Author Topic: Aftermarket Master Cylinder Question  (Read 3256 times)

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Offline Sweep

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Aftermarket Master Cylinder Question
« on: March 28, 2009, 03:10:37 PM »
I have this I bought on ebay...

http://cgi.ebay.com/ebaymotors/FRONT-BRAKE-MASTER-CYLINDER-CB650-CB750-CB900-NIGHTHAWK_W0QQitemZ140309766414QQcmdZViewItemQQptZMotorcycles_Parts_Accessories?hash=item140309766414&_trksid=p4506.c0.m245&_trkparms=72%3A1171%7C65%3A12%7C39%3A1%7C240%3A1318#ht_20011wt_1133

I completely rebuilt my front brake yet again and this front brake does a terrible job of stopping the bike.  Has anyone run one of these MCs?  I'm wondering if it is the problem because my caliper and braided lines are fine and if anything, brake feel is too tight.  Too hard to pull.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #1 on: March 28, 2009, 03:26:44 PM »
Were you having this same problem (poor stopping power) before you replaced the stock master cylinder?

Are you absolutely positive that you thoroughly bled the brake so that there's no air at all trapped in the system?

Is it possible that your brake pads have been contaminated with anything like fork oil or brake fluid? 

Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #2 on: March 28, 2009, 03:44:32 PM »
Were you having this same problem (poor stopping power) before you replaced the stock master cylinder?

Are you absolutely positive that you thoroughly bled the brake so that there's no air at all trapped in the system?

Is it possible that your brake pads have been contaminated with anything like fork oil or brake fluid? 

I bled them as per the FAQ and the manuals I have.  In the end I had no bubbles coming up thru the MC and none from the bleeder, which I had connected to a cup of brake fluid via a rubber hose.  I'd say I bled for about a good 20 minutes and went from no brake feel to the point that I can only pull the brake lever about 40% of it's travel.  I'm thinking that this MC, although sold for cb750s may not be proper for these brakes.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #3 on: March 28, 2009, 03:53:41 PM »
Cool. 
Were you having this problem before, or only after installing this new master cylinder?   

Offline GammaFlat

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Re: Aftermarket Master Cylinder Question
« Reply #4 on: March 28, 2009, 04:48:40 PM »
Wow.. I like this ebay guy's video (I plan on doing similar stuff for my projects to post on the forum) and I'd be very tempted to put one of those MC's on my bike.  Someone else on the forum used that MC (it looks like the same one to me anyway - I thought I remember it being one of our female members... the one that sold manuals and docs) and they were singing it's praises.  I'd really like to know how this turns out. 

The 2 things that might change the "hardness" or distance of travel of the brake lever are 1) the diameter of the piston which appears the same as a Honda (about 14 mm) and the mechanical advantage of the hand lever (length of lever and distance from lever point to "piston pushing point"). 

If it feels real hard but is not stopping you, I'd be looking at the brake pad surface (have they had brake fluid or fork fluid on them?  I hear that's not real good) and if the rotor is glazed.  Beyond that, it's brake lines and it sounds like you have that covered.  I'd love to go with one stainless line from MC to caliper and this MC has a switch (nice!) which avoids the need for the "brake linis interruptus" with the factory brake light switch and all associated hardware.  Having said all this, I understand that large changes in brake performance can be problematic - (cause you to crash).  It's happened with folks on this forum.  Beeeeeee careful. 

I'd also like to find out what's required in making that thing black - scuff and paint?.  I imagine you'd need brake fluid resistant additive in the paint (how come the tanks don't have that stuff ;)). 

One more question before I go :)... Sorry, it doesn't seem that I've answered your question well.  Does this MC have good accessibility to inexpensive rebuild kits? 

This is a Honda piston.  Ruler's not even with the end, but you get the idea.  The ebay listing says 14mm piston which I think we can pretty safely say is the same. 


« Last Edit: March 28, 2009, 04:57:49 PM by GammaFlat »
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Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #5 on: March 28, 2009, 06:22:43 PM »
Cool. 
Were you having this problem before, or only after installing this new master cylinder?   

Oh sorry Gordon, never answered that.  I bought the bike and pretty much tore it down so I don't know.  I have some other cb friends in the area so I'll maybe trade bikes and try their front brakes.

'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #6 on: March 28, 2009, 06:25:30 PM »
Gamma...the pad is new and fine with no residue.  I even have a cyclex crossdrilled rotor.  I am going to get a new line and go directly to the caliper and use the switch on the MC.  Something seems rotten in Denmark with these brake but it could be that I'm just spoiled by my Ducati, Harleys, etc.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

ymracing

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Re: Aftermarket Master Cylinder Question
« Reply #7 on: March 29, 2009, 06:06:54 AM »
I run a Hyabusa master on my dual disc '76 750 with Vintage Brake, brake pads.  Stops real nice.  It is a good idea to take a "scotch brite" green pad with a bit of brake cleaner to your rotors on a semi-routine basis.  This may get rid of that wooden feeling you've described.

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #8 on: March 29, 2009, 06:59:42 AM »
Something seems rotten in Denmark with these brake but it could be that I'm just spoiled by my Ducati, Harleys, etc.

I have a feeling that may be the answer.  If you're used to modern bike brakes, it's going to take some time to get used to 35 year old bike brakes.  You won't be doing any stoppies with these ;), but if working properly they will stop you about as quickly as the tire is able to maintain its grip on the road. 

Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #9 on: March 29, 2009, 07:32:09 AM »
Something seems rotten in Denmark with these brake but it could be that I'm just spoiled by my Ducati, Harleys, etc.

I have a feeling that may be the answer.  If you're used to modern bike brakes, it's going to take some time to get used to 35 year old bike brakes.  You won't be doing any stoppies with these ;), but if working properly they will stop you about as quickly as the tire is able to maintain its grip on the road. 

Then they aren't working properly.  I'll have to take another look, thanks.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #10 on: March 29, 2009, 07:44:02 AM »
You say the brake pads are new.  Is the cyclex rotor brand new, too?  I'm wondering if that combination is causing a lack of friction because both surfaces are still really smooth. :-\

Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #11 on: March 29, 2009, 07:55:05 AM »
You say the brake pads are new.  Is the cyclex rotor brand new, too?  I'm wondering if that combination is causing a lack of friction because both surfaces are still really smooth. :-\

That could be so I'll use the scotchbrite suggestion.  Also can I verify something I've never been sure of from the pictures?  The hollow side of the piston faces the caliper right?
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #12 on: March 29, 2009, 08:48:46 AM »

That could be so I'll use the scotchbrite suggestion.  Also can I verify something I've never been sure of from the pictures?  The hollow side of the piston faces the caliper right?

I think you just figured out the problem.  The hollow end faces the back of the brake pad, and there should be a dome-shaped metal puck that sits between the piston and the brake pad, unless the K6 brakes are significantly different than my K1's.   

Offline hapakev

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Re: Aftermarket Master Cylinder Question
« Reply #13 on: March 29, 2009, 08:55:10 AM »
+1 on that. the hollow side sits against the brake pad.
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Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #14 on: March 29, 2009, 08:57:23 AM »
Guys, thanks for the info but that is how I have it installed.  I was just making sure I did it right.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #15 on: March 29, 2009, 09:14:37 AM »
Guys, thanks for the info but that is how I have it installed.  I was just making sure I did it right.

Okay, now I'm confused. 

You said, "the hollow side of the piston faces the caliper, right?", so I took that to mean that's how you have it installed and were making sure it was correct.  If that is how you have it installed, then it's not installed correctly.  If you have it so the hollow end faces the brake pad, then it's installed correctly.  So, is it installed correctly? 

Offline FunJimmy

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Re: Aftermarket Master Cylinder Question
« Reply #16 on: March 29, 2009, 09:40:53 AM »
Have you had a read through this thread?

http://forums.sohc4.net/index.php?topic=48744.0;topicseen

Check out the hydraulics explanation for some other suggestions.

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Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #17 on: March 29, 2009, 09:42:00 AM »
Guys, thanks for the info but that is how I have it installed.  I was just making sure I did it right.

Okay, now I'm confused. 

You said, "the hollow side of the piston faces the caliper, right?", so I took that to mean that's how you have it installed and were making sure it was correct.  If that is how you have it installed, then it's not installed correctly.  If you have it so the hollow end faces the brake pad, then it's installed correctly.  So, is it installed correctly? 

Sorry Gordon you are right.  I mistyped caliper when I meant rotor.  Thanks and sorry.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #18 on: March 29, 2009, 09:49:08 AM »
Have you had a read through this thread?

http://forums.sohc4.net/index.php?topic=48744.0;topicseen

Check out the hydraulics explanation for some other suggestions.

FJ

Yes I saw this, thanks.

I've ordered longer brakes lines and new fittings.  I'm going to eliminate the junction block containing the brake light switch to simplify the system and I'll see if that helps.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline Gordon

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Re: Aftermarket Master Cylinder Question
« Reply #19 on: March 29, 2009, 10:06:14 AM »
Guys, thanks for the info but that is how I have it installed.  I was just making sure I did it right.

Okay, now I'm confused. 

You said, "the hollow side of the piston faces the caliper, right?", so I took that to mean that's how you have it installed and were making sure it was correct.  If that is how you have it installed, then it's not installed correctly.  If you have it so the hollow end faces the brake pad, then it's installed correctly.  So, is it installed correctly? 


Sorry Gordon you are right.  I mistyped caliper when I meant rotor.  Thanks and sorry.

No prob.  Just wanted to make sure we were talking about the same thing.  Definitely scuff up the rotor some.

Offline MCRider

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Re: Aftermarket Master Cylinder Question
« Reply #20 on: March 29, 2009, 10:21:53 AM »
Have you had a read through this thread?

http://forums.sohc4.net/index.php?topic=48744.0;topicseen

Check out the hydraulics explanation for some other suggestions.

FJ

Yes I saw this, thanks.

I've ordered longer brakes lines and new fittings.  I'm going to eliminate the junction block containing the brake light switch to simplify the system and I'll see if that helps.

Eliminating the junction block is fine. But just remember, you should have a fully functional, able to lock the front tire braking system without doing anything to the way its set up.

Modern braking systems are better in feel, progresivity, resistance to fade, etc. but locking the front wheel, with an acceptable feel of progressivity to that point,  has never been an issue with a stock, single disc on a CB750. If you can't do that something is wrong with the basics.

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Offline Sweep

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Re: Aftermarket Master Cylinder Question
« Reply #21 on: March 29, 2009, 11:34:27 AM »
Hmm.  I think I'll put my stock rotor back on for ships and giggles.  It's in good shape.
'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells