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Discussion Starter · #1 ·
Hi I’m currently rebuilding my front and rear callipers as I was in need of new pads so thought I would take the time to strip clean and rebuild with new seals. I think there fine but I just wanted to get some opinions on the condition of my two front pistons as they are showing some very small signs of corrosion only really on the outer edge. However you can’t feel any signs of corrosion, they feel perfectly smooth all of the way around, so much so I thought they were just black marks until I looked really closely under a bright light and felt them with a pick, some of them are just marks, like blemishes. There’s also some small amount of pitting inside the caliper seal grooves so I’ve attached a picture, any advice much appreciated.

Thanks in Advance

Terence

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Get some 000 steel wool to clean it up and it should be fine, I've rebuilt calipers with far worse pistons than that. Those actually look to be in really good shape.
 
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If you decide to replace therm, what I did was to shop eBay for a front caliper 2000-on from a bike in a southwestern state with dry air. As of right now, there are 5 calipers for less than $15 shipped. But, it's a crap shoot on the pistons.
 

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Discussion Starter · #4 ·
Thanks for the replies guys. I was using some 000 grade steel wool to help clean the seal grooves so I went over the pistons with them like you suggested and used some Autosol with a cloth as well. Some other questions have come to mind, that someone can hopefully answer. I bought some lubricant called Cera Tec Service Products – Textar Brake Technology which I was going to use on the slider pins, however I found out that apparently it’s oil based so not compatible with the rubber boots surrounding the pins. I think it is more just to be used on the back of the pads if there is an issue with squealing. I have some Servisol Silicone Grease servisol AV-701.143UK Silicone Grease, 50 g: Amazon.co.uk: Electronics which I was wondering would be ok to use? Also I was going to lubricate the piston and seal with brake fluid; however I have read some opinions that it is better to use a proper brake assembly lubricant that has been tested as being compatible with Dot 4 brake fluid instead. I think the idea is it should give better protection to the seal in the long run than using just brake fluid as with it being hydroscopic it would draw moisture to the seal? Anyone have any opinions on this it looks like Textar who make the Cera Tec also make a product called Hydra Tec which is says is compatible with brake fluid, the seals and piston. I’m sure other products are available but I just saw it as it is on the same webpage that I have attached a link to.

Thank Yous for any advice it’s much appreciated

Terence
 

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just be sue there are no pits to tear up the seals, rememberers they don't touch any metal.'Just clean and brake fluid is fine, don't make too much of this, this brake system is crud as a cob. Alignment is where you need to spend your time. read my caliper service, the alignment part.

Part copied and pasted here for you:
Now clamp the caliper to the disc with the brake lever.

Look at the space between the fork lugs and the caliper, clamp and release a few times as you tighten the bolts by hand. It one lug touches much before the other the odds are you mounting bracket is bent. You can straighten it. After you get it the best you can. Some shim washers made from alum can stock can be fitted to the loose side.
What we are doing here is trying to mina muse the bedd in time and gets the best pad life.

FOG
 
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If the seal grooves have corrosion in them (almost all do), a fine soft wire brush on a Dremel at low speed will clean the more difficult bits out. Go easy and check with a magnifier as you go.

I would lean toward the use of a brake seal compatible grease on reassembly, as the fluid is indeed hygroscopic. That is best kept indoors, so to speak. And, that is often where the pistons are pitted.

If you look at some of the "curb side" brake rebuilds on YouTube, you know that this is not exactly critical, but why take the chance?
 

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I have always used brake fluid to lubricate the seals during reassembly and have yet to come across an issue with that. It is important to use a pick to clean out the crud and minor corrosion in the seal grooves I've cleaned out some pretty nasty looking brakes before, reused the original seals and they seal up fine. The dust seals are, oddly enough, more likely to give you grief. In my experience, they can expand and become slightly too big to drop back into place. It's not all the time, but does happen.

As for greasing the slide pins, I have always used whatever grease I have, typically it's a high temp wheel bearing grease. Never done me wrong.
 

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Discussion Starter · #8 ·
Thanks for all of the advice. I have ordered some Ate brake assembly paste which is compatible with brake fluid and seals, like you say I suppose why not it can’t do any harm. Thanks Fog, yeh the pistons don’t have any pitting, however like Saabnut says there is some slight pitting in the seal grooves which I have cleaned out with a pick and some 000 grade wire wool. I take it the slight pitting that’s there shouldn’t be an issue. Or would you’s say that it is best to try to smooth some of this pitting out as I would have thought trying to remove the pitting would alter the size or rather shape of the groove slightly.

Thanks

Terence
 

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Do you look/work on the caliper under a magnifier? I have a large lit magnifier on a base like a lamp that is one of my more valuable tools. I just did my rear caliper last night, bike has 47,000 miles on it and never had the rear piston/caliper serviced (routine brake flushes over the life span - pad replaced once maybe?) Anyway, have done countless calipers over my life span, broke stuff/replaced stuff/ have seen alot of crappy stuff NUF-SED.

These/my calipers last night only needed a little attention with a red scotch brite pad inside the two grooves. Bear in mind the main area where the seal goes has an inner groove. Don't use a metal pick if your ham fisted, if you gouge up the aluminum your gona be screwed. I used some 1000 grit or so sand paper folded up in the shape of the groove and used a wooden orange stick (women use them to pick the toe jam out of their toes lol) anyway, pretty easy job compared to some of the rotten brake systems I have seen in the past.

Removed the right hand muffler along with the two allen head bolts holding on the caliper to the carrier and away you walked with the caliper after you broke the banjo bolt. I installed a nice braided line along with my fresh OEM Kawasaki dust seal/inner seals. Used Sil-Glyde Silicone Brake Lubricant, Tube, 4 oz - AGS Company to grease the slide pins slightly, and job done. Have a air assisted bleeding machine (MityVac) and that was it.
 

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Here is a very good tutorial on caliper rebuilding.

 

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Discussion Starter · #11 ·
I haven’t got a magnifier like that, it sounds like a pretty good tool to have, I may look at one thanks. I have some 1000 grade sandpaper so I will try with that and see if it removes some of the pitting, like I say there not dirty but I may as well carefully remove as much pitting as I can. Thanks I have watched that rebuild video before, I think he has carried out some sort of sandblast on his caliper, hence why they look so good.

Thanks
 

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Yeah, he does powder coating and restoration. Do you have a drill press or a corded or cordless drill? You can make a mandrel out of a wood dowel that fits snugly into the piston cavity. Then, drive a screw into the center and cut the head off. This will allow you to chuck it into the drill. As it is spinning - start slowly - wrap the wet/dry around it (wet) work it back and forth and it will be smoothed around the entire circumference, rather than just that one spot. Keep the sadnpaper wet as you do this. Most all small pits are outside of the seal, so are only a concern if they allow fluid from inside the seal to out. And the smaller pits can be covered by the seal depending on the thickness of the pads, so 'technically' no problem.

Also get some crocus cloth and you can make the piston surface extremely smooth. Have never tried it, but tiny amounts of JB Weld might fill the pits.
 

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Yeah, he does powder coating and restoration. Do you have a drill press or a corded or cordless drill? You can make a mandrel out of a wood dowel that fits snugly into the piston cavity. Then, drive a screw into the center and cut the head off. This will allow you to chuck it into the drill. As it is spinning - start slowly - wrap the wet/dry around it (wet) work it back and forth and it will be smoothed around the entire circumference, rather than just that one spot. Keep the sadnpaper wet as you do this. Most all small pits are outside of the seal, so are only a concern if they allow fluid from inside the seal to out. And the smaller pits can be covered by the seal depending on the thickness of the pads, so 'technically' no problem.

Also get some crocus cloth and you can make the piston surface extremely smooth. Have never tried it, but tiny amounts of JB Weld might fill the pits.
Good idea.

One of the things I do is take my dremel and use one of the small fabric polishing bits with some metal polish. I can easily control the speed and get into tight spaces easily. The metal polish is not too aggressive and does a nice good of cleaning metal surfaces.

When I clean the brass carb float needle tubes, I will use a cotton bud in my dremel with metal polish. The tubes are better than new after a short polishing.
 

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all good info and tips. but TBH I believe your over thinking this. the calliper looks fine as do the pistons.
considering some of the brakes I've done over the years they look new. for instance when I decided to make the gen 2 cruiser into twin brakes. I could not find a good gen 1 brake anywhere so decided to use the original brake off the gen 1 when I got it. I might add it was rejected on the first rebuild what a state that was in totally rusted solid.

After a two day soak it just came apart using a vice and breaker bar the slider was so tight I had to drill all the crud out of the calliper but lucky the pistons came out not to bad after a clean with a wire brush and wire wool but were still slightly pitted but it all worked. a service kit (with new rubbers and seals) and fresh pads I put it on in hope it didn't leak.
it was fine, been on the bike for two years now still working and not leaking. if those pistons and grooves didn't leak yours won't.
 

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Discussion Starter · #15 ·
Yeh I knew the pitting was fine but I just wasn’t sure when people mentioned about removing corrosion if they were also referring to the pitting, as I thought well if there is some sort of that method that people were using or just some extra elbow grease then why not. Thanks again for all of the advice guys.
 

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If there is a pit large enough to span the seal, then it's a no-go.

As an aside, fork springs. They heat treat therm. That leaves an oxide coating. Which wears off as they compress and extend. Oxide is abrasive, and is part of the reason your fork oil looks so gunky when you drain it. So, I make up aforesaid mandrel and polish the OD of the fork springs. Hey, I'm retired, but even then it does not take long.

We talk about magnetic drain plugs - well they should ougta' be in the fork drain screws - except gen2 don't have them unless you drill some.

Now, back to finish fixing my 40 year old dryer.
 
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