pretty girl bring it in and they'll "Stop-the-Music" and fight over who gets to do it.)

Or, ... My favorite.

On the way to the Brake Shop ... stop-off at Duncan Donuts and get a few Medium Blacks with all the fixings on-the-side.
Hit the Brake Shop with the rack of Coffee's and stuff in one hand ... and your Brake Caliper in the other.

Tell the busiest, dirtiest, sweatiest guy, wrestling with the most thankless brake job that:
"God sent you with Coffee for him and his pals. Black with all the fixings on-the-side. Just for you!
By the way ... while you're enjoying the Coffee ... God also wants you to hook-up this little Caliper to your high-pressure machine and force the Caliper Piston out!
He sent me to see the right guy; right???

 

i'll pick up a master cylinder rebuild tomorrow and see if i can use the bikes hydralics to pop it. then if that don't work looks like donuts and coffee.

 

I had the same problem with a set of calipers i bought from ebay. They came from denver, and had been sitting for some time.

I read all the posts in this thread and here is what worked for me; I tried to get a grease fitting to replace the bleeder screw, but i needed a M7-1.00mm thread and all i could find off the shelf were M6-1.00mm and M8-1.25mm - i also looked for a replacement bolt for the banjo fitting bolt (M10-1.25 i think) but that was also hard to find off the shelf. Here is what worked. I took one of the caliper mounting bolts (same thread as the banjo) and wrapped some teflon tape on it. I used compressed air with a rubber nipple end and put pressure in the bleeder screw hole - no luck. I bought a decent grease gun for $20 (i have a great gun but it's lost somwhere in my garage or someone elses garage). I took the grease gun fitting and put it over the bleeder screw (backed out a turn or two) and started pumping in the grease. That piston started to move with no problem, and now it's out. Right through that bleeder screw!!

Note: i read somewhere that your piston is scratched?? or has gouges?? - That's not good. That piston needs to be able to travel all the way back in the caliper body when the pads and brake discs are new. ANY scratches on that piston is going to tear up your new rubber seals. Yamaha has a kit with the rubber seals and a piston, but it's not cheap ($50??)

I'm in luck, I am replacing only one caliper (which had the bleeder screw busted off) and i have enough parts to make 4 calipers. I think i have two good pistons on the bike now. I think when i'm done i will have one complete caliper to be able to sell.

 

There is very little room at the end of the Caliper Piston that can be scratched or gouged with tool marks from trying to extract it.

There should be a "Footprint" ... a "Shadow" ... some "Exposure" mark at the front of that Caliper Piston.

That small area is what does not extend into the O-ringed Seals.
If your tool marks are within that very small area ... you might be OK.

Beyond it ... on to the shining portion of the Piston ... Bad news.
Replace the Piston.

 

well so much for thinking i could pick up a master cylinder kit from the stealership lol. the grease through the bleeder worked great. just got the piston out bout 2 mins ago. bore looks darn good. oh thanks for the help guys.
what year did they have a low fluid sensor?

 

Now that you have that Piston out ... remove the two large O-ring Seals and make yourself a tool to scrape ALL of the crud and build-up that are in those two channels right out of there.

I use some genuine Dental Office Instruments and go at it like I'm scaling the tartar off teeth. You have to get the whole channel where the O-ring seats right down to bare Aluminum without gouging the surfaces of the channel.

Dust and Brake Fluid combine to make a pretty solid crud that builds-up in those channels and that stuff is the Number-1 reason that Brakes bind.
The O-rings are supposed to seat without anything behind them but the bare Aluminum of the Caliper.

As the crud builds-up in those channels; the diameter of the fit is affected and causes the Caliper Piston to be slow or freeze-up rather than have the complete travel necessary to retract when pressure from the Brake Lever is relieved.

When you reassemble the Caliper ... lube the channels and the O-rings with a good deal of clean Brake Fluid.
And remember that the Piston needs to be Squared-up and True to the Bore when you are pressing it back into the Bore.
Lube it with lots of clean Brake Fluid.
Keep it horizontally and vertically squared-up and press it back in with a C-clamp.

 

did 82xj750 have low brake fluid sensor? ok i found it did have sensor. will i be able to use a 750 mc on my 650?