Author Topic: Damn!— cb400f master cylinder questions (Read 967 times)

stay youth · « **on:** June 11, 2008, 10:08:04 PM »

I think I may screwed myself. I bought a master cylinder off ebay with a bore of 12.7. Now when I put it on my bike I cant seem to get it to pressurize. So I put on my old OEM leaky MC and it would apply pressure. I thought the stock bore was 10mm, is this correct? I doesn't seem like 2,7mm would cause it to not function. Any suggestions?

Thanks

stay youth · « **Reply #1 on:** June 12, 2008, 12:46:29 PM »

It seems that a larger bore would creat more pressure, is this correct???

Thanks

TwoTired · « **Reply #2 on:** June 12, 2008, 01:37:10 PM »

No, bigger bore pushes more volume at lower pressure for the same piston stroke.

But, then there is the lever and where the fulcrum is compared to each other and the length of the lever to where your hand actuates it. If there is a difference in mechanical advantage with these ratios, it is conceivable to get more volume AND pressure.

TomC · « **Reply #3 on:** June 12, 2008, 05:57:13 PM »

Hi Stay Youth
Stock CB400F1 master cylinder bore is 14mm.
TomC in Ohio

Quote from: stay youth on June 11, 2008, 10:08:04 PM

I think I may screwed myself. I bought a master cylinder off ebay with a bore of 12.7. Now when I put it on my bike I cant seem to get it to pressurize. So I put on my old OEM leaky MC and it would apply pressure. I thought the stock bore was 10mm, is this correct? I doesn't seem like 2,7mm would cause it to not function. Any suggestions?

Thanks

stay youth · « **Reply #4 on:** June 12, 2008, 10:42:49 PM »

Oh really?? SO maybe I'm not moving enough fluid through the system? Hmmm Any suggestions?

Thanks so much

mystic_1 · « **Reply #5 on:** June 12, 2008, 11:52:20 PM »

Sure the new MC is fully bled? If there's any air pockets in there then when you squeeze the lever all you're doing is compressing that air, it acts like a little spring for all intents and purposes. Bleeding a MC from fully dry can be difficult sometimes.

mystic_1

stay youth · « **Reply #6 on:** June 12, 2008, 11:56:51 PM »

Hmmm Well this is the first time I have ever installed a new MC. Do you have any tips for me?

Thanks so much!

bozo4onion · « **Reply #7 on:** June 13, 2008, 06:14:17 AM »

What do you have against rebuilding the leaker. Not that hard. Made my 550F work as new. The kit is cheap too.

stay youth · « **Reply #8 on:** June 13, 2008, 07:25:13 AM »

Mine old MC was horrible looking really scrapped up. I wanted something cleaner looking

mystic_1 · « **Reply #9 on:** June 13, 2008, 09:36:25 AM »

Quote from: stay youth on June 12, 2008, 11:56:51 PM

Hmmm Well this is the first time I have ever installed a new MC. Do you have any tips for me?

Thanks so much!

Go to the main forum page and type "bleed brakes" into the search box, lots of different tips and tricks about this on the site.

cheers
mystic_1

bozo4onion · « **Reply #10 on:** June 13, 2008, 10:29:55 AM »

There are about several different ways to bleed the brakes from repeatedly short pumping the lever to bubble the air from the relief hole to sucking the air out by mouth with a long tube. I went to harbour freight and got a brake bleeder. This only worked in combination with some bubbling of the master cyl. Your search for "master cylinder bleeding" should help. BTW my bike had a Yamaha cylinder on it when I got it. It worked fine but it leaked. I got my Honda master from eBay for $20. Had to be rebuilt though. Good luck.

stay youth · « **Reply #11 on:** June 13, 2008, 04:10:27 PM »

Thank you all so much!

mystic_1 · « **Reply #12 on:** June 13, 2008, 10:05:00 PM »

Let us know how it goes.

mystic_1

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