Topic: Silver braze caliper piston?

[TwoTired]

Seeking opinions:

I have some caliper pistons with pits deep enough to interfere with retraction.  I get squeaking brakes and poor retraction on the worst ones.  Anyway, I'm thinking of filling the pits with silver braze and smoothing them over to restore the original contour.

Is there anything about dissimilar metals, galvanic action, brake fluid reaction, or corrosion I should know about beforehand?
Will the heat from silver brazing destroy the chrome plating on the remainder of the piston?  Does chrome melt at a lower temp than silver?
What about brass or bronze?
Surely silver solder melts at a lower temp than chrome.  Is this too soft for the repair area?

Am I just being too cheap about saving old parts?  It bugs me cause most of the piston is good, apart from the bit that interfaces with the seal.   I know a new piston will just corrode, too.  And, I've got 5 calipers in need, now.

Is this a job for the micro acetylene torch?

Constructive comments welcome.

[Kevin400F]

Lloyd, would you be interested in trying one of my phenolic replacement pistons?

Look here for a description:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=011&sspagename=STRK%3AMESE%3AIT&viewitem=&item=320099300063&rd=1,1

Best regards,

Kevin

[Steve F]

Seeking opinions:

I have some caliper pistons with pits deep enough to interfere with retraction.  I get squeaking brakes and poor retraction on the worst ones.  Anyway, I'm thinking of filling the pits with silver braze and smoothing them over to restore the original contour.

Is there anything about dissimilar metals, galvanic action, brake fluid reaction, or corrosion I should know about beforehand?
Will the heat from silver brazing destroy the chrome plating on the remainder of the piston?  Does chrome melt at a lower temp than silver?
What about brass or bronze?
Surely silver solder melts at a lower temp than chrome.  Is this too soft for the repair area?

Am I just being too cheap about saving old parts?  It bugs me cause most of the piston is good, apart from the bit that interfaces with the seal.   I know a new piston will just corrode, too.  And, I've got 5 calipers in need, now.

Is this a job for the micro acetylene torch?

Constructive comments welcome.

The problem with silver braze (silver solder) is that you have to get t he temp up to around 1100F for the metal to start to flow which would peel the chrome off.  You can't just spot braze something like that because of the mass you need to pre-heat.  See if there's a machinist in the area that can spin off a couple of pistons in stainless for you, or go with the phenolic versions.

[bryanj]

I have done some measuring in the past i it  is my opinion that 1 1/2 inch stainless bar is exactly the right diameter without machining except for "hollowing" out. might be worth talking to a local machinist

[BobbyR]

If you want fiddle with it knowing full well you may need a new parts, you may try common solder or a electronics silver solder. The melting point is fairly low and it has a non corrosive flux. It can be buffed smooth. I am not sure an iron will heat the work enough to get it to flow but it is worth a shot.

[starion88esir]

Lloyd, would you be interested in trying one of my phenolic replacement pistons?

Look here for a description:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=011&sspagename=STRK%3AMESE%3AIT&viewitem=&item=320099300063&rd=1,1

Best regards,

Kevin

Will these fit a 76 750F or do you have ones that will?

[kslrr]

There would be no way to get the entire piston hot enough with a soldering iron, not even a soldering gun.  Have you thougt of trying epoxy?  You might be able to find and epoxy that is silver colored.

[wardmoto]

My holes were not too bad, but I used JB Weld with no problems.  That, a new seal and the piston bore dressed, and I was able to do away with Honda's goofy bolt spring arraingmernt...I have complete retraction and no drag

[bwaller]

TT,
I have several saved used pistons just waiting for a rebuild breakthrough! Yesterday I assembled the two calipers on my 550, had the new OEM pistons here for a couple years. Man those pistons are heavy. I've been watching those phenolic pistons Kevin and haven't heard anything negative, so TT....... go for it, put those damaged pistons on the scrap heap and try phenolic!

[Bob Wessner]

This isn't an area in which I would experiment. I'd just replace them.

The old ones make nice paper weights. If you now have several, hang on to them until Christmas, use them for stocking stuffers.

[jreich]

But it is so fun to experiment!

Try some 95% tin solder with an acid flux core...melts at around 450 degrees, and seems to be pretty strong


If it doesn't set-up correctly, you should know before you get on the road.....and if not, you've always got that rear drum!

[Cowboy]

TT,

I doubt you would need an oxy-acetylene torch to get the piston hot enough to melt silver solder. I suspect that  mini-torch would tend to heat the part unevenly anyway, given the small flame. I would try a straight acetylene torch, like a pestolite, or even just a propane bottle with one of those cheap torches on the end, like people use to sweat-solder copper pipes.  The trick is to use a large flame, keep it moving around the piston, and heat up the part evenly over it's entire surface, until your solder flows. That would be difficult with a mini-torch.

You can get silver solder in a range of alloys that melt at different temperatures. I'm a silversmith, so I keep a range of solders handy from brass (which melts at a pretty low temp, to silver solder in "easy", "soft", "medium, ", or "hard" which melt at progressively higher temps.  I can't offer any advice on their adhesion to a brake piston, but it may be worth trying.  

I won't offer my opinion on the safety aspect, since you didn't ask. (It's my pet peave about internet forums that people continually offer their opinions about how THEY would just throw money at the problem, or how THEY wouldn't take that risk, etc., and rarely adress the question you actually asked.)

[Bob Wessner]

I won't offer my opinion on the safety aspect, since you didn't ask. (It's my pet peave about internet forums that people continually offer their opinions about how THEY would just throw money at the problem, or how THEY wouldn't take that risk, etc., and rarely adress the question you actually asked.)

I believe if you reread his post, he left room for comments beyond the purely technical aspects of what he is contemplating. Hopefully, members would always be willing to post a thought about actions they felt would put another member at risk.

[TwoTired]

I thank you all for your responses so far

Kevin,
I'm very much interested in the phenolic pistons.  However, I need more than one.  And, I don't want to go through an auction cycle and pay excess shipping for each piston.  I still may do that.  But, probably not until I destroy the ones I have through experimentation.
I've heard reports of the phenolic swelling over time with contact from brake fluid.  Have you any data on this?

Steve F,
According to my metal melting chart, Chrome melts at 3034F, the steel melts at 2500F, copper 1980F (if they preplated with that) and my silver braze alloy 45 flows at 1300 F.  Oxy acetylene temps are 5000F.  Are you saying it is not possible to control the temps in order to prevent plating destruction?  Or, is it just very difficult?  Perhaps silver solder's 680 to 771 F temps are a better choice, with a lower temp heat source?

BryanJ
I can't find any local machinists that will do single piece work without paying for production set up time.  They only become interested when there is a minimum of $500 transferred, then they will talk details of the job.  I have a lathe so I may look into the SS bar.  I have no experience with cutting SS, however.  And, I thought the roundness tolerance was critical for this application. Then there are the cutting bits to buy...$$$  Phenolic looks to be a more attractive option, at this point, if I fail to repair what I have.

BobbyR,
Ordinary electronic solder I have lot's of experience with using.  I fear it is simply too soft for this application.  You can gouge it with a thumbnail.  Imagine what crystallized brake fluid could do.  Even frequent fluid changes won't replace the fluid right next to that seal.  Further, I think the mass of the heating iron would need to be as big or bigger than the brake piston, in order to gain enough heat to wet the pitted crevice.  I may still try this, if other methods prove to be too destructive.

kslrr,
Yes thought of epoxy.  JB weld (with its duct tape like utility) is a distinct possibility.  I have yet to learn of its tolerance to brake fluid.  A bit concerned about its heat tolerance.  And all resins seem to deteriorate with age in an unpredictable manner.  Not to worried about the metal contact.  But, the solvents and plasticizers in the seal material may soften the resin binder with constant contact.  Still, I have several pistons to experiment on.

wardmoto,
Ah, a test subject!! How long since you used the JB weld patch?  And, without "Honda's goofy bolt spring arraingmernt" , how do you keep the brake pads from contacting the disc in leanover turns and road bump shock distortions?

bwaller,
But, my pistons are over 90% smooth and good!  It's just that one, somewhat significant area that has a problem.   Do you throw a person away because he has bad knees?  Even with crutches he'd be good for something.

This isn't an area in which I would experiment. I'd just replace them.

That's a generous offer, Bob, that solves a lot of issues.  When can I expect delivery?  I'll be happy to return the stocking stuffers!! Sorry to hear you've run out of coal.

jreich and Cowboy,
I will likely try the high temp solder approach, if I find silver braze too difficult or destructive to the piston host.

As to safety:
 If the pits don't leak with the current seal, filling them will hardly make thing worse.  As long as the brake fluid pressure is transferred to the brake pads and rotor, the dang thing is gonna stop the bike.  It's physics, not magic.  It is very hard to imagine that any kind of failed patch would actually stop the piston movement in the caliper bore.  If the brakes drag before and after the patchwork, it will still stop the bike.  If you understand the physics required to make the caliper work, there seems little risk of actual danger.  Inefficiency, okay.  But, danger?  If someone can tell me of a specific issue besides the "sky may fall", I'll certainly listen to any facts I've overlooked.
I always two hand squeeze the brake lever with all I've got before road testing my brakes.  If nothing pops or leaks during or after that test, I don't think it's going to let go with a one hand squeeze, even with an adrenaline surge.

Thanks ALL for your comments!  Keep 'em coming!

Cheers,

[csendker]

I just took a look at my old piston, similarily corroded at the seal interface.  These obviously have an inside and an outside surface that are different one from another.  The inside (fluid) side is the chromed surface.  The outside (pad) side appears to have some sort of metal 'filler' filling the chrome 'cup' to an almost flush level.  Without putting any consideration at all into the force being exerted on this 'filler' stuff, what about just flipping the piston around and putting it in backwards?  Maybe seal the top with your silver braze, the tolerances would not be a real issue there.  And then the seal would run against the remaining smooth portion of the piston. That said, I have one of Kevin's phenolic pistons just waiting for the full brake replacement I'm going to do this winter.  Oops, it's spring already (...and my brake has stopped giving me any problems ever since I got the new piston).

[Kevin400F]

Lloyd, the pistons are extremely stable dimensionally.  Bear in mind, these are based on OEM-spec automotive brake pistons......all I do is alter the overall length to be compatible with the Honda caliper. 

I'll be happy to work out a quantity purchase with appropriate pricing and shipping cost.  Only one possible glitch......beyond the piston I currently have on eBay, I only have four left.  I need to contact the manufacturer and place an order for additional stock before I can commit.

If you want to discuss further, you can e-mail me at kthunter01@sbcglobal.net

[BobbyR]

OK, here is what I did since my piston fired itself into the woods behind my house as I heated it. I gave the caliper to my friend who distributes import auto parts. His re builder gave me what amounts to a racing caliper with a SS piston and proper seals. It cost me $60 total. I am as cheap a DIY SOB as you will find, but $60 was even ok for me. But  TT go for it, I am with you in spirit. I think the lead free solders today are much harder than the good old lead we inhaled in our youth.

[wardmoto]

TT, here is the rub... Most of my experience is with multi piston calipered sport bikes.  I know from this forum, that my piston wasn't in horrible shape compared to others I saw (I of course neglected to take pictures of it)...perhaps I would have been OK with a new seal and no JB...if that was the case, and my fix has already deteriorated (if it is going to) I might not ever see a problem.  The brake has had fluid in it for 3 months.  As far as rub or drag, they all do to a certain point and I am sure you knew that...I think I know what you are getting at.  In my haste to respond to you while at work in a timely manner, I neglected to tell you that I chose to abort all hope of using the original MC and simply ebayed a fantastic CBR F3 MC for 45$...perhaps that helps a bit to prevent the awful drag the stock set up gives (I have a bone stock 350F...its brakes are problematic).  I know on my SV 1000, when I am on the gas through bumpy undulations and the front end is wiggling all over the place ( and I am giving thanks for the damper!)...when it is time to slow the pace, I need to pump the binders up a bit as the oscillations caused them to retract away from the disk a bit more than usual. I have never had any problems like that on my cafe (obviously I am not power wheeling over bumpy roads at 75 mph either, not with 30ish hp!)).  Regardless of what I do, bumps, abuse etc... ( I practice repeated panic stops often) the brake acts predictably and doesn't drag or squeal.  Hope this helps, sorry for omitting a few details earlier.  Good luck and thanks for all your awesome input...my 350F was my first cafe and everyone here helped tremendously.

[mrbreeze]

OK, here is what I did since my piston fired itself into the woods behind my house as I heated it. I gave the caliper to my friend who distributes import auto parts. His re builder gave me what amounts to a racing caliper with a SS piston and proper seals. It cost me $60 total. I am as cheap a DIY SOB as you will find, but $60 was even ok for me. But  TT go for it, I am with you in spirit. I think the lead free solders today are much harder than the good old lead we inhaled in our youth.

$60 is cheaper than what the stealership will charge you for a piston alone (that will eventualy go south again anyway). What about the dot 5 conversion I have heard about here? No more internal corrosion??

[TwoTired]

What about the dot 5 conversion I have heard about here? No more internal corrosion??

I'm afraid that simply isn't true.  While Dot 5 doesn't attract water and hold in suspension like Dot 3 or 4, any water that does enter the system simply finds the low point in the system and collects there to corrode the inards.

At least with the glycol based fluid, changing the fluid also removes absorbed water.  You pretty much have to dismantle the hydraulic vessel to address internal corrosion with DOT 5 systems, even if you have a routine fluid change schedule.

Cheers,

[mrbreeze]

If dot 5 doesn't attract H2O.......how will it enter the system (unless some smart ass pours it into the master???

[Sam Green Racing]

Seeking opinions:

I have some caliper pistons with pits deep enough to interfere with retraction.  I get squeaking brakes and poor retraction on the worst ones.  Anyway, I'm thinking of filling the pits with silver braze and smoothing them over to restore the original contour.

Is there anything about dissimilar metals, galvanic action, brake fluid reaction, or corrosion I should know about beforehand?
Will the heat from silver brazing destroy the chrome plating on the remainder of the piston?  Does chrome melt at a lower temp than silver?
What about brass or bronze?
Surely silver solder melts at a lower temp than chrome.  Is this too soft for the repair area?

Am I just being too cheap about saving old parts?  It bugs me cause most of the piston is good, apart from the bit that interfaces with the seal.   I know a new piston will just corrode, too.  And, I've got 5 calipers in need, now.

Is this a job for the micro acetylene torch?

Constructive comments welcome.

This has to be a first on this forum...LLoyd asking our help.

Sam.

[mrbreeze]

Seeking opinions:

I have some caliper pistons with pits deep enough to interfere with retraction.  I get squeaking brakes and poor retraction on the worst ones.  Anyway, I'm thinking of filling the pits with silver braze and smoothing them over to restore the original contour.

Is there anything about dissimilar metals, galvanic action, brake fluid reaction, or corrosion I should know about beforehand?
Will the heat from silver brazing destroy the chrome plating on the remainder of the piston?  Does chrome melt at a lower temp than silver?
What about brass or bronze?
Surely silver solder melts at a lower temp than chrome.  Is this too soft for the repair area?

Am I just being too cheap about saving old parts?  It bugs me cause most of the piston is good, apart from the bit that interfaces with the seal.   I know a new piston will just corrode, too.  And, I've got 5 calipers in need, now.

Is this a job for the micro acetylene torch?

Constructive comments welcome.

This has to be a first on this forum...LLoyd asking our help.

Sam.

Ya know Sam........I was thinking the same exact thing!!!!! Don't recall Lloyd ever asking for advice but rather offering it.......I'm kinda afraid to offer my 2 cents on the subject!!!!

[Sam Green Racing]

 

Sam

[TwoTired]

If dot 5 doesn't attract H2O.......how will it enter the system (unless some smart ass pours it into the master???

Each time you open the system to check the level, humidity from the air enters.  On the next cool down cycle is condenses on the inside surfaces.

I also read that water can come in past and actually though the rubber seals. Poly based plastics are water permeable. Is your master reservoir plastic? Is your SS brake line core plastic?

Here is an excerpt from :
http://www.babcox.com/editorial/bf/bf40142.htm

"Moisture also creeps into the system to further add to the contamination problem. Humidity in the air can be drawn into the fluid anytime the fluid reservoir is opened for inspection or anytime a brake hose, line or bleeder valve is opened when servicing the brakes. Even if the fluid reservoir is never opened, moisture will still infiltrate the system through microscopic pores in rubber brake hose. The rate at which this happens depends on the age of the vehicle and the type of brake hose used. Newer hose made with linings that are less permeable to moisture help extend the life of the fluid. Even so, moisture can still slip past piston seals in wheel cylinders and calipers.

DOT 5 also cannot disperse moisture that enters the system throughout the fluid like DOT 3 and DOT 4 fluids. Any water that does get inside tends to "slug" and settle to the lowest point in the system, which is usually the calipers and wheel cylinders. Slugs of pure water are not something you want inside a brake system because they concentrate corrosion and increase the risk of pedal fade if the water gets hot enough to boil (it only takes 212 F to turn liquid water into steam.)"

Obviously, the probelm is more severe in wet, humid areas than it is in dry, arid areas.  But, it is one reason why the Military is looking for way to convert their fleet back to a glycol based fluid.  Dot 5.1 has all the temperature extreme benefits of DOT 5 without the maintenance issues dot 5 brings.  It is much cheaper to simply replace fluid on a regular basis, than to dismantle the system to address corrosion issues.

Cheers,

[TwoTired]

what about just flipping the piston around and putting it in backwards? 

I once read a post from someone who actually did this, claiming success.  I don't think he did anything to seal the plate insert, either.  I haven't seen any posts about it since.  (I hope there isn't an unfortunate connection there.)  Anyway, I can't say I'm too enthralled with that approach.  It just seems...wrong, even if it appears to work.  For me, I think it's going to be repair the pits or replace the piston.  We'll see...

Cheers,

[csendker]

What about this stuff? --> http://www.alumaloy.net/steelaloy1.htm

It's the steel version of alumaloy.

[Dave L]

Hi
I have to say that i have had no issues with my 550 front brakes , but would like to and some of my thoughts  ,  it may not be wise to reverse
a hollowed out piston as this may cause more heat around the edge and hence affect  the seal etc .
on cars its not such a problem but on bikes it well may be !! .
I have worked on cars and found the following its not a good idea to use wd40 or any other solvent based fluid on the piston as this will cause the piston
to stick when the solvent has evaporated and in the case of my car caused a loud noise (EEEK) and this could be felt back up the hose it took some time to
work out the cause!! .
Also i have read that in the case of cars if you push back the piston without opening the bleed nipple you can damage the abs unit seals  and the ecu will then
show up a fault which can prove costly to put right , whilst this may not effect our old bikes it does make you think .
I also have found the only car Ive not had trouble with regard to corrosion on the piston was a old french 205 this had what looked like teflon coated pistons
on the front these were like new unlike the back which i think are steel or alloy these had a lot of corrosion.


I would like to say thanks for all the help Ive had with some of my problems and without the help of this site my bike may well not be running today and each
time i log on i learn a bit more

Thanks

Dave

[Clyde]

LLoyd,
I have brazed chome plated parts before using 45% silver brazing alloy and no problem.
If you are slow on the heat it does not even colour the chrome. Too much heat and you will blacken the chrome and it will not take as well as leaving the chrome yellow/blue
I have not tried brake pistons as I have not been able to clean them up enough to get the braze to take properly in the pits and I have been worried about a bit of braze falling out or jamming the piston.
If you can get them clean enough to flow the silver brazing alloy ( 45% flows very well and has a good capillary action) the I think it would be OK.
Regds Clyde

[puppytrax]

Regarding Kevins' post on phenolic brake pistons, and Lloyds' comment on SS rod made into pistons...

Why couldn't you use Nylon or even Teflon rod of the correct diameter and trim & relieve it to fit??

Lloyd is dead on with the 1.5" measurement; my CB500/550/750SS all use that diameter, with slight differences in head configuration (and the 750F has a lip). Buying medical grade Nylon or Teflon rod and cutting it to size sounds do-able to me...

[TwoTired]

Clyde,
Thanks for sharing your encouraging experiences.  I would surmise from your statements that a high spot temperature is not a good as the a wide area, heating of the braze site.  That's good to know.  Maybe the bigger torch is the way to go for the experiment.  I was thinking of using an acid etch to clean the pits before brazing for good flow and contact.  I wonder if or how it would be possible to test the bond before returning the piston to service?

 Has anybody ever removed that steel insert in piston?  Perhaps if the piston was heated from the inside, the braze might flow and adhere with more confidence?

Why couldn't you use Nylon or even Teflon rod of the correct diameter and trim & relieve it to fit??

From what I know of these materials, Nylon is too soft and would expand in the bore under compression.  The stock caliper has a nylon ring between piston and pad for just this reason, to cushion the engagement of the brakes for a few thousandths of an inch.

Teflon has cold flow characteristics that would allow it to change shape over time.  I remember working with Teflon coated cables.  And they would imprint and void when draped over metal channels in just 6 months.  We needed the Teflon for fire code applications where PVC cables were not allowed.  We had to make special installation procedures, larger bend radius specifications for Teflon cables, as well as resting support pads for places where the cables were suspended.

I like the "thinking out of the box".  It's just that sometimes things are out of the box for a reason.

Cheers,

[Jerry Rxman Griffin aka MuthaF'er]

TT,

Try a dental pick to see if the repair will pop out.

[puppytrax]

Has anybody ever removed that steel insert in piston?

Yes, I can even post a pic if you like. It's about the thickness of an elect box slug. Serves no useful purpose that I can see. One of mine popped out while I was extracting the piston from the bore. My Chevy does not use caps like these. Honda crimps them in place; but if you're taking them out, better to drill a hole & screw in a lag screw and pop it out with a claw hammer & soft-jawed vise...    

(Note: The CB750F Super Sport rear brake pistons don't use these plugs. The piston is left open.)

OK; Nylon & Teflon are out. I can get 304SS in 1.5" dia for ~$33/ft. (I don't have any). I think I'll try that.   

Better than $66 each from Honda...   

[kslrr]

The steel plug might be there to dampen vibration and squeal by adding some mass to the piston.