Yup, another part that needs servicing. Who would have thunk?

Next up is the front brake caliper. I've read a bit and I'm pretty sure I know what I need to do. As mentioned previously in another episode these parts haven't been on a bike in many a year. These pistons are well wed to the caliper. I've been soaking the assembly in Liquid Wrench in hopes that it may do a little but I'm pretty sure that heat and hydraulic pressure are in my future.

The first thing I was trying to figure out is where to get a peg spanner. I happened to be at my favorite Chinese import palace (Harbor Freight) and spotted a peg spanner (adjustable) by the saw blades. I think it's for removing the saw or stones on an angle grinder. For $4 I got it and guess what? The pins are slightly smaller but at least they fit in.





I'll need to heat the caliper up and if everything works the plug might just come out.

But I've got bigger problems first. Those pistons... I've been trying to shoot some air in but it's been completely futile.

My two choices are to hook up the master cylinder (it's newly rebuilt with the smaller piston) and hope that works.

Or I've heard of some people hooking up a grease gun.

Thoughts?

I rebuilt mine a few months back and had to soak it in my gallon can of carb cleaner. Then used the grease gun to push the pistons out. Save your compressed air if it doesn't work the first time. The grease also cleans as it pushes.

chopped850 wrote:I rebuilt mine a few months back and had to soak it in my gallon can of carb cleaner. Then used the grease gun to push the pistons out. Save your compressed air if it doesn't work the first time. The grease also cleans as it pushes.

Did you just put the grease gun right on the bleeder valve? How did you do it?

That is an expensive tool.
I stick 2 neat fitting drill shanks in the holes & undo with a ring spanner.
If you can get the outer piston out, hold the outer piston so that it covers the 2 holes in the bore & use compressed air into the bleed hole. If that don't work, heat it.
It is easiest to move the back cylinder while it is connected to the bike if anyone is thinking of doing theirs.

I've got one I want to rebuild but I can't get the inner piston out. Air and heat have not worked, maybe grease would. Very interested in reading the details of how to actually do that.

Another technique I've read about, it's kind of drastic though, is to drill through the back of the caliper and use a drift to drive the piston out. Then you cut threads and install a bolt to seal the caliper body back up. Seems like spoke clearance could be an issue. I haven't seen any photos from anybody who has actually done it. Definitely a last resort action...

Debby

Debby : drill the hole !
I did a few with great success .
Spoke clearance is absolutely no issue .

This one is gathering dust ,( even made titanium pistons for it ).

I think someone said the grease could be something like 1500psi. If that don't do it, then it's time to get medieval.

Before I try the grease I might try the master cylinder. See what happens.

Liquid Wrench is OK for homeowners, dabblers, and the like but it is not as serious as Kroil - named for Kreeping oil. If you Google search "AeroKroil Google Offer" it will bring you to a special deal from the company (Kano Labs) for 2 large aerosol cans of Aerokroil for $12. You will have to make up some company name if you don't have one already but they don't seem to be very fussy about that. Even one can will last you a long long time so give one to a friend. Amazing stuff. You'll use it I'm sure.

There are some nice new stainless pistons out there too.

Russ Kano
(no, not really...)

ludwig wrote:Debby : drill the hole !
I did a few with great success .

I think I will! This idea appeals to me for some reason. It also looks easier than pumping the caliper full of grease.

How do you seal the threads when done? Will some loctite suffice or is a crush washer necessary? (If so, do you have to face the area under the bolt head with an end mill?)

Regarding penetrating oil, I've read that a homemade mixture of acetone and atf works even better than Kroil. A lot better, they say. I haven't tried it yet but am planning to. So far I've been getting by with Liquid Wrench.

Debby

debby wrote:..How do you seal the threads when done? Will some loctite suffice or is a crush washer necessary? ..

No crush washer !. Just a plain copper or alu washer as used on brake lines .
Maybe a drop of loctite for peace of mind , but I think even 648 won't last because of the possible high temperature .

batrider wrote:Liquid Wrench is OK for homeowners, dabblers, and the like but it is not as serious as Kroil - named for Kreeping oil. If you Google search "AeroKroil Google Offer" it will bring you to a special deal from the company (Kano Labs) for 2 large aerosol cans of Aerokroil for $12. You will have to make up some company name if you don't have one already but they don't seem to be very fussy about that. Even one can will last you a long long time so give one to a friend. Amazing stuff. You'll use it I'm sure.

There are some nice new stainless pistons out there too.

Russ Kano
(no, not really...)

I thought Billy Mays was dead Come to think of it, you didn't say "but there's more"

Jean

ludwig wrote:Debby : drill the hole !
I did a few with great success .
Spoke clearance is absolutely no issue .

This one is gathering dust ,( even made titanium pistons for it ).

Why not a pipe plug? it would be almost flush with the caliper's surface, a dab of aluminum paint it would be fairly invisible.

Jean

I've seen those penetrating oil comparisons and also thought about making some homebrew.... but I don't like the smell of either acetone or ATF very much. The Kroil is pretty strong too - probably about the same as the mix would be!

The two-fer deal on the Kroil would be perfect for a Billy Mays pitch. But wait, order now and get a free brake bleeder syringe.. You pay only the additional $20 shipping and handling.

Russ

Jeandr wrote:Why not a pipe plug?

The back wall is not very thick , so I want to rely on the friction of the copper washer to keep the bolt in place .
Relying only on the thread for sealing might be risky : the caliper expands from the heat .
Because it is on the inside , you allmost have to get down on you knees to see it .

What size bolt? Will a 3/8 inch work ok? I already have the tap and I could use standard brake line washers, of which I have plenty on hand.

Debby