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  1. #1
    CB750 Member Billsboat's Avatar
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    Rear master cylinder

    Hi all! I have a 1972 Rickman. Iím the second owner. When I got the bike a few months back, both the front and rear brakes did not work. In fact, they were both dry as the bike had sat for about 7 years. I rebuilt the front master, and cleaned the calipers. The front now works as it should. I have also rebuilt the rear master... this is where I need help!

    So as mentioned, I rebuilt the master. Iíve bleed the thing I donít know how many times. Iíve also used the vacuum method, and I still get the same results. It pumps up, but once u release the pedal, the brake fluid refills back into the tube and I have no pedal.

    I fairly sure the master cylinder is from a 1978 Honda super sport cb750f.

    Thanks for any guidance!

  2. #2
    CB750 Guru amc49's Avatar
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    You can rebuild until the end of the earth yet if the master bore is not perfect then fluid will simply bypass the piston in a leak all day long. The fluid leaks out through lows which a honing job does not correct unless you remove way too much material, then the seal cup edges roll over backwards to quickly destroy the cup.

    Back hydraulics like that have more trouble than front, they are mounted down low to catch water in them all day long and tend to corrode worse than fronts. I had fits with them on the F DOHC bikes, most of the M/C castings are dead, you cannot hone that much damage out of them.

  3. #3
    CB750 Member Billsboat's Avatar
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    Thanks for responding! I had not considered the reason for the issue Iím having with the M/C but it makes sense.

    Frankly I was thinking I was gonna need to replace the M/C. I just wanted to make sure there was no more I could do.

    Any recommendations for replacement?

  4. #4
    CB750 Guru amc49's Avatar
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    No, you generally do not have the options you do on the front. The backs are always proprietary to the nth degree. Not saying something else won't work but I for one don't know of it. The DOHC has the same issue, I think they found one only off a CBR that works with slight modding, nothing else except the OEM part.

    Maybe Dirtdigger here onsite can offer something up. For sure you're gonna want to strip your cylinder down to look at the bore with a strong light to see how deep the corrosion issue is.

  5. #5
    Moderator dirtdigger's Avatar
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    post a picture of it so we know what your dealing with.

  6. #6
    CB750 Member Billsboat's Avatar
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    the second picture it of the old master cylinder parts.
    Attached Thumbnails Attached Thumbnails image.jpg   image.jpg  

  7. #7
    CB750 Member Billsboat's Avatar
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    Lmk if u need more/better pictures. Thanks for any help on this!

  8. #8
    CB750 Member Billsboat's Avatar
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    Quote Originally Posted by dirtdigger View Post
    post a picture of it so we know what your dealing with.
    added a few more pictures. the second picture is of the m/c and the orientation of the new master cylinder parts.
    Attached Thumbnails Attached Thumbnails image.jpg   image.jpg  

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