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Author Topic: Rear Caliper Issues  (Read 112 times)

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Offline Vintageguy

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Rear Caliper Issues
« on: November 23, 2024, 08:31:20 AM »
1978 CB750 F Super Sport. Last year I rebuilt the rear caliper including cleaning up the piston (very good condition) and cleaning the bore with ScotchBrite. Lubed the piston with brake fluid. This bike has a habit of the rear caliper sticking in colder weather and I thought I had it cured. When it turned colder again this year, I see it is doing the same thing (sticking). Is this a common problem, and what (if anything) can be done about it? Frustrated.

Thanks for any and all responses. 
« Last Edit: November 23, 2024, 08:33:01 AM by Vintageguy »
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Online Don R

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Re: Rear Caliper Issues
« Reply #1 on: November 23, 2024, 08:37:33 AM »
 The brake hose can be swelled up inside closing off the fluid return, the return hole in the M/C may be plugged and the square cut O ring might have deteriorated if it's not new. Lastly did you clean the groove under the o-ring.
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Offline Vintageguy

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Re: Rear Caliper Issues
« Reply #2 on: November 23, 2024, 12:52:53 PM »
Cleaned the grooves well prior to reassembly. Made them immaculate. O-ring brand new. Bled in fresh fluid. Could be a hose swelled up inside, but I still believe temperature has something to do with this problem. I wheeled the bike into the sun for a few minutes to warm the caliper up a bit, problem disappeared! At a loss for a answer.
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Offline newday777

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Re: Rear Caliper Issues
« Reply #3 on: November 23, 2024, 01:09:11 PM »
Quote from: Vintageguy on November 23, 2024, 12:52:53 PM
Cleaned the grooves well prior to reassembly. Made them immaculate. O-ring brand new. Bled in fresh fluid. Could be a hose swelled up inside, but I still believe temperature has something to do with this problem. I wheeled the bike into the sun for a few minutes to warm the caliper up a bit, problem disappeared! At a loss for a answer.
Did you use fresh brake fluid? Or old from an opened jar?
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Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline bryanj

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Re: Rear Caliper Issues
« Reply #4 on: November 23, 2024, 01:13:24 PM »
Did you strip and claen the master at the same time?
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Rear Caliper Issues
« Reply #5 on: November 23, 2024, 05:02:33 PM »
Have you mixed DOT 4 and 5?

I rebuilt both of my 75 masters and calipers front and rear and now go with that dastardly DOT 5 (haha) (that people say not to use) exclusively since it doesn't eat paint should it leak. Works fine but I know not to mix.
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Vintageguy

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Re: Rear Caliper Issues
« Reply #6 on: Today at 09:12:08 AM »
Did not rebuild either masters. Used only new brake fluid from sealer container.
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Offline bryanj

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Re: Rear Caliper Issues
« Reply #7 on: Today at 11:17:39 AM »
Chances are master is either binding or the small hole partialy blockef, could also be pivots siezing in cold
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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).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!
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