Brake caliper rebuild dos and don'ts?

daves79x
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Re: Brake caliper rebuild dos and don'ts?

Post by daves79x »

Nils:
I don't think your seal groove is the problem, unless it's gotten too large to effectively seal. I've probably put lots of them together that weren't perfectly clean there. Your piston is the problem. You do need a new one, or at least a good used one. They aren't that expensive new - that's the way I'd go, but I probably have a good one around here somewhere if you want me to check. At this point I'd get a new seal kit also, since the pitted area may have torn up the seal you have now. Let me know if I can hunt anything up for you.

Dave

PS: I can't see the pic you posted

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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

Ahh, thanks, I uploaded the photo to a personal album that apparently isn't visible to everyone by default. That Gallery software is a bit quirky. I'll dig into it and write a how-to, but it's not exactly intuitive to use.

Anyway, please look again, I uploaded it again to the main album.

Thank you as always for the help. I think I have a line on a new piston, will let you know if I need more of your parts to get my bike on the road :-).

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by EMS »

The caliper pistons are on ebay all the time 8) 8)

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Re: Brake caliper rebuild dos and don'ts?

Post by ericfreeman »

When I got my '79 all the brakes were locked up. You had to smack the calipers with a mallet just to roll the bike. I replaced the seals and all the pistons with kits from Tims. No leaks in 4000 miles now. Highly recommend you replace any pistons that are suspect to avoid future problems.

Eric

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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

ericfreeman wrote:When I got my '79 all the brakes were locked up. You had to smack the calipers with a mallet just to roll the bike. I replaced the seals and all the pistons with kits from Tims. No leaks in 4000 miles now. Highly recommend you replace any pistons that are suspect to avoid future problems.

Eric
Eric,

I am Mr. Learn It The Hard Way. Then I admit it. That's my contribution the the science of repairing these bikes :D .

My most recent lesson is what you said. If I had it to do over I'd have replaced this piston when I first recognized the pit. I would bet money that I could rebuild an early model caliper blindfolded at this point, given my recent repetition.

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

NilsMenten wrote:
ericfreeman wrote:When I got my '79 all the brakes were locked up. You had to smack the calipers with a mallet just to roll the bike. I replaced the seals and all the pistons with kits from Tims. No leaks in 4000 miles now. Highly recommend you replace any pistons that are suspect to avoid future problems.

Eric
Eric,

I am Mr. Learn It The Hard Way. Then I admit it. That's my contribution the the science of repairing these bikes :D .

My most recent lesson is what you said. If I had it to do over I'd have replaced this piston when I first recognized the pit. I would bet money that I could rebuild an early model caliper blindfolded at this point, given my recent repetition.

N.
OK, so my piston arrived, I rebuilt the caliper blindfolded because I could, and it appears to be holding fine.

The master cylinder is now leaking again, out the rear where the plunger assembly meets the front brake lever.

At this point I want to take it off the bike, take it outside with a blowtorch and "get medieval on it's ass" to paraphrase Marcelus Wallace in Pulp Fiction.

I'm ready to conclude something bad happened when it was chemically stripped for powdercoating. It's Just Not That Complicated.

So if I were to replace this with something, is there an uprated MC for these bikes that looks more or less 'correct' and might increase performance while I'm at it?

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by steve murdoch icoa #5322 »

How about an '81/'82 set-up?
I am assuming it would be an upgrade having to handle the dual piston calipers?

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Re: Brake caliper rebuild dos and don'ts?

Post by daves79x »

Nils:
Many of these old M/Cs are pitted in the bore if you look real close. I've got a whole box of them - they will leak and not give a firm lever when bled.

There are some modern Honda M/Cs that will work. The 600 Hornet and 900 (whatever they call the naked one) have black 5/8 bore M/Cs with mirror mounts. I'm pretty sure they fit 7/8 bars. Just go to the Honda showroom and look around - you'll see quite a few possibilities. They are straight like the CBX, not angled. Back a ways, any Honda M/C with a 5/8 bore will work. 1100F, 900F, 750F, some Nighthawks, anything with straight, standard bars. The cruisers have angled M/Cs that don't look so good on the CBX. I'm sure you can find something that will work. I try to gather up M/Cs from those bikes listed above, and maybe 1 out of 3 is good, but they are usually cheap on eBay, as long as it doesn't say 'CBX' in the ad.

Dave

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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

daves79x wrote:Nils:
Many of these old M/Cs are pitted in the bore if you look real close. I've got a whole box of them - they will leak and not give a firm lever when bled...

<snip>

Dave
OK, I have a couple of inquiries into places that resleeve automotive M/Cs using either brass or stainless, including Karp's in LA and Apple in NY. Has anyone had any great success with this route? And if I do find someone to take it on, would any of you like to get your spares resleeved with mine at the same time? It looks to be about a $75-90 service, but if it works as advertised, it'd be pretty darn permanent I imagine.

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by zxbob »

The master cylinder is now leaking again, out the rear where the plunger assembly meets the front brake lever.

At this point I want to take it off the bike, take it outside with a blowtorch and "get medieval on it's ass" to paraphrase Marcelus Wallace in Pulp Fiction.
That cracks me up ~ taking apart my bike i've allready been there, but to "think your finished" and have to
go back . . . . . .

Bob
Good parts aint cheap ~ and cheap parts aint good !

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Re: Brake caliper rebuild dos and don'ts?

Post by NobleHops »

zxbob wrote:
The master cylinder is now leaking again, out the rear where the plunger assembly meets the front brake lever.

At this point I want to take it off the bike, take it outside with a blowtorch and "get medieval on it's ass" to paraphrase Marcelus Wallace in Pulp Fiction.
That cracks me up ~ taking apart my bike i've allready been there, but to "think your finished" and have to
go back . . . . . .

Bob
Yeah, it's been testing my patience for sure :shock:

The update is that I did strip it down, cleaned it scrupulously, and mailed it off to Apple Hydraulics in New York, who promised me 1 week turnaround to resleeve it with bronze. I'd have to think that nice machined bronze is going to seal a lot better than the porous-looking alloy these things were cast in, but the proof will be in the stopping :) .

I should have it in hand middle of this week, and when I do, I will photograph it carefully as I reassemble it and perhaps our little community will benefit sometime in the future from my thrashings now.

N.
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Re: Brake caliper rebuild dos and don'ts?

Post by Mike Cecchini »

Wish I could have gotten to you sooner Nils.....but there is a great way of honing the master cylinder and calipers with Brush Research "flexhone" deburring hones. http://www.brushresearch.com/product-line.php?line=1

Then I found these automatic transmission valve body brushes https://www.benchbuddy.com with micro-media embedded right in the bristles. The beauty of these brushes is that they put a nice fine finish but will not increase bore diameter.

I know you have a lot of experts over here......but don't discount posting your questions and issues on the Brewer List as there are some pretty smart people over there also.

Even with pits like yours it's worked wonders for my master cylinders with pits and corrosion I wouldn't believe were salvageable. I did my 80X 6 yrs ago with pits worse than yours......still perfect today. No leaks and firm lever.

Btw..... you might want to go to DOT 5 silicone brake fluid and never have to deal with DOT3/4 corrosive properties or caliper/master cylinder rebuilds ever again. I did this on my 80X and it's wonderful...... 5--10 yr fluid change-outs. :shock:

My best....... Mike
It's not what you ride.....it's how you ride.

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Re: Brake caliper rebuild dos and don'ts?

Post by EMS »

Do not change to DOT5, Nils. DOT5 is not hygroscopic, like DOT3, DOT4 and DOT5.1 are, but because of that, moisture (water) will settle separate from the fluid at the bottom of any cavity and will cause corrosion there. As any brake expert ( I am not one) will tell you, DOT5 needs to be changed regularly, even more so than the other fluids. And if you change anually anyway, there is no advantage to DOT5 other than it is not agressive to paint, which may be a point for some. Unless you find a way to prevent moisture from forming liquid pools in your brake system.....
Also if you change, it is very important to clean your system COMPLETELY of your old fluid before you fill it with silicone based DOT5.
Then, of course, there are always those who argue that they have done this all and it works fine and is perfect and everything else is just theory and written in handbooks by geeks who don't ride their bikes anyway. 8)
Last edited by EMS on Tue Jul 27, 2010 8:20 am, edited 1 time in total.

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Re: Brake caliper rebuild dos and don'ts?

Post by Mike Cecchini »

Totally untrue. GM says change DOT 5 every 5-10 yrs........and there's no "pooling" of water. Did the Jag almost 20 yrs ago and had the system apart 5 yrs ago. No water anywhere..... no corrosion anywhere.

Changed the 1989 Ducati back in 92 and it's still perfect..... no water anywhere when I took the system apart last year.

Experience is the real teacher...... not hair-brain theories.
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Re: Brake caliper rebuild dos and don'ts?

Post by EMS »

As I said, I am not a brake expert. But let's hear what Mike Nixon, arguably one of the authorities around motorcycles has to say in his "motorcycle project":
http://www.motorcycleproject.com/motorc ... fluid.html (Mike, I hope you don't mind)
Silicone Brake Fluids
In years past, all brake fluids were glycol. Then DOT5, a silicone fluid having a higher temperature rating emerged, initially to meet the higher boiling point requirements of racing use. (race car brake systems include oil-cooler-like heat exchangers and ceramic pads.) Silicone fluid was able to withstand the most heat of any barke fluid, so it earned a reputation as a racing brake fluid. However, silicone brake fluid has properties very different from glycol fluid, and has its own pros and cons. On the advantage side, silicone fluid will not harm paint or plastic, and does not agressively attarct additional ,oisture as glycol fluid does. On the disadvantage side, howver, silicone fluid aerates easily. Harley-Davidson, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before suing it. The trip home in the saddlebag is enough to aerate silicone barke fluid until it looks like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content and worst of all, neither accepts or disperses moisture, making systems more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occuring lubricity, making it incomapatible with the mechanical valving in some antilock braking systems.
..another harbrain theory...

and as far as this is concerned:
Experience is the real teacher...
I have used DOT5 in both performance cars and motorcyles in the past (Corvette ZR1, Ducati 916SPS) and I find it unacceptable as far as pedal and lever feel is concerned. The higher compressibility makes the feel extremely spongy and non-linear.

Then again, I guess, whatever makes you happy.

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