Brake Caliper Teardown (yes, with pictures!)

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 said:

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.

Click to expand...

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

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 said:

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

Click to expand...

I think I will! This idea appeals to me for some reason. :twisted: 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. :roll:

Debby

batrider said:

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...)

Click to expand...

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

Jean

ludwig said:

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 ).

Click to expand...

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

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

Re: Brake Caliper Teardown The Bodger's way

Sometimes the seriously stuck inner pistons can be pumped out if you can get them moving first. It is unlikely that the inner is seized at a point where it is at the back of the bore so if the outer is removed, it should be possible to drift it in deeper which may break the grip of the corrosion. It is one of those 'shit or bust' moments but there is not much to lose.

I've also had some success with auto-jumble purchase calipers by winding out a short hex screw and nut until they jam inside the piston and then turning the piston with an old open-ender* and Mole grips. Once they have rotated a little, they should pump out. The piston will be scrap anyway and they are thick-walled enough for this operation not to cause them to wedge tighter

I'm a bit wary of putting strong penetrants in as if they have a mineral oil base, there is always the risk of them causing the seal to swell and making it grip harder (I think, possibly :? )

*use a metric spanner. They're not much good for anything else anyway

Simply attach the grease gun to the zerk fitting and pump away. If the grease dosn't push the pistons out then throw the caliper away and start fresh. But they will come out. Leave the back cap on so both pistons push out. Remove the brake pads of course.

I agree with 79X100. It seems counterintuitive, since the object of the exercise it to get them out, but if you can push the pistons further into the bore this will often be enough to crack the bond of corrosion and allow them to be subsequently blown or pushed out under hydraulic pressure. I have done this many times and generally coat the bores with copper grease first as I have found this then helps the pistons on the way out. Too much heat can melt the inner seals and exacerbate things.

ludwig said:

debby said:

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

Click to expand...

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 .

Click to expand...

How about some Teflon paste (or tape, but I prefer the paste) on the threads as well? Never really thought about the temp issue before, but I use it on caliper bleed screws and it works a treat.

chopped850 said:

Simply attach the grease gun to the zerk fitting and pump away. If the grease dosn't push the pistons out then throw the caliper away and start fresh. But they will come out. Leave the back cap on so both pistons push out. Remove the brake pads of course.

Click to expand...

Zerk? Do you mean bleeder valve?

batrider said:

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

Click to expand...

Liquid Wrench is sitting on the bench, so it's getting used. When it's gone I'll make some homebrew.

Stainless pistons are waiting patiently for their new home. :mrgreen:

Re: Brake Caliper Teardown The Bodger's way

79x100 said:

*use a metric spanner. They're not much good for anything else anyway

Click to expand...

You kiddin', 79? The 13mm socket/spanner is the single most useful tool in the kit! American bikes, English bikes, Italian, German - my 13mm's never get set down for long. :wink:

Hi,
Drilling and plugging should be left to last resort status. Compressed air works 90% of the time and the grease gun does the rest (although its a mess to clean up). I have a 10mm bolt drilled through with a grease fitting on the top of it (works for all the Japanese stuff I do I don't know what size banjo bolt the Norton uses). Anyway, other posters have covered this, so I posted to say that Dyno Dave Comeau once told me that he filled a grease gun with water and it worked (also a quick clean up).

GB