Author Topic: CB500 master cylinder fluid return hole problem  (Read 18819 times)

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Offline DavePhipps

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CB500 master cylinder fluid return hole problem
« on: March 08, 2011, 07:36:31 PM »
How the heck do you unclog this tiny thing. I've tried a strand of copper wire but it bent too easily. I can't get a thin guitar string through it. Should I just take the MC apart and blast the hole with compressed air?
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Offline bender01

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Re: CB500 master cylinder fluid return hole problem
« Reply #1 on: March 08, 2011, 08:16:29 PM »
Im searching info here about drilling it out and I come across this post!
  I drilled mine out and the hole is considerably larger now! I couldnt get the brakes to work at all after a rebuild and taking it apart several times. This was with 2 cylinders to work on. This am after drilling one of them out i put it together and 5 minutes later I had a front brake! A needle would go through the one that doesnt work. The one working now would not open up at all so I drilled it. I have a 3rd seized one as well.  Im searching to see why more people dont do this! I havent ridden it yet and have another rebuild kit on the way. I assume Honda made that hole small for a reason. Anyone else ever drilled one? Also searching elsewhere I learned Boiling the master cylinder for hours will clean/soften the blockage up.
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So, the strategy is to lie to people you are asking for help?

I think I'll be busy going for a ride.

Good luck!
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Offline DavePhipps

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Re: CB500 master cylinder fluid return hole problem
« Reply #2 on: March 08, 2011, 08:23:25 PM »
I've got a spare MC taken apart and it looks like the hole just goes straight through so if I can get something to penetrate the goo it should work again. The idea of making the hole a bit bigger does appeal to me but like you I'm wondering if it's this small for a reason.
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Offline bender01

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Re: CB500 master cylinder fluid return hole problem
« Reply #3 on: March 08, 2011, 08:36:08 PM »
Yeah wait for some replies before another cylinder gets wasted. I searched a post here the other day about filling it with JB and redrilling another hole. But i cant seem to find it.
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So, the strategy is to lie to people you are asking for help?

I think I'll be busy going for a ride.

Good luck!
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Offline bryanj

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Re: CB500 master cylinder fluid return hole problem
« Reply #4 on: March 09, 2011, 12:23:04 AM »
You need to get a new master seal kit, struggle the circlip out, strip the master right down then poke through the hole till clear. Reassemble with new kit and away you go
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline TwoTired

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Re: CB500 master cylinder fluid return hole problem
« Reply #5 on: March 09, 2011, 12:34:15 AM »
To keep the hole tiny, get high E guitar string, and grind, file, hammer, or snip a spade tip on the end of it.  It will behave just like a tiny drill in the hardened brake fluid.  Just bend the wire in the same general shape as a brace and bit, and crank away.

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Lloyd... (SOHC4 #11 Original Mail List)
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Offline DavePhipps

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Re: CB500 master cylinder fluid return hole problem
« Reply #6 on: March 09, 2011, 09:19:04 AM »
Tank you Two Tired for the high E string suggestion. This still doen't answer the question of the reprecussions of drilling the hole larger. Would it be detrimental to the performance of the baking system?
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Offline TwoTired

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Re: CB500 master cylinder fluid return hole problem
« Reply #7 on: March 09, 2011, 11:41:42 AM »
Tank you Two Tired for the high E string suggestion. This still doen't answer the question of the reprecussions of drilling the hole larger. Would it be detrimental to the performance of the baking system?

The raw physics says yes.  But, I don't know how to exactly quantify it.

The hole releases pressure, air bubbles while the master piston and its rubber seal is retracted.  Once the master piston moves past the relief hole it is no longer a factor.  But, in that short period of travel, a larger hole will allow more fluid to escape, and allow more lever travel to achieve the same pressure as compared to a smaller hole.  I can imagine the speed of the piston would have a relational effect.

Secondly, the lip of the piston seal has to traverse the hole.  There is the opportunity that the edge of the hole becomes abrasive, especially since pressure in building in the system.  This will tend to force bits of rubber into it as you are pushing it past the opening.  A wider opening provides less support for the passing seal, allowing it to ingress the hole more than originally designed.  The seal may wear faster leading to more frequent seal replacement requirements.

Third, if you have done much drilling in metal, you will learn the exit holes often have flash poking out proud of the hole.  Many metal cutting tools don't cleanly remove metal, particularly twist drills.   They can push and deform metal at both the entrance and exit of the hole.  It is common machining practice to chamfer or de-burr both the entrance and exit points. If left behind, these jagged, sharp edges will certainly nick or slice the soft rubber forced across them.
There is fairly easy access to the reservoir side for a deburr operation.  However, the piston bore end of the hole it not so easy.  Instead of a chamfer bit, more likely a hone of the piston bore would be needed to ensure hanging metal chips weren't left proud at the drilled bore.

I can't think of any benefit for making the relief hole bigger.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
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Offline DavePhipps

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Re: CB500 master cylinder fluid return hole problem
« Reply #8 on: March 09, 2011, 12:16:15 PM »
Well, that makes sense to me. Guitar string this weekend it is.
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Offline DavePhipps

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Re: CB500 master cylinder fluid return hole problem
« Reply #9 on: March 09, 2011, 03:28:09 PM »
I found that a wire from a wire brush will also fit in the orifice. I just went out and cleaned mine . MY GOD, it looks like my MC barfed rust and old brake fluid into the reservoir!
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Offline bwaller

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Re: CB500 master cylinder fluid return hole problem
« Reply #10 on: March 09, 2011, 03:42:22 PM »
It just goes to show that brake fluid needs replacing regularly.

Offline DavePhipps

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Re: CB500 master cylinder fluid return hole problem
« Reply #11 on: March 09, 2011, 04:14:26 PM »
The brake fluid was replaced 3 times since last fall. That's just what was stuck in that orifice! Remember folks, check your holes for clogs (sounds wrong somehow).
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Offline bryanj

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Re: CB500 master cylinder fluid return hole problem
« Reply #12 on: March 09, 2011, 11:04:14 PM »
Speaking as a native of the Northern bit of UK (NOT Scotland)

There's Nowt wrong with clogs lad, usefull for dancin' an' ankle tappin!!
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Offline Hush

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Re: CB500 master cylinder fluid return hole problem
« Reply #13 on: March 10, 2011, 12:43:38 AM »
I used a sewing needle for that small hole, worked amazingly well and allowed my frozen on twin sets of pads to return and release their vice like grip on my front discs!
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline techmonkey

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Re: CB500 master cylinder fluid return hole problem
« Reply #14 on: March 15, 2011, 05:12:32 PM »
It looks like everyone is talking about one hole being clogged on their master cylinder (MC).  I have two holes in my MC cup (74 CB550) as shown in the manual.  One hole is clogged (or not all the way through) and the other is all the way through.  From the view inside the cylinder, after disassembling it, I didn't see any indication that the second hole may have once gone all the way through.  I did a rebuild with the MC kit and the brake engages just fine but it won't disengage.  Do both holes have to be unplugged or is the second one not supposed to go all the way through?  Usually blocked holes means bad mojo but in this case I'd rather not unblock it (drill it out) unless it supposed to be.

Also, I found a quick way (quick for me) to remove that darn MC circlip. 
1. Use a vice to hold the MC
2. I put the bolt that holds the brake handle back into where it goes on the MC (minus the brake handle).
3. With a small screwdriver I used that bolt for leverage to press down the piston.
4. I then shoved a block of wood under the screwdriver to hold it in place (didn't need much pressure due to the leverage) and was able to easily use two hands on the special pliers to compress the circlip and pull it out. Hopefully this helps someone frustrated with the circlip.

Back to my question: Do both holes have to be unplugged or is the second one not supposed to go all the way through?
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Offline Kevin400F

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Re: CB500 master cylinder fluid return hole problem
« Reply #15 on: March 15, 2011, 05:38:56 PM »
The one that looks like it might not go all the way through is closest to the hose connection, right?  

It has a very tiny hole in the base of a somewhat larger hole that only goes part way.  The tiny hole absolutely needs to go all the way through!  It is the one that plugs up and causes problems with the brake not releasing properly.

Kevin
« Last Edit: March 15, 2011, 05:53:17 PM by Kevin400F »

Offline jimmiejoe

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Re: CB500 master cylinder fluid return hole problem
« Reply #16 on: March 15, 2011, 05:40:59 PM »
l Just finish cleaning my MC on my 500/4...You really need to disasemable the whole dam thing... The c clip is the hardest thing to get out l used a small pick and was able to achive this in a few minutes...the
piston in the MC with the cups inside will have old brake fluid mixed with water for what ever reason...you then get to inspec the rubber cups for wear..use a piece of 400 grit sander paper on a wooden doll ...clean up the inside as it won't need much...MC rebuild kits are't that expensive and just knowing you'll have great brakes is always a better feeling...For the tiny holes anywhere on your bike including carbs l use a strand of cable that u have laying around..

Offline Spanner 1

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Re: CB500 master cylinder fluid return hole problem
« Reply #17 on: March 15, 2011, 05:48:53 PM »
That tiny hole can be stubbornly blocked.... like you say to yourself " no way this hole ever went through "..... use the smallest sewing needle in yer Mom's sewing box and push it in there with a pliers and twist. Be very careful not to bend the needle tho' or it could snap in the opening.
Also, don't pull the lever while the needle is in there as the tip will be thru' into the bore and rip the seal AND finally don't be tempted to enlarge this return hole, would lower brake pressure to caliper..... good luck  :)
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Offline SohRon

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Re: CB500 master cylinder fluid return hole problem
« Reply #18 on: March 15, 2011, 08:23:27 PM »
This might help clarify things a bit:


« Last Edit: March 15, 2011, 08:28:34 PM by SohRon »
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Offline mrbreeze

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Re: CB500 master cylinder fluid return hole problem
« Reply #19 on: March 15, 2011, 09:40:04 PM »
You don't have to rebuild the master to clean the small hole. You can ream it out with everything already mentioned. I used a guitar string like 4 or 5 years ago because thats what was suggested to me on this forum. Before I realized this..I took my caliper to the dealership at the suggestion of someone on this forum. Of course...I got my wallet raped (usually happens when you take anything to a dealership) and guess what????..........brake still stayed locked. I don't remember who said it but I was told to make sure the small port was clear and to use the guitar string to do it. As I was poking around in that hole (hehe!!!0)....I actually saw bubbles come flyin' outa there and lo & behold......the brake released.
Every since then...I have seen people post here with the same problem and other people tell them to rebuild the caliper or the master. If you wanna go that route....its your money. I will always suggest clearing the hole first. Its easier....its cheaper. I'm not saying that it is the only cause of this problem. I would be rebuilding my cylinders if they were leaking but not because the brake is staying engaged.A quick test would be to crack the bleeder at the caliper. If the brake releases....you can't blame the caliper. Even if you aren't having any problem...its a good idea to flush the system every few years. Brake fluid is very hydrascopic (takes on water like a sponge). Same is true in your car/pickup. It will absorb moisture from the air over time and moisture/water is a big enemy of the brake system. Not only does it not compress as well (spongy pedal) but rust forms and will take out the seals in your master,calipers,wheel cylinders,etc. Hope this tidbit helps someone like it did me.
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Offline techmonkey

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Re: CB500 master cylinder fluid return hole problem
« Reply #20 on: March 15, 2011, 10:31:41 PM »
@SohRon.  Your pictures helped out a lot, thank you!  I see now how small a hole it is; I never would have guessed. 

@mrbreeze I did release some of the pressure from the bleeder to see if the caliper would release and it did.  I had to rebuild my MC as it was leaking like a sieve when I bought it; the previous owner sat the bike out in the hot california sun since 2003 and cracked all the rubber in the MC.  I'll try some of the tips mentioned here to clean it out.  Thanks again guys!!
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Offline DavePhipps

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Re: CB500 master cylinder fluid return hole problem
« Reply #21 on: March 15, 2011, 10:50:17 PM »
I just wanted to mention that after cleaning the fluid return hold my brakes were still locked up. That was puzzling, so out came the wrenches. Turns out the steel backing of the pad was corroded due to moisture , also the pivot arm was frozen in place. After much cleaning and lubricating everything is working perfectly.
Just a word of advice to all of you working on your brakes. Check all parts.
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Offline techmonkey

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Re: CB500 master cylinder fluid return hole problem
« Reply #22 on: March 17, 2011, 05:52:16 PM »
So I took a small needle and within a few seconds of probing the clogged hole it unclogged and the brakes opened right up.  Wow, such a small hole provides such an important job.  Thanks guys for all your help.
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Offline jvandyke

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Re: CB500 master cylinder fluid return hole problem
« Reply #23 on: May 17, 2011, 06:21:54 AM »
This might help clarify things a bit:



Is this a CB500 master?  I have to investigate this issue and a quick glance last night I couldn't find the depression for the second little hole, but I didn't look much yet.  Just checking if this is EXACTLY what I should expect to see.  BTW I cleaned and renewed the sytem last year so the reservoir is nice and pretty, doesn't mean it isn't clogged though, eh?
« Last Edit: May 17, 2011, 07:08:13 AM by jvandyke »
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bollingball

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Re: CB500 master cylinder fluid return hole problem
« Reply #24 on: May 17, 2011, 09:14:38 AM »
SohRon: WOW what camera and setting was it on.
                           Thanks Ken