How-to: Fix a plugged MC return and heal your dragging brake

How-to: Fix a plugged MC return and heal your dragging brake

Postby NobleHops » Sun Jul 21, 2013 1:26 am

So this malady seems to be making the rounds lately.

I had my rear brake suddenly drag last fall requiring me to ride home 2-up and return with my trailer to fetch the X. By the time I returned the brake was free, but damage done, the rotor was showing bluish discoloration from overheating and it obviously could not be ridden till it was fixed. I parked the bike for the winter and just got around to tearing into it today.

Dave McMunn had previously swapped me a complete newly rebuilt 2-pot rear caliper and a like-new Prolink rotor in exchange for some H2 parts a while back and I had a new brake line on hand too. My buddy Joe and I made pretty quick work of the swap, installing the new rotor and caliper, and then the new brake line. When we had it back together it was unusually slow to bleed and pump up, which in hindsight should have been a dead givaway that the problem was indeed in the master cylinder, but we forged ahead anyway. Once we had the air out I went for a short ride down the cul de sac and then out onto the road. By the time I returned from a 2-mile roundtrip it was dragging again, but thankfully I did not appear to have overheated the rotor this time, although it was good and hot. And so the bike went back onto the lift and we pulled the master cylinder as we should have from the start.

There was the usual amount of cruft and goo under the boot at the bottom, and the little reservoir in the master cylinder had crystalized brake fluid from where it was weeping past the sealing o-ring:

Image

See the smaller of the two orifices in this pic (upper)? That's the (tiny) return circuit orifice that allows brake fluid to come back from the 'pump' part of the master cylinder, allowing the pistons to retract after the brakes are applied. If it's clogged then the fluid is slow at best to return and brake fluid can be forced past the other seals in the MC while it's under pressure and getting heated up, causing your brakes to grab and drag, and overheating your rotor, pads, caliper and the fluid. Not good.

In a pinch one could simply remove the plastic fitting that sits over this reservoir on the MC, clear the clogged orifice, and put it back on, but that's likely make a mess and the crystallized crap that caused it to clog would still be floating around in the system. Here's what that looked like on mine (note the dark flecks of crap).

Image

So we opted to disassemble it all, clean it all out and rebuild it. But first, we had to clear out that return orifice, because it was indeed well and truly clogged. That hole should pass straight through to the bore of the cylinder: mine was so clogged I called Dave and Phil to ask if it took a 90-degree turn or something. I plucked a wire from my wire brush, clamped it into a teeny set of vice grips and twisted it like a drill. I could not simply poke it through, it was too solidly blocked. Twisting it was Dave's suggestion when I called him, and that did do the trick.

Image

Then we honed the bore with a rotary brush in a drill, cleaned it all and washed it all with soapy water, and then dried it and set it in the sun for a few minutes to blast off any remaining moisture.

Image

Then it was a simple job to rebuild it, install it, refill the system with fresh fluid, and this time it pumped up good and hard in a matter of 5 minutes with no weirdness.

SO...

Based on my extensive experience of this happening once, if you're dealing with brake drag, I'd do this first, give your brake system a good flush, and see if that does it before you go tearing into your calipers. I had the new parts to install anyway, so I didn't really lose much time for my efforts, but it would have worked a bit better to do it in the reverse order in my case, eg, do the master cylinder first, then go down stream.

N.
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Tucson, Arizona, USA '80 CBX, sort-of restored :-)

http://www.restocycle.com Ikon shocks for your CBX! https://www.ikonshocksusa.com/collections/honda/honda-cbx1000-79-80
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby steve murdoch icoa #5322 » Sun Jul 21, 2013 7:40 am

Nils, using the heart-shaped cake tin means no Valetines treats for you.
As usual, an excellent how-to. Thanks.
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby daves79x » Sun Jul 21, 2013 10:30 pm

Glad it worked out well for you, Nils.

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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby NobleHops » Mon Jul 22, 2013 10:40 am

Thank you for the Nth time Dave, for the great brakes and the help.

N.
I Do Vapor Blasting! http://www.cbxclub.com/forum/viewtopic.php?f=5&t=9881

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http://www.restocycle.com Ikon shocks for your CBX! https://www.ikonshocksusa.com/collections/honda/honda-cbx1000-79-80
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby Steverino » Sat Mar 01, 2014 12:01 am

I'm rebuilding my rear m/c because of this exact problem. I want to make sure I understand exactly what you are saying. The small orifice that is at the roughly 2 o'clock position in the top picture of this post is the one you are referring to. This is the one you've probed with a wire from your wire brush correct? And, you are saying there is no turn, it is supposed to go straight through to the cylinder? I've tried poking through on mine and man, it is clogged tight. I just want to make sure this is the correct passage way because tomorrow I am going to run a bit through it to clean it out. Thanks for your help!
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby daves79x » Sat Mar 01, 2014 12:55 am

Again, no free lunch here - the master cylinder and entire brake system has to come apart and be completely cleaned. Any pitted pistons need replaced as well as caliper seals. Your m/c innards might be re-usable if you clean everything up very well. You'll have nothing but trouble with them if you don't do this.

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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby Steverino » Sat Mar 01, 2014 1:53 am

Yes, I have a m/c kit on order, but is the small port a straight shot that I can run a bit through? I am happy to buy lunch, just let me know how.
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby NobleHops » Sat Mar 01, 2014 3:05 am

Yes Steve, it goes straight through. As Dave taught me, pluck a stiff strand of wire from a wire brush and twist it like a drill. Mine was plugged tight. This will do the trick, but take it all apart and clean it perfectly while you're at it or risk it recurring.
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http://www.restocycle.com Ikon shocks for your CBX! https://www.ikonshocksusa.com/collections/honda/honda-cbx1000-79-80
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby Steverino » Sat Mar 01, 2014 3:39 am

Thanks Nils I've Got her completely apart. It's pretty impressive what 32 year old brake fluid can do. It had really solidified.



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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby daves79x » Sat Mar 01, 2014 9:18 am

A Dremmel tool with one of their Scotchbrite balls really works well for cleaning out the m/c and calipers. You will still have hand work with a dental pic to get all the corners, but saves a lot of time. Check carefully the m/c bores for pitting. The Dremmel will clean out some, but if deep, will probably leak. I have a whole box full of pitted master cylinders. If you need just a touch-up on any painted parts, you can buy caliper paint in a rattle-can - spray a bit into the lid, then touch up the areas with a paper match stick.

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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby Steverino » Sat Mar 01, 2014 9:36 pm

Thank You Dave.
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby NobleHops » Sun Mar 02, 2014 1:45 am

Steverino wrote:Thanks Nils I've Got her completely apart. It's pretty impressive what 32 year old brake fluid can do. It had really solidified.



\\\


Mine had too. Was rock hard in that orifice. You're on to it! Victory soon...
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http://www.restocycle.com Ikon shocks for your CBX! https://www.ikonshocksusa.com/collections/honda/honda-cbx1000-79-80
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby Steverino » Thu Mar 06, 2014 12:17 am

The M/C is back together and the brakes are working perfectly. Thanks Guys!
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Re: How-to: Fix a plugged MC return and heal your dragging b

Postby barryadam » Thu Mar 06, 2014 1:11 am

I checked that hole diameter on my m/c using some wire drill sizes. Turns out it was #78 drill (0.0160 in.), which actually measured @ 0.01575 in. – 0.01580 in.
I did this to compare the hole before and after I anodized the whole thing.

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