Is there a trick to getting a new caliper piston installed?

Slantyface

Slantyface

Been Around the Block
Like the topic would suggest, I got a new piston for the front caliper on my 78 cb550. The thing won't go. I mean, I screwed with this thing for like 45 minutes. No dice. The story on the new piston is that it's aftermarket stainless steel OEM spec. Of course I put them up side by side and they look identical as far as diameter. I didn't bust out the micrometer or anything, but they look spot on. bore is free of gunk as I cleaned it before I attempted the install. I also applied some "lubratory" brake fluid to get things started right. Only thing I can figure is that the new seal that I installed a couple weeks ago got some fluid on it and expanded a bit? The seal hasn't been submersed in fluid, but it definitely got some on it. Any ideas or helpful advice regarding my predicament would be much appreciated. Thanks guys.
 
They're a very tight fit. I just finished rebuilding the brakes on my XJ750 and it took some persuasion with a mallet to get them in there.

If you have access to a press, that might be a better idea.
 
Did you clean the groove that the seal sits in? That's what got me - some corrosion in there caused the seal to not sit as far back in the groove as it needed to.

I also used some brake assembly lube similar to this:
http://www.ebay.com/itm/Red-Rubber-Grease-for-brake-caliper-master-cylinder-clutch-seals-o-rings-1oz-/160965165051

Brake fluid should be good enough, however. I used lube because I wasn't going to install my caliper for a bit after I assembled it, and didn't want the brake fluid exposed to air to absorb moisture.
 
Hey thanks guys. I appreciate the expedient responses. I'll check that groove again. I cleaned it out pretty well, but it wasn't spotless. I know a piston will fit because the old one was in there for a couple weeks while my other one was shipping. I was afraid to use too much force as the new stainless steel was immaculate and I didn't want to gouge it. I'll attempt to use a rubber mallet conservatively tomorrow...
Thanks again guys
 
Crap in the groove wouldn't prevent the piston from going in, it would just push the seal out more than it should be.

Did you try removing the seal and sliding the piston in then? That will tell you if the problem lies with the seal or the piston to caliper clearance?
 
Re: Re: Is there a trick to getting a new caliper piston installed?

Worst cb650 ever said:
Did you clean the groove that the seal sits in? That's what got me - some corrosion in there caused the seal to not sit as far back in the groove as it needed to.

I also used some brake assembly lube similar to this:
http://www.ebay.com/itm/Red-Rubber-Grease-for-brake-caliper-master-cylinder-clutch-seals-o-rings-1oz-/160965165051

Brake fluid should be good enough, however. I used lube because I wasn't going to install my caliper for a bit after I assembled it, and didn't want the brake fluid exposed to air to absorb moisture.
Click to expand...

To this point - I would lightly apply silicone grease to the piston seal before putting the piston in (you can get one-time-use packets at an auto parts store if you don't want to buy more).
 
Re: Re: Is there a trick to getting a new caliper piston installed?

Moa said:
Use a G-clamp/C-clamp to press it in.
Click to expand...

You should not need that kind of force for an empty caliper
 
Never use brake fluid to lubricate a caliper piston. Brake fluid outside of the seal will attract moisture and cause corrosion. ALWAYS use silicone brake caliper lube. Lightly lube the caliper bore and the piston before assembly. Put some in the meticulously cleaned seal groove before putting the seal in.

http://www.ebay.com/itm/Permatex-20356-Ultra-Disc-Brake-Caliper-Lube-/140727924390#vi-content
 
If you need to apply lots of force to the G-clamp something is indeed wrong. But if the piston fits the bore, it should make installation a breeze.
 
Whoa, I've rebuilt quite a few different calipers and never needed a clamp, press, mallet.

Is your bleed screw off or open, caliper on the bench or on bike?
 
Caliper is off the bike and both the brake line and the bleeder are unscrewed. Now that everyone is saying the seal groove is such a big deal I feel much obliged to check it out again. The only reason I'm so thrown off is that i just blew the old piston out. Guess I'll pick up some lube at the auto parts store too.
 
Perhaps you want to remove the new seal, and try the piston in the bore without it. Don't push it in all the way or it'll be hard to get out. If the piston goes in easily with hand pressure (make sure its pushed in straight), then it is probably just a tight seal. If the piston doesn't slide in easily it may be too big for the bore, don't keep forcing it or it'll get stuck.
 
Worst cb650 ever said:
Crap in the groove wouldn't prevent the piston from going in, it would just push the seal out more than it should be.

Did you try removing the seal and sliding the piston in then? That will tell you if the problem lies with the seal or the piston to caliper clearance?
Click to expand...

Not true, if there is crap in the groove it will make the seal stick out further and prevent the piston from sliding in and most likely chip the edge of the seal as it goes in with force causing a leak and a job wasted.
I used a press for installing pistons when I ran the caliper department of Rebco Racing Enterprises where I would build 100 calipers a day. I would not recommend a mallet, it's another way to chip the seal. The piston should be capable of going in with nothing more than hand pressure. You can use a vise (if it's a 2 piece caliper and it is apart and some open face one pc. calipers).I cut a piece of broom handle to go into the hole in the piston and protection on the other side of the caliper and slowly apply pressure keeping the piston square until it pops past the lip of the seal You want to make sure the piston is square as it goes in and constant pressure on it, not banging pressure from a mallet or hammer. You only have to move the piston a couple thousandths of an inch for it to enter the seal, should slide right in the rest of the way from there.
 
You're right o1marc, I worded my reply very poorly. Crap in the groove wouldn't prevent the piston from going in if the seal was not installed. I meant to suggest that he install the piston without the seal to determine if the piston to caliper clearance or the piston to seal clearance was the issue.

As the song says, where is my mind?
 
Piston should slide right in when lubed and no seal. Once installed the piston should touch nothing but the seal and the pad.
 
Maybe I just don't have the magic touch or something. Our shop is closed for the weekend so it'll have to wait till Monday. I had issues last time when I tried to put the old piston in a couple weeks back. It just took one of our old timers about 10 seconds to make it go. Frustrating but I had to laugh...
 
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