View Full Version : OT-motorcycle help

03-08-2005, 05:05 PM
Hi all, here is a pic of my friends front brake caliber/piston assembly. He bought a 1981 400t? Honda motorcycle for 180$ and previous owner told him that the front caliber was sticking, and that it needed to be freed up.

I have it soaking in kroil right now, but that darn piston is siezed in there, not moving. I think I may apply some heat to the main casting as a last resort to removing it. I dont want to damage the o-ring inside it though in any way. Theres also a protective rubber boot that I took off on the outside, it just slipped right off. There was lots of dried up greese that looked kinda like sawdust that I cleaned up.
Other part to the question is that after I get it unstuck, and all cleaned up, is there anything I should do? Was thinking of putting some anti sieze compound on the bolt threads, but how about the piston itself? Should there be greese on it ahead of the o-ring where theres never any brake fluid? And the protective rubber boot that goes on the outside, should that be glued on?

[This message has been edited by BillH (edited 03-08-2005).]

03-08-2005, 05:16 PM
Not sure.. I'd push it back and forth with air pressure and a c-clamp.. If it frees up, reassemble it as you found it.

ALuminum, I have cut the head off numerous instruments that "welded" themselves. Took pains to free them only to break the housings.

The caliper on the passenger side of my wifes car today? Supposed to be a floating single piston caliper, the floating pins-bolts had siezed and would not move. I had to heat the one to get it out. Not good. I worked on that one caliper for about a half hour, replaced both and new bolts. I test drove it and didn't die so I guess I fixed it.. HA HA..


03-08-2005, 05:25 PM
Bill, what I have done with sticky calipers in the past on cars etc. is make an adapter to go in where the brake hose bolts on. A bolt the same size and pitch, through drilled with a grease fitting threaded to the outer end. You can then use a grease gun as kind of a hydraulic pressure device and it will push the piston out. Has worked well for me in the past.

03-08-2005, 05:31 PM
Hello Bill,
Here are two methods of moving that piston.

Pneumatic ---- after you have soaked it make an adapter that will screw in to the caliper ( re instate the bleed nipple ! )that will accept an air coupling AND a valve to cotrol the air. Connect to the air supply and SLOWLY SAFELY apply the air - the piston should pop out, but be sure to protect it as it may come as a projectile.

The other way is hydraulic --- with an adapter that will accept your grease gun, connect them up and pump away.

These are two of the methods used in my mates brake / clutch shop. I hope this is of help to you http://bbs.homeshopmachinist.net//smile.gif http://bbs.homeshopmachinist.net//smile.gif

cheers, Ken

I see that you got there before me sharp http://bbs.homeshopmachinist.net//smile.gif

[This message has been edited by speedy (edited 03-08-2005).]

03-08-2005, 06:40 PM
I had similar issues with a set of Yammie brakes recently. What worked for me was to make an adapter and hook air pressure to the caliper from my compressor. Piston's went POP and would have flown across the room without a rag over them.

The O-ring will be toast and need replacement anyway. The pistons will also likely be corroded and pitted right where the seal sits, that's where water has been in contact for a long time and the reason they're stuck to begin with.

Be prepared to order new pistons if you want to refurb those brakes correctly.

03-08-2005, 06:45 PM
billh you will find the o ring wiil need replacing,remove it and clean out the groove thats were the problem usualy is,eg corrosion in the o ring groove.this jams the o ring against the piston. reasemble with silicone grease,on the piston and the guide pins cc

Michael Moore
03-08-2005, 07:05 PM
Those sliding pin calipers (piston on one side only) are more maintenance intensive than an opposed piston caliper, and will get corrosion and mung buildup on the pins and start sticking.

Definitely replace the O ring, presuming you can get one. You may find that Honda only sells a complete caliper, and for the price they'd want you'd be streets ahead by getting a more modern opposed piston caliper for cheap off of eBay and making a hanger for it. You'd probably find the braking significantly improved too.


is a photo of the disc center and caliper hanger I made for my 750 Laverda race bike. The disc is a 12" stock car cast-iron part.


03-08-2005, 09:50 PM
Thanks guys, I had a feeling this would lead to my lathe getting some use, hehe. It is up to my friend if he wants to go with a new caliber assembly, sounds like a good idea.
I will make an adapter so I can use a greese gun to push it out.

03-09-2005, 05:19 AM
You dont really need to make a hydraulic adapter for your grease gun, there is a very useful hydraulic pump conveniently mounted on the handlebar of the bike.

Single piston calipers are easy, remove the caliper from the bracket & free the brake hose so that you can place the caliper inside an old plastic gallon oil container with the top cut off, wrap a rag around it to prevent splashing, then pump the lever whilst topping up the master cylinder reservoir until the piston pops out.

Multi piston calipers are a little more tricky but if you remove the brake pads & position a flat tyre lever in the caliper disc slots it will usually allow all the pistons to pump out until just on the verge of breaking the hydraulic seal, they can then be "wiggled" out by using a close fitting piece of bar in the piston.

Crewchief is dead right, in 90% of cases with alluminium motorcycle calipers the siezure of the piston is caused by corrosion in the hydraulic seal groove. The best tool for cleaning out the grooves is a HSS internal grooving lathe tool used like a hand scraper, carefully scrape away the corrosion in the bore between the hydraulic seal & outer dust seal with a half round scraper. When assembling thoroughly coat the new hydraulic seal, inside of the outer dust seal & the caliper seal grooves with proprietry brake grease.

Certainly on motorcycle calipers NEVER use a brake cylinder hone, do the cleaning by hand & remove the absolute minimum of material to get a smooth sliding fit for the piston in the bore.



03-09-2005, 10:16 AM
I would use the bikes lever, however it is on the other side of the state!

03-09-2005, 11:44 AM
BillH, here's a puller I made to fit some Gold Wing pistons,

I turned a plug to fit the inside of the piston and split it. On one side I used a blank collet for a Taig lathe, but a nut turned with a taper on the outside would work also. When you tighten it up the split aluminum expands in the piston. I just grabbed the threaded rod in the vise and gave it a few jerks. Or you could grab it with a slide hammer. The rubber band is just to hold it together for the picture.


03-09-2005, 07:58 PM
I am in the midst of a similiar repair for the wife's CB400F. New seal should be available at local Honda shop; I think mine ran $9. Trouble is that mild steel piston will gack up again. Moisture works its way down, being heavier than the brake fluid. Turn one out of stainless, no more rusting. A guy down in Texas makes them out of some type of plastic, and peddles them on e-bay, but I haven't seen him out there lately. I like Michael Moore's approach even better!

03-12-2005, 07:21 PM
Hi all, my friend wanting to keep within the theme of staying cheap as possible, and the very sad fact that I dont have compressed air or a greese gun in CT, we decided on filling the assembly with water, and freezing in the freezer. Hey after about 5 cycles, the cylinder was pushed out far enough that it could be removed. Now I know water freezes in all directions, and I was worried the darn thing was going to split, but it didnt.
The other idea of his was to empty a 9mm cartridge in there and use a long canon fuse to "blow it out". I didnt endorse that idea, but I made it very clear that I wanted to have a front row seat to it.(Safe distance of course).
We were going to find a shrader valve and go to a gas station and use there compressed air, but the ice thing worked before we got to that point.

03-12-2005, 07:59 PM
Pretty slick idea Bill. I'll have to add that to the list.